But when they do develop, light transmission through the eye becomes increasingly scattered, and clarity of vision decreases. The main symptom of cataracts is a decrease in vision. Just how, and under what conditions vision decreases varies, depending on the type of cataract. Some people have difficulty reading, while others have more trouble seeing in brightly lighted conditions, such as being outside on a sunny day. Many people notice that colors are not as vivid, while most find night driving especially bothersome.
Lights often seem to have a spokelike appearance.
Although all cataracts occur in the natural lens of the eye, the cloudiness may develop in different parts of the lens. Furthermore, a number of conditions may cause cataracts. The most common kind of cataract occurs as a natural part of the normal aging process, sometimes as early as age 40, and is called a senile cataract . Injuries to the eye, from a sharp blow for example, can damage the clear lens and cause another type of clouding called a traumatic cataract . Other conditions, including certain infections, drugs or diabetes, can cause a secondary cataract .