14. Binocular Vision. Fusion PDF

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ophthalmology essay for final exam...

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14. BINOCULAR VISION. FUSION Definition= State of simultaneous vision with two seeing eyes that occurs when an individual fixes his visual attention on an object. Grades= ➊ Simultaneous perception  power to see 2 dissimilar objects simultaneously – ceases only when we suppress the image from one eye at will ➋ Fusion  Ability of the eyes to produce a composite picture from two similar pictures, each of which is incomplete in a small detail ➌ Stereopsis  Visual appreciation of three dimensions – ability to obtain impression of depth by superimposition of two images of the same object seen from slightly different angle Advantages= 

Optical defects in one eye are made less obvious by the normal image in the other eye

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Defective vision in one part of the visual field is masked because the same image fall on the functioning area of the other retina

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Field of vision is larger

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Allows individual to converge the line of sight and obtain a reading as to the absolute distance of objects

Approximately 70% of the cells in the striate cortex are binocular cells. Retinal areas from each eye that project to the same binocular cortical cells are called ‘’corresponding retinal points’’. Sensory obstacles è Dioptric obstacles – refractive errors, anisometropia è Prolonged monocular activity – severe ptosis, media opacities è Retinoneural – lesions of retina, optic nerve è Proprioceptive

Motor obstacles è Congenital craniofacial malformations è Conditions affecting extraocular muscles è CNS lesions – involving upper motor neurons

Fusion= is defined as the unification of visual excitations from the corresponding retinal images into a single visual percept. ➊ Sensory Fusion  the cortical process of blending the images from each eye into a single binocular stereoscopic image ➋ Motor Fusion  the mechanism that allows fine-tuning of eye position to maintain eye alignment – this is known as fusional vergence...