Binocular Vision

Define Binocular Vision and Binocular Single Vision.

Binocular Vision (BV) is the simultaneous perception of two images, one from each eye and Binocular Single Vision (BSV) is the simultaneous use of the two eyes to give a single mental impression.

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Evolution of Binocular Vision

Lateral placement of eyes increases visual field, which is essential for hunted herbivore - not much overlap between the two eyes. Forward facing eyes allows stereopsis that improves distance judgments & allows carnivores to locate prey

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Why is Binocular Vision important?

Back up, larger field of view, binocular summation and stereopsis (depth perception)

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What does binocular summation mean?

Binocular summation is the increase in visual ability when using two eyes as our brain receives more info with two eyes. Binocular improvement is ~8% for VA and ~40% for CS.

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What are the 3 main grades of Binocular Vision?

Simultaneous Perception, Sensory & Motor Fusion, Stereopsis

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Explain what is meant by normal retinal correspondence.

This is when the fovea of one eye shares a common visual direction with the fovea of the other eye and as a result stimulates corresponding retinal points. Nasal elements of one eye will correspond to temporal elements of the other eye.

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Explain Visual Direction

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Explain what is meant by abnormal retinal correspondence is in the case of esotropia.

One eye has deviated inwards & as a result sensory adaptation to manifest strabismus has occurred and the deviated eye now uses a new point P to fixate on objects. So, what was considered as the central retinal point has changed and is now temporal.

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Cyclopean Eye

Under binocular viewing conditions, there is compromise between the two eyes individual principle visual directions – brain combines the two images from each eye. We see directions relative to a single reference point: cyclopean eye

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Oculocentric Visual Direction

Position of objects signalled relative to the fovea (everything above fovea is referenced as above and anything below the fovea is below)

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Egocentric Visual Direction

Position of object signalled relative to a single reference point within our head

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Define the term Horopter.

A horopter is a locus of points in space that project images to corresponding points in the 2 retinas. Objects that land on the horopter have zero disparity. Objects that land in front/behind the horopter stimulate non-corresponding retinal points.

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How do the theoretical (Vieth Muller Circle) and empirical horopters differ?

The VMC is theoretical and perfectly circular, passing through the entrance pupil of each eye. The empirical horopter is derived from experimentation and is flatter than the VMC - it has a different shape for different individuals.

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What is Binocular Disparity?

Corresponding points are perceived as arising from targets at the same distance (zero disparity). Objects land on non-corresponding points create disparate images (cause diplopia). Crossed: visual lines cross inside the Horopter. Uncrossed: outside

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Binocular Vision

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