Electrically Evoked Responses Elicited by Transcorneal Electrical Stimulation in Retinitis Pigmentosa

Abstract

Purpose : Electrically evoked response (EER) elicited by trans corneal electrical stimulation (TES) is an objective method to evaluate the visual pathway. This study aims to validate EER to predict the efficacy of advanced therapies for diseases with severe photoreceptor damage. The technical studies and preliminary data were presented in ISCEV 2019/2020/2022 annual symposia. We herein describe EERs in patients with retinitis pigmentosa (RP).

Methods : EERs were recorded under the dark-adapted condition (after 20 minutes’ dark adaptation) using DTL-Fz stimulation, Oz-Pz potential recording at current intensities of 0.5 mA, 1 mA, 1.5 mA, and 2 mA. Two ground electrodes were used: one for the stimulation and one for the recording channels. All tests were conducted with an Espion Profile electrophysiology system (Diagnosys LLC, MA, USA). The presence of EER responses for each component and each stimulus condition was evaluated by two investigators. A positive peak is defined as a peak with an amplitude (> 0.8 μV). The sum of EER amplitudes was calculated.

Results : Twenty-six eyes of thirteen patients with a clinical diagnosis of RP including potentially therapeutic targets of RPE65-retinopathy and RPGR-retinopathy were enrolled. The median age of disease onset/age at examination of thirteen patients was 16.0 years/54.5 years, respectively. The median visual acuity was 1.0/1.0 in the LogMAR unit in the right/left eye, respectively. The full-field ERG responses were undetectable. The presence of positive peaks for 0.5mA/1.0mA/1.5mA/2.0mA components was identified in 50.0%/43.6%/56.0%/66.7% in the thirteen RP patients. The median value of the sum of EER amplitudes in the thirteen RP patients was 2.30 (range, 0.56 – 9.49).

Conclusions : The presence of positive responses in EERs was more frequently (>80%) identified in thirteen RP patients. The sum of EER amplitudes, reduced in the RP patients, can be a parameter to evaluate the visual pathway even when full-field ERGs are undetectable. These findings imply that EERs derived predominantly from residual retinal ganglion cell function in RP patients, which helps in assessing the objective function in patients with severe photoreceptor damage. Further studies such as comparing EER values with the other clinical parameters would be helpful to delineate the utilities and applications of EERs.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.