If you are a geologist, the word cataract means a descent of water over a steep surface. If you are a meteorologist, a cataract is any furious rush or downpour of water. But to the ophthalmologist (eye doctor), cataract means blurry, blocked vision. The word actually comes from a Greek word meaning waterfall. The central idea is an obstruction, making it a good name for the eye problem of cataracts.
As light enters the eyeball, it passes through the cornea, then through the hole in the iris (pupil), and passes through the lens where it is focused onto the retina in back. As people age, the lens in each eye often becomes thicker, less flexible and, as a result, vision gets cloudy and looses its natural clearness. This is caused by a cataract. Cataracts affect over 20 million Americans over 40 years old, and nearly half of those eighty or more. Cataract symptoms include clouded or blurred vision, more difficulty seeing at night, fading of colors, double vision in one eye, and sensitivity to light and glare. Children are sometimes born with cataracts. These are called congenital cataracts. They may be the result of an infection or condition that the mother had.
Several types of cataracts are known. The first type, called the nuclear cataract, affects the center of the lens. As the cataract grows, the lens turns yellow or even brown. Cortical cataracts, on the other hand, affect the edges of the lens. As they grow toward the middle, they especially cause problems with glare. Posterior subcapsular cataracts affect the back of the lens. They often first affect reading vision or cause halos around light at night.
The only treatment for cataracts is the replacement of the lens. The old method of doing this in the 1960s and 1970s was to freeze the lens with liquid nitrogen. Since it is more than 300ºF below zero, that doesn’t take long! A cryoprobe freezes and removes the lens in one piece. This is called cryoextraction. The most common method today is called phacoemulsification. An ultrasonic instrument vibrating at 40,000 Hz emulsifies the lens that is then removed in small pieces. A third method is called extracapsular cataract extraction (ECCE) in which the lens is removed whole. It involves a larger incision in the side of the eyeball. This method may be preferred if the patient has a very stiff lens that will not emulsify easily.
Cataract surgery is usually done one eye at a time with a few weeks for healing between. In each method mentioned above, an intraocular lens is implanted to replace the lens that is removed. The procedure is done while the patient is awake and rarely involves a hospital stay. Vision is improved almost immediately. But be advised: cataract surgery can often increase the risk of retinal detachment.