A cataract is a clouding of the lens of the eye. It may help to think of the lens as a peach, where the nucleus is the peach pit, the cortex is the flesh of the peach surrounding the pit, and the capsule is the peach skin, or elastic covering of the lens. There are three types of cataracts which affect different parts of the lens and cause different symptoms and vision problems. Nuclear cataract is the most common type of cataract, and is related to the aging process. The nucleus gradually hardens and becomes opaque, causing difficulty identifying colors and seeing at a distance.
Cortical cataract is the next most common type, often affecting people who have diabetes.
Wedge-shaped opacities develop in the cortex, interfering with the passage of light. This can result in problems with glare and loss of contrast, as well as difficulty with distance and near vision. Subcapsular cataract develops under the back of capsule or elastic covering of the lens and is common in people with diabetes or high myopia, adults with retinitis pigmentosa, and in people taking cortisone. This type of cataract can cause glare sensitivity and blur. In the early stages, only a doctor can detect a cataract, because there may not be any symptoms.