BV Fundamentals & Stereopsis

Question 1

Define binocular vision and binocular single vision

Answer 1

BV: simultaneous perception of 2 images (1 each eye)

BSV: simultaneous use of 2 eyes to give a single mental impression

Question 2

Explain the evolution of binocular vision

Answer 2

lateral placement of eyes in prey increases visual field
forward facing eyes in hunters allows stereopsis to locate prey

Question 3

Explain binocular summation

Answer 3

increase in visual stability using 2 eyes as the brain receives more info with 2 (8% VA & 40% CS improvements) even when stimuli have no depth

Question 4

Describe the 3 levels of binocular vision

Answer 4

BSV (fusion stereopsis)

Visual Axes Misalign (FD, diplopia, suppression)

BSV Breakdown (FD, diplopia, suppression, strabismus)

Question 5

What are the 3 main grades of BV?

Answer 5

Simultaneous perception

Fusion (Sensory/Motor)

Stereopsis

Question 6

Explain visual direction

Answer 6

stimulated retinal area (local sign)
is perceived in a visual direction

OcVD determines location of other objects in VF

see VD diagram

Question 7

Explain abnormal retinal correspondence for ARC of RE Esotropia

Answer 7

eye deviated nasally, so the object is no longer on the fovea.

fovea shifts temporally therefore the image lands on the nasal retina

Question 8

Explain a cyclopean eye

Answer 8

in BV conditions, compromise between eyes principle VDs so brain combines 2 images from each eye

directions seen relative to single reference point

Question 9

Explain oculocentric and egocentric VD reference frames

Answer 9

Oculocentric: object position signalled relative to fovea

Egocentric: object position signalled relative to reference point in our head

Question 10

Define horopter and how theoretical differs from empirical

Answer 10

Horopter: locus of points in space which project images to corresponding points in both retinas

VMC theoretical is a perfect circle, empirical is experimental and different shapes for different people

Question 11

Explain binocular disparity

Answer 11

objects on non-corresponding points create disparate images causing diplopia

crossed in front/uncrossed behind horopter

Question 12

Explain sensory & motor fusion

Answer 12

sensory: simultaneous use of 2 images from 2 eyes forming single percept using binocular cells of the visual cortex

motor: oculomotor system aligns visual axes using vergence movements to superimpose RCPs to maintain single image

Question 13

What is the prism fusion test used for?

Answer 13

measures motor fusion (N/A for strabismus, no BSV)

px with specs looks at accommodative target, shown prism until diplopia then reduced until BSV again

Question 14

Distinguish depth perception from stereopsis and it’s advantages

Answer 14

stereopsis: awareness of object relative distance from observer (3D viewing, hand-eye coordination, navigation, figure-ground segregation

Depth perception results from monocular/oculomotor cues

Question 15

Explain Panum’s fusional area and it’s dimensions

Answer 15

range of disparities where 2 similar images can be seen as single

binocular images outside range seen as physiological diplopia

10-15 mins/arc at fovea
~30mins/arc at 15 degrees

Question 16

Explain absolute and relative depth

Answer 16

Absolute: object distance from observer

Relative: distance comparison between 2 objects

Question 17

Explain stereoacuity and how its calculated (include normal value)

Answer 17

smallest depth difference visible (measure of stereopsis in radians)

PD x difference between fixated and test objects

normal value ~ 30-60 secs of arc

Question 18

Explain crossed/uncrossed physiological diplopia

Answer 18

Crossed (proximal to fixation)
Uncrossed (distal to fixation)

Question 19

Explain ocular dominance cells in relation to eye response

Answer 19

V1 cortical cells (80% ~ binocular response, 20% ~ monocular evenly between contra/ipsilateral eye)

Question 20

How do visual cortical (ocular dominance) cells encode retinal disparity?

Answer 20

50% binocular cells are disparity tuned, signal if object is in front/behind as wells as RCPs, crossed/uncrossed disparities