Every eye contains a small lens. In a young normal eye this lens is clear and focuses the light entering the eye onto the retina. As we age the lens begins to harden and loses the ability to focus from near to distance and back again. This is known as presbyopia and begins around the age of 40 years. The earliest symptom is difficulty seeing things up close and bifocal or varifocal glasses become necessary for some people to see clearly at all distances.
As the natural lens in the eye continues to age further it starts to become cloudy and brown in colour resulting in hazy or blurred vision and colours lose their brilliance. This is called a cataract. At first frequent changes in glasses prescription can help, but left untreated cataracts can eventually lead to blindness.
Over 60% of people over the age of 60, and quite a few younger than that are affected by cataracts – it is so common that almost everyone will develop a cataract if they live long enough.