INVARIANCE OF THE PATTERN ELECTRORETINOGRAM EVOKED BY PSYCHOPHYSICALLY EQUIVALENT STIMULI IN HUMAN AGING

1. The aim of this study was to assess the contribution of retinal gan glion cells to the decline in contrast sensitivity during human ageing . 2. After determination of the appropriate refraction for each subjec t, younger subjects were arranged to be exposed to a display luminance which was suprathreshold by the same amount as in older subjects wear ing a 4.0 mm diameter artificial pupil with a neutral density filter. 3. In fifty-four subjects, aged 20-99 years, contrast sensitivities me asured in response to phase-reversed grating patterns of 2, 5 and 8 cy cles per degree declined significantly with increasing age at each spa tial frequency studied. 4. Subjects were made psychophysically equival ent by setting the display contrast at x5 and x10 contrast threshold f or each subject: The pattern electroretinogram (PERG) was recorded wit h a sterile silver thread (DTL) electrode placed in the lower canthus of one eye, with the indifferent electrode on the temple and the earth on the forehead. 5. For each contrast multiple at each spatial freque ncy, the PERG implicit time showed no significant change with age, ind icating equivalence of the response across the age range. 6. Control e xperiments with two young and two elderly subjects established that th e PERG implicit time decreased appreciably with increasing contrast, o ver a range of x2 to x20 contrast threshold. 7. Since the psychophysic ally equivalent stimulus displays had generated equivalent PERGs in te rms of implicit time in young and elderly subjects, this was consisten t with the equivalence of retinal ganglion cell function under these c onditions. 8. Adverse changes within the retina were therefore inferre d to play a major role in the decline in contrast sensitivity with age .