Transcorneal electrical stimulation slows down visual field decline in retinitis pigmentosa in a current-strength-dependent manner

Abstract

Purpose : Transcorneal electrical stimulation (TcES) is a clinically available method to slow down disease progression in retinitis pigmentosa (RP). We hypothesize that the effect of TcES on the rate of visual field loss obeys a dose-response relationship with current strength.

Methods : In a prospective, randomized study (clinicaltrials.gov: NCT01837901), one eye of each of 52 subjects with RP was transcorneally stimulated weekly for 30 minutes over a period of 52 weeks with biphasic current pulses (OkuStim, maximum 1.2 mA, 5 ms each phase, 20 Hz). The visual field areas (VFA) were repeatedly assessed in both eyes (Octopus 900, Goldman targets III4e, V4e). Stimulation current strength was 0% (sham), 150% and 200% of the patient’s electrical phosphene threshold in 3 randomized groups of patients, respectively. In addition to the primary analysis, where the effect of TcES on the stimulated eyes was analyzed in relation to randomized group (Schatz et al., IOVS, 2017, 58:1), in the now presented secondary analysis, the percentage reductions of the VFA of the stimulated (R₁) and non-stimulated eyes (R₀) after 52 weeks of stimulation were analyzed in relation to the actual current strength. Mean current strength over 52 weeks stimulation was analyzed both as a continuous variable (linear regression) and an ordinal variable (5 classes, Jonckheere-Terpstra test).

Results : As the current strength increased, the VFA (V4e) decreased more slowly, whereby there was a significant linear relationship (p = 0.049) and a significant ordinal relationship (p = 0.011) between the differences in percentage reduction, (R₁ – R₀), and the current strength. In the eyes stimulated with more than 0.8 mA (n = 9), R₁ was 0.7% ± 7.2% (mean ± SD) compared with R₀ of 8.8% ± 9.1% in the non-stimulated fellow eyes (difference between both eyes: p = 0.098, Wilcoxon signed rank test). In the sham group (n = 20) the mean percentage reductions R₁ and R₀ were 7.0% ± 11.1% and 7,0% ± 16.1%. Analysis of VFA III4e yielded in no signifcant effect of TcES.

Conclusions : Our results are consistent with the hypothesis that by TcES the decline in VFA in patients with RP can be slowed significantly in a current-strength-dependent manner. Furthermore, they provide additional evidence that TcES is an efficient method that can stop or delay the disease progression in RP.

This is a 2021 ARVO Annual Meeting abstract.