Eye Anatomy
A guide to the Human Eye
The eye is a complex optical system - very similar to a camera. Vision begins when light enters the eye through the cornea, a powerful focusing surface. From there, it travels through clear aqueous fluid, and passes through a small aperture called the pupil. As muscles in the iris relax or constrict, the pupil changes size to adjust the amount of light entering the eye. Light rays are focused through the lens, and proceed through a clear jelly-like substance in the center of the eye called vitreous, which gives it form and shape. When light rays finally land on the retina, the part of the eye similar to film in a camera, they form an upside-down image. The retina converts the image into an electrical impulse that travels along the optic nerve to the brain, where it is interpreted as an upright image.
The ability to see is dependent on the actions of several structures in and around the eyeball. The graphic above lists many of the essential components of the eye's optical system. Click the image and then explore the image with your mouse to learn more about the structures of the eye.
The ability to see is dependent on the actions of several structures in and around the eyeball. See if you can identify the basic structures in the image below.
When you look at an object, light rays are reflected from the object to the cornea. The light rays are bent, refracted and focused by the cornea, lens, and vitreous. The job of the lens is to make sure the rays come to a sharp focus on the retina. The resulting image on the retina is upside-down. Here at the retina, the light rays are converted to electrical impulses which are then transmitted through the optic nerve, to the brain, where the image is translated and perceived in an upright position!
Think of the eye as a camera. A camera needs a lens and a film to produce an image. In the same way, the eyeball needs a lens (cornea, crystalline lens, vitreous) to refract, or focus the light and a film (retina) on which to focus the rays. If any one or more of these components is not functioning correctly, the result is a poor picture. The retina represents the film in our camera. It captures the image and sends it to the brain to be developed. The macula is the highly sensitive area of the retina. The macula is responsible for our critical focusing vision. It is the part of the retina most used. We use our macula to read or to stare intently at an object.
Provide the correct matches in the following "Drag 'n Drop" exercise.
A "visual" lecture on eye anatomy is available from YouTube
Macular degeneration is a general term used to describe a number of diseases of the retina. Of these diseases, age-related macular degeneration is the most common, primarily affecting people over the age of 60. The www.macula.org website is intended to educate patients and their families about macular degeneration, its treatment and low vision rehabilitation.
With macular degeneration, a spot called a scotoma may appear in your central vision. This scotoma may look light, or dark, or blurred. Sometimes, part of an image may look wavy or distorted as the surface of the retina becomes uneven.
It occurs in:
Dr. Vivian W. Pinn, director of the Office of Research on Women's Health discusses the most prevalent eye diseases in women, the latest advances in research in eye health, and the prevention of the most common eye diseases with Dr. Janine Smith, deputy clinical director, National Eye Institute. 
To view a transcript of this audio file:http://orwh.od.nih.gov/podcast/Podcast4_Transcript.html
A cataract is a clouding of the lens in the eye that affects vision. Most cataracts are related to aging. Cataracts are very common in older people. By age 80, more than half of all Americans either have a cataract or have had cataract surgery. A cataract can occur in either or both eyes. It cannot spread from one eye to the other.
The lens is a clear part of the eye that helps to focus light, or an image, on the retina. The retina is the light-sensitive tissue at the back of the eye. In a normal eye, light passes through the transparent lens to the retina. Once it reaches the retina, light is changed into nerve signals that are sent to the brain. The lens must be clear for the retina to receive a sharp image. If the lens is cloudy from a cataract, the image you see will be blurred.
Yes. Although most cataracts are related to aging, there are other types of cataract:
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Secondary cataract
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Cataracts can form after surgery for other eye problems, such as glaucoma. Cataracts also can develop in people who have other health problems, such as diabetes. Cataracts are sometimes linked to steroid use.
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Traumatic cataract |
Cataracts can develop after an eye injury, sometimes years later.
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Congenital cataract
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Some babies are born with cataracts or develop them in childhood, often in both eyes. These cataracts may be so small that they do not affect vision. If they do, the lenses may need to be removed
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Radiation cataract
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Cataracts can develop after exposure to some types of radiation
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Age-related macular degeneration (AMD) is a disease associated with aging that gradually destroys sharp, central vision. Central vision is needed for seeing objects clearly and for common daily tasks such as reading and driving.
AMD affects the macula, the part of the eye that allows you to see fine detail. AMD causes no pain.
In some cases, AMD advances so slowly that people notice little change in their vision. In others, the disease progresses faster and may lead to a loss of vision in both eyes. AMD is a leading cause of vision loss in Americans 60 years of age and older.
View the video below to see a simulation of how a person with AMD sees the world. (Double-click the video to start it.)
There are two types of AMD, classified as "wet" and "dry." The most common form is the dry type. Wet AMD, as seen in the animation, occurs when blood vessels growing up from beneath the retina leak blood. Leaked blood pushes on the light receptor cells resulting in damage to the retina.
Dry AMD has three stages, all of which may occur in one or both eyes:
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Early AMD |
People with early AMD have either several small drusen or a few medium-sized drusen. At this stage, there are no symptoms and no vision loss.
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Intermediate AMD |
People with intermediate AMD have either many medium-sized drusen or one or more large drusen. Some people see a blurred spot in the center of their vision. More light may be needed for reading and other tasks.
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Advanced Dry AMD |
In addition to drusen, people with advanced dry AMD have a breakdown of light-sensitive cells and supporting tissue in the central retinal area. This breakdown can cause a blurred spot in the center of your vision. Over time, the blurred spot may get bigger and darker, taking more of your central vision. You may have difficulty reading or recognizing faces until they are very close to you.
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See if you can answer these questions about how the human eye operates:
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