S-cone contrast sensitivity in glaucoma as a function of mean luminance

Abstract

Evaluation of tritan defects is potentially useful for early diagnosis and evaluation of treatment of glaucoma, but the clinical utility of tests such as the Farnsworth-Munsell 100 hue has been limited due in part to effects of individual variations in pupil size and extent of lens yellowing. S-cone contrast sensitivity has been proposed as a more useful tritan test, but it is not known precisely how S-cone contrast sensitivity measured with a computer monitor is influenced by variations in mean S-cone quantal catch due to individual differences in pupil size and lens density. We measured S-cone contrast sensitivity of patients with glaucoma, using 1.0 cycle/degree blue grating superimposed on a bright yellow background. Sensitivity was measured at a range of mean luminances, and pupil size was monitored with a closed-circuit video system. Inter-subject variability was reduced by plotting S-cone contrast sensitivity vs. retinal illuminance rather than stimulus luminance, indicating that much of the variability was due to differences in pupil size. Each patient’s data were fit with a threshold versus retinal illuminance (TVR) function. The TVR analysis suggested that additional variability was due to prereceptoral filters. These results indicate that reductions in S-cone contrast sensitivity at luminances available from computer monitors may reflect, in part, effects of pupillary miosis or lens yellowing, rather than optic nerve damage.KeywordsContrast SensitivityPupil SizeIncrement ThresholdRetinal IlluminanceCone ContrastThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.