Retinal Vascular and Oxygen Temporal Dynamic Responses to Light Flicker in Humans

PURPOSE: To mathematically model the temporal dynamic responses of retinal vessel diameter (D), oxygen saturation (SO(2)), and inner retinal oxygen extraction fraction (OEF) to light flicker and to describe their responses to its cessation in humans. METHODS: In 16 healthy subjects (age: 60 ± 12 years), retinal oximetry was performed before, during, and after light flicker stimulation. At each time point, five metrics were measured: retinal arterial and venous D (D(A), D(V)) and SO(2) (SO(2A), SO(2V)), and OEF. Intra- and intersubject variability of metrics was assessed by coefficient of variation of measurements before flicker within and among subjects, respectively. Metrics during flicker were modeled by exponential functions to determine the flicker-induced steady state metric values and the time constants of changes. Metrics after the cessation of flicker were compared to those before flicker. RESULTS: Intra- and intersubject variability for all metrics were less than 6% and 16%, respectively. At the flicker-induced steady state, D(A) and D(V) increased by 5%, SO(2V) increased by 7%, and OEF decreased by 13%. The time constants of D(A) and D(V) (14, 15 seconds) were twofold smaller than those of SO(2V) and OEF (39, 34 seconds). Within 26 seconds after the cessation of flicker, all metrics were not significantly different from before flicker values (P ≥ 0.07). CONCLUSIONS: Mathematical modeling revealed considerable differences in the time courses of changes among metrics during flicker, indicating flicker duration should be considered separately for each metric. Future application of this method may be useful to elucidate alterations in temporal dynamic responses to light flicker due to retinal diseases.