A cataract is a clouding of the lens of the eye that limits the light that passes through it. The lens focuses images on the retina (which then carries visual signals to the brain), so a clear lens is vital to vision.
Cataracts are very common. Although the most common cause of cataract in developed countries is advanced age, the lens can lose its clarity in a number of other ways, including injury, infection, inflammation, certain medications, a genetic disorder, or radiation (as with treatment of a tumor). Cataract surgery (replacing the hazy lens with a clear plastic or silicone substitute) is also common. This minor surgery has a remarkably high success rate.
But cataracts can be sneaky stealers of sight. They are painless and progress slowly; many people don't realize there is something wrong until they start to seek frequent changes to their glasses or contact lenses. Vision usually turns blurry, hazy, or dim, and glare from lights and the sun can be especially distressing. In the early stages, the eye may become more nearsighted. Night vision worsens, and colors appear duller.
Anyone who experiences blurring or eye discomfort should visit an ophthalmologist immediately for a full examination, because cataract is only one of several important diseases that affect night vision. The doctor will test the sharpness of your vision and will likely dilate your pupils with drops so that she or he can examine the interior of the eye to check for cataract and assess just how extensive the cloudy patches are. Other exams and tests can help rule out other eye problems, such as glaucoma or retinal degeneration.
To keep your vision sharp and clear, and know when to seek potentially sight-saving treatment, purchase The Aging Eye, a Special Health Report from Harvard Medical School.