Lecture 3

Question 1

what do all points along the circumference of the VMO stimulate?

Answer 1

corresponding points and zero binocular disparity

Question 2

what shape is the theoretical horopter in near vision?

Answer 2

bow-shaped

Question 3

what are the 3 assumptions for the theoretical VMO horopter?

Answer 3

both retinas are spherical, both retinas have symmetric distribution of local signs across nasal and temporal retinas, and right and left retina are the same size with the same local sign geometry

Question 4

what is the empirical longitudinal horopter (ELH)?

Answer 4

the actual horopter from experiments on humans - less concave than VMO (flatter)

Question 5

what is the deviation between the VMO and ELH horopters called?

Answer 5

Hering-hillerbrand deviation

Question 6

what are the 2 more commonly used methods of measuring ELH?

Answer 6

identical visual direction and equidistance (stereoscopic depth matching)

Question 7

what are 5 ways to measure ELH horopters?

Answer 7

identical visual direction, equidistance (stereoscopic depth matching), singleness (haplopia), minimum stereoscopic threshold and zero vergence

Question 8

which horopter method using this: when 2 targets, each presents to one eye, are perceived as lying in a single visual direction, the images of those targets must be formed on corresponding points?

Answer 8

identical visual direction horopter

Question 9

which method of measuring a horopter is the only true horopter and most accurate? why?

Answer 9

identical visual direction = only one that directly measures the visual direction

Question 10

when using the AFPP method (equidistance) - what is the percept of the horopter when the rods are physically lined up in a row?

Answer 10

they are perceived as curving away from the observer

Question 11

when using the AFPP method (equidistance) - what is the percept of the horopter when the rods are physically curved inwards?

Answer 11

they are perceived as being in a straight horizontal line/row

Question 12

what is the advantage of the equidistance horopter?

Answer 12

examiner can actually see the shape of the horopter directly

Question 13

what is the disadvantage of the equidistance horopter?

Answer 13

AFPP method doesn’t reflect the effects of fixation disparity, unlike the identical visual direction

Question 14

which the the most popular way to measure a horopter?

Answer 14

the Howard-Dolman apparatus - using the equidistance or AFPP method

Question 15

what does the singleness (haplopia) horopter measure?

Answer 15

the extent of Panum’s area at the fovea and eccentric locations

Question 16

what does the width of the zone of singleness reflect in the singleness (haplopia) horopter?

Answer 16

Panum’s area

Question 17

what are 2 variables that affect the shape of the ELH?

Answer 17

skew (relative magnification, R) and curvature (hering-hillerbrand deviation, H)

Question 18

what is the relative magnification (R) when the target is on the horopter?

Answer 18

zero

a1 = a2, R = 1

Question 19

what does it mean when R = 1 (relative magnification or skew)?

Answer 19

objective space matches the perceived space = no relative magnification

Question 20

what happens to an image if a size lens in placed in front of an eye?

Answer 20

the image is magnified and puts the image more nasally = creating uncrossed disparity (larger internal angle)

Question 21

what happens to the horopter when an eye is magnified?

Answer 21

the new horopter is rotated towards the magnified eye

Question 22

what does it mean if R > 1?

Answer 22

OD image is magnified

Question 23

what does it mean if R < 1?

Answer 23

OS image is magnified

Question 24

what is the typical value of H (hering-hillerbrand deviation)?

Answer 24

+0.1 to +0.2 = indicating the horopter is flatter than VMO

Question 25

why is the ELH flatter than the VMO?

Answer 25

the original assumption for VMO is not true - nasal packing phenomenon: local sign in nasal retina are spaced closer together and the temporal visual space is overestimated

Question 26

what happens to the ELH horopter with distance?

Answer 26

with increasing distance the curvature of the horopter changes so that it goes from convex = flat = concave (mirror changes in VMO curvature)

Question 27

what is abathic distance?

Answer 27

the viewing distance at which the apparent and objective frontal plane coincide in the ELH (when it is truly flat) = about 6m

Question 28

what is fixation disparity?

Answer 28

the vergence angle of the eye and the angle between the visual axis is slightly inaccurate - the fixation point doesn't coincide with the actual target

Question 29

what is exo-fixation disparity?

Answer 29

two eyes slightly under-converge - fixation point behind the target

Question 30

what is eso-fixation disparity?

Answer 30

two eyes slightly over-converge - fixation point is in front of the target

Question 31

how big is a normal fixation disparity?

Answer 31

small - usually a few minutes of arc (larger than normal may indicate potential binocular problems)

Question 32

why is fixation disparity purposeful?

Answer 32

normal FD is beneficial - it serves as a stimulus for the vergence system to maintain its innervation level (doesn't disrupt sensory fusion)

Question 33

how does strabismus affect the offset of the ELH?

Answer 33

horopter shifts towards the intersection of the visual axis and sensory fusion is disrupted

Question 34

what happens in the geometric effect and the induced effect to the horopter?

Answer 34

``` geometric = magnification along the horizontal meridian induced = magnification along the vertical meridian ```

Question 35

what is a size lens? what is a meridional size lens?

Answer 35

size lens = special lens that only changes the image size with no optical effect meridional = only changes the size along one meridian

Question 36

what happens when you use an axis 090 meridional size lens on the OD?

Answer 36

the image is magnified in the 180 (horizontal) meridian, makes the internal angles larger = uncrossed disparity

Question 37

what is "induced" when you use a 180 meridional size lens to one eye and the image is magnified vertically?

Answer 37

the effect is identical to the effect produced by an axis 090 meridional size lens in front of the fellow eye

Question 38

which horopter method can you use to measure the induced effect?

Answer 38

AFPP (Howard-Dolman) not the Nonius (it won't rotate because no physical horizontal binocular disparity is being created)

Question 39

what type of distortion do prisms cause?

Answer 39

non-uniform magnification = more magnification at the apex than the base

Question 40

what happens when you place BI prisms in front of both eyes?

Answer 40

temporal sides are magnified, horopter bends towards observer at temporal sides and the perceived world bends away from the observer

Question 41

what are 2 clinical situations where the EHL is more curved than the VMO (H < 0)?

Answer 41

divergence excess and intermittent esotropia

Question 42

what is an irregular horopter?

Answer 42

a distortion of the horopter from its normal smoothly arced shape - it deviates closer to the observer in a region near the crossing of their visual axes

Question 43

what are 3 situations that can have an irregular horopter?

Answer 43

early onset constant esotropia, metamorphopsia, and keratoconus

Question 44

what is the flom notch?

Answer 44

in an inrregular horopter = retional spatial distortion - may be the result of anomalous retina correspondence