Pilot study: non-invasive binocular fundal pulsation measurements using infrared photorefraction.

Choroidal blood flow plays an important role in myopia development, and non-invasive techniques to measure both eyes simultaneously would be valuable. We explored the potential of infrared photorefraction to measure pulsation-related fundal reflectance changes. Tiny pulsation-related variations in pupil brightness were detected using custom-developed software written in Visual C++. Pupil brightness changes needed to be corrected for spontaneous fluctuations in pupil size. The software also included video eye tracking to verify that the same fundal location was measured. Two subjects (ages 27 and 70) were successfully measured. Pulsation amplitude was quantified as the absolute difference between the baseline and raw signal over time. Standard deviations from repeated measurements ranged from 6 to 10 percent. However, reasons for some residual variability in the traces have not yet been fully explained. Measurements had the advantages that hardware was cheap, easy to perform, in real-time, binocular, non-cycloplegic, and from a distance of 1.2 m. Some variability in the fundal reflectance traces still needs better understanding to make the technique suitable for clinical use.