Shaobo Lei

Full-field chromatic pupillometry for the assessment of the postillumination pupil response driven by melanopsin-containing retinal ganglion cells.

PURPOSE The postillumination pupil response (PIPR) is produced by intrinsically photosensitive retinal ganglion cells (ipRGCs). We aimed to refine the testing conditions for PIPR by investigating whether a greater PIPR can be induced using full-field light stimuli of shorter duration and lower intensity than that produced by existing protocols that use central-field stimuli. METHODS Pupil response was recorded with an eye tracker in 10 visually-normal subjects. Red and blue light stimuli were presented using a Ganzfeld system. In Experiment 1 (intensity trials), PIPR was induced using 1-second full-field stimuli of increasing intensities from 0.1 to 400 cd/m(2) (11 steps). For comparison, PIPR also was induced using a 60° × 90° central-field blue stimulus of 400 cd/m(2). In Experiment 2 (duration trials), PIPR was induced using 100 and 400 cd/m(2) full-field stimulus of increasing duration from 4 to 1000 ms (10 steps). RESULTS Results indicated that PIPR increased monotonically with increasing stimulus intensity. Full-field stimulation using blue light at 400 cd/m(2) intensity induced significantly more sustained PIPR than central-field stimulation (P = 0.001). In addition, PIPR increased as the stimulus duration increased from 4 to 200 ms; however, no further increase in PIPR was observed when the duration increased from 400 to 1000 ms. CONCLUSIONS Compared to existing central-field protocols, larger PIPR can be induced with a full-field stimulus with lower intensity and shorter duration, indicating that PIPR is a function of stimulus intensity, stimulus duration, and retinal area stimulated. The testing protocol can be refined with this new knowledge to target particular clinical populations.

Test–Retest Reliability of Hemifield, Central-Field, and Full-Field Chromatic Pupillometry for Assessing the Function of Melanopsin-Containing Retinal Ganglion CellsTest–Retest Reliability of Chromatic Pupillometry

PURPOSE We evaluated the test-retest reliability of current methods of inducing the melanopsin-driven postillumination pupil response (PIPR) under hemifield, central-field, and full-field stimulation conditions. METHODS Pupil response was recorded with an eye tracker in 10 visually normal participants. Light stimuli were presented using a Ganzfeld screen with a custom-built device that allows specific regions of the retina to be stimulated. Blue light stimulation at 400 cd/m(2) intensity was presented for 400 ms to the lower and upper halves of the central 30° fields (hemifields), central 30° field (central-field), and full-field to induce PIPR. Red light full-field stimulation also was presented with the same intensity and duration as a control condition. Test-retest reliability of the PIPR measures was assessed by calculating the intraclass correlation coefficient (ICC) of six repetitions for lower and upper hemifield stimulation, and three repetitions for central-field and full-field stimulation. RESULTS Hemifield, central-field, and full-field blue light stimulation induced increasingly greater PIPR in ascending order, while full-field red light stimulation induced no PIPR. Mean lower and upper hemifield PIPR was highly symmetric. Mean ICC of blue light PIPR was 0.87 for lower hemifield, 0.88 for upper hemifield, 0.95 for central-field, and 0.94 for full-field stimulation. CONCLUSIONS We validated a new and repeatable method to measure PIPR induced by hemifield, central-field, and full-field light stimulation. Good PIPR measurement reliability was obtained under all conditions. This practical and reliable protocol will facilitate the clinical application of PIPR testing in different disease populations.

GAPO syndrome: a case associated with bilateral interstitial keratitis and hypothyroidism.

Zhe-Yi Eye Centre, Hang Zhou, ORBIS, Second Affiliated Hospital of Harbin Medical University, China, LV Prasad Eye Institute, India and Department of Ophthalmology and Vision Sciences, University of Toronto and The Hospital for Sick Children, Canada Correspondence to Dr Agnes M.F. Wong, MD, PhD, FRCSC, Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada Tel: + 1 416 813 7654 x2642; fax: + 1 416 813 5159; e-mail: agnes.wong@utoronto.ca

The Relation Between Light-Induced Lacrimation and the Melanopsin-Driven Postillumination Pupil Response

Purpose To investigate the chromatic characteristics and intensity-response function of light-induced reflex lacrimation and its correlation with the melanopsin-driven postillumination pupil response (PIPR). Methods Eleven visually normal participants completed the experiment. Lacrimation was measured in one eye by placing a calibrated filter paper strip in the conjunctival sac over a 1 minute-interval (Schirmers test) during which participants received either no light stimulation (baseline trial) or one flash of blue or red light stimuli presented binocularly with a Ganzfeld stimulator, while the pupil response was recorded simultaneously from the fellow eye by using an eye tracker. Light stimulation trials were presented in alternating fashion at seven incremental intensity steps (0.1, 1, 3.16, 10, 31.6, 100, and 400 cd/m2). Postillumination pupil response was defined as the mean pupil constriction from 10 to 30 seconds post illumination. Results The amount of lacrimation in response to 10 to 400 cd/m2 blue light was significantly greater than baseline and increased monotonically with increasing light intensity. Red light did not induce significant reflex lacrimation until the brightest stimulation at 400 cd/m2. There was a positive linear correlation between PIPR and lacrimation in response to blue light (r = 0.74, P < 0.001) but not to red light (r = 0.13, P = 0.25). Conclusions The chromatic characteristics and intensity-response of light-induced lacrimation are highly consistent with the features of melanopsin phototransduction. This finding is the first in vivo evidence in humans, supporting the hypothesis that light-induced reflex lacrimation is mediated primarily by melanopsin photoactivity, and provides new insight into the putative mechanisms of photophobia.

Binocular Summation in Postillumination Pupil Response Driven by Melanopsin-Containing Retinal Ganglion Cells

Purpose To investigate how melanopsin-mediated intrinsically photosensitive retinal ganglion cell (ipRGC) signals are integrated binocularly using chromatic pupillometry. We hypothesized that if the melanopsin system is summative, there will be a greater postillumination pupillary response (PIPR) under binocular conditions after viewing bright blue light. Methods Pupillary responses in 10 visually normal participants were recorded with an eye tracker following full-field stimulation of red (long wavelength) and blue (short wavelength) light of equal intensity (dim: 0.1 cd [candela]/m2, bright: 60 cd/m2) and duration (400 ms). Individual monocular (left eye) pupil responses were measured first, followed by binocular responses. Each participant repeated the same protocol on 3 separate days, at similar times of day. PIPR was recorded for bright red and blue conditions only, whereas maximum pupillary constriction (MPC) was measured under both bright and dim conditions during red and blue light stimulation. Results Bright blue light stimulation induced greater PIPR under binocular than monocular viewing conditions (F(1,9) = 79.52, P < 0.001). Bright red light stimulation induced minimal PIPR and showed no significant difference between viewing conditions post Bonferroni correction (F(1,9) = 5.49, P = 0.04). MPC was greater during binocular than monocular viewing conditions for all light stimuli, but was greatest following blue compared to red light stimulation. Conclusions A larger PIPR was induced using a binocular than a monocular full-field stimulus of equal intensity and duration, demonstrating that melanopsin-mediated ipRGC signals are summated binocularly. This study expands our current understanding of the melanopsin system and may be used as an additional marker to stratify diseases according to their etiologies.