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L. Naycheva, A. Messias, T. Röck, H. Zhang, K. U. Bartz-Schmidt, E. Zrenner, F. Gekeler; Effects of Transcorneal Electrical Stimulation on Evoked Phosphene Thresholds in Retinitis Pigmentosa and Retinal Artery Occlusion - Preliminary Results. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5412.
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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 to assess a possible effect of transcorneal electrical stimulation (TES).
39 eyes of 39 individuals (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 (total 6 times). EPT was determined at 3, 6, 9, 20, 40, 60 and 80 Hz at a baseline and after TES in 9 visits, over a total follow-up time of 17 weeks. Patients were sub-divided into 3 groups according to TES intensity: 0 mA (sham); 150 % or 66% of the EPT at 20 Hz.
Eight patients with RP (TES=sham: n=2, TES=150%: n=3 and TES=66%: n=3), and five with RAO (TES=sham: 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’s groups than in healthy subjects, but no differences between RP and RAO (Tukey-Kramer HSD at 0.05). In RP patients the EPTs tended to decrease over the study period, showing a visible difference between sham and stimulation groups. However, due to the small sample sizes, this comparison currently evades statistical analysis. In RAO patients this tendency was not as marked as in RP patients.
Our data show that phosphene thresholds are higher in RP and RAO than in healthy subjects over a large range of stimuli frequencies, and that after repeated TES there is a tendency for a decreasing EPT in RP.
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