Adaptation recovery of the photopic full-field and multifocal ERGs in normal young and old adults

Abstract

Purpose: To compare fast adaptation recovery between healthy young and old adults using the photopic full-field and multifocal ERGs, both with m-sequence flash stimulation.

Methods: The photopic full-field ERG (ffERG) was recorded from 10 young (21±2yrs; mean±SD) and 10 old (73±8yrs) adults using an m-sequence flash stimulus. Photopic ffERG flash intensities ranged from 0.7 to 10cd*s/m² and the base interval was 10ms. The multifocal ERG (mfERG) was also recorded from 10 young (21±2yrs) and 10 old (74±6yrs) adults. The mfERG stimulus contained 103 hexagons with a luminance of 200cd/m² and was divided into macular and peripheral regions. The base interval was 13.3ms. The complete binary kernel series from the responses to an m-sequence cycle were obtained for both the ffERG and mfERG using the VerisPro software (EDI). Single-flash responses following a double flash were extracted from the signal at different inter-stimulus intervals (ISIs). The b-wave (ffERG) and P1 (mfERG) amplitudes were plotted as a function of ISI and fitted with an exponential function. The rate constant of the exponential was used to estimate the rate of recovery. We also measured the normalized amplitude of the subsequent flash response (SFR) to determine the amount of recovery at the first ISI. A two-way ANOVA was used for statistical analysis.

Results: Photopic recovery rates were greater for the older adults compared to the younger adults for both the ffERG (p<0.001) and mfERG (p<0.05). In the mfERG data, however, differences in recovery rates between the younger and older adults appeared more prominent in the macula. The older adults had larger SFRs at 10ms compared to the younger adults (p<0.05) using ffERG, but there was no significant difference in SFRs at 13.3ms using mfERG.

Conclusions: The results of this study suggest that older adults recover more quickly after an adapting flash than younger adults. However, with the ffERG, the difference in recovery rates may be due to older adults recovering from a lower physiological state of adaptation compared to the younger adults, which is demonstrated by the older adults also having a larger normalized SFR. Furthermore, the mfERG data suggest that fast adaptation recovery is affected differently between the macula and periphery when examining the effects of age.