Phosphene thresholds elicited by transcorneal electrical stimulation in healthy subjects and patients with retinal diseases

Abstract

Purpose: To evaluate electrically evoked phosphene thresholds (EPTs) in healthy subjects and in patients with retinal disease and to assess repeatability and possible correlations with common ophthalmologic tests.

Methods: In all, 117 individuals participated: healthy subjects (n = 20) and patients with retinitis pigmentosa (RP, n = 30), Stargardt's disease (STG, n = 14), retinal artery occlusion (RAO, n = 20), nonarteritic anterior ischemic optic neuropathy (NAION, n = 16), and primary open-angle glaucoma (POAG, n = 17). EPTs were determined at 3, 6, 9, 20, 40, 60, and 80 Hz with 5 + 5-ms biphasic current pulses using DTL electrodes. Subjects were examined twice (test-retest range: 1-6 weeks). An empirical model was developed to describe the current-frequency relationship of EPTs. Visual acuity, visual field (kinetic + static), electrophysiology (RP, RAO, STG: Ganzfeld-electroretinography [ERG]/multifocal-ERG; POAG: pattern-ERG; NAION: VEP), slit-lamp biomicroscopy, fundus examination, and tonometry were assessed.

Results: EPTS varied between disease groups (20 HZ: healthy subjects: 0.062 ± 0.038 mA; STG: 0.102 ± 0.097 mA; POAG: 0.127 ± 0.09 mA; NAION: 0.244 ± 0.126 mA; RP: 0.371 ± 0.223 mA; RAO: 0.988 ± 1.142 mA). In all groups EPTs were lowest at 20 Hz. In patients with retinal diseases and across all frequencies EPTs were significantly higher than those in healthy subjects, except in STG at 20 Hz (P = 0.09) and 40 Hz (P = 0.17). Test-retest difference at 20 Hz was 0.006 mA in the healthy group and 0.003-0.04 mA in disease groups.

Conclusions: Considering the fast, safe, and reliable practicability of EPT testing, this test might be used more often under clinical circumstances. Determination of EPTs could be potentially useful in elucidation of the progress of ophthalmologic diseases, either in addition to standard clinical assessment or under conditions in which these standard tests cannot be used meaningfully. (ClinicalTrials.gov number, NCT00804102.).