Revealing a retinal facilitatory effect with the multifocal ERG.

Area of Science:

• Ophthalmology
• Neuroscience
• Visual Electrophysiology

Background:

• The amplitude of multifocal electroretinogram (mfERG) responses to a single large hexagon is typically smaller than the sum of responses from multiple smaller hexagons covering the same area.
• Previous studies indicated a significant difference in mfERG amplitude based on stimulus configuration.

Purpose of the Study:

• To confirm initial findings on mfERG amplitude summation in normal subjects across different age groups.
• To investigate the potential of mfERG amplitude summation as a diagnostic tool in patients.

Main Methods:

• Binocular mfERGs were recorded from 40 normal subjects (25 young adults, 15 children) using arrays of 1, 7, 19, 37, and 61 hexagons.
• mfERG waveforms from multi-hexagon arrays were summated and compared to the single-hexagon response to calculate amplitude ratios.

Main Results:

• In normal subjects, the amplitude ratio of the 7-hexagon array to the single hexagon was 119.5% ± 9.2%, decreasing to 109.4% ± 20.6% for the 61-hexagon array.
• These amplitude summation effects were consistent across all tested age groups.

Conclusions:

• Summating mfERG responses from hexagon arrays significantly enhances composite waveform amplitude compared to a single hexagon stimulus.
• This enhancement may involve retinal lateral pathways (horizontal or amacrine cells), requiring further investigation.
• Preliminary data suggest this mfERG analysis method may offer insights into macular function distinct from standard mfERG ring ratio analysis, particularly in patients treated with Plaquenil.