Metabolic Long-Term Monitoring of Transcorneal Electrical Stimulation in Retinitis Pigmentosa

Introduction: Transcorneal electrical stimulation (TES) is a new therapeutical approach for retinitis pigmentosa (RP). With progression of RP, degeneration of photoreceptors results in lower oxygen consumption of the retina. Retinal oximetry (RO) is a noninvasive method to analyze oxygen saturation in retinal vessels and has shown promising short-term results as a therapy monitoring tool for TES. The aim of our study was to measure the long-term effects of TES on RO parameters over a period of 3 years (3Y). Methods: A total of 18 eyes of 9 subjects (5 female 4 male) suffering from RP were examined at baseline (BL), 6 months, and 3Y of TES (OkuStim (R)) treatment. TES was performed for 30 min once a week at 200% of the individual phosphene threshold simultaneously on both eyes. The oxygen saturation was examined at BL and following TES therapy with the oxygen saturation tool of the Retinal Vessel Analyser (IMEDOS Systems UG, Jena, Germany). The global oxygen saturation parameters (in %), within 1.0-1.5 optic-disc diameters from the disc margin, in retinal arterioles (A-SO2) and venules (V SO2) were measured and their difference (A-V SO2) was calculated. In addition, we recorded the diameters in the main arterioles (D-A) and venules (D-V). ANOVA-based linear mixed-effects models were employed for statistical analysis using SPSS (R). Results: After 3Y of TES treatment both the mean A-SO2 (from 96.35 +/- 12.76% to 100.89 +/- 5.87%, p = 0.22) and V SO2 (from 62.20 +/- 11.55% to 64.55 +/- 8.24%, p = 0.77) increased slightly. The A-V SO2, which corresponds to the oxygen consumption of the retina, presented also with a slight increment from 34.15 +/- 9.68% at BL to 36.23 +/- 7.71% without reaching statistical significance (p = 0.27). TES also did not appear to alter the vascular diameter parameters, D-A and D-V (p > 0.05). Conclusion: Our long-term observations indicate that TES therapy in RP might lead to a slight increment in oxygen consumption of the retina. However, a larger cohort and longer duration may be needed to adequately power a follow-up study and to confirm this trend reflecting a possible benefit of TES for RP.