Figure 4.
Visual photoreceptors are required for pupillary responses to track intermittent light stimuli. A, Pupillary constriction is shown in normally sighted individuals (n = 4) and in a blind patient without rod and cone function in response to a single 6 s pulse of 480 nm light (13 log photons cm−2 s−1). B, Participants were exposed to 4 min of continuous or intermittent 480 nm light at 13 log photons cm−2 s−1. During exposure to continuous light, sighted participants and the blind individual showed sustained pupillary constriction (top row). During an intermittent light stimulus with alternating periods of 5 s of light and 5 s of darkness, normally sighted participants' pupils were able to track each successive light pulse, whereas in the blind individual, responses were integrated over time until reaching a steady response ∼1 min after the onset of the stimulus (middle row). With alternating periods of 5 s of light and 15 s of darkness, the blind individual's pupil was still able to integrate light information across longer episodes of darkness (bottom row). The pattern of light exposure is shown at the top of each plot, with upward deflections indicating times when participants were exposed to light. To highlight differences in pupillary constriction responses to intermittent light, pupil diameter in the blind individual is plotted on a different scale than for sighted participants. The gray traces in the left panels indicate SEM.