Figure 1-3. Confrontation method.

(3) Color sense is tested by using specially designed color plates to

distinguish reds, greens, and blues.

(4) Visual acuity testing is done with the Snellen chart or one of its

modifications. Each eye is tested separately, both with and without glasses, if worn.

(a) Since the distance at which rays of light from an object are

practically parallel and no accommodation of the lens is necessary to focus the object,

the test is performed at a distance of 6 meters (20 feet),

(b) The Snellen chart contains rows of letters of varying sizes,

arranged to that the normal eye can see them at distances of 6, 9, 12, 15, 21, 30, and

60 meters. (20, 30, 40, 50, 70, 100, and 200 feet.) If a patient is seated 6 meters (20

feet) from the chart and can read the line of letters for 6 meters, his vision is expressed

by the fraction 6/6 (or 20/20).

(c) Vision is expressed by a fraction, the numerator denoting the

distance at which the test was performed (normally, 6 meters or 20 feet), and the

denominator denoting the smallest line of letters which could be read at that distance. If

a patient is seated 6 meters from the chart and the smallest line of letters he is able to

read is the one that should be read at a distance of 30 meters, then his vision is

expressed at 6/30 (or 20/100).

(d) If the largest letters on the chart cannot be read at a distance of 6

meters, the patient is moved toward the chart until he can read the largest letters.

Vision is then expressed as a fraction, with the numerator denoting the distance at

which the largest line could be read, and the denominator denoting the number of the

largest line.

MD0919

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