Exploring kinetics of the ganglion cell contribution to standard light-adapted flash electroretinograms by interocular comparison in patients with unilateral ganglion cell loss

Abstract

Purpose : The conventionally measured components of standard light-adapted flash electroretinograms (ERGs) arise largely from photoreceptors and bipolar cells. A later negative component, the photopic negative response (PhNR), arises from retinal ganglion cells (RGCs). Due to inter-individual variation, defining the kinetics of this response is challenging in humans. Here, we recorded ERGs from individuals with unilateral marked RGC loss and compared waveforms between eyes.

Methods : Bilateral recordings were made to the international standard LA3 stimulus. Pupils were pharmacologically dilated and conductive fibre electrodes were placed in the lower conjunctival fornix. Patient 1 was a 54 year old female who had complete loss of RGCs in her right eye secondary to a presumed prior ischaemic event. Patient 2 was a 60 year old male with marked RGC loss in the left eye. Seven healthy participants underwent recordings in which the conductive fibre electrode position was varied between eyes to investigate the effect on ERG components.

Results : When superimposing ERGs from both eyes, for both patients, the a-wave and b-wave components were very similar. The ERG from the affected eye remained higher following the b-wave (more positive) compared with the healthy eye, suggestive of loss of a negative component. When the trace from the affected eye was subtracted from that from the healthy eye, a waveform emerged that appeared to be close to baseline until around 20-25 ms and later dropped below baseline. In control individuals, all components (a-wave, b-wave, PhNR) were affected when the electrodes were positioned differently (greater amplitudes when electrodes were closer to the limbus).

Conclusions : RGC signals give rise to a negative component (with no clear evidence in these recordings of a prior positive component) discernible in the standard LA3 response. The interocular differences in the patients could not be attributed to variations in electrode position as control recordings indicated that the a-wave and b-wave would also be affected. Recordings in further patients with unilateral substantial RGC loss could help define the RGC contribution to the LA3 ERG.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.