Rod, cone and melanopsin contributions to the pupil light reflex

Abstract

AbstractPurpose To define the relative contributions of rod, cone, and melanopsin to the human pupillary light reflex (PLR) and to determine the optimal conditions for assessing their status in patients with retinal and optic nerve disorders.Methods The pupil light reflex was measured with an eye tracker, and stimuli were precisely controlled with a Ganzfeld ERG computerized system. For rod mediated transient pupil responses, a low intensity 1‐second duration blue light was given under dark adaptation. For cone mediated transient pupil responses, a red, high intensity 1‐second duration light was given on a blue background to suppress rod contributions. For melanopsin mediated sustained pupil responses, a bright 1‐second bright blue light was given without background.Results Rod mediated transient pupil responses were present in normal eyes but not in patients with moderate to advanced retinitis pigmentosa. A blue background suppressed rod and melanopsin responses, enabling assessment of cone contributions with a red flash. Robust melanopsin sustained pupil responses could be seen in patients with lack of contributions from the rods and cones.Conclusion The rod, cone, and melanopsin contributions to the PLR can be assessed with a simple clinical protocol with blue flashes at two or three intensity levels in the dark and one red flash on a blue background, allowing for diagnosis and differentiation of retinal and optic nerve diseases.