Senescence of Multifocal Electroretinogram Parameters in Monkeys

Abstract

Abstract: : Purpose: Some multifocal electroretinogram (mfERG) parameters decrease with age in humans. There are no published studies to address if such a relationship exists in monkeys. The purpose of this study was to investigate the effect of age on amplitude and temporal parameters on the 1st order kernel of mfERG. Methods: Eleven cynomolgus monkeys (2.5 – 7 kg) with age range 5 to 12 years participated in this study. The animals were anesthetized with ketamine (10 mg/kg) and paralyzed with vercuronium bromide (10 mg/kg). Direct fundus observation and projection of the stimulus was provided by VERIS^TM 1.5 fundus camera stimulator (EDI, San Mateo, CA). MfERGs were recorded monocularly with the use of Burian–Allen contact lens electrodes. The stimulation protocol had the following parameters: 241 hexagonal areas, m–sequence at 75Hz refresh rate, 600 cd/m² stimulus luminance, 98% Michelson contrast, 300 cd/m² background luminance, exponent m = 14 (resulting in a total recording time of 7 min). VERIS Science^TM v. 4.9 was used for recording and v.5.0 was used for data analysis. Results: The average scalar product amplitude from all stimulated areas decreased with age (R² = 0.398, p<0.001). Analysis of the changes in concentric rings averages (9 rings) revealed more pronounced age effect on the central rings compared to the peripheral rings (slope range –0.775 to –0.33 nV/deg²/yr for rings 1–3 vs. –0.26 to –0.21 nV/deg²/yr for rings 4–9). Hemifiield comparison between upper and lower hemirings demonstrated higher values from the upper retina (rings 2,4,5,6) compared to symmetrical portions of the lower retina (p<0.05, Wilcoxon signed ranks test, related samples). The decrease with age was similar for both the upper and lower hemifiled with a tendency for the amplitude from the upper retinas to decline faster with age. The temporal parameter peak time of P1 from all stimulated areas increased with age (R² = 0.187, p<0.001). No significant difference was observed between the upper and lower retina hemifields for the timing of P1. Conclusions: Similar to humans, scalar product mfERG amplitude declines with age in monkeys. This similarity extends to the effect of age on P1 peak time. This information should allow improved quantitative monitoring of retinal disease progression and evaluation of pharmacologic effects on disease states.

Keywords: aging • aging: visual performance • electroretinography: non-clinical