Cataract

A cataract is a clouding of the lens inside the eye which leads to a decrease in vision. It is the most common cause of blindness and is conventionally treated with surgery. Visual loss occurs because opacification of the lens obstructs light from passing and being focused on to the retina at the back of the eye. 

It is most commonly due to biological aging, but there are a wide variety of other causes. Over time, yellow-brown pigment is deposited within the lens and this, together with disruption of the normal architecture of the lens fibers, leads to reduced transmission of light, which in turn leads to visual problems.

Those with cataracts commonly experience diffculty in appreciating colors and changes in contrast, driving, reading, recognizing faces, and coping with glare from bright lights.

Sign and symptoms

Signs and symptoms vary depending on the type of cataract, though there is considerable overlap. 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 that no other eye disease is present, is judged primarily by 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.

Cause

1. Age

Age is the most common cause.  Lens proteins denature and degrade over time and this process is accelerated by diseases such as diabetes and hypertension. With the passage of time, environmental factors including toxins, radiation and UV light have a cumulative effect. These effects are worsened by the loss of protective and restorative mechanisms due to alterations in gene expression and chemical processes within the eye. 

2. Trauma

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 water 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. Following electrical injuries, cataracts may develop in 0.7 to 8%.