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cataract is a cloudy or opaque area in the normally clear lens of the eye. Depending upon its size and location, it can interfere with normal vision. Most cataracts develop in people over age 55, but they occasionally occur in infants and young children. Usually cataracts develop in both eyes, but one may be worse than the other.
The lens is located inside the eye behind the iris, the colored part of the eye. The lens focuses light on the back of the eye, the retina. The lens is made of mostly proteins and water. Clouding of the lens occurs due to changes in the proteins and lens fibers.
The lens is composed of layers like an onion. The outermost is the capsule. The layer inside the capsule is the cortex, and the innermost layer is the nucleus. A cataract may develop in any of these areas and is described based on its location in the lens:
nuclear cataract is located in the center of the lens. The nucleus tends to darken changing from clear to yellow and sometimes brown.
A cortical cataract affects the layer of the lens surrounding the nucleus. It is identified by its unique wedge or spoke appearance.
A posterior capsular cataract is found in the back outer layer of the lens. This type often develops more rapidly.
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Signs and symptoms of a cataract may include:Blurred, hazy, or vision
Reduced intensity of colors
Increased sensitivity to glare from lights, particularly when driving at night
Increased difficulty seeing at night
Change in the eye's refractive error
What causes a cataract?Most cataracts are due to age-related changes in the lens. However, other factors can contribute to their development including:
Diabetes mellitus - Persons with diabetes are at higher risk for cataracts.
Drugs - Certain medications have been found to be associated with the development of a cataract. These include:
Corticosteroids
Chlorpromazine and other phenothiazine related medications
Ultraviolet radiation - Studies have shown that there is an increased chance of cataract formation with unprotected exposure to ultraviolet (UV) radiation.
Smoking - An association between smoking and increased nuclear opacities has been reported.
Alcohol - Several studies have shown increased cataract formation in patients with higher alcohol consumption compared with people who have lower or no alcohol consumption.
Nutritional deficiency - Although the results are inconclusive, studies have suggested an association between cataract formation and low levels of antioxidants (e.g. vitamin C, vitamin E, carotenoids). Further studies may show that antioxidants have a significant effect on decreasing cataract development
Rarely, cataracts can be present at birth or develop shortly after. They may be inherited or develop due to an infection, i.e. rubella, in the mother during pregnancy. A cataract may also develop following an injury to the eye or surgery for another eye problem, such as
glaucoma.How is a cataract diagnosed?Cataracts can be diagnosed through a comprehensive eye examination. This examination may include:
Patient history to determine vision difficulties experienced by the patient that may limit their daily activities and other general health concerns affecting vision.
Visual acuity measurement to determine to what extent a cataract may be limiting clear vision at distance and near.
Refraction to determine the need for changes in an eyeglass or contact lens prescription.
Evaluation of the lens under high magnification and illumination to determine the extent and location of any cataracts.
Evaluation of the retina of the eye through a dilated pupil.
Measurement of pressure within the eye.
Supplemental testing for color vision and glare sensitivity
Source:
http://www.aoa.org/x4714.xml?video=x8297&Play=truehttp://www.youtube.com/Sng6uZEt_TQ
