Pulsatile Red Reflex: Identification and Quantitative Characterization of a Previously Unreported Phenomenon

Abstract Purpose To describe and quantitatively characterize a previously unreported pulsatile component of the red reflex, which we term the pulsatile red reflex (PRR). Methods Thirty-one phakic participants underwent red-reflex video recording using a slit lamp and smartphone adapter after pharmacological mydriasis. A multichannel imaging photoplethysmography pipeline extracted pulse-related intensity changes. Relative signal amplitude and recording quality were characterized, and PRR-derived pulse rates were compared with contemporaneous fingertip pulse oximetry using Bland–Altman analysis. Results Twenty-one participants provided valid recordings (67.7%); three acquisitions failed because of dense posterior subcapsular cataract and seven did not meet the 10-s duration criterion. Green-channel root mean square alternating-to-direct-current (AC/DC) ratios ranged from 0.19% to 0.52% (median 0.28%). Reference pulse rates ranged from 55 to 90 beats per minute (bpm). Mean difference was + 0.03 bpm (SD 1.34), with 95% limits of agreement of − 2.60 to + 2.66 bpm. Mean absolute error was 1.04 bpm and root mean square error 1.31 bpm. Signed differences increased with the paired mean (slope 0.11 bpm/bpm; 95% confidence interval 0.07–0.15). Conclusion The familiar red reflex contains a measurable pulsatile intensity component at a frequency consistent with the peripheral pulse. These findings identify and quantitatively characterize PRR, with pulse rate agreement providing evidence of its pulse-related nature. PRR introduces a dynamic dimension to red-reflex assessment and a basis for further investigation of ocular pulsatile signals.