Changes in rod and cone-driven oscillatory potentials in the aging human retina

We recorded oscillatory potentials (OPs) to document how age impacts on rod- and cone-driven inner retina function. Dark- and light-adapted electroretinogram (ERG) luminance-response functions were recorded in healthy human subjects aged 20 to 39, 40 to 59, and 60 to 82 years. Raw ERG traces (0.1-300 Hz) were filtered (75-300 Hz) to measure OPs trough-to-peak in the time-amplitude domain. Morlet wavelet transform (MWT) allowed documenting OPs time-amplitude-frequency distribution from raw traces. Under dark adaptation, both methods revealed reduced OP amplitudes and prolonged implicit times by 40 years of age. The MWT identified a high-frequency band as the main oscillator, which frequency (150-155 Hz) was unaffected by age. Under light adaptation, most OP peaks were delayed by 40 years of age. Peak-trough measures yielded inconsistent results in relation to luminance. Contrastingly, MWT distinguished two frequency bands at all luminances: high frequency (135 ± 6 Hz) time locked to the onset of early OPs and low frequency (82 ± 7 Hz), giving rise to early and late OPs. By 60 years, there was a consistent power reduction specific to the low-frequency band. Age-related OP changes precede those seen with a- (photoreceptoral) and b-waves (postphotoreceptoral). In addition, MWT allows quantifying distinct low- and high-frequency oscillators in the human retina, which complement traditional OP analysis methods. The identification of an age-independent OP marker (light-adapted high frequency band) opens a new dimension for the screening of retinal degenerations and their impact on inner retina function.