Updated: January 17, 2018
A cataract is an eye disease in which the clear lens of the eye which lies behind the iris and the pupil becomes cloudy or opaque, causing a decrease in vision. Cataracts are the most common cause of vision loss in people over age 40. Although vision can be restored in most people with cataracts, age-related cataracts are still the principal cause of blindness in the world.
A cataract can occur in either or both eyes. Usually a cataract in one eye develop a cataract in the other eye as well. A cataract is not contagious and do not spread from one eye to the other or from person to person. Cataracts do not cause the eye to tear abnormally. They are neither painful nor make the eye itchy or red.
Light passes through the transparent lens to the retina in a normal eye. The lens must be clear for the retina to receive a sharp image. If the lens is cloudy from a cataract, the image striking the retina will be blurry or distorted and the vision will be blurry. The extent of the visual disturbance is dependent upon the degree of cloudiness of the lens.
Loss of the normal transparency of the lens is called a cataract. The cloudier the lens, the more advanced the degree of cataract. A cataract may be mild, moderate or severe. If the lens is totally opaque it is called as mature cataract which is usually white in color. Any cataract that is not opaque is called an immature cataract.
It occurs at the back of the lens. People with diabetes or those taking high doses of steroid medications have a greater risk of developing a subcapsular cataract. A posterior subcapsular cataract often interferes with your reading vision, reduces your vision in bright light, and causes glare or halos around lights at night. These types of cataracts tend to progress faster than other types do.
Nuclear cataracts usually are associated with aging and forms deep in the nucleus of the lens. It will have a temporary improvement in your reading vision. But the lens gradually turns more densely yellow and further clouds your vision with time. The lens may even turn brown as the cataract slowly progresses. Advanced yellowing or browning of the lens can lead to difficulty distinguishing between shades of color.
This type of cataract occurs in the lens cortex, which is the part of the lens that surrounds the central nucleus. It begins as whitish, wedge-shaped opacities or streaks on the outer edge of the lens cortex. As it slowly progresses, the streaks extend to the center and interfere with light passing through the center of the lens.
Some people are born with cataracts or develop them during childhood. These cataracts may be genetic or associated with an intrauterine infection or trauma. These cataracts also may be due to certain conditions, such as myotonic dystrophy, galactosemia, neurofibromatosis type 2 or rubella.
Early cataracts may not have any noticeable symptoms. At initial stage the cloudiness in your vision caused by a cataract may affect only a small part of the lens of your eye and you may be unaware of any vision loss. As the cataract grows larger, it clouds more of your lens and distorts the light passing through the lens which may lead to more noticeable symptoms. Signs and symptoms of cataracts include:
A cataract does not cause discomfort or pain in the eye or alter the external appearance of the eye.
Factors that increase your risk of cataracts include: