The nasal field represents the temporal retina and the temporal field represents the nasal retina. Tangent screen field testing is much more sensitive than either confrontation fields or finger counting fields. The later two are useful, but are best reserved for neurological field testing. Confrontation fields are most likely superior to finger counting fields, however, both may have merit if a advanced retinal detachment or neurological problem is suspected. There have been at least two cases, in the clinic, when these tests missed temporal lobe cysts. Neither will plot a field defect which is diagnostic of the causative problem or possible location.

1.) The smaller the target size the more sensitive the test. The more difficult the target is to see the more sensitive the test. The brighter the background illumination on pigmented targets the easier the targets are seen. Hence, there will be a reduction in the sensitivity of the test. This concept is just the opposite if the targets are illuminated targets (targets which are spots of light).

2.) The patient should be wearing their Rx. If they are presbyopic they should have a +1.00 D lens placed in a trial frame over their distant correction, assuming the tangent screen is at one meter. Patients should never wear glasses with multifocal lenses when being tested.

3.) If a patient has reduced central vision you should place a strip of masking tape from each corner forming an (X) through the fixation point. You would then ask the patient to look in the direction where they feel the two strips of tape would intersect.

4.) All plotting is done from non-seeing to seeing. It is a good idea to plot their blind spot first so the patient understands everyone has an area of non-seeing which is normal, plus, they will have a better understanding of what it is like when the target disappears.

5.) One must be careful when interpreting your findings. There are some conditions that may cause field defects that resemble glaucoma defects, (i.e., cataracts and drusens of the optic nerve heads) may result in an arcuate fiber scotomas. Only enlargement of the blind spot is not diagnostic of glaucoma.

6.) You should always plot from non-seeing to seeing from the periphery starting on only one side of the Bjerrum screen. Plot on both the upper and lower part of the horizontal Raphe' (looking for a difference of at least 5 degrees or more difference between the upper and lower nasal horizontal field; indicative of a nasal step and glaucoma). Plot one side of the vertical meridians (a difference could be indicative of a neurological problem: optic nerve and higher centers). You should never lean across to plot the opposite side, but rather walk around the back of the patient to the other side and repeat the same procedure. Make sure as you plot the hemi-field that you run the target through the blind spot to insure the patient is paying attention. You should also turn the target over so the patient can no longer see it, again checking to see if the patient is paying attention. About 90% of the time you should be watching the patient insuring they are indeed look at the fixation point and not your target.

White—Largest Target - Tests Both Rods And Cones

Blue— Next Largest—Make Sure The Patient Can Tell You The colour of the target.

Red—Next Largest Target

Green—The Smallest Target