Cataracts An Age-Related Clouding of the Natural Lens
A cataract is a clouding of the lens inside the eye. Cataracts generally occur as part of the aging process, but they can have other causes as well. According to the American Society for Cataract and Refractive Surgery, about 60 percent of Americans over age 60 and 70 percent of those over age 75 have cataracts.
The lens, which about the size and shape of an M&M candy, is located directly behind the iris and the pupil of the eye (see Figure 1). The lens is normally clear, and therefore also is called the crystalline lens.
The lens and the cornea (the clear front surface of the eye), focus light onto the retina to create visual images.
The lens, which is flexible in a young eye, also can change shape (or "accommodate") to enable a person to focus on close-up objects. This ability diminishes with time, and some time after age 40, people find it hard to read without bifocals or reading glasses. This normal, age-related vision change is called presbyopia.
The lens has three distinct components. To visualize each component, it's helpful to think of the lens as a peach. The outer layer of the lens is a thin, clear membrane called the capsule (the skin of the peach). It covers a soft, clear layer called the cortex (the fleshy fruit). The firm center of the lens is called the nucleus (the peach pit).
These distinctions are important because they help describe the location of a cataract. Examples include: a cortical cataract, a nuclear cataract and a posterior subcapsular cataract. Each of these cataracts has different characteristics.
What Causes Cataracts
The lens consists primarily of protein fibers and water. The protein fibers are arranged in a precise fashion that allows the lens to be clear and able to focus light properly. With aging, the protein fibers in the lens appear to break down and form clumps. The areas of the lens where the orderly arrangement of protein fibers is destroyed become opaque or cloudy. These cloudy areas are cataracts.
No one knows for sure what causes age-related cataracts, but one possibility is oxidation by unstable molecules called free radicals. Smoking and ultraviolet (UV) radiation are two sources of free radicals, and both have also been associated with a greater risk for cataracts.
Other causes of cataracts include eye injuries and side effects from long-term use of certain medications, especially corticosteroids. Some cataracts, called congenital cataracts, are present at birth.
Cataract symptoms usually occur very gradually. The primary symptoms of cataracts are:
- Blurred vision
- Poor night vision
- Colors appearing less vivid or "washed out"
- Glare and halos around lights at night
- Sensitivity to light
- The need for frequent changes to your glasses prescription
- The need for brighter light when reading
- Double vision (especially if present with one eye closed)
Cataracts are painless and typically do not cause eye redness, itchiness, discomfort, a "scratchy" sensation or the feeling that something is "in" the eye (known as a foreign body sensation).
Risk Factors for Cataracts
Advancing age is the primary risk factor for cataracts. According to the Mayo Clinic, by age 65, about half of all Americans have cataracts, and perhaps 70 percent of those over age 75 have cataracts that are significant enough to impair vision.
In addition to advancing age, other risk factors for cataracts include:
- Significant cumulative exposure to solar UV rays
- Previous eye injury or inflammation
- Exposure to ionizing radiation
- Prolonged use of corticosteroids
- Previous eye surgery
Once a cataract occurs, it cannot be reversed. The only treatment is cataract surgery. In cataract surgery, the cloudy natural lens is removed and replaced with an artificial intraocular lens (IOL) to restore vision.
Not all cataracts require surgical treatment. It depends on the severity of visual symptoms attributable to the cataract. But it's important to know that it's possible for a cataract to cause a significant impairment of your night vision without appearing to significantly affect your visual acuity as it is tested during a routine eye exam.If your optometrist or ophthalmologist detects a "mild" cataract during your eye exam, be sure to discuss any problems you are having with your vision when driving at night. Some doctors will recommend contrast sensitivity testing or glare testing. These tests are more sensitive than a standard eye chart and may better identify visual impairments caused by cataracts.
It's best not to wait too long to have cataract surgery. If you have a cataract that is affecting your vision, consult with an experienced cataract surgeon. Modern cataract surgery is very safe and has a success rate over 95 percent (defined as better vision after surgery). Also, if you wait too long to have surgery, there may be greater risk of complications because the cataract has become too dense (or "ripe") or because of your advanced age.
Another reason to have cataract surgery sooner rather than later is to restore vision you aren't even aware you have lost. Replacing a natural lens that has become cloudy due to cataracts with a clear IOL usually will make colors more vivid and significantly improve your night driving vision.
You can even opt for cataract surgery with new premium IOLs that can correct presbyopia, increasing your range of clear vision and decreasing your dependence on reading glasses after surgery. Examples of presbyopia-correcting IOLs include accommodating IOLs such as the Crystalens and Crystalens HD lenses (Bausch & Lomb) and multifocal IOLs such as the ReSTOR, ReZoom and Tecnis multifocal lenses (Alcon).
Other premium IOLs include aspheric lenses that promise sharper, more defined vision than standard IOLs, and toric IOLs that correct astigmatism.
Note: This information is for general education purposes only. It is not to be used as a substitute for medical advice from your eye doctor or refractive surgeon.