A cataract is an eye disease in which the clear lens of the eye becomes cloudy opaque, causing decrease in vision. Although the word cataract to describe this condition has been part of the English language only since the middle of the 16th century, the eye disease has been recognized and surgically treated since ancient times.
The lens is a portion of the eye that is normally clear. It assists in focusing rays of light entering the eye onto the retina, the light-sensitive tissue at the back of the eye. In order to get a clear image onto the retina, the portions of the eye in front of the retina, including the lens, must be clear and transparent. Once light reaches the retina, the light initiates a chemical reaction within the retina. The chemical reaction, in turn, initiates an electrical response which is carried to the brain through the optic nerve. The brain then interprets what the eye sees.
In a normal eye, light passes through the transparent lens to the retina. The lens must be clear for the retina to receive a sharp image. If the lens is cloudy from a cataract, the image striking the retina will be blurry and the vision will be blurry. The extent of the visual disturbance is dependent upon the degree of cloudiness of the lens.
Most cataracts are related to aging. Cataracts are very common in older people. By age 80, more than half of all Americans either have some degree of cataract or have already undergone cataract surgery in one or both eyes. By age 95, this percentage increases to almost 100%. A cataract can occur in either or both eyes. Individuals with a cataract in one eye usually go on to develop a cataract in the other eye as well.
A cataract is not contagious and cannot spread from one eye to the other or from person to person. Cataracts do not cause the eye to tear abnormally. They are neither painful nor make the eye itchy or red.
Although vision can be restored in most people with cataracts, age-related cataracts are still the most common cause of blindness in the world, primarily because many third-world nations lack appropriate surgical services.
As life span increases in the developed world due to modern technology and new methods of treatment of acute and chronic disease, the incidence of age-related cataracts will continue to increase.
Having cataracts is often compared to looking through a foggy windshield of a car or through the dirty lens of a camera. Cataracts may cause a variety of complaints and visual changes, including blurred vision, difficulty with glare (often with bright sun or automobile headlights while driving at night), dulled color vision, increased near sightedness accompanied by frequent changes in eyeglass prescription, and occasionally double vision in one eye.
Some people notice a phenomenon called "second sight" in which one's reading vision improves as a result of their increased nearsightedness from swelling of the cataract.
A change in glasses may help initially once vision begins to change from cataracts; however, as cataracts continue to progress and opacify, vision becomes cloudy and stronger glasses or contact lenses will no longer improve sight.
Cataracts are usually gradual and usually not painful or associated with any eye redness or other symptoms unless they become extremely advanced. Rapid and/or painful changes in vision are suspicious for other eye diseases and should be evaluated by an eye-care professional.
The lens is made mostly of water and protein. Specific proteins within the lens are responsible for maintaining its clarity. Over many years, the structures of these lens proteins are altered, ultimately leading to a gradual clouding of the lens. Rarely, cataracts can present at birth or in early childhood as a result of hereditary enzyme defects, and severe trauma to the eye, eye surgery, or intraocular inflammation can also cause cataracts to occur earlier in life.
Other factors that may lead to development of cataracts at an earlier age include excessive ultraviolet-light exposure, diabetes, smoking, or the use of certain medications, such as oral, topical, or inhaled steroids. Other medications that are more weakly associated with cataracts include the long-term use of statins and phenothiazines.
The standard cataract surgical procedure is typically performed in either a hospital or in an ambulatory surgery center. The most common form of cataract surgery today is a process called phacoemulsification. With the use of an operating microscope, your surgeon will make a very small incision in the surface of the eye in or near the cornea.
A thin ultrasound probe is inserted into the eye that uses ultrasonic vibrations to dissolve (phacoemulsify) the clouded lens. These tiny fragmented pieces are then suctioned out through the same ultrasound probe. Once the cataract is removed, an artificial lens is placed into the same thin capsular bag that the cataract occupied. This intraocular lens is essential to help your eye focus after surgery.
There are three basic techniques for cataract surgery:
- Phacoemulsification: This is the most common form of cataract removal as explained above. In this most modern method, cataract surgery can usually be performed in less than 30 minutes and usually requires only minimal sedation and numbing drops, no stitches to close the wound, and no eye patch after surgery.
- Extracapsular cataract surgery: This procedure is used mainly for very advanced cataracts where the lens is too dense to dissolve into fragments (phacoemulsify) or in facilities that do not have phacoemulsification technology. This technique requires a larger incision so that the cataract can be removed in one piece without being fragmented inside the eye. An artificial lens is placed in the same capsular bag as with the phacoemulsification technique. This surgical technique requires a various number of sutures to close the larger wound, and visual recovery is often slower. Extracapsular cataract extraction usually requires an injection of numbing medication around the eye and an eye patch after surgery.
- Intracapsular cataract surgery: This surgical technique requires an even larger wound than extracapsular surgery, and the surgeon removes the entire lens and the surrounding capsule together. This technique requires the intraocular lens to be placed in a different location, in front of the iris. This method is rarely used today but can be still be useful in cases of significant trauma.