Rhodopsin and melanopsin contributions to the early redilation phase of the post-illumination pupil response (PIPR)

Links

Summary

This study identifies that the early phase of the post-illumination pupil response (< 1.7 s after light offset) is driven by combined contributions from melanopsin and rhodopsin, while later phases (≥ 1.7 s) are purely melanopsin-mediated. This establishes a precise temporal cut-off for using PIPR as a non-invasive tool to isolate and assess ipRGC and rod function in clinical eye health diagnostics.

Key Findings

PIPR spectral sensitivity at ≥ 1.7 s post-stimulus is best described solely by the melanopsin nomogram (peak ~480 nm).
At < 1.7 s post-stimulus, peak PIPR sensitivity shifts to longer wavelengths (range: 482–498 nm), best described by a combined melanopsin + rhodopsin spectral nomogram.
Five narrowband wavelengths tested (409, 464, 508, 531, 592 nm) using 1 s light pulses; rhodopsin contribution to early PIPR is consistent with electrophysiological evidence of rod signalling in ipRGCs after light offset.
The 1.7 s cut-off provides a practical criterion for isolating melanopsin-specific vs. rod-influenced pupil responses in both healthy and diseased eyes.

Categories

The Science of Light: Characterizes the spectral sensitivity and photoreceptor contributions (melanopsin and rhodopsin) to the post-illumination pupil response (PIPR), establishing a temporal boundary for isolating melanopsin-specific function.

Eye Health & Vision: Provides a methodological framework for using the PIPR to assess photoreceptor-specific function in healthy and diseased eyes, relevant to diagnosing retinal conditions.