Abstract
Rods, cones and melanopsin contribute in various proportions, depending on the stimulus light, to the pupil light response. This study used a first derivative analysis to focus on the quantification of the dynamics of pupillary dilation that immediately follows light-induced pupilloconstriction in order to identify novel parameters that reflect rod and cone activity. In 18 healthy adults, the pupil response to a 1 s blue light stimulus ranging from − 6.0 to 2.65 log cd/m2 in dark-adapted conditions and to a 1 s blue light stimulus (2.65 log cd/m2) in light-adapted conditions was recorded on a customized pupillometer. Three derivative parameters which describe the 2.75 s following the light onset were quantified: dAMP (maximal amplitude of the positive peak), dLAT (latency of the positive peak), dAUC (area under the curve of the positive peak). We found that dAMP and dAUC but not dLAT have graded responses over a range of light intensities. The maximal positive value of dAMP, representing maximal rate of change of early pupillary dilation phase, occurs at − 1.0 log cd/m2 and this stimulus intensity appears useful for activating rods and cones. From − 0.5 log cd/m2 to brighter intensities dAMP and dAUC progressively decrease, reaching negligible values at 2.65 log cd/m2 indicative of a melanopsin-driven pupil response that masks the contribution from rods and cones to the early phase of pupillary dilation.
Highlights
Rods, cones and melanopsin contribute in various proportions, depending on the stimulus light, to the pupil light response
Pupil responses to blue light stimuli ranging from − 5 to 2.6 log cd/m2
We show that the dark-adapted pupil response to a very bright blue light (2.65 log cd/m2) has a visibly different waveform compared to blue light stimuli having lower intensities and to the same very bright blue intensity (2.65 log cd/m2) we presented under light-adapted conditions
Summary
Cones and melanopsin contribute in various proportions, depending on the stimulus light, to the pupil light response. From − 0.5 log cd/m2 to brighter intensities dAMP and dAUC progressively decrease, reaching negligible values at 2.65 log cd/m2 indicative of a melanopsindriven pupil response that masks the contribution from rods and cones to the early phase of pupillary dilation. We had presented very dim short wavelength stimuli to healthy eyes and noted that subjects could perceived the light stimulus but did not see the blue color until brighter intensities were presented, when cones were recruited[6] These rod-mediated pupil responses have been correlated with clinical disease in monogenetic retinal degeneration and hold promise as an alternative clinical tool for quantifying rod function. The derivative curve describes the rate of change of constriction and dilation during the initial 3 s of the pupil response to a brief light stimulus. A maximal dilation in the first 3 s of a light stimulus was found to be a purely rod and cone-driven phase of the pupil response in mice
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