On the symptoms that the person is experiencing, the appearance of the eyes, and the results of an examination diagnosis of eye disorders is initially based. A variety of tests can be carried out to confirm a problem or to determine the extent or severity of the disorder.Each eye is tested separately.
Refraction
Refraction is the procedure by which focusing error is assessed. Problems with visual acuity that outcome from refractive errors, such as nearsightedness, farsightedness, astigmatism, and presbyopia, are diagnosed by refraction. Acuity is usually measured on a scale that compares a person’s vision at 20 feet with that of someone who has perfect vision. Thus, a person who has 20/20 vision sees objects that are 20 feet away with the same clarity as a person with normal vision, but a person who has 20/200 vision sees at 20 feet only as clearly as a person with perfect vision sees at 200 feet. One important visual acuity test uses the Snellen chart (eye chart), which is a large card or lighted box that displays rows of letters in smaller and smaller sizes. The chart is read from a standard distance. The degree of visual acuity is determined by the size of the row of letters that the person can read. For those who are unable to read, a modified chart can be used in which the letters are represented by an upper case “E,” which is rotated randomly. The person is asked to describe the way the “E” is facing.
