Optics is one of the most advanced fields of scientific research and application. Eye doctors can use amazingly sophisticated machines to examine your eyes microscopically, detecting even the abnormal proteins that are present in cataracts.

Chances are, though, that the first thing you'll do at your eye exam is look at a good old-fashioned eye chart-the same kind eye doctors have been using since the mid-eighteenth century.

Having you read the letters on the eye chart-the visual acuity test-is one of the ways your doctor checks for signs of cataracts. For a definite diagnosis, the doctor will use eye drops to dilate your pupils. The wider the pupil, the better he or she can use special lights to examine the inside of the eye and actually see cataracts on the lens.

The various tests described in this chapter give you and your doctor information about the overall health of your eye and about other conditions that might be affecting your eyesight. The tests can reveal how much of your vision loss is due to cataracts rather than, for example, presbyopia, myopia, or eye disease.