Cataract is a term used to describe the clouding of the crystalline lens in the eye. The most common cause of cataracts is the normal aging of the lens. This is the reason why most of those afflicted with cataracts are seniors. Less common causes of cataract include trauma, systemic diseases , inflammatory eye diseases, and the use of certain drugs.
Cataracts are classified as one of three types:
A nuclear cataract forms in the nucleus, the center of the lens, and is due to natural aging changes.
A cortical cataract, which forms in the outer layers of the lens, gradually extends its spoke-like opacities from the periphery of the lens to the center. Many diabetics develop cortical cataracts.
A posterior subcapsular cataract begins at the back of the lens. It is commonly seen in people who are on chronic steroid therapy. Because of its posterior location it tends to produce early symptoms.
The lens lies behind the iris and the pupil (see diagram). It works much like a camera lens. It focuses light onto the retina at the back of the eye, where an image is recorded, and sent to the brain as electrical impulses through the optic nerve. The ability of the lens to change shape allows us to see things clearly both up close and far away.
When the lens has become clouded from the development of a cataract, light rays become distorted and are not focused clearly on the retina, which reduces vision. Cataracts are a leading cause of preventable vision loss in adults. Over fifty percent of the population aged sixty will exhibit some degree of cataract formation. The cloudiness does not spread from one eye to the other; though, cataracts tend to develop in both eyes at some time. Some cataracts mature over a period of years, whereas others can form rapidly within a few months.
What Causes Cataracts to Develop?
The lens is made of mostly water and protein. The protein is arranged in a precise way that keeps the lens clear and lets light pass through it. As we age, some of the protein may clump together and start to cloud a small area of the lens. This is a cataract. Over time, the cataract may grow larger and cloud more of the lens, making it harder to see.
Other causes of cataracts include trauma, exposure to toxic chemicals, ultra violet radiation, , use of certain medications, most notably steroids, metabolic disorders, such as diabetes, and intrauterine infections. The latter can cause congenital cataracts. In each of these instances the delicate balance of water and protein is disturbed in he lens causing opacities to develop.
Symptoms of a Cataract
Early cataracts can be very mild with minimal symptoms. As they progress one or more of the symptoms listed below will become evident, depending on what type of cataract is developing.
Diagnosing a Cataract
If a cataract is suspected, a comprehensive examination by an ophthalmologist should be performed. The eyes will be dilated and using a special biomicroscope, the lens will be examined to determine whether a cataract is present. Other eye structures such as the cornea, retina and optic nerve will be closely examined to make sure that no additional vision threatening disease is present; for example, glaucoma, or macular degeneration which would influence the outcome of cataract surgery. If other disease is present further diagnostic testing will be performed. At the Ullman Eye Center we are equipped with advanced visual field and laser optic nerve imaging technology to aid in the diagnoses of eye diseases.
For more information on the treatment of cataracts, please see Cataract Surgery.
Facts About Cataracts
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