The contribution of the rod/melanopsin driven ganglion cells to the dynamic pupil light reflex response

Abstract

AbstractPurpose Intrinsically photosensitive retinal ganglion cells have been shown to contribute to the control of the steady‐state pupil response. The extent to which melanopsin contributes to rapid pupil responses elicited with brief stimuli remains less clear. The principal objective of this study was to examine how the dynamic pupil light reflex response changes with the level of light adaptation for stimuli that isolate luminance, colour or combined rod and melanopsin. The range of light levels that yield useful rod signals was also investigated.Methods The study involved ten normal subjects, one patient with rod deficiency, one patient with retinitis pigmentosa (RP) and one rod monochromat. The pupil responses were measured to stimuli that isolate photopic luminance, colour or combined rod and melanopsin at three light levels (456, 74.4 and 4.8cd/m2). Visual acuity, contrast sensitivity and chromatic sensitivity were also measured in all subjects.Results The patients with rod deficiency and RP exhibit pupil responses to luminance and colour modulation, but much reduced or absent response to rod/melanopsin modulation. Conversely, the rod monochromat shows complete absence of pupil colour and luminance responses, but exhibits large pupil rod/melanopsin responses at all light levels.Conclusion The findings from this study suggest that pupil responses to briefly presented stimuli are mediated largely by rod and cone signals with no contribution from melanopsin. The results also suggest that rod signals remain unsaturated and can contribute to dynamic pupil responses at much higher light levels.