Standardized full-field electroretinography. Normal values and their variation with age

Abstract

Full-field electroretinograms were obtained in 269 normal subjects with the International Standardization Protocol endorsed by the International Society for Clinical Electrophysiology of Vision and the National Retinitis Pigmentosa Foundation Inc. Log rod and cone amplitudes decreased exponentially with age in adults; amplitudes declined to one half those in the young adult level (ages 15 to 24 years) by ages 69 and 70 years for rod and cone responses, respectively. B-wave implicit times increased with age for all responses. Lower limits of normal peak-to-peak amplitude and upper limits of normal b-wave implicit time (P < .05) were determined for each decade from birth to age 79 years. Naka-Rushton functions relating rod peak-to-peak amplitude to retinal illuminance were determined in 50 normal subjects. A significant decline in the log maximum asymptotic amplitude with age accounted for most of the amplitude decline in the standard protocol rod response. The average value of log k, the semisaturation constant, was only 0.1 log unit higher at age 70 years than at age 20 years, consistent with previous studies showing little decrease in photopigment optical density with age.