A cataract is a clouding of the natural intraocular crystalline lens that focuses the light entering the eye onto the retina. This cloudiness can cause a decrease in vision and may lead to eventual blindness if left untreated. Cataracts often develop slowly and painlessly, so vision and lifestyle can be affected without a person realizing it. Worldwide, cataracts are the number one cause of preventable blindness. There is no medical treatment to prevent the development or progression of cataracts. Modern cataract surgery, which is the removal of the cloudy lens and implantation of a clear intraocular lens (IOL), is the only accepted treatment for cataracts. Cataract surgery is the most effective and most common procedure performed in all of medicine with 3 million Americans choosing to have cataract surgery each year, with an overall success rate of 97 percent or higher.
Cataracts often develop slowly with a gradual decline in vision that cannot be corrected with glasses. Common complaints include blurry vision, difficulty reading in dim light, poor vision at night, glare and halos around lights, and occasionally double vision. Other signs of cataracts include frequent changes in the prescription of glasses and a new ability to read without reading glasses in patients over 55.
There are several types of cataract including age related, traumatic, and metabolic. Age related is the most common type and the pathogenesis is multifactorial and not fully understood. A traumatic cataract can occur following both blunt and penetrating eye injuries as well as after electrocution, chemical burns, and exposure to radiation. Metabolic cataracts occur in uncontrolled diabetics, patients with galactosemia, Wilson disease, and Myotonic dystrophy.
A cataract is defined as any opacification of the eye’s crystalline lens, and any of these changes that then lead to a degradation in the optical quality of the lens can cause visual symptoms. As there are a wide variety of cataract types, there is a large spectrum of visual symptoms associated with cataractous changes.
These symptoms may include:
- Blurred vision at distance or near (different types may affect distance greater than near or vice versa, see below)
- Glare (halos or streaks around lights, difficulty seeing in the presence of bright lights)
- Difficulty seeing in low light situations (including poor night vision)
- Loss of contrast sensitivity
- Loss of ability to discern colors
- Increasing near-sightedness or change in refractive status (including “second sight” phenomenon)