A cataract is an eye disorder in which the lens of the eye becomes cloudy and obscures vision, according to the National Eye Institute. The risk of developing cataracts increases as a person ages and by age 80, more than 50 percent of Americans have either had, or been treated for, cataracts. There are three main types of cataracts, which are named based on the region of the lens affected.
Nuclear Cataract
Merck Manuals, an online medical library, reports that a nuclear cataract is characterized by difficulty in seeing objects clearly that are far away. In fact, in the early stages of this form of cataract, near vision actually improves due to the changes in the lens caused by the cataract. When a person who needed reading glasses in the past no longer needs them, he is said to have "second sight." The Mayo Clinic adds that a nuclear cataract affects the center of the lens. As the cataract progresses, second sight vanishes, and the lens turns a cloudy yellow, and then a shade of brown. The ability to see in dim light and night vision becomes gradually more impaired. The affected person also has difficulty distinguishing between the colors blue and purple, or dark blue and black.
Subcapsular Cataract
This form of cataract begins as a very small cloudy area underneath the lens capsule, according to the Mayo Clinic. The cloudy area thus obstructs light from passing through the lens to hit the light-detecting region of the eye, the retina. One sign of a subcapsular cataract is difficulty reading. Other symptoms are poor vision in bright light and poor night vision, for which glare or halos around objects affect a person's ability to see clearly. Merck Manuals adds that ability to read and see in bright light are affected because a subcapsular cataract obstructs light entering the eye maximally when the pupil constricts, which occurs especially during reading and while under bright lights.
Cortical Cataract
A cortical cataract begins at the outer edge of the lens, and is visible as white opaque regions or streaks that are wedge-shaped, according to Merck Manuals. As this type of cataract progresses, the white streaks grow toward the center of the lens, and block light from passing through the lens to the retina. Glare is the biggest problem for people with this type of cataract.
