Photopic negative response during and after ocular direct current stimulation

Abstract

AbstractPurposeOcular current stimulation (CS) exhibits potential for the treatment of neurodegenerative ocular diseases. Until today, the underlying mechanism of the CS is unknown. For the pattern electroretinogram (ERG) the CS have a decreasing effect on the amplitudes but no influence on latencies. The photopic negative response (PhNR) is an amplitude in the full‐field ERG originating like the patter ERG in the GCs. The aim of the study was to investigate whether CS can also influence the PhNR.Methods14 healthy volunteers (7m, 27.7 ± 4.5 years) were stimulated with an anodal, cathodal and sham (randomized) direct CS of 800 µA for 5 min. A cut‐sized ring rubber electrode (outer/inner diameter: 7.5 cm/3 cm) placed around the eye and a square rubber electrode (25 cm2) placed at the ipsilateral temple were used for CS. Before (ERG1), during (ERG2) and after (1, 5, 10, 15 min) the CS, the PhNR was measured with a full‐field ERG (light adapted, white flash, strength: 3 cds/m2, frequency: 2 Hz, duration: < 5 ms). For ERG recording, Ag/AgCl ring‐shaped skin‐electrodes were placed at the lower eyelid (active), the ipsilateral earlobe (reference) and the forehead (ground). For analysis, the data distribution of the amplitude and latency differences to the ERG1 wasevaluated. A confidence interval analysis and the Wilcoxon test (α = 0.05, after Bonferroni correction p* ≤ 0.0167) for the difference between ERG1 and ERG2 were performed.ResultsIn the mean, the data distribution showed an increasing PhNR amplitude during the cathodal CS. The confidence interval analysis and the Wilcoxon test of the difference between ERG1 and ERG2 were significant for the cathodal CS (anodal: [−1.94 µV/2.08 µV], p = 0.826; cathodal: [0.98 µV/3.04 µV]*, p = 0.002*; sham: [−1.08 µV/0.28 µV], p = 0.272). No current effect could be found for all latencies and all after‐stimulation measurements.ConclusionsWe found a significant increase in the PhNR during a cathodal CS which suggest a modulation of GC activity.