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Sarah Catherine Flanagan, Kathryn Saunders, Hope M Queener, Patrick Richardson, Lisa A Ostrin; Effects of mydriatics on the ipRGC-driven post-illumination pupil response. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5262.
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The post-illumination pupil response (PIPR) can be used to evaluate intrinsically photosensitive retinal ganglion cell (ipRGC) activity. Protocols vary and often use mydriatics on the stimulated eye whilst recording the consensual pupil. Mydriatics regulate retinal illuminance and ensure maximal stimulus exposure, but also cause visual blur, photophobia and may influence retinal physiology. Understanding the influence of mydriatics on the PIPR is essential in the development of robust pupillometry. This study aims to determine the repeatability of PIPR metrics across sessions without mydriasis and compare PIPR metrics following dilation with two different mydriatic agents- atropine, a muscarinic antagonist, and phenylephrine, an adrenergic agonist.
Twenty adults, aged 21-42, participated. Consensual pupil responses were recorded to six alternating 1-second long (651 nm [red]) and short (456 nm [blue]) wavelength full field stimuli at baseline and 45 minutes following dilation with either 0.5% atropine or 2.5% phenylephrine. The experiment was repeated at the same time of day, at least five (phenylephrine) or ten (atropine) days later with the alternate mydriatic. Pupil recordings were analyzed and PIPR metrics (6s PIPR, early area under the curve [AUC], late AUC, and 30s PIPR) calculated using custom MATLAB software.
Data for one subject were removed due to extreme pupil fluctuations. Dark adapted pupil diameter at baseline was 6.17 ± 0.90 mm. The intraclass correlation coefficient for repeat baseline measures of 6s PIPR, early AUC, late AUC, and 30s PIPR to blue stimuli were 0.63, 0.78, 0.44 and 0.50 respectively; metrics did not vary significantly across baseline sessions (p > 0.05 for all). Pupil diameter of the dilated eye with phenylephrine was 6.25 ± 1.05 mm and with atropine was 8.23 ± 0.53 mm. Compared to baseline measures, dilation of the stimulated eye with either mydriatic significantly enhanced the 6s PIPR, early AUC and late AUC for blue stimuli and the early AUC for red stimuli (p < 0.05 for all). PIPR metrics (relative to baseline) did not differ significantly between dilated sessions (p > 0.05 for all).
Undilated PIPR metrics demonstrated good repeatability and did not differ significantly between sessions. Dilation with either phenylephrine or atropine resulted in similar short-term enhancement effects on PIPR metrics, despite differing mechanisms of mydriatic action.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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