Abstract
Purpose: :
To apply new information about the physiology of melanopsin expressing retinal ganglion cells mediating the pupil light reflex in order to understand which stimulus conditions and dynamics of the pupil light reflex help to localize the site of damage in the visual pathway to the outer photoreceptor layer by comparing red and blue light stimuli as a function of light intensity.
Methods: :
44 normal eyes and 37 eyes with possible inherited photoreceptor degeneration seen consecutively were evaluated by recording the pupil light reflex to a Ganzfeld red (620nm+/-20nm) and blue (480nm+/-20nm) light stimulus of 13 seconds duration, increasing in 3 stimulus stair-steps (1, 10, and 100 cd/m2) under mesopic conditions.
Results: :
In normal eyes, photoreceptor mediated transient pupil contractions to red light were followed by pupil escape during each 13 second stimulus step. With 1 cd/m2 blue light there was a transient pupil response followed by pupil escape, similar to red light, but during the stimulus starting at the middle 10cd/m2 stimulus intensity and at the brightest 100 cd/m2 blue light stimulus, a sustained pupil contraction occurred with very little, if any, escape, corresponding to intrinsic activation of melanopsin ganglion cells. 3 patients with no light perception (NLP) vision from severe photoreceptor disease had no pupil response, except to bright blue light, which produced a delayed, slowed, large amplitude pupil contraction. Photoreceptor mediated pupil responses produced a transient pupil contraction, which was significantly decreased to bright red light in patients with cone degeneration and decreased to low intensity blue light in rod degeneration compared to normal eyes (p<0.05 ANOVA Dunn’s). Sustained pupil contraction to bright blue light mediated by melanopsin was not significantly affected by rod or cone degeneration. Seeing eyes with non-recordable ERGs produced diminished, but still recordable transient pupil contractions.
Conclusions: :
Rod, cone and melanopsin mediated light transduction has both a transient and a sustained component of pupil response in humans, which can be used to assess their respective function in eyes to help diagnose, localize and monitor vision loss due to diseases of the retina and optic nerve.
Keywords: pupillary reflex • retinal degenerations: hereditary • ganglion cells