Sankara Nethralaya
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How the EYE Works

Your eye works very much like a camera. Light enters the eye through the cornea, the clear front surface or “window” of the eye. As the light passes through the cornea, it is bent or refracted. This bent light then travels through the pupil (the opening in the coloured iris) and into the natural “crystalline” lens. The lens acts to fine tune the focus of light onto the retina. The retina turns the light energy into electrical impulses that travel along the optic (eye) nerve from the eye to the brain, where the image is interpreted. (You actually see with your brain, not with your eyes).

Below are short descriptions of the various parts of the eye that will help you understand the vision process, why vision is sometimes blurry, and how these vision disorders can be corrected.

Diagram of the anatomy of the eye
Normal eyesight is present when light rays are in focus on the retina, causing a clear image to form


The cornea is the front-most surface of the eye, like the crystal of a watch. It provides most of the eye's focusing power. Most of the refracting (bending) of light is achieved by the cornea, so small changes in the surface of the cornea can have a large effect on how your eye focuses light.

There are three main parts of the cornea : The epithelium is the thin outer protective layer that undergoes continuous regeneration. The stroma comprises the bulk of the corneal tissue and is inert. The endothelium is a single cell layer comprising the innermost cornea and serves to maintain corneal clarity by regulating corneal fluid content. The cornea is approximately the diameter of a dime and the thickness of a credit card.


The colored diaphragm in the anterior chamber of the eyeball, which contracts and expands to adjust for light intensity.


The opening in the center of the iris through which light passes.


The transparent, dual-convex body, which focuses light rays onto the retina. It is normally capable of changing shape to allow the eye to focus on both near and distant images.

Retinal Cell Layers:

The membrane on the inner wall of the eyeball, which receives the image from the lens and converts it into nerve impulses.

Vitreous Gel:

A clear jelly-like substance, which fills the posterior chamber of the eyeball. Normally attached to the retina, it can become detached in clumps or strings, called "floaters," which are usually harmless, but can cast annoying shadows on the retina.


The center of the retina. The region of highest visual acuity and cone cell density.


The area in and around the fovea. Made up mostly of cone cells, it is responsible for central vision and contains the fovea. The macula is less than 5% of the total retina.


The white, dense, fibrous outer coating of the eyeball.

Optic nerve:

Transmits nerve impulses from the retinal cell layers to the brain.