THE TEMPORAL FREQUENCY-RESPONSE FUNCTION OF PATTERN ERG AND VEP - CHANGES IN OPTIC NEURITIS

Steady-state pattern electroretinograms (PERGs) and visual evoked pote ntials (VEPs) in response to sinusoidal gratings (2 c/deg), sinusoidal ly counterphased at closely spaced temporal frequencies (TFs) between 4 and 28 Hz, were recorded from 11 patients with unilateral optic neur itis (ON; 11 affected eyes and 10 healthy fellow eyes) and 7 age-match ed normal subjects (7 eyes). Amplitude and phase of responses' second harmonics were measured. Responses' apparent latencies were estimated from the rate at which phase las ed with TF. When compared to control values, mean PERG and VEP amplitudes of ON eyes were reduced (by about 0.4 log units) at both low (5-10 Hz) and high (16-20 Hz) TFs. Mean PE RG amplitudes of fellow eyes were selectively reduced at low TFs (by a bout 0.3 log units). Mean PERG apparent latencies of both ON and fello w eyes were delayed (by 15 and 9 ms, respectively). Mean VEP apparent latency of ON eyes was delayed al both low and high TFs (by 24 and 30 ms, respectively), while that of fellow eyes was selectively delayed a t high TFs (by 28 ms). The results in ON eyes indicate non-selective a bnormalities of PERG and VEP generators responding at both low and hig h TFs. VEP TF losses may be in part accounted for by corresponding PER G losses. In the fellow eyes of patients, more selective PERG and VEP TF abnormalities may suggest differential impairment of retinal and po stretinal subsystems responding better to low and high TFs (i.e. parvo -and magnocellular streams).