Abstract
Purpose :
To determine the dynamics of pupil redilation following melanopsin activation with suprathreshold light stimuli.
Methods :
Consensual PLR was recorded from normal subjects (n=4, 23-53 years of age) using a custom pupillometer (Diagnosys LLC) to full-field blue (450nm) LED test stimuli of -3.47 log W/sr/cm2 (14.88 log photons/cm2/sec) presented to the dilated fellow eye following 5 minutes of dark adaptation. PLR and its recovery was sampled from 3 seconds prior to stimulus onset till 16 minutes after stimulus onset for several durations of the test stimuli in the range of 5 – 120 seconds. Maximal constriction and Post Illumination Pupillary Response (PIPR) at 6 seconds after stimulus offset and for 10 seconds each minute thereafter was calculated. The responses following light offset was fit with an equation of the form y = a (1-e-bx) that describes the exponential increase in pupil diameter to the maximum.
Results :
Pupil diameter was reduced to 40% (±5) of the pre-stimulus baseline diameter and was similar for all stimulus durations and was sustained for the entire duration for which the test stimuli were presented. The 6s PIPR was 58% (±6%) of the pre-stimulus baseline diameter and PLR recovered to 85% (±3.5) of pre-stimulus baseline diameter by 16 minutes following light onset for all stimulus durations. The time constant b in the equation describing the exponential rise to maximum gradually increased from 0.37 to 0.9 as stimulus duration increased from 5 to 120 seconds.
Conclusions :
Suprathreshold test stimuli for melanopsin activation elicit prolonged tonic constriction of the pupil that can take a significant amount of time to recover back to baseline. These preliminary results highlight the importance of allowing adequate inter-stimulus interval durations while performing repetitive testing of PLR with suprathreshold stimuli for melanopsin activation.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.