Cataracts require surgery once they interfere with a person's quality of life to a sufficient degree, explains Mayo Clinic. This is an individual decision based on subjective preference, as the passage of time does not usually affect the effectiveness of surgery, and cataracts do not typically harm the rest of the eye.
Cataracts occur in the lens of the eye, where they cloud the normally transparent tissue, notes Mayo Clinic. They can cause sensitivity to light, less vivid color perception, impaired vision, poor vision in the dark and double vision in a single eye. Cataracts usually affect both eyes, but not normally to the same degree. Cataracts typically develop slowly and cause no symptoms at first. Once symptoms begin to appear, better lighting and glasses are often sufficient for vision, but the condition is degenerative.
During cataract surgery, a permanent artificial lens replaces the natural lens of the eye, reports Mayo Clinic. Even if both eyes need surgery, the surgeries usually take place with one or two months between them. Some people have eye conditions that make it impossible to implant a lens, but contact lenses or glasses can still restore some vision. Cataract surgery is generally safe, but it increases a person's risk for retinal detachment.