The influence of age on the recovery of the ERG photostress test

INTRODUCTION: Focal ERG associated with photostress test could be a useful diagnostic method for evaluating macular visual function. The main aim of this study was to evaluate the effect of age on the recovery time constant of the ERG photostress test. The second aim was to assess the sources of variability which affect the measurements. METHODS: Fifty-four healthy subjects (108 eyes), aged between 21 and 77, with corrected VA of 20/20 or more and absence of any ocular or systemic disease were recruited. For each eye ERG response to Focal (20° in diameter) 42 Hz stimulation were recorded: three series of 200 summations in base conditions and a six series of 42 Hz ERGs (100 summations each) at 10, 40, 80, 180, 300 and 420 seconds after bleaching by a white spot of light (20° in diameter) from a direct ophthalmoscope (800 cd/m²) pointed at macular region for 30 seconds. Fourier analysis was performed and amplitude of the 1st harmonica calculated. The relationship of basal amplitudes with subject age and gender, and the kinetics of macular function recovery were assessed through mixed-effects models. RESULTS: Mean basal amplitude decreases by 0.046 microvolts for year of life. The recovery after bleaching is proportional to age with an increase of 4.31 seconds for decade. Restoration of amplitude is slower in older subjects. DISCUSSION: There is a significant decrease in macular ERG amplitude with age. The macular recovery after photostress shows exponential kinetics that are less efficient in older subjects: this could be related to lower effectiveness of photopigment restoration in advanced age.