VS 5 Lecture 1 + 2

when visual space does not match physical space

unique oculocentric direction associated with a specific retinal point.

It's determined by retinoptic mapping of retinal locus in LGN and cortex. Mechanical visual phosphenes show the neural basis of local signs.

1/7; basis for hyperacuity.

Larger than peripheral cones.

Neuroanatomical - retinal disease (most common and evident) and Strabismus/amblyopia (subtle, asymptomatic)

Optical - extreme K distortion such as keratoconus

is the oculocentric sense of "straight ahead" signaled by the fovea, Zero Direction.

is a PVD associated with the local sign of peripheral retina. Pt NOT AWARE its off center. 

Found in strabsimic amblyopia or Long term macular Dz

PVD assciated w/ fovea but Pt is AWARE of using peripheral vision to see.

Found in short term macular dz or low vision rehab.

A reference point by the visual system located right b/w the eyes. Cyclopean eye if you will.

• 1) Retinal location of the object's image in each eye.
• 2) Eye orientation. Possibly determined by EOM proprioception or neurons that drive the mm.

Law of identical visual direction.

For every retinal point in one eye there is a corresponding point in the other eye w/ an identical sense of visual direction.

Objects on the visual axis of either eye in symmetrical convergence appear to be on the median plane of the head. 

i.e. images on corresponding points are seen from cyclopean eye

• alphaL = alphaR. Meaning the angle from each eye's PVD is the same which also mean the image lays on corresponding points.
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• Eyes are fixed on a target. There is a circle/sphere where the angles are = in L&R eyes that stimulate corresponding points.
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Tolerance of binocular vision when images deviate from corresponding points.

longer version: An area on the retina of one eye where an image can be placed and still can be fused with an image on a single location in the fellow eye.

Zone on either side of Horopter's line where the brain can still accomplish sensory fusion; refers to physical space.

1) Size of PA increases with retinal eccentricity. @ fovea = 5-20' of arc. As one goes to the periphery the area will increase.

2)Target spatial freq strongly influenced PA size. Higher spatial freq = smaller PA. (ex. small snellen letters make Pts more sensitive to diplopia.

3) Both target motion and Pt motion increase PA.

• Brief stimulus = round shape
• Stationary = larger size, elliptical, larger horizontally. Allows fusional eye movement. Therefore Pts sensitive to vertical diplopia.

• Both retina are spherical.
• Both retina have symmetrical local signs nasal and temporal.
• Right and Left retina are the same size w/ local sign geometry.

Fusion Line that is less concave than VMO when determined experimentally.

• 1) ID visual direction
• 2) equidistance (stereoscopic depth matching)
• 3)Singleness (haplopia)
• 4)minimum stereosopic threshold
• 5) zero vergence

Most accurate horopter b/c it directly measures the visual direction.

Most popular way to measure horopter. Tells Pt to place rods in the same plane while looking at the center rod.