The spectral sensitivity at the opponent stage of the visual system is traditionally measured by a hue-cancellation procedure. Comparison with a direct hue-matching method shows that cancellation overestimates short-wavelength sensitivity by as much as a factor of 30. The observation implies that different mechanisms control the perception of short-wavelength and long-wavelength redness.

Thirty-five diabetic patients who had undergone pan-retinal photocoagulation were surveyed to determine the frequency and severity of visual difficulties they experience. Among the most frequent problems were difficulty adjusting to dim lighting, difficulty adjusting to bright lighting, and trouble in sorting dark colors. Judging distances, negotiating stairways, and avoiding obstacles were identified as having become more difficult since the laser treatment. According to a correlation analysis, the difficulties encountered in some important tasks, such as driving in the daytime, were highly related to visual acuity. However, many of the problems reported most frequently, and many of the problems whose frequency had increased the most since the laser therapy, were not related to acuity. Despite their many visual complaints, the patients expressed very positive attitudes toward the photocoagulation treatment.

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Adaptation ability in the center of vision was tested in diabetic patients treated with pan-retinal photocoagulation for diabetic retinopathy and in normal control subjects. This was accomplished with a specially designed contrast sensitivity testing regimen. Patients with retinopathy showed "hidden" deficits, losses in adaptation ability that could not be measured by standard clinical tests, such as visual acuity. This new test thus quantifies a previously unmeasured visual problem that affects the everyday visual function of these patients.