Effect of Stimulus Intensity and Visual Field Location on Rod- and Cone-Mediated Pupil Response to Focal Light Stimuli.

Purpose: To assess the effect of stimulus intensity on rod- and cone-mediated pupil light reflex (PLR) to small stimuli presented at central and peripheral visual field (VF) locations. Methods: The PLR to small (0.43°) chromatic stimuli was tested in the right eye of healthy subjects. Blue (485 ± 20 nm) and red (625 ± 15 nm) stimuli were presented at incremental light intensities (0.5-3.75 log cd/m2) at peripheral (21.21°) and central (4.24°) VF locations using a chromatic pupilloperimeter under mesopic or blue light adaptation conditions. The percentage of pupil contraction (PPC), maximal pupil contraction velocity (MCV), latency of MCV (LMCV) and the ratio of central to peripheral responses for PPC (QPPC value) were determined. Results: Under mesopic light adaptation conditions, the mean PPC recorded in response to red stimuli was lower than blue stimuli in all VF locations and light intensities, and the QPPC values were higher in response to red compared with blue light stimuli across the light intensity range tested. With blue background light, the pupil responses for red and blue light stimuli were approximately the same in the peripheral VF. LMCV was nearly constant in all VF locations for blue and red stimuli, respectively. Conclusions: The chromatic pupilloperimeter enables the assessment of rod- and cone- contribution to the PLR in different VF locations. The optimal light intensities determined here for the assessment of focal activation of the two photoreceptor systems may be used for clinical evaluation of photoreceptor health.