Abstract
Purpose :
A peripheral pattern ERG (pPERG) stimulus source was created to probe ganglion cell function in the peripheral retina, beyond approximately 20 degrees of visual angle. Dividing the peripheral retina into sectors for analysis can increase the sensitivity to localized functional deficit. Stimulating multiple visual field sectors in series increases the test time proportionally. Here we demonstrate a method for recording pPERG responses from 2, 3 or 4 visual field sectors simultaneously.
Methods :
The pPERG stimulus is divided into 30 radial columns and four circumferential rows of checks that form the PERG checkerboard pattern. Visual field sectors were defined by 2, 3 or 4 subsets of columns. The mean ON luminance was 300 photopic candelas per square meter for all experiments. Normally-sighted subjects (n=4, 19-38 yrs old) participated. Proparacaine HCl 0.5% was administered prior to placement of DTL fiber electrodes. For simultaneous sector recording, each sector was run at a different reversal rate (4.3, 4.4, 4.5 or 4.6 reversals per sec); responses to 900 reversals were recorded for each protocol. Post-processing of the mixed responses obtained during simultaneous recording separated the respective sectoral responses by time-windowing based on the reversal rate for each sector.
Results :
Sector responses recorded individually (serially) were similar to those recorded simultaneously, e.g. N amplitudes changed, on average, by 10-21%, and N implicit times changed by 2-9%, between recording methods for 2, 3 and 4-sector protocols. Comparing response amplitudes for each sector across subjects, variability was high when analyzed as absolute amplitudes, but decreased significantly when responses were normalized within each subject. For N amplitudes, the decrease in coefficient of variation, across subjects, when using the normalizing approach was 31%, 37% and 67% for 2, 3 and 4 sector protocols, respectively.
Conclusions :
A novel technique for probing ganglion cell function in sectors of the peripheral retina is demonstrated for up to four sectors, resulting in localized responses that may be more sensitive to local functional deficit. This advantage is gained with no increase in test time. Normalizing sector response amplitudes within each subject significantly reduces intersubject variability and should narrow reference ranges.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.