What is the lens?
The lens is a clear part of the eye that helps to focus light, or an image, onto the retina. The retina is the light-sensitive tissue at the back of the eye. (See diagram below.)
In a normal eye, light passes through the transparent lens to the retina. Once it reaches the retina, light is changed into nerve signals that are sent to the brain.
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The lens must be clear for the retina to receive a sharp image. If the lens is cloudy from a cataract, the image you see will be blurred.