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Cataract

A Cataract is a clouding of the lens in the eye leading to a decrease in vision. It can affect one or both eyes. Often it develops slowly. Symptoms may include faded colors, blurry vision, halos around light, trouble with bright lights, and trouble seeing at night. This may result in trouble driving, reading, or recognizing faces. Poor vision may also result in an increased risk of falling and depression. Cataracts are the cause of half of blindness and 33% of visual impairment worldwide. Cataracts are most commonly due to aging,

but may also occur due to trauma, radiation exposure, be present from birth, or occur following eye surgery for other problems.Signs and symptoms vary depending on the type of cataract, though considerable overlap occurs. People with nuclear sclerotic or brunescent cataracts often notice a reduction of vision. Those with posterior subcapsular cataracts usually complain of glare as their major symptom. The severity of cataract formation, assuming no other eye disease is present, is judged primarily by a visual acuity test. The appropriateness of surgery depends on a patient’s particular functional and visual needs and other risk factors, all of which may vary widely.

Blunt trauma causes swelling, thickening, and whitening of the lens fibers. While the swelling normally resolves with time, the white color may remain. In severe blunt trauma, or injuries which penetrate the eye, the capsule in which the lens sits can be damaged. This allows fluid from other parts of the eye to rapidly enter the lens leading to swelling and then whitening, obstructing light from reaching the retina at the back of the eye. Cataracts may develop in 0.7 to 8.0% of cases following electrical injuries.
Ultraviolet light, specifically UVB, has been shown to cause cataracts, and some evidence indicates sunglasses worn at an early age can slow its development in later life. Microwave radiation has also been found to cause cataracts. The mechanism is unclear, but it may include changes in heat-sensitive enzymes that normally protect cell proteins in the lens. Another possible mechanism is direct damage to the lens from pressure waves induced in the aqueous humor. Cataracts have been associated with ionizing radiation such as X-rays. The addition of damage to the DNA of the lens cells has been considered. Finally, electric and heat injuries denature and whiten the lens as a result of direct protein coagulation.
The genetic component is strong in the development of cataracts, most commonly through mechanisms that protect and maintain the lens. The presence of cataracts in childhood or early life can occasionally be due to a particular syndrome. Examples of chromosome abnormalities associated with cataracts include deletion syndrome (part of chromosome gets deleted), cri-du-chat syndrome (rare genetic disorder due to missing part of chromosome), Down syndrome (presence of third copy of chromosome), Patau’s syndrome (chromosomal abnormality), trisomy 18 (Edward’s syndrome) and Turner’s syndrome (female misses all or part of X chromosome), and in the case of neurofibromatosis type 2 (an inherited disease), juvenile cataract on one or both sides may be noted.
The skin and the lens have the same embryological origin and can be affected by similar diseases. Those with atopic dermatitis (inflammation of skin) and eczema occasionally develop shield ulcers cataracts. Ichthyosis (scaly skin) is an autosomal recessive disorder associated with cuneiform cataracts and nuclear sclerosis. Basal-cell nevus and pemphigus have similar associations.
Cigarette smoking & consumption of alcohol has been shown to double the rate of nuclear sclerotic cataracts and triple the rate of posterior subcapsular cataracts. Evidence is conflicting over the effect of alcohol. Some surveys have shown a link, but others which followed patients over longer terms have not.
Age is the most common cause. Lens proteins denature and degrade over time, and this process is accelerated by diseases such as diabetes mellitus and hypertension. Environmental factors, including toxins, radiation, and ultraviolet light, have cumulative effects, which are worsened by the loss of protective and restorative mechanisms due to alterations in gene expression and chemical processes within the eye