Week 2 Flashcards by Nishan Pressley

WIT: Image is held steadily on the fovea by the eye and head

Fixation

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What 3 purposes is there for fixation?

to see stationary object
for 20/20 vision
To study targets of high spatial frequency

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For fixation to occur, motion of the image on the fovea can be NO MORE than ___ degrees per second

5 degrees/sec

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For fixation, image should like within ___ degrees of the center of fovea

0.5 degrees

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Is a tremor a conjugate movement between the 2 eyes?

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Microsaccades correct for ____.

Drifts

MS is larger by 4x in peripheral positions of gaze

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Microsaccades occure how many times per second in all directions?

1-5 times

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Are MS correlated between the two eyes in (1) time of onset and (2) direction?

Yes, but many not be correlated in amplitude

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By concentrating, can you suppress MS?

Yes!

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WIT: Deviation from the point of fixation of about 0.1 deg (6mins) w/ a velocity of about 0.25 deg/sec

Drifts

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Can drifts occur in opposite directions in the two eyes?

Yes

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In darkness, velocity of drifts increase by ___.

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WIT: Visual cues to fixate are important for steady control of gaze called ?

Field holding reflex

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Fixation + Saccades = ?

Reading

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WIT: Illusion of motion, caused by a nystagmus disrupting steady fixation

Oscillopsia

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WIT: Initial slow-phase drift w/ fast reset

Pathological nystagmus

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WIT: Small, less than 2 degree movement, this starts with an abnormal saccade

Saccadic intrusions

- more common in smokers, medications and caffeine ppl

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What is an abnormal saccadic intrusion?

Anything more than 20/min

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WIT: Repetitive to and from movment of the eyes initiated by slow phases

Nystagmus

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What is the vertical gaze holding NI?

Interstitial Nucleus of Cajal

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What is the horiontal gaze holding NI?

NPH - Nucleus Prepositus Hypoglossi

MVN - Medial Vestibular Nuclei

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What part of the cerebellum is important for gaze holding?

Flocculus

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What neurotransmitters to the NI use?

ACH
GABA
NMDA

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A leaky neural integrator create a mismatch between what 2 things?

Pulse and Step!

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WIT: Pulse signal keeps attempting to move eye to eccentric position but eye keeps drifting back due to fault step signal

Gaze- evoked nystagmus

When attempting to look back in primary gaze after adapting to gaze-evoked nystamus you get what?

Rebound nystagmus

WIT: Slow, large nystagmus toward thel lesion (R), but rapid small nystagmus away from lesion (L)

Brun's nystagmus

Brun's nystagmus occurs in ___% of large acoustic tumors > 3.5 cm

11%

What disorder occurs when there's a lesion in the MLF?

Internuclear Ophthalmoplegia (INO)

What controls horizontal conjugate gaze?

Abducen's nucleus in pons

With a lesion to the LEFT abducen's nucleus causing a horizontal gaze palsy, what results?

1. No VOR | 2. No left gaze (pt can't look left)

Lesion of the right MLF, what happens?

1. INO | 2. Right eye cannot adduct (Abducen's nucleus can't tell MR to adduct for left gaze)

Is there such thing as a normal endpoint nystagmus?

Yes, dampens after 3 beats

What is the most common cause of gaze-evoked nystagmus?

A drug side effect (sedatives, tranquilizers, anticonvulsants, alcohol)

WIT: Occurs naturally during sustained self-rotation in the light or stimulated by motion of the VF

Optokinetic Nystagmus

What are the 3 dynamics of OKN?

1. Gain 2. Frequency 3. Amplitude

WIT: the ratio of slow phase velocity to stimulus velocity

Gain

WIT: the extent of each slow phase excursion

Amplitude

WIT: The rate at which the gaze is reset by the fast phase

Frequency

What is the purpose of OKAN?

To help neutralize PRN

What is the purpose of OKN/OKR?

To stabilize images on the retina

What is circularvection?

The sensation of self-rotation, feeling like we're moving - becomes more sensative w/ age

What factors affect OKN?

1. Target Luminance 2. Spatial Frequency 3. Velocity of Target Motion 4. Direction (gain is highest horiontally) 5. Torsion (watching a revolving disk)

When does VOR tend to stop?

When acceleration = 0 and there's a constant velocity

What type of VOR do ice skaters use when doing long high-speed spins

VOR Habituation - VoR adjust and adapts to a changing environment

Since OKN is a reflex, it must be ____ to follow a small moving target. What other eye movement do you use to suppress this?

Suppressed Smooth pursuits

What is the first neural pathway to develop? What's another name for it

NOT - Nucleus of Optic Tract Subcortical pathway

What is the second neural pathway to develop? What's another name for it?

MT, MST, PP Higher Level Cortical Pathway

The subcortical pathway for OKN is mediated by what two things?

Accessory Optic System (AOS) and Nucleus of Optic Tract (NOT)

The cortical Pathway is mediated by what pathway?

Geniculo-Striate Pathway

Naso-temporal asymmetry is observed when visual cortex is not well-developed in who?

Infants, amblyopes, albinos

In under-developed cortex, what direction dominates?

Naso-Temporal direction dominates

Infants show OKN asymmetry until about what month?

2 months

OKN is much stronger for monocular stimulus toward _____?

toward the nose (drum is rotating toward the nose, temporal --> nasal)

T or F: In normal adults, there is no assymetry evident.

True, cortex is fully developed

What are the 2 consequences of the VN providing information to the sensory cortex?

1. Vestibular Sensation = circularvection | 2. Ability to distinguish between self-motion and environmental motion

The ability to distinguish between self-motion and environmental motion aids in what?

helps to maintain sense of stability during locomotion

The VN-complex receives feedback and feed-forward inputs from many areas, that allow for the effectiveness of ?

Vision Therapy - ability to improve one's eye movements

What are the 4 types of nystagmus?

1. Vestibular 2. Gaze-Evoked 3. Congenital Jerk 4. Pendular

WIT: Constant velocity drift of the eyes w/ quick phases, vestibular disease

Vestibular Nystagmus

WIT: Drift back to center, negative exponential slow phase

Gaze-evoked

WIT: Well-defined slow and fast phases, Positive exponential waveform, sometimes found in amblyopia

Jerk Nystagmus

NO defined fast-phase, found in patients with known foveal disorder

Pendulum Nystagmus

What are the 2 types of congenital nystagmus?

1. Latent/Jerk Nystagmus | 2. Pendulum Nystagmus

T or F: Latent/Jerk nystagmus only occurs when the eye is occluded

True

What are the 4 different treatments for nystagmus?

1. Pharmaceutical (muscle relaxant) 2. BCVA, w/ CL 3. Find Null Point w/ prisms or surgery 4. Vision Therapy

Week 2 Flashcards

(66 cards)