As people age, the lens in their eyes gradually becomes less transparent (hardens with age). The lens becomes cloudy and this interferes with the passage of light to the retina. At this stage it is called a cataract. As the cataract worsens, it becomes more and more difficult to see through it, and eventually the lens becomes opaque, blocking out all light to the retina. This is the most common form of cataract blindness.

The treatment for cataract is surgery. The natural lens is extracted and replaced by an Intraocular lens (IOL). IOLs are permanent optical implants for visual correction following cataract extraction. Insertion of an IOL is now the most commonly performed eye surgical procedure; cataracts are the most common eye disease. The procedure can be done under local anesthesia with the patient awake throughout the operation which usually takes less than 30 minutes in the hands of an experienced ophthalmologist.