Increased retinal sensitivity after transcorneal electrical stimulation in patients with retinitis pigmentosa.

Abstract

Purpose: To evaluate retinal sensitivity using electrically evoked phosphene thresholds (EPTs) and investigate the individual stimulation currents in patients with retinitis pigmentosa, and to assess the impact of transcorneal electrical stimulation (TES).

Methods: Fifty-two patients were examined per protocol in this prospective sham-controlled study. EPTs were determined at 20 Hz with 5-ms biphasic current pulses using the OkuEl^®-DTL electrode and an OkuStim^®-stimulator (Okuvision GmbH, Germany). Subjects were examined 13 times during the study period of 12 months including one screening visit. Patients were divided into 3 groups: sham-stimulation (n = 20), 150% of individual EPTs (n = 15) and 200% of individual EPTs (n = 17) and were compared using a REML model with significance level of p=0.05. Currents needed for stimulation were descriptively analyzed for both stimulated groups (150% and 200%).

Results: At the end of the study stimulation currents had decreased in 47% and increased in 53% of patients in the 150% group (mean intra-individual ratio between baseline and the last visit 1.02±0.21 as 95% confidence interval). In contrast, 71% of patients treated with 200% of EPT showed a decrease and 29% an increase with a mean decrease of 9% (0.91±0.15). During the study period intra-individual ratios of EPTs were 0.92±0.10 for the sham group, 1.02±0.11 for 150% and 0.98±0.11 for 200% group. No significant differences between groups were found (p>0.05).

Conclusions: Considering previous data of the pilot study (EST1; Schatz et al. IOVS 2011), where a significant improvement of retinal function has been observed after TES, we were able to detect an improved retinal sensitivity by decreased electrical currents needed for treatment in patients with retinitis pigmentosa treated by TES and 200% of individual EPTs. Stimulation with 150% of individual EPTs revealed unchanged retinal sensitivity at the end of the study. However, values did not reach levels of significance.