When protein buildup obstruct light rays, cataracts may occur. Because light can not clearly pass through the eye lens, the brain receives blurry images. Inside the eye lens, when new cells form, all the older cells are compacted, thus causing the cataract to occur.

When light rays enter the eye, they pass through the cornea, the aqueous humor, the eye pupil, and then the eye lens. From the eye lens, the image will be focused onto the retina lining. Then the image will pass the retinal cells, the optic nerve, and finally arrive at the brain.

Prescription eyeglasses (such as bifocals) or cataract surgery can be used to treat cataracts and restore eye vision.