vision: The Role of the Optic Nerve and Brain

The Role of the Optic Nerve and Brain

The nerve impulses from the rods and cones are transmitted by nerve fibers across the retina to an area where the fibers converge and form the optic nerve. The area where the optic nerve passes through the retina is devoid of rods and cones and is known as the blind spot. The optic nerve from the left eye and that from the right eye meet at a point called the optic chiasma. There each nerve separates into two branches. The inner branch from each eye crosses over and joins the outer branch from the other eye. Two optic tracts exit thereby from the chiasma, transferring the impulses from the left side of each eye to the left visual center in the cerebral cortex (see brain) and the impulses from the right half of each eye to the right cerebral cortex. The brain then fuses the two separate images to form a single image. The image formed on the retina is an inverted one, because the light rays entering the eye are refracted and cross each other. However, the mental image as interpreted by the brain is right side up. How the brain corrects the inverted image to produce normal vision is unknown, but the ability is thought to be acquired early in life, with the aid of the other senses.

Sections in this article:

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2024, Columbia University Press. All rights reserved.

See more Encyclopedia articles on: Anatomy and Physiology