Abstract

P 193

Effects of transcorneal electrical stimulation on evoked phosphene threshold in retinitis pigmentosa and retinal artery occlusion – Preliminary results

Tobias Röck, André Messias, Lubka Naycheva, Karl Ulrich  Bartz-Schmidt, Eberhart Zrenner, Florian Gekeler
Universitäts-Augenklinik Tübingen

Objective
To determine electrically evoked phosphene thresholds (EPT) in patients suffering from retinitis pigmentosa (RP) and retinal artery occlusion (RAO) over a range of frequencies and evaluate a possible effect of transcorneal electrical stimulation (TES).
Methods
39 eyes of 39 participants (11 healthy subjects, 12 patients with RP and 16 with RAO) were enrolled in the study. Patients were treated with TES (1 ms biphasic pulses at 20 Hz; applied with DTL electrodes) for 30 minutes once a week. EPT was determined at 3, 6, 9 20, 40, 60 and 80 Hz at a baseline visit and after TES in 8 visits over a total follow-up time of 17 weeks. The group of patients with RP and RAO were subdivided into 3 subgroups according to TES intensity: 0 mA (sham); 150 % or 66% of the EPT at 20 Hz.
Results
Eight patients with RP (TES=0 mA: n=2, TES=150%: n=3 and TES=66%: n=3), and five with RAO (TES=0 mA: n=2, TES=150%: n=2 and TES=66%: n=1) completed the entire follow-up. At baseline, mean ± SE EPT at 20 Hz was 0.07 ± 0.01 mA in healthy subjects, 0.40 ± 0.10 mA in RP, and 0.44 ± 0.06 mA in RAO (ANOVA: F=20.5; p<0.0001), showing statistically significant higher levels in both patient groups than in healthy subjects, but no differences between RP and RAO (Tukey-Kramer HSD at 0.05). – There was a strong tendency in RP patients of decreasing EPTs over the study period, showing a visible difference between sham and stimulation groups. However, due to the small groups this comparison currently evades statistical analysis. In RAO patients this tendency was not as marked as in RP patients.
Conclusions
Our data show that phosphene thresholds are higher in RP and RAO than in healthy subjects over a large range of stimulus frequencies, and that after repeated TES there is a tendency for a decreasing EPT in RP but not in RAO patients.

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