adjustments in the eyes as an object moves from distant vision to close vision
A. Three components
1. Convergence - contraction of medial rectus muscles causes eyes to rotate medially
a. Allows image of object to fall on fovea of both retinas.
2. Rounding (accommodation) of lens - the ciliary muscles normally suspend the lens tautly, keeping the lens somewhat flattened. When the ciliary muscles contract, the tension on the lens is released and the lens rounds. (presbyopia=loss of elasticity)
a. Assures that the object is in focus on the retina
3. Pupillary constriction - constriction of the sphincter pupillae muscles
a. Decreases the amount of light, thus increasing the depth of focus
B. Accommodation pathways (sight must be intact)
1. Eye to visual cortex
Visual information projects via retinal ganglion cells through the optic nerve and optic tract to terminate in the lateral geniculate body. Axons from lateral geniculate project to the primary visual cortex (Area 17). The visual data projects to the association areas of the visual cortex (Area 18 and 19), which interpret the visual data.