Optical coherence tomography angiography findings in patients undergoing transcorneal electrical stimulation for treating retinitis pigmentosa

Full-field sensitivity threshold and the relation to the oxygen metabolic retinal function in retinitis pigmentosa

PURPOSE

The aim of our study was to evaluate retinal function with white light dark-adapted full-field sensitivity threshold (FST) and find possible correlations with metabolic function measured with retinal oximetry (RO) in patients with retinitis pigmentosa (RP).

METHODS

In this prospective observational study (BASEC 2020-00,122), FST and RO measurements were performed on 66 RP eyes (33 subjects, 12♀ 21♂) aged between 18 and 80 years (mean 43.2 years); all eyes were graded for disease severity. Main outcome parameters were white FST thresholds using the Diagnosys Espion system with the ColorDomeTM LED full-field stimulator (Diagnosys LLC, Lowell, MA) as well as the main RO parameters: the mean arterial (A-SO₂; %), venular (V-SO₂; %) oxygen saturation, their difference (A-V SO₂; %), and the corresponding mean diameters of the peripapillary retinal arterioles (D-A; μm) and venules (D-V; μm) recorded with the oxygen saturation tool of the Retinal Vessel Analyser (RVA; IMEDOS Systems UG, Jena, Germany). In addition, semi-automated kinetic perimetry (V4e, III4e, I4e, III3e isopters, Octopus 900®, Haag-Streit AG Bern, Switzerland) was performed and included in the linear mixed-effects models analysis calculated with SPSS®.

RESULTS

Neither the oxygen saturation parameters (p > 0.21) nor the D-A and D-V (p > 0.13) showed significant correlations with the FST. However, when compared systematically with the visual field (VF) areas of the different isopters, RO parameters V-SO₂ (p = 0.024) and A-V SO₂ (p < 0.02) showed significant correlations. Furthermore, both V-SO₂ and A-V SO₂ showed gradual changes with more pronounced impairment in oxygen metabolic function in advanced stages of RP when analyzed in subgroups of disease severity grades.

CONCLUSION

In contrast to standardized VF parameters, white dark-adapted FST appears not to correlate with retinal oxygen metabolic function measured with RO in patients with RP, suggesting that the two examinations may capture unrelated aspects of the retinal pathological process. However, RO showed a significant association with standardized VF testing parameters and may, therefore, offer an alternative outcome measure for interventional trials.

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♀ 4♂) suffering from RP were examined at baseline (BL), 6 months, and 3Y of TES (OkuStim®) 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®.

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.