The apparatus and stimuli used to elicit and record the PLR are described elsewhere.
11,18 In brief, full-field stimuli were generated by the Diagnosys ColorDome ganzfeld associated with the Espion E
3 system (Diagnosys, LLC, Lowell, MA, USA), with narrow-band LEDs of 465 nm (blue), and 642 nm (red). Pupil responses were measured with a plastic frame-mounted infrared camera system (Arrington Research, Scottsdale, AZ, USA).
19 The PLR was measured in the better-seeing eye of each patient by using 1-second long luminance pulses under conditions designed to target the rod, cone, and melanopsin pathways.
11 The rod response was elicited by a pulse of −3 log cd/m
2 blue light after a period of 10 minutes dark adaptation. The melanopsin response was elicited by a pulse of 2.6 log cd/m
2 blue light without a background light. The cone response was elicited by a 1 log cd/m
2 red light on a blue background of 0.78 log cd/m
2. The rod- and cone-mediated PLRs were defined as the maximum constriction relative to baseline pupil size (before light onset), per convention,
11 and the melanopsin response was measured as the median pupil size between 5 and 7 seconds after the stimulus offset, relative to baseline.
11 All three conditions were tested twice, and threshold was calculated as an average of the two trials for each condition. Nine similarly aged, visually normal subjects (mean age 28.4 years; SD 6.2) were tested with the same pupillometry protocol.