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Shakoor Ba-Ali, Henrik Lund-Andersen, Adam Brøndsted; Post-illumination pupillary light response (PIPR) to intermittent light exposure is larger than the response evoked by the continuous light stimulus.. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5091.
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© ARVO (1962-2015); The Authors (2016-present)
The intrinsic photosensitive retinal ganglion cells (ipRGCs) are known to integrate the light signals over time in order to synchronize the circadian rhythm. We tested the hypothesis that the pupillary light response (PLR) is larger as result of intermittent light stimuli compared to continuous light exposure.
PLR was recorded in 36 healthy subjects, one patient with choroideremia (rod-cone degeneration) and one glaucoma patient (melanopsin dysfunction) using three different pupillometry protocols. Each protocol began with five minutes of dark-adaptation. Protocol-1 consisted of 20 s continuous illumination (463 nm, 100 lux) followed by post-illumination pupillary response (PIPR) recording in 40 s. Protocol-2 included seven sequences of 5 s light-on and 5 s light-off, followed by PIPR recording in 40 s. Protocol-3 consisted of three sequences of 10 s light-on and 40 s light-off periods. Maximum contraction amplitude during the illumination period constituted the mixed response of rod/cone and melanopsin, while the late re-dilation phase of PIPR (PIPR) was used as a marker of melanopsin-mediated pupil response.
Both the maximum contraction amplitude and the PIPR were larger with intermittent light stimuli of shorter duration (protocol-2) compared to a single continuous illumination (protocol-1) (p < 0.0001). Protocol-3 produced also a larger contraction amplitude compared to protocol-1 (p = 0.0001), but failed to elicit a larger PIPR (p = 0.12). The three protocols could differentiate between cone- and melanopsin-mediated PLR in the choroideremia and the glaucoma patients (Figure 1). While the PIPR was reduced in the glaucoma patient, we observed an increased PIPR in the choroideremia patient.
Our results are consistent with our hypothesis that intermittent light stimuli elicit larger PIPR than continuous stimulus.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
The pupil light response in a healthy subject (black), a glaucoma patient (blue) and a choroideremia patient (turquoise), using three different pupillometry protocols. The glaucoma patient showed reduced post-illumination pupil responses in all three protocols, while the choroideremia patient had increased post-illumination pupil response. The pupillary re-dilations during light-off periods in protocol-2 and 3 were almost absent in the choroideremia patient.
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