Basics of Eye Movement

Question 1

Describe the motion of the eye when it is rotating and when it is translating.

Answer 1

• Rotation

o Eye turns around center of rotation (cr)
o Visually significant (keep foveal fixation)

• Translation
o Not visually significant / Tiny side to side movements not expected to be seen

Question 2

Define the optic axis, the visual axis, the pupillary axis, and the line of sight

Answer 2

Optical Axis

• Straight line that connects the centers of curvature of the refracting surfaces of the eye and extends to the posterior pole DOES NOT represent where eye is looking

Visual Axis

• Line that runs from the fixation target (F) 1st nodal point 2nd nodal point fovea • Close to LOS and FA

LOS

• Gaze Direction and rotation are defined by LOS
• LOS is used in clinic
• LOS= the line from the fixation target to the center of the entrance pupil

o Entrance pupil= IMAGE of pupil seen when looking at patients’ eye
o Continues as ‘foveal chief ray’ from exit pupil to the fovea

Question 3

Define primary, secondary, and tertiary positions of gaze.

Answer 3

Primary Position of Gaze (PPG)

• Eye is in the PPG when the LOS is perpendicular to the plane of the face
• Agonist and antagonist EOM innervations are approximately in balance in the PPG

Secondary Position of Gaze

• Gaze position directly above, below, left, or right of the PPG. Vertical mer stays vertical

Tertiary Position of Gaze

Gaze position which is neither primary or secondary Vertical meridian does NOT remain vertical, and instead tips

Question 4

Define angle lambda.

o Where fovea is with respect to posterior pole is #1 determinant of angle lambda!

A normal angle lambda ≈ +11 PD (0.5mm nasal)

Answer 4

Angle lambda is the angle between the LOS and the pupillary axis

The genesis of the normal nasal corneal reflex in angle lambda tests:
o Temporal displacement of the fovea from the posterior pole
o LOS exits the cornea nasally from the optic axis
o The optic and pupillary axes are turned outward during fixation
o The cornea acts as an outward-turned convex mirror, displacing the corneal reflex relatively nasally from
the center of the entrance pupil

Question 5

Identify the usual cause of an abnormal angle lambda

Answer 5

Monocular vision:

Eccentric fixation/viewing is the MOST common disorder of angle lambda uses off foveal location for fixation

Binocular vision (Hirschberg test):

Strabismus - Any difference between angle lumdas of eyes signifying that only 1 eye is fixating

Question 6

List three advantages of using eye movement recording technologies to measure
eye movements, compared to standard clinical assessments such as the
Hirschberg test.

Answer 6

Advantages of accurate objective methods:

1. Some are more accurate than standard clinical tests
2. We can assess movement dynamics
3. We can assess eye movement with minimal interference with vision

Question 7

Select which eye movement recording technology is most accurate – EOG,
infrared reflection, video tracking, or search coil.

Answer 7

Search Coil

• Most difficult to use
• Costliest technology
• Most obtrusive
o Must put large hard lens on the eye with corneal anesthesia
o Can only be worn for 20 minutes
• By far the most accurate of all methods
• The search coil is best method for measuring
torsion

Question 8

List the four types of versional eye movements in the horizontal, vertical, and
torsional planes

Answer 8

Versional Movement

• Horizontal dextroversion, Levoversion
• Vertical hyperversion, hypoversion
• Torsional dextrotorsion, levotorsion

Question 9

List the two types of vergence eye movements in the horizontal, vertical, and
torsional planes.

Answer 9

Horizontal- convergence, divergence

Vertical - hypervergence, hypovergence

Torsional -encyclovergence, Excyclovergence

Question 10

List the three synonyms that name equal movements of the eyes.

Answer 10

If the eyes move equally, the movement is called

Conjugate

Conjunctive

Versional

Question 11

List the three synonyms that name unequal movements of the eyes.

Answer 11

If the eyes move differently, the movement is called

Dysjugate

Disjunctive

Vergence

Question 12

Identify the purpose of each of the following eye movements:

• saccades
• pursuits
• vergence jumps
• vergence tracking
• vestibular
• optokinetic.

Answer 12

Saccades

• Voluntary movement - to put new images on the foveas by shifting gaze direction o Innervation: conjugate

Smooth Pursuit

• Voluntary movement - to MAINTAIN foveal fixation of moving objects by smoothly changing gaze direction o Innervation: conjugate

Vergence Jumps

• Change gaze direction in depth
• Place new images on the foveas by shifting fixation distance looking near to far or vice
• Innervation: dysjugate eyes rotate in opposite directions

Vergence Tracking

• Change gaze direction in depth
• Purpose: to maintain fixation on objects moving in depth by smoothly changing gaze distance, images on foveas
• Innervation: dysjugate

Vestibular

• Maintain image contrast in peripheral vision along with foveal vision Reflexive system
• Purpose: to maintain a steady retinal image when the HEAD moves
• Innervation: conjugate

Optokinetic

• Maintain image contrast in peripheral vision along with foveal vision
• Purpose: to maintain a steady retinal image when the VISUAL ENVIRONMENT moves
• Innervation: conjugate

Question 13

Define oculomotor “kinematics”.

Answer 13

Kinematics is the study of how the eye rotates in the orbit

Question 14

Select the type of visual perception (visual acuity, contrast perception, color
vision, stereopsis) most affected by a failure of cyclovergence.

Answer 14

Proper torsion is a binocular vision concern…

o Torsional misalignment can disrupt fusion and stereopsis even if bifoveal vision is attained

Question 15

Define the “torsional posture” of the eye.

Answer 15

“torsional posture”

is the orientation of the vertical meridian of the eye relative to objective
vertical

Question 16

Define “false torsion”.

Answer 16

A change of torsional posture caused by a combo of horizontal and vertical rotations is called

“false torsion”

Question 17

State Donder’s Law.

Answer 17

Donder’s Law:

“the torsional posture of the eye at any position of gaze is the same, regardless of how the eye got there”

Question 18

Distinguish between

Fick’s,

Helmholtz’

Listing’s

theoretical ocular rotation axis systems.

Answer 18

Fick - proposed a system in which horizontal rotation precedes vertical rotation axis: NO False Tortion

Helmholtz - proposed a rotation system in which vertical rotation precedes horizontal rotationMUCH
false torsion

Listing’s Law: “The torsional posture of the eye in tertiary gaze will be the same as if the eye rotated from the PPG about a single axis in Listing’s plane, that axis being perpendicular to the direction of the target”

o Listing’s Plane: a vertical plane passing through the center of rotation and approximately parallel to the face

Question 19

State Listing’s Law.

Answer 19

Listing’s Law: “The torsional posture of the eye in tertiary gaze will be the same as if the eye rotated from the PPG about a single axis in Listing’s plane, that axis being perpendicular to the direction of the target”

Listing’s Plane: a vertical plane passing through the center of rotation and approximately parallel to the face
Listing’s law predicts a small amount of false torsion less than Helmholtz’ axes and more than Fick’s axes

Question 20

List the two types of eye movement in which the eyes do not strictly follow

Listing’s Law

Answer 20

1. There is more extorsion during CONVERGENCE than Listing’s law predicts, especially in down gaze Optimizes where eyes fall based on corresponding points to improve binocularity
2. There is LESS false torsion during VISTIBULO OCULAR REFLEX than Listing’s law predicts
   • Optimizes where eyes fall based on corresponding points to improve binocularity

Question 21

Distinguish between “covert” and “overt” attention.

Answer 21

o Covert Attention: attending to something you are not directly looking at

o Overt attention: attentional target that you move your eyes to
• Overt attention for motion is “spatial”

Question 22

Distinguish between reflexive (“bottom-up”) and voluntary (“top-down”) attention.

Answer 22

Control of Overt attention:

“top-down” Voluntary
• Driven by higher order processing in the brain occurs most of the time

o “bottom-up” (reflexive)
• Not consciously attending to something
• Ex: response to a startling event/loud sound in your environment
• Driven by lower order processing in the brain

Question 23

Describe how the role of attention differs between

reflex attention eye movements,

psychooptic reflex eye movements,

voluntary eye movements,

pure reflex eye movements.

Answer 23

Pure Reflex Movement

• NO attention involved
• Pupilary light Reflex, Vestibolo ocular reflex(total dark)

Reflex Attention Movement

• Patient is aware of movement AFTER it happens
• Controlled by reflex attention shifts
• Refex to a loud noise

Psychooptic Reflex Movement

• Voluntary overt attention to target will not respond to covert attention
• NO conscious intent needed to initiate the eye movement occurs reflexively
• Reflex accomodation , fusional vergence

Voluntary eye Movements

• movement initiation are voluntarily controlled
• Aware of movement
• Voluntary Saccade

Question 24

Describe the role of attention in each of the six types of eye movements

Answer 24

Saccades - Voluntary, put images on the fovea buy shifting gaze direction

Smooth persuits - Attention Maintain foveal fixation while targets move

Vergence Jumps - Attention Change gaze direction in depth, images on foveas by shifting fixation dist, near to far

Vergence Tracking - Attention Smooth movement vith image staying on fovea, Change gaze direction in depth

Vistibulocular reflex - NO Attention Maintain a steady retinal image when HEAD moves, Maintain image contrast in peripheral and foveal vision

Optokinetic - Attention Maintain steady retinal image when the visual environment moves

Question 25

Describe the meaning of boxes, circles, and arrows in eye movement cybernetic box diagrams.

Answer 25

Boxes - Neural or muscular Mechanisms

Circles - represent arithmetic operations
• These are usually assumed to be addition or subtraction neural summation or inhibition

Arrows - represent signals going from one part of the system to the other

• Signals are quantifiable events in a system

Question 26

Distinguish between “feedback” and “feedforward” oculomotor control.

Answer 26

“feedback control”

When a movement system checks the accuracy of its response and makes corrections.

“feedforward control”

When an eye movement system generates responses without checking for accuracy

o There is NO “feedback loop”
o There is NO “error” in feedforwardcontrol
• The advantage of feedforward control is a QUICK response

Question 27

Describe the role of “error” in feedback control.

Answer 27

Feedback control systems are driven by “error”

• The signal that says “you should make a correction”
• want stimulus to equal response
• o Error=stimulus - response (gain 1.0)

Question 28

Give an example of an eye movement that uses feedback control and an eye movement that uses feedforward control.

Answer 28

Feedback control:

It is NORMAL to have a tiny amount of error in fusional vergence → you need a little retinal disparity to stimulate fusional vergence

Feedforward Control

Vestibulo-ocular reflex you move your head and you get innervation to move your eyes almost instantly

Question 29

Identify the principal advantage of feedback control in eye movement

Answer 29

The advantage of feedback control is accuracy

Question 30

Identify the principal advantage of feedforward control in eye movement.

Answer 30

The advantage of feedforward control is a

QUICK response - Less thinking is involved

Question 31

Define the term “gain” as it relates to eye movement.

Answer 31

Gain refers to mechanism performance (ex. Fusional vergence gain= fusional vergence innervation/retinal disparity)

How efficient/sensitive the neural mechanism is when doing its job

Saccades + Vergence Jumps

Gain= initial response magnitude/ stimulus

Sustained Vergences + Accommodation

Gain= sustained response magnitude/stimulus

All Smooth Movements
Gain= response velocity/stimulus velocity

Question 32

List the gain value which represents “perfect” oculomotor control.

Answer 32

“Gain” = ratio of response/ stimulus stimuli and responses are measured in the same units

o A gain of 1.0 is ideal, but is rarely achieved

Question 33

Identify an example of an agonist/antagonist extraocular muscle pair.

Answer 33

“when an agonist contracts, its antagonist relaxes” reciprocal action

Agonist: muscle that pulls the eye in the intended direction Antagonist: muscle pulling oppositely from the agonist

in temporal gaze, agonist=LR, antagonist=MR

Question 34

State Sherrington’s Law

Answer 34

ALL eye movements follow Sherrington’s Law, regardless of type “when an agonist contracts, its antagonist relaxes” reciprocal action

Question 35

Describe how the high resting firing rate of extraocular muscle fibers supports
Sherrington’s Law.

Answer 35

Amount of energy produced by the agonist as it increases force = a reduction of energy from the antagonist

o The EOM muscle fibers have a high “resting” firing rate in the PPG
o As agonist innervation goes up one unit, the antagonist drops one unit
o Linear reciprocity helps ensure precise gaze innervation during slow movements and steady fixation

Question 36

Identify an oculomotor condition in which Sherrington’s Law appears to fail.

Answer 36

Extreme gaze

Retraction of the globe during strong convergence

All-or-none reciprocity during high speed saccades

Agonist is turned on the full amount for the amount of eye turn Much more force than what you would need to hold the eye at the target to overcome inertia

Antagonist is turned off completely during the saccades no residual innervation
o This would slow down the agonist, brain turns it off

Question 37

Define yoked extraocular muscles

Answer 37

EQUAL innervation yoked muscles in each eye receive equal innervation

o Yoked agonists pull each eye in the “same” direction
o Yoked antagonists receive equally reduced innervation

Question 38

Describe how extraocular muscle yoking is different in conjugate and dysjugate eye movements.

Answer 38

Some muscles are yoked for CONJUGATE movement

• RLR and LMR are yoked rightward agonists
• RMR and LLR yoked rightward antagonists
• Similar for vertical motion

Muscles are yoked differently for DYSJUGATE movement

• RMR and LMR are yoked NEAR agonists
• RLR and LLR are yoked NEAR antagonists
• Brain has separate neural controls for dysjugate innervation same convergence or divergence signal os sent to both eyes

Question 39

Define Hering’s law

Answer 39

EQUAL innervation yoked muscles in each eye receive equal innervation

o Yoked agonists pull each eye in the “same” direction
o Yoked antagonists receive equally reduced innervation

Question 40

Select the extraocular muscles that are yoked for conjugate motion and those that are yoked for dysjugate motion.

Answer 40

Some muscles are yoked for CONJUGATE movement

• RLR and LMR are yoked rightward agonists
• RMR and LLR yoked rightward antagonists
• RSR and LSR / RIR and LIR

Muscles are yoked differently for DYSJUGATE movement

• RMR and LMR are yoked NEAR agonists
• RLR and LLR are yoked NEAR antagonists

Question 41

Select the part of Herings law (conjugate or dysjugate) that serves as the basis for testing extraocular muscle paralysis.

Answer 41

Hering’s Law is the basis of testing EOM paralysis due to oculomotor nerve damage

We apply a conjugate stimulus – equal movement of the eyes is expected
Paralysis prevents equal muscle response even when conjugate innervation is equal

o Unequal movement is easy to detect → unequal movement indicates PARALYSIS

Question 42

Describe how the eyes will move in a “versions” test of oculomotor paralysis if the patient has a left lateral rectus paralysis

Answer 42

Eyes would be able to Do Dextroversion

On levoversion - LEFT eye would not Abduct Right to the left side as normal

Question 43

Identify, in an eye movement recording, the difference between saccades and pursuit,

Answer 43

Eyes have same pattern of motion BOTH Saccades and Persuits

• Eyes fixate on a word together then jump together to the next word→ patterns identical between the two eyes

SACCADES - Changes of position are very rapid → takes almost no time to go the next position

PERSUITS - Slow steady change

Question 44

Identify, in an eye movement recording, the difference between conjugate and
dysjugate movement.

Usually put right eye above left eye (based on convention)

Y axis → eye position (motion convention)

o Rightward motion of eyes = upward shift in the graph

o Leftward motion of the eyes = downward shift in the graph

Answer 44

DYSJUGATE
o Right eye turns relatively leftward
o Left eye turns relatively rightward
o SLOWER than saccade
o Movement in the two eyes are EQUAL but OPPOSITE

CONJUGATE

Saccade, Both eyes make a fast movement in the same direction, Or slow

Question 45

.Read, in an eye movement recording, the amount and direction of eye movement.

Answer 45

Usually put right eye above left eye (based on convention)

Y axis → eye position (motion convention)

o Rightward motion of eyes = upward shift in the graph

o Leftward motion of the eyes = downward shift in the graph

Straight line - FAST Saccade

Curved line PERSUIT

Question 46

An observer makes a slow and smooth eye movement from far to near along the line of sight of his left eye. The left eye remains stationary as the right eye adducts. Explain, on the basis of Hering’s law, how equal conjugate and dysjugate innervations sent to each eye can cause this unequal eye movement behavior.

Answer 46

• Can only occur is you SUM conjugate/dysjugate innervation

o Lateral gaze signal pushes eyes to the left (smooth pursuit innervation) → the conjugate signal

o At the same time, the approaching near target stimulates convergence → the dysjugate signal

• When you sum up conjugate/dysjugate innervation you get UNEQUAL movements even though EQUAL innervation is present

o In the eye that did rotate, the conjugate/dysjugate signals are in the SAME direction and cause eye movement in that direction

o In the eye that did not rotate, the conjugate/dysjugate signals pull the eye in opposite directions and cancel each other out

o Causes UNEQUAL physical rotation between the eyes even though the eyes are receiving EQUAL amounts of innervation

Question 47

Describe the primary purpose of accommodation.

Answer 47

Accommodation is the adjustment of ocular focus for the sake of optimal visual acuity and contrast

Question 48

Describe the purpose of vergence eye movements.

Answer 48

Vergence is the adjustment of ocular alignment for the sake of stereoscopic acuity

o Convergence: inward turning (positive)

o Divergence: outward turning (negative)

Question 49

Distinguish between retinotopic and spatiotopic stimuli

Answer 49

Retinotopic:

innervations stimulated by specific retinal image characteristics (ex: blur and absolute disparity)

Spatiotopic:

innervations stimulated by perceived distance – voluntary at a conscious level

Question 50

Select the type of oculomotor control (feedforward or feedback) used by
accommodation and convergence.

Answer 50

Both use continuous feedback control

*no feed forward* need the best precision, and the movements are slow anyways so more time can be taken for feedback

Question 51

Calculate the value of the accommodative stimulus for a target 33cm from the spectacle plane, when viewed through a -2.00D add by an uncorrected 1.00D myope.

Answer 51

AS=1/d–S
Sis(+)or(-)

o Fixation target distance (d) from the spectacle plane

o Lenses (S) added to the far refractive correction

Patient is emmetropic or corrected to emmetropia (correct first so you know that their problems are not related to RE)

Question 52

Consider a patient with the following uncorrected refractive error: OD +1.00 sph,
OS +2.00 sph, who is viewing a target at 50cm. Calculate the effective
accommodative stimulus if the eyes are (1) equidominant and (2) if the right eye
were amblyopic.

Question 53

Define “blur accommodation” (reflex accommodation).

Answer 53

A retinotopic process → process driven by characteristics of the retinal image alone/ stimulated by retinal image blur

BA innervation is proportional to blur

Question 54

Describe qualitatively how target spatial frequency and retinal eccentricity affect blur accommodation gain.

Answer 54

BA is dominated by FOVEAL Vision

BA is poor in people with macular disease or amblyopia

The gain of BA is low when you have poor vision
Hard to see blur when your macula isn’t working properly or when accommodative targets are
off-fovea
Peripheral vision is NOT good at seeing blur therefore the sensitivity of BA DECREASES

Question 55

Identify the type of attentional control used by blur accommodation

Answer 55

Initiated by psychooptic reflex attention

Observers are aware of attending their fixation target, but are usually not aware of the associated accommodation to keep the target clear continuously why BA is also known as “reflex accommodation” (no associated effort)

You can stop your BA to a target by choosing not to look at the target (overt attention mechanism)

Question 56

Explain how blur can stimulate normal blur accommodation when steadily accommodating to a near target even though normals don’t usually see blur in that situation.

Answer 56

Sensitive BA prevents blurred vision
o BA induces an accommodative change you don’t consciously see blur
o Your acc system may leave 0.25D (lag) because this is the minimum amount of defocus

normals need to activate their blur accommodation → this sustained lag drives your near accommodative response without you perceiving it because 0.25D is below your subjective depth of focus

Question 57

List a common clinical disorder in which the patient has weak blur
accommodation.

Answer 57

BA is poor in people with macular disease or amblyopia

The gain of BA is low when you have poor vision

Question 58

Define the stimulus to proximal accommodation.

Answer 58

Proximal accommodation innervation (PA) is stimulated by perceived nearness (not blur), so it is “spatiotopic”

Question 59

Identify the special role of proximal innervation in the accommodative system.

Answer 59

The primary role of PA is to initiate large changes of accommodation (and vergence)

Question 60

Define instrument myopia.

Answer 60

The nearness stimulus is much STRONGER than the optical accommodative stimulus, causing blur

• Strong magnification stimulates nearness percept
• Optical accommodative stimulus is typically ZERO
o Ex: Any microscope Perceive that the patient’s eye in the slit lamp is very close which causes you to reflexively accommodate

Question 61

Identify optometric tests that are sometimes disturbed by instrument myopia in
both patients and examiners.

Answer 61

Slitlamp evaluation

Question 62

List the two main roles of voluntary accommodation in normal vision

Answer 62

o To initiate LARGE changes of focus similar to PA
o To supplement other accommodative innervations when they are fatigued
• Not good at sustaining → more of a short-term strategy

Question 63

Define tonic accommodation

Answer 63

Automatically generated steady innervation that is NOT stimulated directly by vision (always there)

Purpose: to reduce the workload on positive blur accommodation, and thereby improving near visual acuity

Question 64

Distinguish between “static tonicity” and “tonic adaptation” in accommodation.

Answer 64

• Static tonicity – a baseline innervation
• Tonic adaptation – adjusting to sustained demand

Question 65

Define the “tonic resting state of accommodation”.

Mean TA in population = 1D (1 meter away)
o Normal range of TA ≈ 0.5-1.5
o This is why it is a bad idea to over fog a patient during refraction eye will go into tonic accommodation

Answer 65

intermediate distance the eye focuses at ( zero accommodative
innervation to relax at infinity) – this is the distance where your eye focuses with no stimulus

Methods for removing accommodative stimuli:
• Darkness (“dark focus”; “night myopia”) – can happen while driving
o Can give spectacles with extra (-) to compensate for night myopia
• Ganzfeld luminance “empty field myopia”)
• Pinhole aperture with monocular occlusion at distance
o

Question 66

Describe the three different stimulus conditions used to measure the tonic
accommodation resting state

Answer 66

Methods for removing accommodative stimuli:

• Darkness (“dark focus”; “night myopia”) – can happen while driving
o Can give spectacles with extra (-) to compensate for night myopia

• Ganzfeld luminance “empty field myopia”)
• Pinhole aperture with monocular occlusion at distance

Question 67

Select the posture of normal emmetropic accommodation (slight lead, slight lag,
or in-focus) with respect to a far target.

Answer 67

Slight Lead

Question 68

Select the type of reflex accommodation innervation – positive, negative, or none
– that is active during normal emmetropic far vision.

Answer 68

Negative

Question 69

Describe the visual conditions which induce the adaptation of tonic
accommodation.

Answer 69

Very slow, requiring several minutes to adapt to each new change of demand (not done instantly to
carefully adjust to the distance of demand)

Accommodative adaptation is the adjustment of TA innervation in response to a prolonged change of
other accommodative innervations

Question 70

Define “consensual accommodation”.

Answer 70

The eyes accommodate EQUALLY accommodation is cyclopean

o The ciliary muscles receive the same cyclopean innervation from the EW nuclei
o Accommodative innervation cannot differ between the eyes in a healthy person, even if the ocular stimuli differ

Question 71

Define “step accommodation”.

Answer 71

Transient accommodation innervation initiates “step” changes of accommodation
o Step response = a shift of response from one level to another (ex. far to near)
• Transient = shift from one distance to another
• Sustained = staying on target
o Sustained innervation completes step responses

Question 72

Differentiate the roles of transient and sustained innervation in accommodation.

Answer 72

Transient accommodation is a large burst of innervation that moves the ciliary muscle ‘quickly’ o This innervation is generated by accommodative “burst cells” in the brainstem

Sustained accommodation innervation maintains or slowly changes accommodation

Question 73

List the latency and duration of the transient phase of the average normal step accommodative response.

Answer 73

Compared to all other eye movements, step accommodation is slow

o 1070 msec response time:

• 370 msec latency
o Involves slower brainstem neurons (konio cells slow responders)

• 700 msec average movement time (duration of accommodative change)
o 10D/sec peak velocity

Question 74

List the innervations that drive the transient accommodative response.

Answer 74

This innervation is generated by accommodative “burst cells” in the brainstem

Konio Cells in Brainstem

Question 75

List the sustained accommodation innervation that is directly controlled by
feedback in the accommodative system.

Answer 75

Blur accommodation innervation dominates normal sustained accommodation when retinal image defocus < 1D

o Other innervations such as Tonic Accomodation

o Neural integrator cells create persistent innervation
• Cells that generate sustained innervation have a property that they can produce innervation in a steady low (transient neurons cannot do anything in sustained manner, only bursts)
o This persistence can last up to ten seconds after accommodative stimulation is removed

Question 76

Distinguish between accommodative “lead” and accommodative “lag”.

Answer 76

Lag = sustained underaccommodation

• The retinal image is focused BEHIND the retina
• Lag blur is similar to hyperopic blur

Lead = sustained overaccommodation

• The retinal image is focused in FRONT of the retina
• Lead blur is similar to myopic blur

Question 77

Describe the role of accommodative lead and lag in the control of reflex
accommodation.

Lag and lead are behaviors of sustained accommodation does NOT apply to transient accommodation

Answer 77

Normal lags and leads create the sustained retinotopic blur that stimulate sustained blur accommodation innervation

Question 78

Describe the two processes that indicate to reflex accommodation whether a
retinal image blur comes from a lead or lag of accommodation.

Answer 78

Longitudinal chromatic aberration between L, M, and S cones

Accommodation adjusts itself to eliminate red or green fringes on yellow images
o o
The retinal image looks like a circle with a yellow circle and red fringe green is more in focus in front of the retina, red is more out of focus and diffuse behind the retina
The area where the two wavelengths overlap is yellow represents UNDERACCOMMODATION
• there are specialized ganglion cells that sense this image

o Sometimes the image can look yellow with a green border/fringe→ this represents OVERACCOMMODATION
• There are specialized ganglion cells that sense this image

Question 79

Identify, on a graph of accommodative response versus stimulus, the parts of the function that quantify accommodative amplitude, gain, accommodative resting distance, and lag.

Answer 79

o At large stimulus values, the function flattens out reached the accommodative amplitude limit

o At the bottom end, your accommodation cannot go absolutely to zero (tonic accommodation)
• Need some myopic blur on the retina to stimulate negative reflex accommodation

• Key parameters:
o 1/1 line – normal standard
o mid slope
o lag conveys the accommodative gain Most likely less than 1.0
separation between the slope line and the 1:1 line dependent on accommodative demand
o zero lag point the eye is exactly in focus here (no need for accommodative innervation) • relates to the accommodative resting point of the eye
o far limit
o near limit

Question 80

Calculate the convergence stimulus for a target 17.3cm from the spectacle plane when viewed by a patient with a 60mm PD wearing 3∆ base-out prism.

CS=PD/d+Δ

o PD = the far interocular distance (in cm)
o d, in meters, is measured to the interocular baseline

Answer 80

It is assumed that the distance from the spectacle plane to the interocular baseline is 2.7 cm • We usually ignore the 2.7 constant if d ≥ 33 cm

o Base-out Δ is (+) because it increases the stimulus to convergence o Base-in Δ is (-) because it decreases the stimulus to convergence o Examples: (assume PD=6)

d = 0.173m, Δ = 3Δ BI; CS = 30 + 3 = (6/.2) + 3 = 33

Question 81

Identify the type of attention the visual system uses to control disparity vergence
(no attention, pure reflex, psychooptic reflex, or voluntary).

Answer 81

Psychooptic reflex attention initiates DV

o Similar to reflex accommodation if the retinal disparities are within limits of the visual system, it will automatically align your eyes reflexively

Question 82

List the value of the average threshold retinal disparity of disparity vergence.

2’-20’ Fine DV

10’ - 10deg

Answer 82

Threshold of fine DV ≈ 2’ (very small)
• Fine DV weakens for disparities > 20’
• Critically important in sustaining convergence keeps you a straight eyed person

Coarse Disparity Vergence
• Controlled by coarse disparity neurons in visual cortex
• Threshold disparity ≈ 10’
o Need at least 10’ in depth from where you are looking to stimulate coarse disparity

• Response weakens for disparities > 6Δ
o Very large retinal disparities will just produce diplopia (exceeds the range of fusional vergence)
o Operating range: 10’-6Δ

Question 83

List the types of vergence innervation stimulated by crossed and uncrossed retinal disparities, respectively.

Answer 83

Crossed disparity stimulates convergence
• Total convergence response is the sum of convergence innervations

Uncrossed disparity stimulates divergence

Question 84

Define the stimulus to proximal vergence innervation

Answer 84

Proximal vergence innervation (PC) is stimulated by perceived nearness it is spatiotopic

o Same precept that drives proximal accommodation

Question 85

Describe the special role played by proximal innervation in convergence

Answer 85

The primary role of PC is to initiate LARGE changes of vergence

o Stronger transient effect

o Weaker sustained effect

Question 86

Define instrument convergence.

Answer 86

instrument convergence”
o Instruments where the nearness stimulus is much STRONGER than the optical convergence stimulus
• Ex: slit lamp, binocular indirect, etc.

o Overconvergence with UNCROSSED DIPLOPIA

Question 87

List two clinical instruments prone to cause instrument convergence.

Answer 87

BIO, and Slitlamp

Question 88

List the two main roles of voluntary vergence in normal vision.

Answer 88

o Initiate LARGE changes in vergence
o To supplement other fatigued vergence innervations

Question 89

List two nonspatiotopic stimuli to voluntary convergence.

Answer 89

o Diplopia – this is retinotopic behavior:— observing the retinal image characteristic

o Strained feeling about the eyes

o Pure volition

Question 90

List patient instructions that would minimize a patient’s voluntary innervation during tests of convergence

Answer 90

To discourage voluntary effort:
o “look at the letters; make no special effort to see them”

Question 91

List patient instructions that would maximize a patient’s voluntary innervation
during tests of convergence.

Answer 91

To elicit voluntary effort:
o “keep the letters clear and single.”
o “imagine looking at your nose and feeling the strained sensation around your eyes”

Question 92

List three disadvantages of using voluntary innervation instead of fusional
vergence innervation for sustained convergence.

Answer 92

Patients who use voluntary effort continuously:
• See targets go in and out of focus and alignment
o If controlling vergence to prevent diplopia, they think that they have good single vision and eventually stop paying attention once attention is lost the patient will have diplopia again
• Experience asthenopia
• Cannot concentrate on their reading

Question 93

List the purpose of training voluntary convergence during vision training.

Answer 93

This training is done when fusional vergence is very weak and needs temporary voluntary help

The ultimate goal of VT is to move the patient beyond the need for voluntary effort

Question 94

Define the anatomical position of rest.

Answer 94

Anatomical position of rest = vergence posture in the absence of all EOM innervation determined by passive mechanical forces on orbit
o Not seen in clinical setting unless patient under anesthesia

Question 95

Define the physiological position of rest.

Answer 95

Physiological position of “rest” – the vergence posture when…

• o Binocularity is dissociated
• o Accommodation is “active” in far vision
• o Otherwise known as the “far phoria”

Question 96

Define the tonic vergence resting distance

Answer 96

Mean tonic vergence, TV = 3Δ eso (roughly 2 meters)

Eliminate all visual stimuli for accommodation/vergence eye will go into tonic vergence resting state

TV determines the CR when accommodation and vergence stimuli are eliminated by way of:

o Darkness (“dark vergence”) – no stimuli in the dark
o Ganzfield luminance
o Pinhole apertures or nonaccommodative target, dissociation and far fixation

Question 97

List the necessary stimulus conditions to measure the tonic vergence resting
distance.

Answer 97

TV determines the CR when accommodation and vergence stimuli are eliminated by way of:

o Darkness (“dark vergence”) – no stimuli in the dark
o Ganzfield luminance
o Pinhole apertures or nonaccommodative target, dissociation and far fixation
Takes time for eye to return to phoria posture or to TV state

Question 98

Describe the stimulus to tonic vergence adaptation.

Answer 98

Tonic Vergence (TV) is an automatic steady vergence innervation which is not stimulated by vision (it is always present there is always minimal tonicity in your extraocular muscles
o Static tonicity
o Tonic adaptation
o Neither static TV or TV adaptation are synkinetic with accommodation

Question 99

Select the time needed for a normal observer to fully adapt tonic vergence from far vision to near vision (i.e., milliseconds, seconds, minutes, hours, or days).

Answer 99

o If the brain finds that it needs to supply a lot of vergence for a long time, it adapts and adds more
tonicity for sustained near vision (
• TV adaptation slowly changes TV throughout the day
• It takes many minutes of time to adapt TV significantly

Question 100

.Match these horizontal vergence innervations: sustained disparity vergence,
transient disparity vergence, proximal vergence, and voluntary vergence, to their
appropriate stimuli (small retinal disparity, large retinal disparity, stereoscopic
depth perception, and large magnitudes of diplopia)

Answer 100

horizontal vergence innervations ; stereoscopic

sustained disparity vergence : small retinal disparity

transient disparity vergence : large retinal disparity

proximal vergence : depth perception

voluntary vergence: arge magnitudes of diplopia

Question 101

List the average latency and duration of the normal step vergence response to near

Answer 101

Latency - 150 msec (milliseconds)
• This is the time between when your stimulus is
introduced and when the eye movement start

Duration - 500 msec
• Duration increases with magnitude

Question 102

Define the role of transient innervation in vergence

Answer 102

Transient vergence innervation initiates step changes of vergence

o Looking far, then suddenly changing to reading distance

o Transient vergence is a strong burst of innervation that moves the EOMs quickly, but does not sustain convergence once the eyes reach destination the transient innervation goes away

Question 103

List the vergence innervations that support the transient vergence response.

Looking for infinity to near

Answer 103

•
Proximal vergence innervation plays the biggest role

Spatiotopic voluntary innervation can also play a role depends on how strong proximal innervation is
Stronger proximal innervation= less voluntary innervation needed

These two innervations will get you close to the near target sustained innervation mechanisms will take over after

Question 104

Define the role of sustained innervation in vergence.

Answer 104

Sustained vergence innervation MAINTAINS vergence after a vergence step, and can SLOWLY change vergence

Sustained vergence is controlled by the retinotopic innervation “fine DV”

Question 105

List the vergence innervations that maintain the sustained vergence response.

Answer 105

• Vergence resting state → determined by tonic vergence
• Proximal= small contribution, but helps you get closer to near point
• Accommodative vergence is an important contributor to sustained near convergence response - sends info to the convergence system
• Fine disparity vergence controls the remainder of the convergence response at near → means that some fixation disparity is present

Question 106

List the average gain of normal sustained vergence.

Answer 106

The average gain of sustained vergence ≈ 0.99

o Size of retinal disparity needed to stimulate vergence = 1% of total convergence innervation

o Convergence is extremely PRECISE/ACCURATE and tolerates very little retinal error
• Why is vergence so precise?
o You need very precise vergence to keep images on/near the horopter (where the best stereo is) o Tolerance for single vision only is more relaxed than for stereo

Question 107

.Normal sustained vergence gain is much higher than normal sustained
accommodation gain. What is thought to be the reason for this difference?

Answer 107

Why is vergence so precise?
o You need very precise vergence to keep images on/near the horopter (where the best stereo is) o Tolerance for single vision only is more relaxed than for stereo

Question 108

Describe the role the vergence neural integrator performs in normal vergence.

Answer 108

Sustained vergence innervation is maintained by “vergence neural integrator” cells
o These cells maintain innervation even in the ABSENCE of a stimulus
o In vergence, neural integrator persistence can last longer than ten seconds
o Sustained vergence persistence causes the SLOW decay of vergence observed when an occluder is
applied in a cover test

Question 109

Describe how the vergence neural integrator reveals itself in clinical tests.

Answer 109

Sustained vergence persistence causes the SLOW decay of vergence observed when an occluder is applied in a cover test

Question 110

Define fixation disparity.

Answer 110

Fixation disparity (FD) is a small misalignment of the eyes which does NOT disrupt foveal fusion

o Centers of the foveas do not point exactly at the target
o FD is a property of SUSTAINED disparity vergence normal property of vergence control system o FD causes stimulation of the foveal retinal disparities this stimulates fusional vergence

Question 111

Compare and contrast eso and exo fixation disparity from crossed and uncrossed retinal disparity

• Its normal to have a little bit of exo disparity in your vision Analogous to accommodative lead and lag
• Exo FD as you are looking closer misalignment is small and within Panum’s Area so no diplopia

Answer 111

Underconvergence (normal) EXO
• The fixation target subtends a CROSSED foveal disparity
• Positive fine sustained DV is stimulated by the fixation target
• Causes targets to fall on temporal retinas (but not exactly on corresponding points) Creates crossed retinal disparity which is a stimulus for fusional convergence

Overconvergence (abnormal)ESO
• Lines of sight cross at a point closer than the target any eso FD is abnormal
• The fixation target subtends an UNCROSSED disparity stimulates negative fusional vergence (NFV) and turns the eyes out to the target
• Negative fine sustained DV is stimulated

Question 112

List the oculomotor responses involved in the “near triad”

Answer 112

The “near triad” synkinesis:

1. Accommodation
2. horizontal vergence
3. pupil constriction

Question 113

Define “AC/A ratio”

Answer 113

The AC/A ratio is the ratio of accommodative vergence (AC) generated by each unit of accommodation (A)

Question 114

Distinguish between the “stimulus AC/A ratio” and the “response AC/A ratio” test
methods.

Answer 114

Response AC/A = measured vergence change/measured accommodation change
Stimulus AC/A = measured vergence change/accommodative stimulus change

The response AC/A is usually HIGHER than the stimulus AC/A o Accommodation usually changes less than its stimulus
Population stimulus AC/A values:

o Average AC/A = 4/1 (response AC/A ≈ 5)

Normal range = 3/1 to 6/1
• Patients will have comfortable vision with good fusion and stereo

Question 115

List which AC/A ratio test method is more accurate and which is easier to run.

Answer 115

More Accurate :

Calculated AC/A = there are combined blur and spatiotopic accommodative stimuli (ex. Proximal stimuli)
• Comparing far and near phorias based on the PD more phoria change =higher AC/A
• GREATER accommodative stimulation and innervation
• MORE accommodative vergence
• HIGHER stimulus AC/A

Easier:

Gradient AC/A = there is ONLY a blur stimulus to accommodation
• This is when you put a lens on the eye and measure the effect on the phoria
• Gives us a change of phoria caused by a change in blur patient’s accommodative change is not
going to be 1D even though you put +1D in front of their eye
o Measure the phoria change for the true response)

Question 116

List the average normal stimulus AC/A ratio

List the range of normal stimulus AC/A ratios

Answer 116

Population stimulus AC/A values:

o Average AC/A = 4/1 (response AC/A ≈ 5)

o Normal range = 3/1 to 6/1

• Patients will have comfortable vision with good fusion and stereo

Question 117

Describe how the response and stimulus AC/A ratios change with age.

Both AC/As rise rapidly in early presbyopia a lot of ciliary muscle demand generates a lot of accommodative innervation for only a little bit of accommodative response

Answer 117

The response AC/A rises modestly with age

The stimulus AC/A is unchanged by age, up to presbyopia
• Can’t measure AC/A in absolute presbyopes

Presbyopia
But all the accommodative efforts will generate synkinetically a lot of accommodative vergence Small amount of accommodation for A LOT of convergence

Question 118

Define the CA/C ratio.

Answer 118

The CA/C ratio is the ratio of convergence accommodation (CA) per unit of convergence (C)

o ‘Convergence’ in this case means only fusional vergence

Question 119

List the average CA/C ratio in young adults.

Answer 119

Average = 1/12 in young adults

o 1D for every 12Δ of change in convergence

Question 120

Describe how the CA/C ratio changes with age.

Answer 120

The CA/C ratio is highly age-dependent, like the amplitude of accommodation
o It drops to near zero at age 40
The CA/C ratio is NOT often tested in clinical practice

Question 121

Identify each of the components of the dual interaction diagram of
accommodation and vergence.

Answer 121

Accommodation and vergence mutually innervate each other without dual interaction the 2 systems do NOT work together
Dual interaction reduces innervation loads on BA and DV enables better vision

o Tonic and proximal would REDUCE the AR and CR loads, leaving less work for dual interaction

Question 122

Describe, in terms of “increase”, “decrease”, or “no change”, how normal near
tonic adaptation affects blur accommodation innervation, accommodative lag, fusional vergence innervation, and fixation disparity.

Answer 122

Near tonic adaptation

DECREASES blur accommodation innervation

NO CHANGE accommodative lag

DECREASES fusional vergence innervation

DECREASES fixation disparity.

Question 123

Select the posture of normal convergence with respect to a 6M fixation target
(small eso FD, small exo FD, or aligned).

Answer 123

Alligned

Question 124

Select the posture of normal convergence with respect to a 40cm fixation target
(small eso FD, small exo FD, or aligned).

Answer 124

Small EXO

Question 125

A normal observer has a slight exo fixation disparity in normal near vision.
Describe the effect of adding base-out prism before both eyes to the fixation disparity.

Answer 125

Increase the amount of Crossed fixation Disparity and stimmulate convergence

Question 126

A normal observer has a slight exo fixation disparity in near vision. Describe the effect of adding minus sphere lenses before both eyes on the fixation disparity.

Answer 126

Minus Stimulates ACC responce and produces Positive fusional vergence

Move the posture to Over convergence / stimulate Neg fixation disparity

Question 127

A patient’s reflex accommodation innervation is 2.5D and his AC/A ratio is 5/1. Calculate the amount of accommodative vergence innervation.

Question 128

A patient’s total accommodation innervation is 3D. The tonic accommodation
innervation is zero. His disparity vergence innervation is 8∆ and the CA/C ratio is
1/10. Calculate the amount of blur accommodation innervation. (hint: the dual
interaction diagram can help you solve this problem)

Answer 128

Question 129

List the components of the dual interaction model of accommodation and
vergence that are not included in the Maddox model of vergence.

ONLY RELEX ACC was recognised

Answer 129

o Tonic

o Accommodative

o Fusional

o Proximal

o Has no concepts for transient versus sustained innervations
o Tonic adaptation effects were NOT considered significant
o Convergence-induced accommodation was not in the Maddox model
o Multiple sources of accommodative innervation were not in the Maddox model

Question 130

Describe the roles of the cerebral cortex in the control of accommodation and vergence.

Answer 130

Coarse disparity neurons calculate transient vergence stimuli

Fine disparity neurons calculate sustained vergence stimuli

o Coarse and fine disparity vergence neurons travel down from visual cortex to the brainstem -

o supraoptic area (this area has a lot to do with accommodation/convergence)

Perception of blur for voluntary vergence is processed here

Question 131

Describe the role of parietal cortex in accommodation and vergence

Answer 131

• Computes perceived distance for spatiotopic responses

o For where you perceive things relative to your body, and for visually guided movements

• Switches reflex attention to targets
o Driven by loud sounds or rapid motions of large objects in peripheral vision

Generates proximal responses

Electrical stimulation initiates the near triad

Question 132

Describe the role of frontal cortex in accommodation and vergence.

Answer 132

• Voluntarily select static or moving stimuli for spatiotopic vergence jumps

Question 133

List the roles of the cerebellum in horizontal vergence control.

Answer 133

• Generates pulse (transient) and step (sustained) for jumps which are sent to SOA
• Adjusts vergence gain for best alignment of the eyes
• Mediates vergence adaptation
• Cerebellum assembles the signals that move the eyes according to Hering’s law

Question 134

Describe the roles of the neural cells in the Supraoptic area of the brainstem in
accommodation and vergence.

• Cell activity is only correlated with accommodation & vergence

Answer 134

• Convergence vs. divergence cells
o Burst cells: (“transient burst neurons”)
fire briskly during the transient phase of accommodation and vergence – not action during sustained accommodation & vergence

o Tonic cells: relates closely to sustained accommodation & vergence

o Burst-tonic cells: adds up burst and tonic innervations

o More convergence cells than divergence
cells
• SOA cells project to the EWN and 3rd & 6th nerve
requires more energy
• SOA cells generate Hering’s law dysjugate
nuclei innervation
cyclopean eye

Question 135

List the target nuclei receiving supraoptic innervation.

Answer 135

• SOA cells project to the EWN and 3rd & 6th nerve Nuclea

Question 136

List the average value of the vertical vergence resting state (i.e., phoria).

Answer 136

Vertical TV is usually zero (ortho)

Question 137

List the range of normal vertical vergence.

Answer 137

Normal values: +/-3Δ from ortho for smooth vergence

o Range of adaptation is less than horizontal

Question 138

Compare and contrast the cybernetic control of vertical vergence to horizontal vergence

Answer 138

NO accommodative or proximal influence these are horizontal influences
o Vertical vergence is a product of vertical disparity

Vertical vergence is controlled by psychooptic reflex attention NO voluntary influence

Question 139

List the accommodation and vergence mechanisms which malfunction, causing
“convergence insufficiency” and “convergence excess”.

Answer 139

Convergence Insufficiency (CI)
• Synopsis – weak convergence to near
o Differential Dx: pseudoCIs also have AI
• Pathophysiology:
Receded NPC – low total vergence innervation Low AC/A ratio, which causes:

1. Weak transient and sustained accommodative vergence

• Must generate PFV at near for long periods of time and when breaks down it causes diplopia
High load on near + FV with high exo FD
Need a lot of crossed retinal disparity= a lot of PFV
2. Weak positive vergence adaptation mechanism (many CIs), which causes:
o Very slow or nonexistent vergence adaptation
o High sustained near load on positive FV with high exo FD Patients cannot maintain alignment at near
3. If TV adaptation is weak, it compounds the effects of a low AC/A on sustained near vision
4. Relative near accommodative lead from high +CA

Convergence Excess

Synopsis – excessive accommodative convergence innervation at near Pathophysiology:
o High AC/A ratio (>>6/1)
Excessive accommodative vergence at near due to high AC/A
Negative FV compensates for high accommodative vergence
Eso FD accompanies negative FV Negative fusional vergence at near is not normal
• Causes an accommodative lag

1. Relatively large near accommodative lag from -CA
2. Weak TA adaptation in many CEs can NOT adjust TA efficiently to near vision so tend to stay far away

• Causes high sustained load on +BA

Large accommodative lag
o Causes excessive accommodative vergence
High BA x high AC/A = excess accommodative vergence

Question 140

Distinguish “overt” attention from “covert” attention.

Answer 140

Most saccades are led by a voluntary shift of overt attention

Question 141

List the types of attention that initiate saccades.

Answer 141

1. Voluntary saccades
2. Reflex saccades
3. Spontaneous micro saccades during fixation • NOT driven by stimuli or attention!!
4. Saccade-Like movements

No attentional control

Attentional effect depends on the stimulus, like watching Saccade Stimuli
• Fast phase of vestibular nystagmus
• Fast phase of optokinetic nystagmus

Question 142

List the average latency of saccades.

Answer 142

Reflex and voluntary latencies: 200 msec +/- 50 msec

o Express latency: 100 msec latency

Question 143

Distinguish express, predictive, and voluntary saccades from each other.

Answer 143

Voluntary saccades
• Most saccades are led by a voluntary shift of overt attention

Types:
o Visual search
o Reading eye movements
o Scan pathes saccades complex eye movement mediated by brain remembrance of previous
o Movements during REM sleep

Express saccades
• The current fixation target is turned OFF when the new target is presented→ shortens saccade latency
• Usually when you shift attention it takes some time to disengage your attention from the original stimulus to the new

Predictive (anticipatory) saccades
• Attention and eye movement is voluntarily directed to a known location at or before target appearance make educated guess about when target will appear based on past experience
o Will find NO latency with this type of saccade if you can anticipate accurately

Question 144

List two types of involuntary eye movement that contain periods of motion that
are as fast as saccades.

Answer 144

• Fast phase of vestibular nystagmus
• Fast phase of optokinetic nystagmus

Question 145

Compare the role of saccades to the role of head movements in shifting gaze
direction.

Answer 145

Voluntary and reflex saccades are stimulated by target direction “error”

Question 146

Define saccade stimulus in terms of oculocentric direction.

Answer 146

Oculocentric error= nonzero oculocentric target direction

• Threshold error=15 minarc

Monocular cue

Question 147

Define saccade stimulus in terms of egocentric direction.

Answer 147

Egocentric error=egocentric direction-registered gaze

• Minimum error is 15 minarc

• Targets are not on the foveas eccentricity serves as an error signal
o When target visual egocentric direction ≠ egocentric gaze direction, you have a stimulus for a saccade

Question 148

Select the type of saccade system error, oculocentric or egocentric, that initiates
saccades to unseen sounds

Answer 148

• Error computation for nonvisual targets:
o e.g. sounds, tactile targets, remembered targets
o Egocentric keeps spatial location for all of the senses

o Egocentric error=egocentric direction-registered gaze
• Threshold error= 3° gaze error

EGOCENTRIC

Question 149

Identify the threshold error (in degrees) for stimulating saccades when there are
visual targets.

Answer 149

Egocentric error=egocentric direction-registered gaze
• Threshold error= 3° gaze error

Question 150

.Identify the threshold error for stimulating saccades when there are no visual targets.

Answer 150

Threshold error=15 minarc

Question 151

Distinguish “sampled-data” eye movement control from “continuous” eye movement control

Answer 151

“Sample data control” means that vision intermittently samples error to check whether the eye is off target
• Saccades are processed at a conscious level and is only done intermittently

Continious - Acc feedback system

Question 152

Identify the type of control - feedback or feedforward - used in saccades.

Answer 152

Saccades are feedback controlled
o Saccades are repeated until the target image is on the fovea
o Usually one saccade is enough to foveate
o Corrective saccades are additional attempts to fovea the initial saccade image when the initial saccade is
inaccurate

Question 153

Define “corrective saccade”.

Answer 153

o Corrective saccades are additional attempts to fovea the initial saccade image when the initial saccade is inaccurate

Question 154

Define saccadic neural gain.

Answer 154

Neural Gain= saccade INNERVATION/ error

Question 155

Define saccadic response gain.

Answer 155

Response Gain= saccade MOVEMENT/error

Question 156

List two factors that cause a normally-sighted observer to make more frequent
corrective saccades.

Answer 156

Inaccuracy is usually LESS than 10% not as accurate as sustained convergence
UNDERSHOOTS occur for LARGE saccades and OVERSHOOTS for SMALL saccades

Fatigue and age reduce accuracy

Question 157

Define “ballistic” eye movements.

Answer 157

Once started cant be stopped

Question 158

Define “saccade trajectory”.

Answer 158

A trajectory is the path of the line of sign through 3D space

Question 159

Contrast the roles of the “pulse” and “step” innervations in saccades

Answer 159

Pulse Innervation

o Strong but brief neural innervation that rapidly moves the eye, and determines saccade velocity “gets you there”

o Pulse innervation determines saccade VELOCITY Pulse overcomes orbital resistance to move the eye

Step Innervation

o A lesser but steady innervation which holds the eye in position after a saccade o Step innervation alone would move the eye slowly

• Too weak to move the eye rapidly
o Neurologically, step innervation is usually a fixed percentage of the pulse innervation

Question 160

Identify the reason that the pulse innervation in a given saccade is stronger than
the step innervation in that same saccade.

Answer 160

Pulse innervation determines saccade VELOCITY Pulse overcomes orbital resistance to move the eye

overecome inertia

Question 161

Identify the highest velocity attained by saccadic eye movements

Answer 161

The fastest saccade ≈ 700 ̊/sec ~ 10x faster than the fastest convergence movement

Average movement duration~50ms (1/20 of a second)

Question 162

Describe how saccade duration relates to saccade size.

Answer 162

Larger saccades take longer.

Average movement duration~50ms

Question 163

List a naturally occurring anatomical change in the normal oculomotor system
that demands saccadic gain adaptation in order to maintain accuracy.

Answer 163

Normal aging: more innervation may be needed to make the same eye movement because of changes in the orbital contents
o Older people do NOT have inaccurate saccades because they get older have the same accuracy if they are healthy, but have a longer latency

o There is more orbital resistance with age, but the brain adapts so that the saccadic gain is correct to maintain accuracy

Question 164

List the consequences to the patient if their oculomotor system does not adapt its
saccadic gain to a new pair of glasses.

Rule of thumb for magnification: 1.5% magnification per diopter o Ex: a pair of 5D lenses, there is a change of gain by 7.5%

Answer 164

More PLUS: HIGHER gain needed

More MINUS: LOWER gain needed

Consequences of incorrect gain:
o Habitual need for corrective saccades

• slows reading and other visual tasks
• Eye strain

Question 165

Explain how saccadic gain adaptation to new anisometropic spectacles “violates”
Hering’s law of equal innervation

Answer 165

Motor aniseikonia caused by anisometropic spectacles demands

DIFFERENT ocular rotations for what should be a “conjugate” stimulus → this is done by a saccade and a positive corrective fusional vergence movement

• Saccadic system can learn to do PARTIAL UNEQUAL GAIN ADAPTATION violates Hering’s law

Question 166

.List the roles of the oculomotor neurons, in the following areas of the brain, in saccade generation:

cerebral cortex

Answer 166

Cortical role: select targets and process stimuli

Posterior parietal cortex (PPC): calculates egocentric direction

Parietal Eye Fields (PEF): start REFLEX saccades

Frontal Eye Fields (FEF): initiates VOLUNTARY saccades & PREDICTIVE saccades

o Remember: this is the area of the brain that also initiates vergence jumps • Areas closely related to FEF:

o Supplemental eye fields (SEF): initiates complex sequences of saccades such as scan paths

o Dorsolateral prefrontal cortex (DLPC): initiates memory-guided saccades
o The connections of SEF and DLPC to other brain areas are like the FEFs

Question 167

.List the roles of the oculomotor neurons, in the following areas of the brain, in
saccade generation: superior colliculus,

Answer 167

Superior colliculus (SC) **calculates where your eyes are and where you want to go(cyclopean)** Role: controls **gaze trajectory of a saccade**
o **SN, PEF, and FEF inputs** end up in the SC o Gaze trajectory = eye + head
o *Right SC sees left VF, left SC sees right VF*

Superficial: sensory input
Intermediate: sensorimotor
• Involved in saccadic movements
Deep: motor outputs
• Not eye movements, more for body movements Superficial layer inputs:
o A direct retinal input to the SC shows “retinotopic” mapping in the superficial layer
o Visual cortex also projects to the superficial layer with matching retinotopic mapping

Inputs:
• FEF and PEF project to the build-up layer
o The build-up layer represents the part of the visual field where the target of interest is

o This is a crude selection of the part of your visual field that will be the destination of your saccade
• SN projects to the fixation zones
o Where the foveal neurons are
o When the fixation zone is turned off, the burst layer is allowed to be active

o Cellular types:
• Fixation cells: activate while fixating;

0°=central fovea
• Buildup cells: represent intended target location
• Burst cells: send gaze shift command to brainstem
o Burst layers remains on as long as eyes are moving
o When the eye moves to the destination, the activity moves to the fixation zone

Question 168

Distinguish the roles of the frontal eye fields and parietal cortex in the control of saccades

Answer 168

• Parietal Eye Fields (PEF): start REFLEX saccades
• Frontal Eye Fields (FEF): initiates VOLUNTARY saccades & PREDICTIVE saccades

Question 169

Describe the “antisaccade” task.

The SN pathway to the SC acts as an on-off switch in the interaction between PEF and FEF
• Parkinson’s damages the SN and its inhibitory control

Answer 169

“antisaccade test”

• Have patient fixate on your nose
• Hold up your left and right and simultaneously
• Tell patient to look at your left hand as soon as I wave my right hand (or vice versa)
• Pt needs to employ voluntary control the moving hand will cause a reflex saccade that patient must turn off
• Parkinson’s patient will look at the moving hand → reflexive saccade overpowers the voluntary saccade

Question 170

Select the regions of the brainstem that generate the pulse and step innervation
for vertical saccades.

Answer 170

Excitatory Burst Neurons (EBN)

• Vertical & Torsional: rostral interstitial nucleus of the MLF (riMLF) o Outputs: to each N3, N4 and inC

• Neural Integrator Neurons (NIN)

Vertical & torsional NINs:
• Located in the interstitial nucleus of Cajal (inC)
• Output sent to N3 and N4

Question 171

Select the regions of the brainstem that generate the pulse and step innervation
for horizontal saccades.

Answer 171

Excitatory Burst Neurons (EBN)

Horizontal: paramedian pontine reticular formation (PPRF)
o Outputs: ipsilaterally to PAB/N6 and NPH, and contralaterally to N3 (via PAB & MLF)

Inhibitory Burst Neurons (IBN)

• Horizontal: nucleus paragigantocellularis dorsalis (NPG)

Neural Integrator Neurons (NIN)

Horizontal NINs

Located in the medial vestibular nucleus & nucleus propositus hypoglossi (VN &NPH)

Output sent to the ipsilateral parabducens and N6

Question 172

Briefly describe the roles of the following oculomotor neurons in the production of saccade innervation: long-lead burst neurons, excitatory burst neurons, pause
neurons, inhibitory burst neurons, and neural integrator neurons.

Answer 172

Long-lead burst neurons
• Separates gaze shift into eye and head portions decides if you need to move your head, and if so, how much it needs to move
• Partitions spatial maps into horizontal, vertical and torsional vectors for the appropriate saccade muscle groups
• Converts spatial map eccentricity to saccadic pulse magnitude/innervation
o origin of the “main sequence” behavior of saccades

Excitatory burst neurons

Role: generate saccadic PULSE for AGONISTS
• Activity profile of EOMs= activity profile of EBN where muscular force begins
• All EBN starts at once to have the max excitatory effect for EOMs

Pause neurons

Role: synchronizing the EBNs for high speed pulse generation

Does NOT directly initiate activity that goes to muscle >regular muscular energy shuts down the EBNs when the saccade is done
• Inhibitory neuron When it is turned on, the saccade is paused. When it is turned off, the saccade is allowed to happen

Inhibitory burst neurons

Role: inhibit antagonist EOMs and promotes saccade completion

Neural integrator neurons

Role: generating the saccadic step
• Helps generate steady fixation after the saccade is done
• Steps are smaller signals than pulse associated with it
o They receive input from the LLBNs or EBNs on the SAME SIDE

Question 173

Identify, in eye movement recordings, a pulseless saccade, a glissadic
undershoot, a glissadic overshoot, and a multi-step saccade.

Answer 173

Question 174

Define the stimulus to smooth pursuit eye movement.

Answer 174

The observer must perceive motion to generate smooth pursuit

Voluntary attention chooses the pursuit target
o However, pursuit movement cannot occur purely by volition

o Pursuit is a psychooptic

Question 175

List the latency and the maximum velocity of smooth pursuit eye movements in the average normal observer.

Answer 175

Maximum velocity ≈ 70 ̊/sec 1/10 velocity of saccade

Latency = 100 msec

About half of a voluntary saccade
• Short latency because no need to shift attention in smooth pursuit already fixating on the target they want to pursue
• Latency is only in the oculomotor calculation, not in attention shifting

Question 176

Select the type of attention that controls smooth pursuit movements

Answer 176

Voluntary attention chooses the pursuit target
o However, pursuit movement cannot occur purely by volition o Pursuit is a psychooptic reflex not reflexive

Question 177

Select whether smooth pursuit is controlled continuously or by sampled-data.

Answer 177

Continuous feedback control

Question 178

List the average gains of smooth pursuit for target motions which are
unpredictable and for those which are predictable

Answer 178

Gain ≈ 0.9 for brief pursuit, perhaps 1.0 if > 1sec duration
o When pursing, the eye is rotating at 90% of the velocity of the target (0.9 gain)
o The target will eventually be off the fovea, so you’d have to perform a saccadic eye movement to put it
back onto the fovea so you can pursue it again retinal image slip

Prediction:
• Creates zero-error pursuit, if motion is predictable (gain = 1.0)

Question 179

Describe the two types of error signal that can drive smooth pursuit

Answer 179

1) Difference between perceived target velocity and eye’s rotational velocity (egocentric)

o Brain perceives motion of target compared to self possibly from auditory or proprioceptive stimuli
o Not very effective method used by brain

2) Retinal image slip (oculocentric)
o Target slides across fovea away from the center if target is moving faster than the eye is rotating
o Velocity of retinal movement is the stimulus for smooth pursuit to keep image on retina

Question 180

Identify that property of smooth pursuit affected by prediction.

Answer 180

In pursuit, the target’s velocity is predictable

Question 181

List the two properties of normal pursuit that can change pursuit gain.

Answer 181

New spectacles and old age change pursuit innervation demands for the same reasons as in saccade adaptation need to adjust pursuit gain as you AGE

Question 182

List two factors in normals that reduce pursuit gain.

Answer 182

Fixation target retinal eccentricity

Fatigue,

and old age

all REDUCE pursuit gain

Question 183

Describe the roles of areas MT, MST, FEF, DLPN, NRTP, the cerebellum, inC,
and NPH in the control of smooth pursuit eye movement.

Answer 183

• Afferent pathway: retina→LGN→visual cortex

• Midtemporal cortex (MT): calculates target retinal motion
• Midsuperior temporal cortex (MST) - Calculates target egocentric motion - respect to you

• Posterior parietal cortex (PPC): drives attention to a moving target by selecting the target in MT/MST
Projects to the FEF (it tells the FEF what target is been selected for pursuit)
• Frontal eye fields (FEF): predicts target motion
• Dorsolateral pontine nucleus (DLPN): calculates the HORIZONTAL vector of target velocity sends to cerebellum
• Nucleus reticularis tegmentum ponti (NRTP): calculates the VERTICAL vector of target velocity sends info to
cerebellum

• Cerebellum (CB):
o Computes INTENDED eye velocity Computes for both horizontal and vertical based on info from the DLPN and NRTP
o Adapts pursuit gain
o Direct computation pathway for pursuit no cerebellum=no pursuit

• VN (vestibular nucleus)/NPH (nucleus prepositus hypoglossi): converts intended HORIZONTAL eye velocity to
changing position innervation passed on to the oculomotor nuclei
• inC (interstitial nuclei of Cajal): converts intended VERTICAL eye velocity to changing position innervation
passed on to the oculomotor nuclei

Question 184

Select the type of eye movement that typically replaces smooth pursuit when it fails

Answer 184

Reduced pursuit gain is revealed by “catch-up saccades” which replace the defective pursuit, and are often visible by direct observation

Question 185

List two binocular anomalies known to reduce pursuit gain.

Answer 185

Amblyopia
Poor vision lowers motion sensitivity: low gain will see more catch-up saccades

Infantile (“congenital”) Esotropia
o Background information
• Onset in 1st 6 months
• Latent nystagmus - Only appears if the patient is monocular

Question 186

Disease induced persuit anomalies

Answer 186

• Cerebellar disease and Alzheimer’s disease also reduce pursuit gain (you will see more catch-up saccades)

• Alcohol and barbiturates reduce pursuit gain
o Pursuits are used in road-side sobriety testing

Question 187

Define, in a general sense, the stimulus for vestibular eye movement.

Answer 187

Vestibular-ocular reflex (VOR)
o Eye movement designed to maintain fixation and visual contrast during transient or oscillatory head movement
o Happen at almost every moment of the day

Question 188

List the latencies of the rotational and translational VOR.

Answer 188

Rotation VOR

The latency of the rotational VOR = 16 msec shortest of all eye movements

Translation VOR

Latency = 30 msec 2x slower than rotational VOR

Gain = 1.0

Question 189

Sort the following eye movement list in the order of shortest latency to longest latency: translational VOR, rotational VOR, saccades, smooth pursuit, accommodation, and vergence.

Answer 189

1. Rotational VOR
2. Ttransitional VOR
3. Saccades
4. Smooth persuit
5. Accomodation
6. Vergence

Question 190

Compare the rotational, translational, and counterrolling VORs in terms of the type of head movement that stimulates them, their gains, and the vestibular mechanisms that drive them.

Answer 190

Rotational:

Nodding (pitch) - VERTICAL eye rotation to compensate for head movement Gain = 1.0

Turn (yaw) - Causes HORIZONTAL eye rotation - Gain = 1.0

Tilt (roll) Causes TORSIONAL eye rotation Gain = 0.5

Endolymph flow direction causes augmentation or inhibition of the sustained rate for agonist or antagonist muscular effects respectively

Anterior & posterior canals: flow away from the ampulla causes excitation • Flow towards the ampulla causes inhibition

Lateral canal: flow toward the ampulla causes excitation • Flow away cause inhibition

Question 191

Compare the rotational, translational, and counterrolling VORs in terms of the type of head movement that stimulates them, their gains, and the vestibular mechanisms that drive them.

Answer 191

The Translational VOR

• Stimulus= any head motion that is not rotational
o Heave (side-to-side) - moving the head for motion parallax
horizontal
o Bob (up and down)- when walking or running vertical
Probably the MOST COMMON head translation
o Surge (fore-and-aft) An uncommon VOR Horizontal

Anatomical basis – Otolith organs
o Utricles sense HORIZONTAL translations in any direction (heave, surge, and intermediate directions)

o Saccules sense VERTICAL translation (bob) and horizontal surge

Question 192

Compare the rotational, translational, and counterrolling VORs in terms of the type of
head movement that stimulates them, their gains, and the vestibular mechanisms
that drive them.

Answer 192

The Counterrolling VOR

Stimulus= static head tilt (no motion)

o Ex. your head is tilted to one side, but you are not rotating your head This is the only VOR NOT stimulated by motion

o The semicircular canals are not involved

o Gravity stimulates the Utricular hair cells Very weak signal and doesn’t last too long Eye movement components:

WEAK cyclorotation opposite the head
Ex: If you tilt your head to the left, there is a small dextrotorsion that rotates the eyes to the right
Static torsional gain = 0.1 (a vestigial response)
High threshold

Unequal vertical rotation – depending on target nearness
The vertical movement components underpins the Bielchowsky head tilt test

Clinical test in which you passively roll the patient’s head and observe the counterroll of the eyes
Can pick up on SO paralysis

Question 193

Match semicircular canal type (anterior, posterior, lateral) to the agonist innervation
they generate (elevation, depression, horizontal).

Answer 193

Anterior Canal

• Stimulated by head nod with chin DOWN innervate elevation agonists

Posterior Canal

• Stimulated by head nod with chin UP innervate depression agonists

Lateral (horizontal) Canal

• Each lateral stimulated by head-turn to the SAME side

Each lateral is inhibited by head-turn to the OPPOSITE side

Innervation for “contraversional” agonists

NOT stimulated by head tilt

Right Tilt
Right anterior stimulated & left posterior inhibited and vice versa Vertical effects cancel out
Levotorsion agonists innervated

Left Tilt
Right anterior inhibited & left posterior stimulated and vice versa Vertical effects cancel out
Dextrotorsion agonists innervated

Question 194

Describe how the three semicircular canals of the left vestibule are coupled with the three semicircular canals of the right vestibule for agonist / antagonist function.

Answer 194

The interconnected vestibular nuclei treat innervation from the 6 total canals as 3 excitation/inhibition pairs:

o Left and right laterals
o Left anterior and right posterior
o Right anterior and left posterior

Question 195

Define Flouren’s Law.

Answer 195

Flouren’s law: _stimulation of a single semicircular canal generates movement in the plane of that cana_l

o The movement is a VOR for a brief stimulus, or nystagmus for prolonged stimulated

Question 196

Describe the type of nystagmus, in terms of horizontal motion, vertical motion, and
torsional motion, that would be caused by a lesion of each semicircular canal when the patient is attempting to look straight ahead.

Answer 196

Damage in a single canal** causes an o**pposite direction of movement as stimulation,** but in the same
plane imbalance shows rotation in the canal
EX: damage to the right lateral semicircular canal would cause the left semicircular canal to **push the eyes to the right while the left canal is unopposed

Question 197

Identify the type of control (feedforward or feedback) that drives the VOR

Answer 197

Continuous feed forward control
o brain does not have feedback processing but instead finetunes its gain to ensure accuracy VOR needs to be efficient

Question 198

Describe the role of “velocity storage” neurons in vestibular eye movements.

Answer 198

The key to effective sustained vestibular nystagmus is innervation persistence (velocity storage)
o Semicircular canals drive vestibular nystagmus
• Vestibule output lasts ~6 seconds after the start of head rotation, because of endolymph inertia

• The vestibular nucleus (VN) extends “vestibular” innervation to 15 seconds by way of a neural process called
“velocity storage”

Question 199

List two causes of rapid VOR gain change that are not gain adaptation.

Answer 199

VOR gain can be quickly changed when needed
o Convergence induces HIGHER gain
o Voluntary gaze change turns off the VOR
o VOR gain needs to be higher during NEAR fixation than distance fixation

Question 200

Identify a natural cause of vestibular gain adaptation.

Answer 200

A natural VOR adaptation stimulus is the increased orbital friction caused by the effects of aging

Question 201

Describe how spectacle-induced vestibular gain adaptation is similar to spectacle induced saccade adaptation, and how it is different.

Answer 201

New spectacle corrections demand VOR adaptation

o PLUS lenses INCREASE the motor error as in voluntary movements opposite for minus
o Unlike voluntary movements, there is NO VISUAL SENSORY ERROR in the VOR because the vestibules

don’t “see” optical space
More of a challenge for VOR adaptation compared to saccade and pursuit adaptation in the same glasses

o The VOR must then adapt to all of the increased motor error caused by spectacle magnification on its own!

Recall that voluntary movements adapt to the difference between the sensory and motor errors

o Patients may experience a little vertigo and even nausea until they adapt VOR gain to their new glasses

o Partial adaptation to anisometropic spectacles can also occur

Question 202

Define VOR habituation.

Answer 202

Habituation is a REDUCTION of VOR gain that occurs over repeated vestibular stimulation in the DARK

o Eyes will make VOR movements even in the dark because it is not stimulated by visual input

o VOR is only a thing that can move eyes in a predictable way in the dark

The practical significance of habituation is that tests of VOR gain in the dark

Question 203

.Describe a behavior that would stimulate normal vestibular nystagmus.

Answer 203

Vestibular nystagmus is a “jerk” nystagmus

There is a fast phase & a slow phase
Fast phase – a saccade-like “jerk” to a new direction of gaze

• Innervated by saccadic EBNs and IBNs
Slow phase – a slow rotation that stabilizes the retinal image

• Innervated by vestibular neurons – same as VOR
• The key to effective sustained vestibular nystagmus is innervation persistence (velocity storage)

o Semicircular canals drive vestibular nystagmus

Question 204

List the two types of voluntary eye movement that have similar velocities as the slow and fast phases of normal vestibular nystagmus.

Answer 204

Saccade and Persuit

Question 205

List the four types of vestibular nucleus cells.

Answer 205

Head Velocity Cells

Eye Velocity Cells

Eye Position Cells

Vestibular Pause Cells

Question 206

List the roles of the four types of vestibular nucleus cells in controlling the VOR and
vestibular nystagmus.

Answer 206

Head Velocity Cells

These cells receive 8th nerve afferents

They convert the acceleration signal from the ear to a velocity signal tell the vestibular nucleus how fast the head is rotating in space

Eye Velocity Cells

Firing rate represents intended eye velocity

Eye velocity = head velocity x VOR gain

Calculates the needed velocity of the eyes to maintain fixation during head rotation

Eye Position Cells

These cells generate the changing innervation which will move the eye

Eye position = ∫ (eye velocity) dt

The velocity-to- position conversion happens in the MVN (medial vestibular nucleus) & NPH (nucleus propositus hypoglossi)

Vestibular Pause Cells

Receive info from the cortex and superior colliculus

Inhibit the VOR during voluntary gaze shifts

Question 207

Identify the purpose of each connection of the vestibular nucleus with each of the following regions of the brain: neocortex, cerebellum, paramedian pontine reticular formation, and the oculomotor nuclei.

Answer 207

VN→ oculomotor nuclei: innervates the VOR

VN→ cerebellum→ VN: adjusts VOR gain

Cerebellum→ VN:)OKN sensory signal stimulates VN to generate nystagmus

VN→ PPRF: triggers nystagmus quick phases (triggers EBNs to generate the quick phase of nystagmus)

VN→ thalamus→ vestibular cortex: awareness of body orientation, posture, balance

PPC→ VN: VOR suppression during voluntary gaze shifts

There are also nonvisual connections (ex. spinal reflexes for balance)

o Typically a 3-5 neuron arc

Question 208

Explain how to test for labyrinthine damage using the Barany and caloric tests

Answer 208

The Barany Test

• The patient sits in a rotating chair
• The patient’s head is positioned to isolate a pair of semicircular canals
• The patient is then rotated in darkness Use darkness so that vision doesn’t interfere with the vestibular nucleus
• 1. Oscillatory rotation for VOR
     2. Prolonged one-way rotation for nystagmus
• Rotation can be accurately calibrated for Both rotation directions are tested quantitative analysis
• Objective eye movement recording is used

The Caloric Test

• The patient sits in a stationary chair
• Patient’s head is tipped back 60 degrees so that lateral canals are vertical
• Warm or cold water is inserted in one ear ears can be individually tested
• Endolymph convection currents stimulate the lateral canal
• “COWS” predicts the nystagmus direction “Cold opposite, warm same”

This test only assesses lateral canal function Cold and warm water don’t affect the vertical canals because they are too far away from the auditory meatus

Objective eye movement recording is usually used

Allows us to test each ear individually

Question 209

List how eye movements and symptoms differ between patients having unilateral
labyrinthine damage and bilateral labyrinthine damage.

If vestibular, is the case peripheral or central?
o Ex: is it caused by an ear infection or brain disease?

• Peripheral is usually horizontal + torsional
• Fixation effort and a good fixation stimulus often suppress peripheral nystagmus
• central is often unidimensional and nystagnus not supperesed

o OKN can directly test vestibular nystagmus generation
If the vestibular nucleus is damaged, it won’t respond to OKN nystagmus motion signals

• If the nystagmus cause is peripheral, what is its direction?
o The nystagmus direction indicates which ear is defective

Answer 209

Bilateral labyrinthine disease & Nystagmus

• There is no nystagmus because there is no rotation sensing or vestibular tonus to affect the EOMs
• Loss of VOR
• Degraded visual acuity and oscillopsia occur when the head is in motion

Unilateral Labyrinthine Disease & Nystagmus

• Most unilateral cases affect all 3 canals on one side
• Horizontal nystagmus is present when the head is stationary because left/right tonicity is unbalanced

Fast phase is away from the damaged ear
The vertical movement effects of the anterior and posterior canals cancel out – NO vertical nystagmus

The VOR is also reduced

Continuous oscillopsia and vertigo are experienced

Question 210

Describe how the oculomotor system attempts to compensate for the deleterious
effects of nystagmus caused by unilateral vestibular disease.

Benign paroxysmal positional vertigo

Answer 210

Benign paroxysmal positional vertigo
o A common cause of vestibular jerk nystagmus in older patients age-related degeneration

o Exceptional because it is caused by damage in a single semicircular canal (the posterior)

Question 211

Differentiate passive OKN from active OKN in terms of the innervations for each.

Answer 211

Active OKN

• voluntary movement
• Slow phase = smooth pursuit
• Fast phase = saccade

Therefore, active OKN has pursuit and saccade dynamics
The pursuit responds to ALL SIZES of moving objects (Ex: a moving train or line of moving ants) Active OKN functions for a few seconds and then may be replaced by passive OKN for some stimuli

Passive OKN

Responds to LARGE moving objects or environmental motion

Watching a moving train

Watching scenery from a bus window
Many seconds of motion stimulation are needed to activate passive OKN

slow Passive OKN dominates the control of prolonged OKN
Passive OKN uses vestibular nystagmus neurons to create the nystagmus

Question 212

Compare and contrast the stimuli for smooth pursuit versus OKN.

Answer 212

The pursuit responds to ALL SIZES of moving objects (Ex: a moving train or line of moving ants)

Active OKN functions for a few seconds and then may be replaced by passive OKN for some stimuli

Question 213

Compare the control mechanisms of passive OKN versus active OKN.

Answer 213

Therefore, active OKN has pursuit and saccade dynamics
The pursuit responds to ALL SIZES of moving objects

Responds to LARGE moving objects or environmental motion

Passive OKN dominates the control of prolonged OKN
Passive OKN uses vestibular nystagmus neurons to create the nystagmus

Question 214

Describe how vestibular nystagmus and OKN interact with each other during whole body rotation.

Answer 214

OKN also helps stimulate nystagmus during prolonged head rotation
o Vestibular innervation controls EARLY nystagmus during head rotation, but then decays

Remember: Any vestibular response is stimulated by acceleration of your head

o Vestibular innervation decay leads to retinal image motion begins optokinetic nystagmus
o Retinal image motion stimulates active and then passive OKN, which sustains the rotational nystagmus

Question 215

Control of Passive OKN

Answer 215

REFLEX behavior passive OKN happens automatically and cannot be voluntarily created o Retinal image motion causes the nystagmus

Continuous feedforward control

Slow phase gain = 0.8

o Reduces retinal image speed enough so you can see clearly

Question 216

Identify those neural pathway components involved in smooth pursuit, OKN, and vestibular nystagmus.

Answer 216

MT & MST create motion perception signals information received from magnocellular cells

o Remember: MT represents retinal image motion while MST represents egocentric motion

MT & MST project to the Nucleus of the Optic Tract (NOT) & Accessory Optic System (AOS) on the SAME side

o NOT and AOS are specific for nystagmus

NOT & AOS also receive direct vestigial crossed inputs directly from the retinas

NOT & AOS project to the DLPN and NRTP

o Rightward motion processed by MT & MST projects to NOT &A OS on the right side of the brainstem and then projects to the DLPN & NRTP → cerebellum …same pathway as smooth pursuit

Prolonged stimulation of the vestibular nucleus creates velocity storage innervation

Velocity storage innervation drives the nystagmus

Question 217

Define OKAN.

Answer 217

Passive OKN is tested by way of OKAN

o Lights are extinguished after prolonged viewing

o Smooth pursuit stops immediately, but not passive OKN

Question 218

Identify the stimulus conditions that activate levotorsion, dextrotorsion, and excyclovergence

Answer 218

Dynamic head tilt:

conjugate rotational VOR tilting you head towards one shoulder or another Remember: Innervation of the vertical canals & utricles (gain of 0.5)

Static head tilt:

conjugate counterrolling VOR
Remember: when your head is stationary, the semicircular canals are nonfunctional The utricles bend hair cells due to gravity and can then sense the tilt

Near cyclovergence

Eyes EX cyclorotate when looking at near
Synkinetic with HORIZONTAL vergence
Feedforward control Brain doesn’t check accuracy for this

Fusional cyclovergence

Stimulated by torsional binocular disparities (inaccurate cyclorotation)

process: Psychooptic reflex attention control
Continuous feedback control

Question 219

List the ranges of fixation in supraduction, infraduction, adduction, and abduction.

Answer 219

Range of fixation: KNOW THIS

1. Supraduction: 42 ̊ age related decrease in ability to look up
2. Infraduction: 51 ̊
3. Adduction: 57 ̊
4. Abduction: 54 ̊

Question 220

Describe the process for stimulating “endpoint nystagmus” in normals.

Answer 220

A small normal nystagmus when the eyes are at a limit of gaze

Sustained innervation does not last forever due to weakening & the eye drifts back

The person then makes a saccade back to the target → causes nystagmus o Drift towards the PPG due to neural integrator leak

Question 221

Distinguish between the three types of eye movement occurring during normal “steady fixation” with respect to their speed, magnitude, and interocular conjugacy.

Answer 221

Tremor

High frequency: 30-100 Hz

Low amplitude: <30’’

Binocularity uncoordinated

o Eyes going in independent directions so not occurring from cyclopean innervation

Probably caused by muscle fiber action potentials

NOT a registered eye movement

Slow Drift

• 5 minarc/sec drift rate
• 1-2 per second about one 20/20 Snellen letter per second 1-5 minarc magnitudes

Binocularity uncoordinated

o Likely caused by oculomotor nuclei innervation instability/muscular response instability

• Probably the cause of the autokinetic effect

o Look at a dim light in a totally dark room. After looking at it for a while, the light starts to drift around (illusory)

• NOT a registered eye movement

Microsaccades

5 minarc average magnitude tiny

Can be as large as 25 minarc

Binocularly coordinated

o Supranuclear innervation origin

o Probable purpose: to prevent fixation target fading

ARE registered eye movements neurons are sending corollary discharge signal to the cerebral cortex to tell it that your eyes moved

• A demonstration of microsaccades
• o View the black dot for ten seconds
• o Change your view to the white dot
• o An afterimage of the grid moves with your microsaccade

Question 222

Identify the type of nystagmus expected in alcohol and barbiturate intoxication.

Answer 222

Gaze- Evoked Nystagmus

The slow phase decelerates away from the fixation target and toward the PPG

Fast phase moves the eye back to the target

o The eye cannot maintain sustained innervation after a saccade sustained neurons fail (inC, NPH)
• Caused by abnormal neural integrator leakage

Question 223

Distinguish between the symptoms “oscillopsia” and “vertigo”.

Answer 223

Vertigo is an illusion of self-motion damage to VN is telling your body you are rotating in space because the net difference between the 2 ear signals

Oscillopsia is an illusion of environmental motion

Question 224

Describe how age relates to oscillopsia in nystagmus patients.

Answer 224

Acquired nystagmus causes oscillopsia and vertigo congenital nystagmus does NOT

o Nystagmus eye movement is registered in perception if it develops early (congenital)
o These patients with congenital nystagmus still have poorer acuity, but no oscillopsia/vertigo patients with symptoms probably have disease

Several factors reduce the impact of nystagmus on visual acuity:

Null position

A direction or distance of gaze where the nystagmus is reduced to a minimum
If you see a severe nystagmus, have the patient look in different directions of gaze and find where the nystagmus is smallest

You could Rx BO prism to keep eyes always converged to promote stability
nystagmus may allow patient to see better

Head tilt improves some cases Slow-phase fixation

Question 225

Define the null position of nystagmus.

Answer 225

Null position

A direction or distance of gaze where the nystagmus is reduced to a minimum

If you see a severe nystagmus, have the patient look in different directions of gaze and find where the nystagmus is smallest

You could Rx BO prism to keep eyes always converged to promote stability
nystagmus may allow patient to see better

Question 226

Identify the impact of looking in the null position on a patient’s visual acuity and oscillopsia.

Answer 226

Nystagmus can reduce visual acuity due to retinal image motion

VA and Oscillopcia reduced in Null Position

Acquired nystagmus causes oscillopsia and vertigo congenital nystagmus does NOT

Question 227

Define “slow phase fixation” in nystagmus, and how it affects the patient’s vision

Question 228

.Given videos of patients’ eye movements and a description of what the patients were watching, identify the following eye movement abnormalities: oculomotor apraxia, gaze palsy, slow saccades, hypermetric saccades, hypometric saccades, internuclear ophthalmoplegia, macrosaccadic oscillation, pendular nystagmus, and jerk nystagmus.

Answer 228

internuclear ophthalmoplegia

macrosaccadic oscillation

ARE registered eye movements neurons are sending corollary discharge signal to the cerebral cortex to tell it that your eyes moved

Binocularly coordinated

• o Supranuclear innervation origin
• o Probable purpose: to prevent fixation target fading

pendular nystagmus

• Eye movement waveform Congenital
• EARLY visual loss impairs oculomotor stability
• The nystagmus is mostly HORIZONTAL
• Other examples: rod monochromatism, albinism,
• Acquired Caused by inherited degeneration or acquired disease
• Can be any combination of HORIZONTAL, VERTICAL and/or TORSIONAL movements
• Present in Pelizaeus- Merzbacher Disease

jerk nystagmus.

The slow phase accelerates AWAY from the fixation target

o Accurately fixate for some time and then drift away until a saccade is made to regain fixations

• Gets worse by any effort to fixate

o Best thing to do is gaze passively

Question 229

Opsoclonus

Answer 229

Rapid and variable amplitude saccadic oscillations WITHOUT an intervening refractory period

• looks like fast pendular nystagmus
• o Eyes NEVER stop moving at saccadic speed followed by saccade continuously
• o EBNs are continuously stimulated
• Associated with encephalitis, toxicity, neoplasia, especially in neonates
• Probably caused by cerebellar fastigial nucleus damage in adults

Question 230

List the percentages of total refractive power of the unaccommodated eye provided
by the cornea and the lens.

Answer 230

Cornea
o 75% of the eye’s focal power in far vision is from the cornea o Unchanging power

• Lens
o 25% of the eye’s refractive power in far vision o INCREASES power for near vision

Question 231

Describe the roles of parasympathetic and sympathetic autonomic innervation on ciliary muscle function.

Answer 231

Parasympathetic Innervation
o Drives agonist ciliary muscle action for near accommodation
o All forms of accommodative innervation (e.g. blur, proximal, tonic) produce parasympathetic innervation
o Far accommodation is achieved by:

• Relaxation of parasympathetic innervation
• Elastic tissues pulling the CB backward:
• • Posterior zonule stretched in near accommodation

• Elastic tendon of the ciliary muscle stretched in accommodation

• near: activate parasympathetic innervation
• far: relax parasympathetic innervation

• Sympathetic Innervation

o There are NO β1 (agonist) receptors in CM
o Β2 receptors inhibit parasympathetic innervation

Acts on the same muscle fibers as the parasympathetic innervation
This sympathetic innervation changes very SLOWLY: 40 seconds not used dynamically to change accommodation
This innervation is thought to be an aid in restoring far accommodation

Question 232

Identify which ciliary muscle fibers, longitudinal or circular, not only change lens
shape during near accommodation, but also move the lens forward.

Answer 232

Longitudional Fibers

Primary action: pull the back of the ciliary body towards the scleral spur

o Moves CB zonule attachment towards the lens

• Secondary action: opening the trabecular meshwork

Question 233

Describe the relative contraction speeds of extraocular striated muscle, gut smooth muscle, and ciliary smooth muscle.

Answer 233

All CM fibers work together as a single functional unit

Ciliary muscle is smooth (nonstriated) muscle

Nevertheless, ciliary muscle resembles striated muscle in several respects:

o Most myofibrils are parallel - Provide unidirectional force

Unlike gut smooth muscle fibers which are omnidirectional

o A large number of mitochondria supports fatigue resistance

Question 234

Identify the mechanical changes of ciliary muscle tension, posterior zonule tension, anterior zonule tension, lens capsule tension, anterior radius of curvature, posterior radius of curvature, and lens thickness when accommodating to near vision according to the “relaxed tension” theory of accommodation espoused by Young, Helmholtz, Gullstrand, and Fincham.

Answer 234

Events in accommodation to near:

o Ciliary muscle moves anteriorly and toward the lens equator (forward motion due to longitudinal fibers) o PPZ (pars plana zonules) & CM tendon are stretched
o AZ force is reduced
o Lens capsule force is reduced ”relaxed tension”

o Lens rounds out

• *Anterior** surface moves forward and becomes more curved
• *Posterior** surface moves slightly back (mostly blocked by vitreous) and becomes more curved

Lens thickens
Equatorial diameter is reduced (accommodated lens = smaller diameter & thicker)

• Events in restoring accommodation to far:

o Ciliary muscle force is reduced

o The ciliary body is pulled backwards by elastic forces: CM tendonPPZ fibers
o AZ tension is increased

o Increased capsule force flattens the lens

Question 235

Identify the effects of normal aging on ciliary muscle tendon elasticity, anterior
zonule elasticity, unaccommodated lens diameter, lens capsule elasticity, and lens
substance plasticity

Answer 235

An old lens has the same diameter as a young unaccommodated lens o A presbyopic lens is thicker than its younger counterpart

The “lens paradox”: a thicker lens is associated with hyperopic refractive shift
The paradox is explained by the loss of graded indices of refraction Layers of the lens falls apart making a uniform index of refraction

o The lens is much less plastic in old age
Does not change shape during attempted accommodation – even when the zonules are slack This is the main cause of presbyopia

Cilliary Muscle changes:

• Tissue changes reduce CB motility
• Loss of CM tendon elasticity replaced by collagen
• Increase of inelastic collagenous tissue in CM

Question 236

Describe the two theories on how the lens hardens in presbyopia.

Answer 236

Multifactorial theory

• Lens hardening biggest factor causing loss of accommodative power
• Capsule inflexibility
• Reduced ciliary body motility
• Probably closest theory to correct

Lens Hardening Theories

Donder’s theory – the lens hardens uniformly

Gulstrand’s theory – hardening begins in the nucleus and extends outwards with age

o Evidence favors Gulstrand’s theory of hardening

Question 237

List the minimum amount of accommodation an accommodating intraocular lens
should generate in order to provide clear and comfortable near vision.

Answer 237

Any device should yield ≥5D amps of accommodation
o Half amp in reserve at 40 cm for comfort

o Amp of accom <5D yields prepresbyopia Sx in natural accommodation

Question 238

Accomodating IOL’s

Answer 238

Single Lens Translations
o Tetraflex IOL and Crystalens IOL
o Lens more forward without shape change
Many nonmammalian vertebrates do this o Theoretical limit: 1.5D in man (not enough)

Dual Lens Translation o Synchrony IOL

o Galilean lens pair
o Front (+) lens moves forward
o Theoretical limit: 3D (not enough)

Alvarex Optical System

• o Turtle IOL
• o Two nonlinear lenses slide across each other to cause a net spherical focus change
• o Theoretical limit: 8D

Question 239

List the primary, secondary, and tertiary actions of each of the six extraocular muscles, according to the classical interpretation of muscle mechanical action.

Answer 239

Question 240

Distinguish a muscle’s “field of action” from its “primary action”.

Answer 240

Each muscle action is a vector of the line of action with respect to the center of rotation

A muscle’s actions are ordered by their relative amounts of vector force

• o Primary: strongest
• o Secondary: intermediate
• o Tertiary: weakest

• The relative strength of a muscle’s actions depends on the direction of gaze

Question 241

Describe how the “field of action” concept is used to identify a paralyzed muscle.

Answer 241

Premise: a muscle’s weakness is most evident in its “field of action”: the direction of gaze where the muscle has only a horizontal or vertical primary agonist action (no secondary or tertiary actions)

o When you do the EOMs test, you are isolating each much as best as possible intentionally move the eyes into a direction of gaze where we will challenge the selected muscle without synergism help from other muscle

o Don’t look at torsional because too hard to see

Question 242

Describe the locations of the rectus muscle fascia pulleys

Answer 242

Coronal section:
o The pulleys are thick collagen rings through which each muscle moves
o The pulleys are interconnected by collagen bands
o The pulleys are bands together comprise Tenon’s posterior capsule
o Elastin and smooth muscle in the nasal bands provide TENSION, keeping the ring/band structure taught

The pulley structure is halfway between the center of rotation and the posterior pole

Question 243

Identify the three types of tissue found within extraocular muscle “fascia” pulleys

Answer 243

**Collagen bands

Elastin**

Smooth muscle

Question 244

Define a “heterotopic” pulley.

Answer 244

EOM Pulley Pathophysiology

Pulley heterotopy

A pulley displaced from its proper position in the coronal place is heterotopic

o Inappropriate secondary and tertiary actions and strabismus

Question 245

Identify the type of strabismus associated with horizontal rectus heterotopy.

Identify the type of strabismus associated with vertical rectus heterotopy.

Pulley anomalies tend to cause NONCOMITANT STRABISMUS

• *o Noncomitant strabismus:** the deviation changes with direction of gaze
• *o Comitant strabismus:** the deviation does NOT change with direction of gaze

Answer 245

Vertical rectus pulley heterotopy causes torsional noncomitancy that stimulates oblique paralysis

Horizontal rectus pulley hetertopy can induce changes of horizontal pulling force during elevation or depression

that can cause the A and V pattern

Question 246

List the four types of extraocular muscle fiber.

Answer 246

Fiber types and function:

White: greatest force, but fatigue rapidly Important for saccadic velocity
Red twitch and tonic: provide lower but steady force More important for maintaining eye position + Control the pulleys

Intermediate: behavior between white and red types

Tonic: Important for steady eye position and pulleys

o ALL fiber types contribute to ALL types of eye movement

Question 247

Identify which types of extraocular muscle fiber are associated with the global and
orbital layers of the extraocular muscles.

Answer 247

Global Layer
Singly innervated 3 types of twitch fibers

• Red: highly oxidative, fatigue resistant Holds pulleys in position
• White: minimally oxidative, fatigueable, very fast - saccadic pulse
• Intermediate

Multiply innervated tonic fibers

• Slower than twitch
• Smooth ongoing force No action potential
• Contain proprioceptive nerve endings

Orbital layer

Generating sustained force

Singly innervated red twitch fibers
Multiply innervated tonic fibers important for maintaining eye position and controlling pulleys

Question 248

.Select the two types of EOM muscle fiber most important for rapid eye movement.

Select the two types of EOM muscle fiber most important for maintaining steady
fixation.

Answer 248

Rapid eye movement:

White & Intermediate

Steady fixation:

RED twitch & Tonic

Question 249

.Differentiate the roles of the global and orbital layers of the extraocular muscles in ocular motility.

Answer 249

o Global layer inserts on the eye ROTATES the eye

o Orbital layer inserts on the pulley (does NOT attach to eye) do NOT directly rotate eye

Question 250

.Define the “motor field” of an EOM twitch fiber

Answer 250

Motor Fields
• A “motor field” is the range of gaze positions linearly related to a motor unit’s innervation
• Motor field size ranges between 20 to 60 degrees

• Motor units have a range of thresholds:
o Low threshold neurons become active in antagonist directions
o High threshold neurons become active in agonist directions

Question 251

Compare the ratio of muscle fibers to neuron in EOM muscle units to typical skeletal muscle units.

Answer 251

Motor unit: a motor neuron and its associated muscle fibers
o 10 muscle fibers/neuron in EOMs

(50 fibers/1 neuron in skeletal muscle)

Question 252

Describe the presumed importance of proprioceptive fibers to the control of eye movement as opposed to registered gaze.

Answer 252

What the proprioceptors don’t do:

• o Adjust muscle force to varying loads
• o Register gaze direction

• What the proprioceptors might do:

• Long term oculomotor recalibration
• Feedback of saccade trajectory

Question 253

.Explain how differences between extraocular muscle and skeletal muscle physiology make extraocular muscle relatively susceptible to the effects of some systemic muscle diseases like Myasthenia Gravis and relatively immune to the effects of the systemic muscle disease Duchenne’s Dystrophy.

Answer 253

Myasthenia Gravis
o Autoimmune disease that attacks acetylcholine receptors
o Poor eye position control with micro diplopia

WHY:

Unique embryonic-like acetylcholine receptors in tonic fibers are especially hard hit- more than twitch fibers

• This leads to loss of fine alignment control and pulley heterotopia High twitch firing rates (in saccadic pulse) are ill-sustained

Duchenne’s muscular dystrophy

Systemic muscle atrophy & X-linked recessive disease

The striated muscle protein “dystrophin” degenerates, starting in early childhood
The EOMs substitute “utrophin” for decaying dystrophin, which skeletal muscles CANNOT do

Slow saccades

Question 254

Describe the behaviors of burst, burst-tonic, and tonic oculomotor nucleus neurons during saccadic eye movement.

Answer 254

• *Burs**t – most active in rapid movement
• *Tonic** – most active in steady gaze and slow movement
• Steady innervation and steady position*
• *Burst/tonic** – combination of burst and tonic activities

Question 255

List the three ways in which the pupil can enhance vision.

Answer 255

• Controls retinal illumination
o MUCH FASTER than photoreceptor adaptation

• Constriction increases depth of focus in near response
o Assists accommodation Especially important in older people who are losing accommodative ability

• Constriction reduces peripheral aberrations for best acuity in photopic vision

Question 256

Describe the roles of the sphincter and dilator in pupil function and their placement in the iris.

Answer 256

Parasympathetic Innervation sphincter
• Innervation is stimulus-contingent - light/nearness
• EWN pupil fibers are in the UPPER portion of the CN3 in the MIDBRAIN
• These pupil fibers then move to the MEDIAL side of CN3 in the CAVERNOUS SINUS
o Vascular anomalies in the Circle of Willis can affect the efferent pupillary fibers
• Pupil efferent synapse ciliary ganglion

o Out of the ciliary ganglion come short
posterior ciliary nerves→ innervate 20
sectors in the sphincter

Sympathetic innervationDilator

• Hypothalamic innervation (follows 1st preganglionic nerve) passes to the Ciliospinal center of Budge in cervical spinal cord
• 2nd preganglionic axons leave the spine, crossing over the lung apex to synapse on the superior cervical ganglion
o Damage here (due to lung infection, tumor, etc.) is the basis of HORNER’S SYNDROME→ ptosis, miosis, anhidrosis on side of lesion
• Postganglionic axons follow the carotid artery, ophthalmic nerve, and the long ciliary nerves to enter the eye and dilator
• Hypothalamus also sends INHIBITORY inputs to EWN
o Is necessary to inhibit the sphincter because the sphincter is STRONGER than the dilator

Question 257

Identify the type of retinal ganglion cell - alpha, beta, or gamma - thought to be most important for pupil control.

Answer 257

gamma (konio) ganglion cells (melanin-containing ganglion cells) sends iris control signals to the pretectal nucleus

Question 258

Describe the neural pathway which controls the pupillary light reflex.

Answer 258

• Both rods and cones serve vision and the pupil
• A subgroup of gamma (konio) ganglion cells (melanin-containing ganglion cells) sends iris control signals to the
pretectal nucleus
o Thin axons, small cell bodies, and long retinal circuits make for SLOW response
o Alpha and beta ganglion cells project to the LGN/cortex to serve vision
• Gamma cell axons partially decussate then symmetrically innervate each pretectal nucleus
• Pretectal cell axons bifurcate to symmetrically project to each EWN
• Consequence: direct and consensual responses are EQUAL

Question 259

Describe the neuroanatomical pathway that controls the pupillary near response.

Answer 259

The Near-Reflex Afferent Pathway
• PEF and FEF cortical eye movement fields send cyclopean near response signals to the midbrain supraoptic areas
• Supraoptic innervation projects to the EWNs to activate both irises
• BOTTOM LINE ON AFFERENT PATHWAYS Any light or near stimulus, monocular or binocular, EQUALLY
innervates both irises!

o A sensory defect in EITHER EYE equally affects BOTH pupils
o Differential iris responses to the same stimulus must arise within the efferent pathways o For instance, anisocoria (unequal pupils) is an EFFERENT pupil anomaly

Question 260

Identify the two oculomotor responses that usually accompany the pupillary near reflex

Answer 260

Lid Closure Response
• Neurologically equivalent to the near triad response (accommodation, convergence, miosis)

• Used on non-cooperative patients who won’t look at a near target
• Testing:
o Hold eyelids open with fingers
o Patient tries to close eyes
o Near response is triggered by the effort to close the eyes

Question 261

Identify the type of control - feedback or feedforward - that drives the pupillary light reflex.

Answer 261

Feedback control regulates the pupil response to light

Pupil gain = pupil-induced retinal illuminance reduction / retinal stimulus luminance increase

Question 262

.Identify the factor that causes the transient pupillary light reflex gain to be higher than the sustained pupillary light reflex gain.

Answer 262

Transient gain > sustained gain because of light adaptation → causes “pupillary escape”

Once illuminated, the pupil slowly starts to re-dilate even through the light stimulus is still present

Question 263

Define “anisocoria”.

Define “hippus”.

Answer 263

Hippus → pupillary unrest

• o Random oscillations by autonomic noise
• o Higher rate in bright light

anisocoria (unequal pupil sizes)

• o 1/5 of pop has aniso >0.4mm
• o Size spontaneously varies

Question 264

Diseased and pupil responce differ

Answer 264

Light Reflex and Gamma Ganglion Cells

• Gamma ganglion cells dominate the light reflex pupillary light reflex does not always respond to disease similarly to vision

• *o Leber’s optic neuropathy:**
• *Gamma cells minimally** affected while alpha and beta ganglion cells are severely damaged Light reflex is near normal despite severe visual impairment

o Retrobulbar optic neuritis
All ganglion cell types are damaged

Both vision and the pupil are impaired