How the Eye Works
Vision is made possible when light rays are captured, focused, and processed by the various interrelated parts of the eye. When the eye is opened, light first passes through the cornea, the eye's transparent front "window" and main focusing element. The cornea takes a wide spectrum of light and bends it through the pupil , a round opening in the center of the colored iris - Directly behind the pupil is the lens (crystalline lens). It fine focuses the light directly on the retina, a photosensitive membrane that lines the inside back wall of the eye. The retina changes light images into electrical impulses and sends them through the optic nerve to the processing center of the brain where vision becomes a vivid reality. Eyes are responsible for about 75% of what people perceive. The various parts of the eye are designed to fulfill their specific roles in the amazing process of turning light into sight.
LENS
The fine focusing element of the eye. Until a person is 40 - 50 years old, it can vary its curvature to focus at different distances.
PUPIL
The opening in the center of the iris that regulates the amount of light that enters the inner parts of the eye.
CORNEA
The front "window" and main focusing element of the eye. The outer layer (epithelium), serves to protect the eye. This layer consists of unique clear cells that have the ability to regenerate quickly. The inner layer is also clear, consisting of sturdy tissue that allows light to pass.
IRIS
Pigmented tissue lying behind the cornea that (1) gives color to the eye (e.g. blue eyes) and (2) controls the amount of light entering the eye by varying size of the black pupillary opening. The most forward extension of the middle (uveal) layer of the eye which separates the anterior chamber from the posterior chamber.
Optic nerve
The largest sensory nerve of the eye; carries impulses for sight from the retina to the brain. Composed of retinal nerve fibers, which leave the eyeball through the optic disc.
Vitreous gel
Transparent, colorless, gelatinous mass (fine collagen fibrils and hyaluronic acid); fills rear two-thirds of interior of the eyeball, between the lens and the retina.
Retina
A photosensitive membrane that lines the back of the eye. It captures the images of light, changes them into electrical impulses, and sends the messages to the brain for interpretation into sight.
Sclera
Opaque, fibrous, protective outer layer of the eye; contains collagen and elastic fibers. Directly continuous with cornea in front and with shealth covering the optic nerve behind.
Micron
Unit of measurement that represents 1/1000 of 1 millimeter curvature to focus at different distances.
Emmetropia
Refractive condition in which no refractive error is present when accommodation is at rest. Distant images are focused sharply on the retina without the need for accommodation or corrective lenses.