Group average pupil responses for all stimuli showed high reproducibility across sessions 1 and 2.
-directed contrast elicited a prolonged pupil response compared to cone-directed contrast.
Responses to melanopsin and cone-directed stimuli were similar despite variations in background radiance.
Increased radiance resulted in enhanced persistent pupil constriction specifically to blue light.
The method of silent substitution may reliably assess the function of the melanopsin system in humans.
Disruption of the melanopsin system could be associated with clinical pathology.
Simplified
PURPOSE: To measure the pupil response to pulses of -directed contrast, and compare this response to those evoked by cone-directed contrast and spectrally narrowband stimuli.
METHODS: Three-second unipolar pulses were used to elicit pupil responses in human subjects across three sessions. Thirty subjects were studied in session 1, and most returned for sessions 2 and 3. The stimuli of primary interest were "silent substitution" cone- and melanopsin-directed modulations. Red and blue narrowband pulses delivered using the post-illumination pupil response (PIPR) paradigm were also studied. Sessions 1 and 2 were identical, whereas session 3 involved modulations around higher radiance backgrounds. The pupil responses were fit by a model whose parameters described response amplitude and temporal shape.
RESULTS: Group average pupil responses for all stimuli overlapped extensively across sessions 1 and 2, indicating high reproducibility. Model fits indicate that the response to melanopsin-directed contrast is prolonged relative to that elicited by cone-directed contrast. The group average cone- and melanopsin-directed pupil responses from session 3 were highly similar to those from sessions 1 and 2, suggesting that these responses are insensitive to background radiance over the range studied. The increase in radiance enhanced persistent pupil constriction to blue light.
CONCLUSIONS: The group average pupil response to stimuli designed through silent substitution provides a reliable probe of the function of a melanopsin-mediated system in humans. As disruption of the melanopsin system may relate to clinical pathology, the reproducibility of response suggests that silent substitution can test if melanopsin signals differ between clinical groups.
Key numbers
1.47%
Reproducibility of Pupil Response
Max absolute difference in amplitude for LMS response between sessions 1 and 2.
76%
Persistence of Response
Percent of total pupil response area for stimulation.
74%
PIPR Effect Increase
Median PIPR effect measured as a difference between blue and red stimuli.
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