Articles For Doctors
How Does The Eye Work?

Light rays enter the eye through the clear front covering called the cornea. The central black portion of the eye, the pupil, regulates light by dilating (opening) and constricting (closing). The colored portion of the eye, the iris, also helps regulate the amount of light entering the eye. The eye's lens, behind the iris, helps focus images onto the back inner lining of the eye, the retina. The retina contains tissue sensitive to light and that transmits impulses it receives through the optic nerve to the brain where these images are interpreted and sight is achieved. Six bands of muscles attach to the eyeball to control the ability of the eye to look up and down, side to side, and across. These muscles are controlled by three cranial nerves (CN III, CN IV, CN VI)

Visual Pathways

1. Light enters the eye to synapse upon the rods and cones located in the retina of the eye

2. The information leaves the eye by way of the optic nerve, and there is a partial crossing of axons at the optic chiasm where collateral fibers extend to the pituitary and pineal glands

3. Information then enters the optic tract which wraps around the midbrain (mesencephalon) and ends in the lateral geniculate nucleus (LGN) of the thalamus

4. From there, the LGN axons fan out through the white matter of the temporal lobes (ventral pathway) and parietal lobes (dorsal pathway) of the brain as optic radiations, which ultimately travel to the primary visual cortex at the back of the brain

5. The upper retina project in the optic radiation through the parietal lobes to the upper part of the visual cortex

6. The lower retina project in the optic radiation through the temporal lobes to the lower visual cortex





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