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—We are gratified by Dr Fankhauser's comments with respect to our article, "Background Illumination and Automated Perimetry."We are certain that his clarification of the psychophysical phenomenon involved in the clinical testing of visual field function will enhance understanding of our manuscript. It was not our intent, however, to compare or contrast the relative usefulness of perimeters using different background illumination for routine visual field testing. Specifically, we wanted to quantitate the effects of further reduction in background illumination by neutral density filters on threshold determination in otherwise normal subjects.The change in retinal illumination by fluctuation in pupillary diameter can be estimated by geometric considerations. The extent to which lenticular opacities absorb light is unknown. It is true that a cataractous lens rarely, if ever, produces an afferent pupillary defect. Consequently, the extent to which lenticular opacities may reduce retinal illumination may be greater than 0.3 log
Klewin KM, Radius RL. Background Illumination and Automated Perimetry-Reply. Arch Ophthalmol. 1986;104(8):1126. doi:10.1001/archopht.1986.01050200032024