The visual fields can be examined in several ways. The first is by confrontation:
- one must check visual acuity is first satisfactory to permit the rough discrimination of the objects used for mapping visual fields - corrective spectacles are not worn
- the patient is sat opposite the examiner at the same level and about an arm's length away
- the patient closes one eye, and then focuses with the other on the diametrically opposite eye of the examiner
- a finger, or more classically, a red pin, is brought in from the periphery of the visual field from four diagonal positions, and the patient is asked to say when this is seen while still focussing on the examiners eye
- to test the acuity of the fovea centralis more precisely, the patient is asked to state when the pin is first discriminated as being red
- from the verbal response of the patient, the examiner gleans a gross idea of their visual field loss by comparison with his own appreciation
- the other eye is then checked
More accurate assessment of visual fields is with perimetric apparatus.
If appropriate, map out the patient's blind spot:
- the patient and examiner are seated as for the visual field test
- both close one opposite, non-tested eye
- with a dark background behind the examiner, both gaze directly into the eye of the person opposite, and a red pin is introduced at the midpoint between the two individuals and slightly below the level of the pupil
- the pin is moved laterally, and the patient is asked to say when it disappears from view and then reappears - this is compared with the examiners perception of their own blind spot
- the other eye is then tested