A cataract is a clouding or opaque area over the lens of the eye – an area that is normally transparent. This clouding is caused when some of the protein that makes up the lens begins to clump together and interferes with vision.
In its early stages, a cataract may not cause a problem. The cloudiness may affect only a small part of the lens. However, the cataract may grow larger over time and affect more of the lens, making it harder for you to see. As less light reaches the retina, your vision may become dull and blurry. Cataracts generally do not cause surface irritation or pain. While cataracts cannot spread from one eye to another, many people develop cataracts in both eyes.
Scientists do not know for sure what causes cataracts, but suspect there could be several possible causes including:
- Excessive exposure to sunlight
- Steroid use
- Diuretic use
- Use of certain major tranquilizers
- Trauma to the eye
- Geographic location (Recent studies have shown that people who live in high altitudes are more at risk for developing cataracts.)
According to the National Eye Institute, part of the National Institutes of Health (NIH), there are several different types of cataracts. These include:
Age-related cataracts: The majority of cataracts are age-related. Typically, age-related cataracts are nuclear, meaning that they develop in the center of the lens and can induce myopia (nearsightedness) – a temporary improvement in reading vision that is sometimes referred to as "second sight." Unfortunately, "second sight" disappears as the cataract grows.
Congenital cataracts: Even though most cataracts are the result of aging, in rare instances they can be present at birth (congenital).
Secondary cataracts: Secondary cataracts develop primarily as a result of another disease occurrence in the body (for instance, diabetes). Secondary cataract development also has been linked to steroid use. Secondary cataracts also can develop years after cataract surgery and often are called after-cataracts.
There are two main types of secondary cataracts: cortical or subcapsular. A cortical cataract initially develops as wedge-shaped spokes in the cortex of the lens, with the spokes extending from the outside of the lens to the center. When these spokes reach the center of the lens they interfere with the transmission of light and cause glare and loss of contrast. While this type of cataract usually develops slowly, it may impair both distance and near vision so significantly that surgery is often suggested at an early stage.
A subcapsular cataract usually starts as a small opacity under the capsule, at the back of the lens. Because this type of cataract develops slowly, significant symptoms may not occur until the cataract is well-developed.
After-cataracts are subcapsular and occur when part of the natural lens not removed during cataract surgery becomes cloudy and blurs vision. Unlike a cataract, an "after-cataract" can be treated with an outpatient technique called YAG laser capsulotomy during which your doctor uses a laser beam to make a tiny hole in the lens to let the light pass through.
Traumatic cataracts: Eye(s) that have sustained an injury may develop a traumatic cataract either immediately following the incident, or several years later.
Cataracts may be inevitable, but there are things you can do to make sure you don’t get them before your time. To prevent early cataracts:
- Wear sunglasses with proper UV protection.
- Stop smoking.
- Prevent eye injury by wearing protective glasses or goggles when needed.
- Talk to your doctor about your cataract risk and how you can reduce it.