• Vision

Clinical testing of visual fields is usually done by confrontation. Formal perimetry may then be performed to document any abnormality. Several variations of confrontation visual field tests have been described, but all are insensitive at detecting visual field loss when performed individually.1 Combining confrontation tests may improve sensitivity.

You can test visual fields quickly and easily in a co-operative patient using a laser pointer and a wall. You should sit next to the patient at least 2 m away from a blank wall on which a small target is visible. You both close (or cover with your hand) your right (or left) eye and look at the target. You then shine the laser pointer at the wall to test areas of visual field that are of interest (figure 1). The stimulus may be dynamic (bringing the laser light in from the periphery until it is seen) or static (turning the laser on and off in different areas). Some pointers make a click when turned on, but simply covering and uncovering the light beam with your hand will avoid giving the patient an auditory cue. If you detect a scotoma, you can map out its shape and size. The blind spot can be assessed in this way: if you and the patient are at the same distance from the wall and close together, your blind spots should roughly coincide and an enlarged blind spot is readily apparent.

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Figure 1

The patient (left of figure) sits with the target on the wall directly in front of her. The examiner also looks at the target but from a slightly different angle so that the wall is not precisely perpendicular to his line of gaze. The visual fields of the two are thus not precisely superimposed, but this produces no difficulty in practice; the discrepancy is obviously minimised the closer the two sit together and the greater the distance from the wall.

This technique has several advantages over standard confrontation testing:

• The laser light beam is small so that tiny paracentral scotomata can be detected.

• There is no clue for the patient from the movement of the hand holding the red pin

• The results of testing are obvious to anyone watching so that this is a valuable teaching tool

• If a standard examination format (distance from wall, etc) is used, a semiquantitative record of the findings can be achieved—this is useful, for example, in following blind spot size in a patient with papilloedema

• For accurate comparisons of your visual field with that of the patient, it is easier to be sure you are both the same distance from the wall than that the target in confrontation testing is exactly midway between you.

• The principle is, of course, similar to the Bjerrum screen. A Bjerrum-style ‘grid’ on the wall would allow the exact size and position of any visual field defect to be more accurately assessed—this might be practical in some clinics where the technique was used frequently.

There are obvious potential problems with this technique:

• It relies on the patient maintaining fixation; fixation loss, which is immediately visible in confrontation testing, is not so obvious. It can only be used in co-operative patients

• Visual inattention is not easily tested (unless you have two laser pointers and close rather than cover your unused eye!)