Pulsatile Red Reflex: A New Phenomenon In Ophthalmic Hemodynamic Imaging

Single-center, prospective study conducted at an outpatient ophthalmology clinic.

In this prospective observational study, 50 eyes of subjects with pharmacologically dilated pupils were recorded at 4K resolution and 60 fps via a smartphone mounted on a biomicroscope. Simultaneous finger photoplethysmography (PPG) was used as a physiological reference. A stable region of interest (ROI) within the pupillary aperture was segmented, and intensity-based signals were extracted primarily from the red channel. Data were processed using band-pass filtering (0.5–4.0 Hz) and Fast Fourier Transform (FFT) to isolate cardiac frequency and analyze synchronization with systemic pulse waveforms.

A strong periodic signal was successfully obtained in 92% of cases. Spectral analysis revealed a dominant power peak that perfectly matched the heart rate frequency (Mean Error < 0.02 Hz). PRR showed high synchronization with the reference PPG (r=0.89, p<0.001). Extrapupillary region and ambient light controls confirmed that the signal was a biological phenomenon, not an optical artifact.

Although the red reflex has traditionally been considered a static optical signal, our findings demonstrate that this reflex involves a dynamic hemodynamic component. PRR, which has not been previously reported at this level in the current literature, is likely an optical manifestation of ocular pulse amplitude (OPA) and choroidal volumetric changes. This study presents PRR as a novel and contactless biomarker for monitoring ocular perfusion, particularly in telemedicine and clinical settings with limited resources.