Increased velocity of retinal blood flow in RP subjects with significantly improved visual function following transcorneal electrical stimulation in a randomized controlled trial

Purpose: To examine the repeatability of and changes in retinal blood velocity (RBV) in the macular capillaries of retinitis pigmentosa (RP) participants in a randomized controlled trial evaluating the efficacy of Transcorneal Electrical Stimulation (TES) for improving visual function. Methods: Four eyes of 3 TES subjects who developed significantly improved visual function (i.e., >0.4 logMAR visual acuity or >100% log retinal area of Goldmann visual fields) and six other eyes that received TES but did not have a significant visual function change were compared to 3 control subjects' eyes that received placebo sham intervention (inactive laser acupuncture). Coefficients of variation (CoV) for RBV were measured at 2 baseline visits, as well as after 2 and 6 weeks of TES/intervention sessions. We used a retinal blood cell tracking system similar to a speckle imaging system; it relies on tracking the non‐uniform distribution of red blood cells within the capillary and is capable of dealing with very low signal‐tonoise ratios. Results: CoV for RBV were 5% and 8% on average within a single vessel location in an image for arteries and veins, respectively. Test‐retest CoV were 13% on average within a single artery or vein location for 2 within‐visit or between baseline visit images. The eyes with and without visual improvements had a significant 32% and 19% increase in RBV on average in arteries, respectively, after 2 TES sessions when compared to control eyes (95%CI:16‐48%;p<0.001)(95%CI:0.3‐38%;p=0.047). The eyes with visual improvements had a significant 31 % increase in RBV in veins after 2 TES sessions (95%CI:4‐59%;p=0.02), but those without visual changes had no significant RBV change in veins (p=0.70) compared to control eyes. For eyes with improved vision, the increases in RBV were slightly reduced after 6 TES sessions to 14% and 24% in arteries and veins (p=0.18 and p=0.07), respectively, and RBV was not significantly different than controls for eyes that did not improve post‐TES after 6 weekly intervention sessions (p=0.68 and p=0.95). Conclusions: RBV measurements in RP patients are reliable outcomes supporting a physiological basis for visual function improvements in RP subjects who received TES.