Intro Binocular Vision Exam 1

1. monocular: 170 deg horizontal
2. binocular: 200 deg horizontal

binocular:
1. better visual sensitivity
2. lower contrast sensitivity
3. better spatial resolution
4. stereopsis

1. frontal placement of two eyes
2. foveal fixation with each eye
3. approx equal VA of each eye under binocular conditions
4. similar retinal image size for each eye
5. normal oculomotor system
6. normal retinal correspondence and fusion

light rays entering (or leaving) the eye and passing through the nodal point are NOT DEVIATED!!

the line that connects an object point in the visual field of one eye with its image on the retina

the visual line that passes from the fovea to an object of regard

1. principal: direction signaled by fovea
2. secondary: direction signaled by retina locus other than fovea (defined relative to the principal visual direction in angular terms)

1. clockwise deviations are POSITIVE
2. counterclockwise deviations are NEGATIVE

1. for every point in the left eye, there is a point on the right eye that has the same local sign
2. associated with the same oculocentric visual direction

when the corresponding oculocentric local signs of the two eyes are combined by the brain, the visual space is seen as if from an imaginary single eye

1. a single frame of reference related to the head to perceive visual direction
2. perceived visual direction is the EGOCENTRIC VISUAL DIRECTION

monocular: oculocentric direction
binocular: egocentric direction

objects sharing the same oculocentric visual direction in each of the two eyes will be perceived as having the same egocentric visual direction when viewed binocularly

1. the perceived single visual direction of an object that simultaneous stimulates of the two foveaes
2. coincides with the median plane of the head

1. the perceived single visual direction of an object that simultaneous stimulates of two corresponding points other than the foveaes

common subjective principal visual direction

the horizon of vision

1. the loci of all object points that are imaged on corresponding retinal elements at a given fixation distance

1. a geometric circle passing the fixation point and the nodal points of the two eyes
2. geometric horizontal horopter is located on this circle

1. when an object NOT lying on the horopter is imaged by disparate retinal elements
2. the difference of an object's two retinal image positions in relation to corresponding points

binocular parallax - vergence angle

1. binocular parallax: the angle formed by the intersection of the two visual lines of an object
2. vergence angle: the angle formed by the intersection of the visual axes of the two eyes at the fixation point

1. zero: any object ON the horopter have ZERO binocular disparity
2. crossed: all objects INSIDE the horopter
3. uncrossed: all objects OUTSIDE the horopter

ZONE OF SENSORY FUSION

the zone on either side of the horopter within which it is still possible to see objects singly

1. suppresion
2. anomalous retinal correspondence (ARC): sensory remapping of one retina (bad eye) to correspond to the retina of the other eye (good eye)

1. consciously directing fication with a retinal locus OTHER than the fovea
2. usually a learned adaptation due to foveal injury or disease

VISUOSCOPY

reticle target in direct opthalmoscope allows direct visualization of eccentric fixation

1. if the patient is asked to quickly point to an object in the field of action of the paralyzed muscle while the fellow eye is covered, his finger will tend to point beyond the actual object location
2. an error of subjective localization caused by discrepancy between the inn. effort to move the eye and the amplitude of the elicited eye movement.

1. first: simultaneous perception of each eye's image
2. second: two images are simultaneously perceived as a single view
3. third: stereopsis

1. alternation theory: alternating processes
2. fusion theory: simultaneous processing

1. without fusional vergence: SAME
2. with fusional vergence: horizontal is larger than vertical because range is greater in the horizontal axis

1. larger for low spatial freq stimuli
2. larger for longer stimulus durations (partly related to allowing motor fusion)

1. flatter central region indicates healthy vergence adaptation, symptom free.
2. 70% of patients at distance and 60% at near.

1. found in 25% of patients at distance and 25% at near
2. most often in esophoric patients who adapt poorly to BI prism

1. found in 10% of patients at NEAR and 0% at distance
2. found most often in highly exophoric patients who adapt poorly to BO prism

1. found in 5% of patients at distance and 5% at near
2. little change in FD with either the addition of BO or BI prism
3. adapts well to BOTH BI and BO prism

READ ABOUT ANOMALOUS RETINAL CORRESPONDENCE

BINOCULAR CONFUSION

they look superimposed

DIPLOPIA

1. Physical distortion of the retina can produces some corresponding distortion of spatial localization

LARGER IN PERIPHERY than CENTRAL

periphery: 6-7% magnification
central: less tolerated

Existence of both NRC and ARC in the same strabismic patient.

NRC during normal oculomovement
ARC under strabismic conditions