Abstract
Purpose::
To characterize the transient and sustained pupil contraction to luminance matched red and blue light as a function of brightness in order to correlate these responses to recently elucidated physiologic properties of melanopsin containing retinal ganglion cells.
Methods::
The pupil responses of 10 normal subjects were recorded by infrared computerized pupillography (Arrington Research Inc) to equal luminance red (600-620nm band) and blue (465-485nm) light stimuli presented in a Ganzfeld bowl (Diagnosys Inc) in 10 second duration steps of 1, 10, and 100 cd/m2 to each eye.
Results::
The pupil contraction to low intensity light (1cd/m2) was transient during the 10 second stimulus for both red and blue light stimuli and was greatest for blue light. At 10 and 100 cd/m2 the pupil response to red light stimulus was still transient and less than the blue light stimulus, but the blue light caused a sustained pupil contraction during the 10 second blue stimulus, always exceeding the pupil response to luminance matched red light in both the transient and sustained reaction. With termination of either the red or blue light at 100 cd/m2, there was a brisk pupil redilation in normal eyes, even with longer duration light stimuli of 60 seconds.
Conclusions::
In normal eyes, the pupil responses to red light show characteristics of photoreceptor mediated pupil contractions, with an initial, intensity-dependent transient contraction followed by escape, with a residual sustained pupil contraction, also intensity dependent. The transient pupil responses to blue light stimuli are greater than those of luminance matched red stimuli, and at brighter light intensities, the sustained pupil contraction dominates with very little pupil escape, a characteristic attributed to the physiologic intrinsic response properties of the melanopsin containing retinal ganglion cells.
Keywords: pupil • photoreceptors • ganglion cells