The most common symptom of cataracts is a painless blurring of vision. Everything becomes dimmer, as if seen through glasses that need cleaning. Most often, both eyes are affected, though vision is usually more compromised in one eye than the other.
Changes in vision can occur rapidly--in a matter of months--or almost imperceptibly over many years. In some cases, double vision occurs. This is caused by the passage of light through a lens that has irregular areas of opacity, which can split the rays of light from a single object and focus them on different parts of the retina. Other possible symptoms of cataracts include increasingly frequent changes in eyeglass and contact lens prescriptions and a yellowish tinge to objects.
In the early stages of a nuclear cataract (affecting the nucleus of the lens), some people who previously needed reading glasses are able to read without them, a change referred to as second sight. This improvement occurs because the cataract alters the shape of the lens, making it better able to focus on nearby objects. Over time, however, progression of the cataract generally impairs vision.
Individuals with cortical (in the lens cortex) or posterior subcapsular (in the rear of the lens capsule) cataracts often have worse vision in bright light; for example, they may have problems with night driving because of the brightness of oncoming headlights. Bright light causes the pupils to contract and restricts the passage of light to the center of the lens--the part that may be most severely affected by the cataract.