Lecture 2

Question 1

what is Hering’s second law (law of identical visual direction)?

Answer 1

for every retinal point in one eye there is a corresponding retinal point in the fellow eye with an identical sense of visual direction

Question 2

what are corresponding points?

Answer 2

they unify the visual direction of the two eyes - objects that fall on corresponding points will be seen as lying in a single visual direction under binocular viewing conditions

Question 3

in the hering window experiment - why do you perceive the house and the tree as overlapping images?

Answer 3

they both have oculocentric directions of 0 (they fall on the fovea) and are on corresponding points

Question 4

what is Hering’s third law?

Answer 4

objects on the visual axis of either eye in symmetrical convergence appear to be on the median plane of the head - images on corresponding points are seen from the cyclopean eye

Question 5

what are 4 characteristics of corresponding points?

Answer 5

have identical oculocentric direction in normals, each pair of corresponding oculocentric directions form a single cyclopean eye, all retinal points have a corresponding partner except ONH and monocular crescents of the VF, and normal correspondence is highly stable, not altered by image luminance, contrast, color, size or orientation

Question 6

what is a binocular substance angle?

Answer 6

when an image stimulates corresponding points they have the same oculocentric direction under binocular conditions

Question 7

what is the Vieth-Muller circle (VMO)?

Answer 7

or the geometric or theoretical horopter = all points along the circumference of the VMO subtend equal angles in the R and L eyes, they stimulate corresponding points, it passes through the fixation point and the 2 nodal points

Question 8

what is binocular disparity?

Answer 8

when an image stimulates non-corresponding points on the retina - they create binocular disparity

Question 9

what is disparity?

Answer 9

it is defined as the difference between the binocular substance angle (n = aL - aR)

Question 10

what does horizontal binocular disparity allow?

Answer 10

stereoscopic depth perception (crossed or uncrossed disparity)

Question 11

what might crossed disparity stimulate?

Answer 11

stereoscopic “nearness”, crossed diplopia, and ocular convergence

Question 12

what might uncrossed disparity stimulate?

Answer 12

stereoscopic “farness”, uncrossed diplopia and ocular divergence

Question 13

what is the binocular disparity angles in crossed and uncrossed disparity?

Answer 13

crossed = n is positive
uncrossed = n is negative

Question 14

what are the 3 degrees of binocular sensory fusion?

Answer 14

1. simultaneous perception (keystone)
2. flat fusion (worth 4 dot)
3. fusion with stereopsis (stereo acuity testing)

Question 15

what is motor fusion?

Answer 15

bifoveal fixate on a target by vergence eye movement and aligns corresponding points in the two eyes

Question 16

how are motor and sensory fusion related?

Answer 16

motor fusion is a prerequisite for sensory fusion

Question 17

what is an exception for motor fusion being a prerequisite for sensory fusion?

Answer 17

micro-strabismus or mono-fixation syndrome = small angle (usually esotropia) they will have flat fusion even with slightly misaligned eyes they have adapted some sensory fusion using peripheral retina to fuse

Question 18

what is sensory fusion?

Answer 18

images near corresponding points are fused by visual cortex to create a single perception - requires similarity between 2 monocular images

Question 19

what is Panum’s fusional area?

Answer 19

an area on the retina of one eye where an images can be placed and still can be fused with an image on a single location in the fellow eye (the zone on either side of the horopter within which it is still possible to maintain sensory fusion)

Question 20

what type of space does Panum’s area refer to?

Answer 20

physical space

Question 21

what happens to Panum’s area with retinal eccentricity?

Answer 21

it increases with retinal eccentricity = the further away from fovea the larger the size

Question 22

what is the size of Panum’s area at the fovea?

Answer 22

about 5-20’ of arc

Question 23

is diplopia easier to observe in central or peripheral vision?

Answer 23

easier to observe in central vision than peripheral

Question 24

what happens to Panum’s area with spatial frequency?

Answer 24

the higher the spatial frequency the smaller the PA size (during vergence test small Snellen letters makes the patient more sensitive to the onset of diplopia)

Question 25

what happens to Panum’s area with target motion and patient motion?

Answer 25

both increase Panum’s area

Question 26

what is the shape of Panum’s area with a brief stimulus?

Answer 26

round shape

Question 27

what is the shape of Panum’s area with a stationary stimulus?

Answer 27

elliptical shape, larger horizontally (larger than brief stimulus) - allows fusional eye movements = patient is more sensitive to vertical diplopia