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Shaobo Lei, Herbert C Goltz, Manokaraananthan Chandrakumar, Agnes MF Wong; Full-Field Chromatic Pupillometry in the Assessment of the Post-Illumination Pupil Response Driven by Melanopsin-Containing Retinal Ganglion Cells. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4110.
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A sustained pupil constriction can be observed after the offset of a bright blue light stimulus. This post-illumination pupil response (PIPR) is produced by the intrinsically photosensitive melanopsin-containing retinal ganglion cells (ipRGCs), and can be measured by chromatic pupillometry. While chromatic pupillometry holds promise as a new diagnostic and outcome measurement tool to assess ipRGC function, current testing protocols use central-field stimulation and require a very bright light of long duration which can be difficult for some subjects. We test the hypothesis that a more robust PIPR can be induced with full-field blue light stimuli of shorter duration and lower intensity than with existing protocols.
Ten visually-normal adult subjects (mean age: 31 years, range 22 - 56) were tested. Pupil responses were recorded with an infrared eye tracker at 60 Hz. Full-field red (640±10 nm) and blue stimuli (467±17 nm) were presented in a darkened room using a Ganzfeld system. In experiment 1 (intensity trials), PIPR was induced using 1-second full-field stimuli of increasing intensity from 0.1 to 400 cd/m2 (11 steps). For comparison with a previously published protocol, a 60°×90° central-field blue stimulus at 400 cd/m2 was also presented for 1 second. In experiment 2 (duration trials), PIPR was induced using 100 and 400 cd/m2 full-field stimuli of increasing duration from 4 to 1000 ms (10 steps).
PIPR increased monotonically with increasing stimulus intensity. Full-field stimulation using blue light at 400 cd/m2 intensity induced significantly more sustained PIPR than central-field stimulation (p = 0.001, post-hoc Student’s t-test). In addition, PIPR increased as the duration of stimulus increased from 4-200 ms; however, no further increase in PIPR was observed when the duration increased from 400-1000 ms.
Compared to existing central-field protocols, robust PIPR can be induced with a full-field protocol with lower intensity and shorter duration. This study is the first to demonstrate that saturating PIPR can be induced in vivo with a strong blue flash lasting only a few hundred milliseconds. This refined protocol will improve the recording quality and the subjective experience of future pupillometry testing.
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