gms | German Medical Science

Purpose: The electroretinogram (ERG) and Visually Evoked Potential (VEP) are widely used in clinical diagnostic testing to examine the function of the retina and higher visual pathways, respectively. In this study, we examined whether electrical stimulation of the retina with an Argus II implant would lead to recordable responses at the cornea (EERG) and occipital scalp (EVEP).

Methods: Three participants in the Argus II clinical trial volunteered for these experiments. EERG recordings used bipolar Burian-Allen electrodes, since in proximity of the implant electronics the stimulus artifacts picked up by monopolar (Jet or DTL) electrodes precluded recovery of the underlying response activity. For the EVEP, where the recording electrodes were much farther from the implant, standard scalp recordings could be used, with a high mid-frontal reference electrode. To allow stimulus artifacts to die down and to reduce premature adaptation to prolonged stimulation, stimulus pulses were separated by at least 2.5 s, and each recording lasted 500 s. Depending on stimulus amplitude, 4 – 12 such recordings were combined to obtain an averaged waveform.

Results: Reproducible EVEP waveforms, with a plausible dependence on stimulus attributes, could be recorded in all 3 participants, whereas this was not the case for EERG responses. Even for the EVEP, response amplitudes and waveforms are highly variable and not significant when patterned stimulation is applied to a subset of electrodes.

Conclusions: We have demonstrated that EVEPs can be used to examine properties of the visual pathways. The EERG, on the other hand, cannot be recorded reliably from the ocular surface. Recordings of retinal signals from the implant electrodes, immediately following stimulation at those same or neighboring electrodes, will be required to obtain reliable EERGs. High-quality reverse telemetry will be an essential tool for such recordings to become possible