A modified Global Flash Multifocal ERG protocol with coloured stimulus for obtaining L and M cone responses

Abstract

Purpose : Multifocal (mfERG) and Global Flash multifocal ERGs (MOFO mfERG) have been explored in the past with standard black and white stimulus. As exploratory research, we aimed to create a cone isolating stimuli for LED-based stimulator using the method of silent substitution (SS). Previous studies have used conventional CRT monitor in mfERG for SS-based research, nevertheless due to discontinuation of CRT monitor and popularity of LED monitors, there is a need to develop an SS stimulus for LED monitors which are instrumental for mfERG recordings.

Methods : The appropriate cone isolating stimuli were calculated by integrating the emission spectrum from the three primary LED monitors (Samsung S24E650PL) obtained using a Topcon SR-3AR Spectroradiometer (Japan) and Stockman and Sharpe (10°) cone fundamentals. The LED energies were converted into quantal numbers and by setting specific conditions to a matrix equation the corresponding luminance for the L and M cone conditions were obtained. Screen calibrations were done under experimental conditions.

Results : The created L and M cone isolating stimulus had a cone contrast of 45%. The multifocal, dark, and global flash frames were arranged with the standard MOFO mfERG frame arrangements as a reference. The luminance of the Multifocal Frame was based on SS calculations. The dim and bright states of the respective cone-isolating condition acted as the dark (O) and global flash (F) frames respectively. The background area had a mean luminance of 53 cd/m² for both conditions, which had a chromaticity of bluish-purple in the CIE chromaticity diagram. Two colour normal adults were recruited as samples to measure the L- and M-cone responses by modified MOFO mfERG based on the SS method. The obtained ERG waveforms with the stimulus had two prominent peaks which corresponded to the Direct (N1, P1 points) and induced components (P2, N2 points). The L response amplitudes were higher than that of the M cones.

Conclusions : We hypothesize that the use of Global flash mfERG paradigm which has incorporated adaptive components (MOFO) will provide useful information on the outer and inner retinal layers under single cone class stimulated state.

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

 

Figure 1: a) Normalised cone fundamentals (Stockman and Sharpe 1998) b)Emission spectrum of the LED monitor c) matrix calculations for silent substitution

 

Figure 2: The standard and the modified conditions of MOFO mfERG