The lens of the eye sits just behind the iris, the colored, visible muscle in the eye. As a normal part of aging, protein deposits gradually form on the lens, causing the lens to turn thick and hard. This is called a cataract. When a person can no longer perform daily activities, an eye doctor can remove the advanced cataract with surgery. Cataracts in the early stages don't need to be removed.

Presence Noted in Examination

In the earliest stage of cataracts, a person doesn't notice changes to vision. Typically, a person has an eye examination, and the doctor mentions the presence of mild cataracts. This may come as a surprise to many people, because they have no noticeable changes with their eyes or vision. In order for the doctor to determine if someone has cataracts, he uses eye drops to dilate the pupils in both eyes. Once the drops widen the pupils, the doctor uses a slit lamp--a microscope designed specifically for eyes--to evaluate the front and back of the eye, says the National Eye Institute. If the person has a cataract, the doctor can see the cloudiness during the examination.

Vision Changes

Cataracts occur slowly, and vision changes happen over many years. In the beginning stages of cataracts, the hardening of the lens may require the need for frequent changes in eyeglass prescription, says the National Eye Institute. With updated lenses, vision likely improves for a short time. At some point, however, a new prescription for glasses doesn't improve vision. Cataracts have a yellow tint, and since the eye uses the lens as a window to let in light, the yellow cataract will cause the person to see muted colors or a yellow haze. In the early stages, many people don't recognize the color change, though artists--as well as others who rely on color perception--may notice the color change in the beginning stages of the cataract.

Glare

As light enters the eye, the deposits on the lens distort the light, causing glare problems. Many people have difficulty seeing at night, says The Foundation of the American Academy of Ophthalmology. In this situation, people with early cataracts often stop driving at night because they don't feel safe. Glare from headlights may create a starburst effect in the vision, which often adds to the difficult driving conditions.