Effect of stimulus intensity, visual field location and duration on the rod- , cone- and melanopsin- mediated pupillary light reflex

Abstract

Purpose : To determine the optimal light stimulus intensity and duration for eliciting rod-, cone- and melanopsin- mediated pupil light reflex (PLR) using very small (0.43°) stimuli at central and peripheral visual field (VF) locations.

Methods : The PLR for very small (0.43°) chromatic light stimuli was tested in the right eye of twenty healthy subjects, aged 24–45 years. Blue (485±20 nm) and red (625±15 nm) light stimuli, were presented at ten increasing light intensities (0.5 – 3.75 log cd/m2) and durations of 50-1000 milliseconds in four peripheral (24°) and four central (6°) VF locations using a computerized multifocal pupillometer.

Results : The PLR monotonically increased with increasing light intensities in all VF locations. The red light induced smaller PLRs compared with photopically matched blue light in all VF locations. A substantial rod-mediated PLR was obtained by presenting blue light stimuli at 1.5 log cd/m² for 200 milliseconds in central and peripheral VF locations. To achieve a similar PLR for the red light, a 10- and 18- fold higher light intensity was required at central and peripheral VF locations, respectively and a minimal duration of 500 milliseconds, suggesting that the PLRs under these conditions are mainly cone-mediated. A sustained melanopsin-mediated PLR was induced in central VF locations using blue stimuli at 3.8 log cd/m² for at least 6 seconds.

Conclusions : Chromatic multifocal pupillometry enables the assessment of rod-, cone- and melanosin- mediated PLR at different VF locations by using very small light stimuli. The optimal light intensity and stimulus duration determined here for assessing the focal activation of the three photoreceptor systems will be used as a model for objective testing of VF defects in subjects with retinal and optic nerve degenerations.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.