Ocular Motility: Lecture 12: Vergence Eye Movement

Question 1

Overview of Vergence

1. When is Vergence needed?
2. When is Version needed?

Answer 1

1. For Changing Viewing Distance

2. For accomplishing tasks when changing direction of gaze

Question 2

Maddox Classification of Vergence

1. 4 types

Answer 2

1. Accommodative Vergence; Disparity Vergence; Proximal Vergence; and Tonic Vergence

Question 3

Stimuli of Vergence: Subsystem

1. Disparity
2. Accommodative
3. Proximal
4. Tonic

Answer 3

1. Target Disparity
2. Target Blur
3. Apparent Nearness of Perceived Distance of Target
4. Baseline Neural Innervation (Midbrain)

Question 4

1. What is a HOROPTER?

2. What marks the Limit of PANUM’s Space/Area

Answer 4

1. a Volume Centered on the Fixation point that contains all points in space that yield single vision.
2. When retinal disparities become too large for the visual system to fuse and diplopia will begin

Question 5

Disparity Vergence

1. Vergence driven by what?
   a. goal?
2. Fusional or Disparity Vergence is Analogous to what?
   a. Fine Adjustment Mechanism that holds or maintains fixation of a given target and corrects for minor changes of disparity caused by what?

Answer 5

1. Binocular retinal Disparity (angular positional difference at the eyes b/w an object in the field and the bifixation point)
   a. and Whose System Goal is to Reduce the Retinal Disparity sufficiently to Obtain a Fused Binocular Percept of the New Object of Regard
2. to Optical Reflex Accommodation
   a. by Small movements of the Head or the Target being inspected

Question 6

Three Categories of Disparity Vergence

1. Zero Disparity: Objects lying on what?
2. Uncrossed Disparity: Objects lying where?
3. Crossed Disparity: Objects lying in what?
   a. Occlusion of 1 eye causes what?

Answer 6

1. on the Horopter
2. Lying Behind the Horopter Requires a Divergence Movement
3. Lying in Front of the horopter Requires a Convergent Movement
   a. Occlusion of 1 eye causes the Diplopic Image on the Opposite Side as the Occluder to Disappear

Question 7

Features of Disparity Vergence

1. The Disparity Vergence System is quite ROBUST to changes in quality of the stimulus, like what?
2. The System will initiate a disparity vergence response to very dissimilar or decorrelated targets, resulting in what?
   a. But it requires quite similar or correlated targets to obtain what?

Answer 7

1. Like Contrast and Luminance, so that it will fuse 2 blurry lines just about as well as 2 sharply focused lines
2. in a Transient Pulselike Movement
   a. to Obtain a Sustained Fusion Response

Question 8

Symmetric and Asymmetric Stimuli

1. If the targets are placed along the midline, what occurs?
2. If targets are placed in any other location, what happens?
3. An asymmetric vergence response typically consists of a small initial vergence movement, followed by what?

Answer 8

1. relatively saccade-free symmetric disparity vergence occurs
2. Asymmetric disparity vergence occurs
3. followed by a saccade to position the eyes to have reasonable SYMMETRIC RETINAL DISPARITY PLACEMENT

Question 9

Time Constant and Latency

1. Disparity Vergence will typically precede ANY Accommodative Vergence by about how much?
   a. This may be functionally beneficial, because it allows what?

Answer 9

1. 100 msec

a. allows the retinal image to approach the Fovea, where the accommodative gain is highest

Question 10

Disparity Vergence

1. COARSE STEREOPSIS: Initial what?
   a. It’s effectively what?
   b. with only the Latter portion being under what?

Answer 10

1. 200 msec portion
   a. an Open-loop, Preprogrammed Response
   b. under CONTINUOUS VISUAL FEEDBACK control to reduce the residual vergence error to w/in Panum’s Fusional Areas

Question 11

Disparity Vergence

1. A Horizontal Disparity Vergence Response takes about how long to complete?
   a. Vertical and Cyclodisparity Vergence responses are typically what?

Answer 11

1. about 1 second to complete

a. roughly eight to ten times SLOWER

Question 12

Slow and Fast System

1. Fast System: Reduces disparity error to w/in what?
   a. For sustained Vergence gaze at any new level, the Slow Fusional Vergence System Gradually does what?
   b. The Motor Output of the Fast System Controller Inputs and drives what?
2. As the Slow System continues to be innervated, the fast system innervation effectively does what?
   a. with the sum of the Fast and slow system outputs being CONSTANT to sustain what?

Answer 12

1. Panum’s Area in 1 second or so
   a. Subsumes Responsibility (time constant of greater than 1 minute)
   b. the Slow “adaptive” system
2. Decays
   a. the Proper Fixed Gaze Angle

Question 13

Accommodative Vergence

1. Refers to what?
   a. Associated w/what?
   b. Present in what?
2. During Convergence, what happens?

Answer 13

1. to Synkinetically driven vergence response
   a. with a Change in blur-driven accommodation
   b. in Monocular and binocular viewing conditions
2. slow nasalward movement occurs is associated w/the far-to-near blur drive, with this amt being dictated by the neurologically based ACA ratio

Question 14

Accommodative Vergence (2)

1. Under symmetric Binocular Viewing Conditions, the isolated accommodative vergence responses are what?
2. With NONCONGRUENT STIMULATION, the accommodative and vergence stimuli are not what?
   a. This occurs during what?
3. with normal midline CONGRUENT STIMULATION (that is, the accommodative and vergence stimuli are numerically equal), the disparity vergence response typically precedes what?
4. Which is slightly faster: convergence or divergence?

Answer 14

1. are Relatively EQUAL in the 2 eyes
2. are NOT NUMERICALLY EQUAL
   a. during relative accommodation (and vergence) testing in the clinic
3. the Accommodative vergence response because of the slightly shorter Latency of the former
4. Convergence

Question 15

AC/A Ratio

1. What is it?
   a. Derived from what?
2. Gradient AC/A is calculated by assessing the change in what?
   a. But the distance of the target is held constant and lenses are interjected into the lines of sight of what?
3. In the Far-Near AC/A, proximal vergence affects what?
   a. In the Gradient AC/A, Proximal Vergence affects what?

Answer 15

1. a Fundamental Aspect of an individual’s Oculomotor system.
   a. by Measuring the change in Vergence related to the change in accommodation when fixation is altered from 1 distance to another (i.e., the far-near AC/A)
2. in Vergence Related to the Change in Accommodation of the eyes.
   a. of Both eyes to alter the magnitude of Accommodation
3. the Near Assessment of Vergence
   a. Affects both Assessments

Question 16

Proximal Vergence (1)

1. What does it refer to?
2. How is it measured?
3. How do you Open-Loop the Accommodative System with what?

Answer 16

1. the change in vergence angle of the eyes caused solely by the relative apparent or perceived nearness of an object in the field
2. Openloop the disparity vergence system either by fully occluding one eye or by vertical dissociation.
3. with Pinholes

Question 17

Proximal Vergence (2)

1. Does it change with age?
2. Under Optimal Open-Loop Viewing Conditions, proximity can alter what?
3. Under Normal Binocular Closed-Loop Viewing Conditions, Preliminary Modeling results suggest that Proximal Vergence has relatively Little what?
4. With Disparity Vergence Openloop, but with Accommodation Closed-loop, Proximal Vergence may Enhance the response by what?

Answer 17

1. No
2. the Static Convergence Position of the eyes by 40% of that demanded by the actual distance of the Object
3. little impact (

Question 18

Tonic Vergence

1. In the absence of Disparity, blur and proximal stimuli, the vergence position of the Eyes shifts to what?
2. This Convergence Position presumably reflects what?

Answer 18

1. to an Intermediate Distance

2. baseline Midbrain Neural Stimulation

Question 19

Vertical Vergence

1. Vertical Disparity Vergence is stimulated by the presence of what?
2. The Vertical Vergence Break finding is often what?
3. Vertical Vergence Exhibits adaptive behavior when challenged with what?

Answer 19

1. of Global Vertical Retinal Disparity
2. 3-5 PD
3. with a Prolonged and Fusible Vertical Vergence Demand

Question 20

Main Sequence

1. There is a Neurologically based relation between what?
2. Vergence peak velocities are roughly 10% of that found for what?
3. Peak Vergence Velocity INCREASES as vergence Amplitude increases, with a ratio of about what?

Answer 20

1. Disparity Vergence AMPLITUDE and its peak VELOCITY
2. for a similarly sized saccade
3. 4:1

Question 21

Striate Cortex

1. Tuned-Zero Neurons
2. Tuned-Far Neurons
3. Tuned-Near Neurons

Answer 21

1. respond to Binocular stimuli, narrow range about the fixation point responsible for FINE STEREOPSIS
2. Respond to binocular stimuli that are farther from fixation, responsible for COARSE STEREOPSIS
3. Respond to Binocular stimuli that are nearer than fixation, responsible for COARSE STEREOPSIS

Question 22

1. Lesion of NRTP leads to what?
2. Lesion of Dorsal Vermis leads to what?
3. Lesion of Fastigial Oculomotor Region leads to what?

Answer 22

1. Impaired Convergence
2. Esodeviation (excess convergence)
3. Exodeviation (Excess divergence)

Question 23

Abnormal Vergence

1. Prevalence of Strabismus is what % in the general population?
2. Binocular suppression is the process whereby all or part of the ocular image of one eye is prevented from contributing to what?

Answer 23

1. 5%

2. to the Binocular Percept and Commonly found in strabismus