Area tested

To compare visual field charts, the same region of the visual field must be tested during serial examinations (Fig. 9-4). For most purposes, tests that examine alongside vertical and horizontal meridians are more useful than are tests that examine on the meridian (the latter are rarely used today).

Equipment and techniques

General principles

Regardless of the equipment used, there are certain fundamental requirements for accurate visual field testing. Accurate distance refraction, with the appropriate addition for the distance from

patient to stimulus, should be used. Because accommodative capacity varies with age, the amount of addition should be adjusted for the patient’s age and the instrument used (Table 9-1).

In kinetic perimetry, the rate of motion of the test object should be constant within a given test and for subsequent field examinations. Two degrees per second is conventional. The test object should be moved from the non-seeing area of the visual field to the seeing area. Most important, however, is that the same technique be used each time.

Constant fixation is necessary to obtain reliable visual fields.The visual field is mapped accurately only if the patient looks steadily at the central fixation target. Some assessment of the patient’s fixation should be recorded on the field chart, and the patient should be gently encouraged throughout the test to look at the fixation target.

For valid comparison of visual fields, follow-up field examinations should use the same stimulus sizes and intensities for