The Human Eye

The human eye is an amazing organ. Many complex processes in the eye and brain enable us to see the world around us.

How the Eye Works

Here we break down the key structures of the eye and explain what they do. In healthy eyes, all of these parts work together to provide clear vision.

Optic nerve

The optic nerve, a bundle of retinal fibers at the back of the eye, passes electrical signals from the retina to the brain.

Signals from the optic nerve to the brain are interpreted in the primary visual cortex to form an image. The optic nerve is a critical conduit for visual information!

Vitreous gel

The large posterior (back) portion of the eye is filled with clear, jelly-like substance called the vitreous gel. It contains tiny fibers that attach to your retina.

Macula

The macula is the area in the center of the eye’s retina. It is responsible for central vision, like seeing faces or reading text.

Fovea

The fovea is a depression at the center of the macula, responsible for the eye’s sharpest vision, including fine details and color.

Retina

The retina, the membrane that lines the back wall of the eye, contains photoreceptor (rod and cone) cells. These cells convert light to electrical impulses.

Iris

The iris is the part of the eye that gives the eye its color. Each iris is unique in color. The muscles of the iris control the pupil.

Cornea

Light rays enter the eye through a transparent layer of tissue, known as the cornea. The cornea bends light through a watery substance called the aqueous humor.

Pupil

The dark, round opening in the center of the colored iris is known as the pupil. The iris changes the size of the pupil from very small to large in order to regulate the amount of light that can enter the eye.

Lens

The lens, also called the crystalline lens, is a clear, flexible structure behind the iris. It is attached to muscles that contract or relax in order to allow light to be focused for clarity.

When a part of the eye does not work as it should, it can result in an eye disease or condition.

Click a box below to learn about symptoms, incidence and potential treatments.

Eye Diseases That Can Affect Vision

Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a vision disorder caused by abnormalities in a portion of the eye's retina called the macula. It can lead to loss of central vision.

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Amblyopia & Strabismus

Amblyopia (or “lazy eye”) refers to reduced vision due to incorrect signaling between the eye and brain. Strabismus, a condition of misaligned eyes, is the most common cause of amblyopia.

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Cataract

Cataract is a cloudy area on your normally clear lens, located behind your eye's colorful iris, that reduces vision.

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Color Blindness

Research to Prevent Blindness makes the following eye screening tool available. While this tool does not replace a visit to an eyecare specialist, we hope you find it helpful.

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Corneal Disease

Corneal damage, such as clouding or scarring can be caused by injuries, infections, hereditary defects and inflammation from chronic dry eye.

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Diabetic Retinal Disease

Diabetic eye disease is a term for a group of conditions (including diabetic retinopathy, diabetic macular edema, cataracts, and glaucoma) that can affect people with diabetes.

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Dry Eye

Dry eye is a chronic medical condition that develops when the eye's tear film does not lubricate and protect the eye's outer surface.

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Glaucoma

Glaucoma is a progressive, vision-threatening disease that damages the cells and fibers of the optic nerve, affecting the transmission of signals from the eye to the brain.

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Inherited Retinal Diseases & Retinitis Pigmentosa

IRDs are vision-threatening genetic disorders (caused by a defect with at least one gene) that affect retinal cells, causing photoreceptor degeneration or dysfunction. There are hundreds of genes that can cause an IRD.

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Low Vision

Low vision is a broad term for conditions resulting in reduced sight that cannot entirely be corrected with eyeglasses, contact lenses, medicines or surgery. It can affect central and/or peripheral vision.

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Ocular Cancer

Primary ocular (eye) cancers, meaning that they start in the eye and are not cancer that has spread from somewhere else in the body, include uveal melanoma and retinoblastoma.

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Uveitis / Infectious Diseases

Uveitis refers to inflammation of the uvea, the middle layer of the eyeball, which includes the iris, ciliary body and choroid. It can be the result of an infectious eye disease.

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