Cataracts - What Are They?
What Are They?
cataract is a cloudy or opaque area in the normally transparent lens of the eye. As the opacity thickens, it prevents light rays from passing through the lens and focusing on the retina, the light sensitive tissue lining the back of the eye. Early lens changes or opacities may not disturb vision. But as the lens continues to change, several specific symptoms including blurred vision; sensitivity to light and glare; increased nearsightedness; or distorted images in either eye, may develop.
The lens is located behind the iris, the colored portion of the eye, and the pupil, the dark center of the eye. Tiny ligaments, called zonules, support the lens capsule within the eye.
The lens has three parts, the capsule, the nucleus, and the cortex. The outer membrane, or capsule, surrounds the cortex which in turn surrounds the center or nucleus of the lens. If you imagine the lens as a piece of fruit, the capsule is the skin, the cortex is the fleshy fruit, and the nucleus is the pit.
Types of Cataracts
There are three types of cataracts. Each is described by its location on the lens. The most common type of cataract and the one associated with aging is called a nuclear cataract.
A nuclear cataract occurs in the center of the lens. Common symptoms include blurring or dimming of your vision, glare and visual distortion. A nuclear cataract can induce myopia, or nearsightedness, a temporary improvement in your reading vision sometimes referred to as "second sight." Unfortunately "second sight" disappears as the cataract gets worse.
The cortical cataract begins as wedge-shaped spokes in the cortex of the lens. The spokes extend from the outside of the lens to the center. When the spokes reach the center, they interfere with the transmission of light and cause glare and loss of contrast. Many people with diabetes develop this type of cataract. Although a cortical cataract usually develops slowly, it may impair both distance and near vision so significantly that surgery may be suggested at a relatively early stage.
A subcapsular cataract develops slowly and starts as a small opacity under the capsule, usually at the back of the lens. Significant visual symptoms may not appear until the cataract is well developed. Typical symptoms are glare and blur. A subcapsular cataract is often found in people with diabetes or high myopia, adults with retinitis pigmentosa, and in people taking steroids.
photos courtesy of The Lighthouse Inc., (Lighthouse National Center for Vision and Aging) New York, NY, 800-334-5497