Prior Light Exposure Enhances the Pupil Response to Subsequent Short Wavelength (Blue) Light

Abstract

Background and Purpose: The photo pigment melanopsin initiates cell depolarization in response to highintensity, short-wavelength light. Antecedent long-wavelength light may potentiate regeneration of the melanopsin photo pigment, We investigated the influence of red or blue exposure on the pupil response to subsequent blue light. Methods: Nine healthy subjects were examined using chromatic pupillometry. With a sequence of 3 consecutive blue exposures or a sequence in which the middle exposure was red light, both sequences repeated in the darkadapted state. The summed pupil response during light was obtained as the area under the curve and the percentage difference (diff %) between the first and last blue stimulus was calculated for each sequence. Findings: The pupil response to the third blue exposure was greater than to first blue light. No significant difference was seen in the diff% when comparing a sequence with a blue intervening versus red intervening light, in the light adapted (P = 0.39) or dark adapted state (P = 0.58). Conclusion: Prior light exposure enhances the pupil response to subsequent blue light stimulation, no differential effect was found between blue and red light. This study suggests that antecedent light history is important when designing protocols and evaluating results of chromatic pupillometry.