Wavelength Dependency for Photopotentiation of Pupil Responses to Red Light

Title Wavelength Dependency for Photopotentiation of Pupil Responses to Red Light
Author, Co-Author Phillip Yuhas, Andrew Hartwick
Program Number
Great Hall Foyer
Ohio State University College of Optometry
Abstract Purpose: We have shown that pupil responses to red light are enhanced (greater constriction, slower redilation) after exposure to preceding flashes of blue light. One hypothesis is that this effect involves intrinsically photosensitive retinal ganglion cells (ipRGCs). Here, we sought to determine whether photopotentiation exhibits wavelength dependency consistent with the action spectrum of the melanopsin photopigment in ipRGCs.

Methods: Two subjects each sat for 4 sessions. Light was applied to the dilated left eye and consensual pupil responses were measured. Each session had 7 trials of 1 min duration flashing (0.1 Hz) light stimuli, with 10 min darkness between trials. The 1st, 3rd and 5th pulses were always red (630 nm) light, while the wavelength of the 2nd, 4th and 6th pulses varied. In two sessions, the trial order for the variable wavelength was 630, 600, 570, 540, 510, 480 and 450 nm. This order was reversed in the other two sessions.

Results: Combining the normalized pupil responses from all 8 sessions, there was no significant difference (p = 0.97, ANOVA) between the 7 wavelengths in potentiating light-evoked pupil constriction, measured as the difference in average constriction during the first two and last two light pulses. However, the presentation order affected the results, as mean overall photopotentiation was significantly greater (p = 0.003, t-test) when lights were presented in long-to-short wavelength order (7.9 ± 0.8% increased constriction) compared to vice versa (3.9 ± 1.0%).

Conclusions: Although different from our original hypothesis, light wavelength did influence photopotentiation, as evident by the significant order effect. Potentiation was greater when the short wavelength light was presented later in the session. These results show that 10 min is not long enough to wash out the effect of prior light exposure, which confounds the accurate measurement of an action spectrum for the photopotentiation effect.
Affiliation of Co-Authors The Ohio State University College of Optometry