Threshold Amsler grid testing. Cross-polarizing lenses enhance yield.

The Amsler grid is a commonly used test for evaluation of the 10 degrees of visual field surrounding fixation. The Amsler grid is a suprathreshold stimulus and thus may not detect relative scotomas. Therefore, we had ten patients with optic neuropathies view the grid through cross-polarizing filters that created low luminance conditions in which the grid was barely perceptible. The patients were also surveyed with a 2-m tangent screen protocol and threshold automated perimetry. The threshold Amsler grid technique increased both the number of defects found and the total area of these defects by approximately a factor of 5. Two thirds of the defects found were confirmed by one of the other screening techniques. Threshold Amsler grid testing is a rapid, inexpensive, and sensitive technique for the evaluation of the central 10 degrees of the visual field.