Forty-one eyes in 21 cases of ethambutol optic neuropathy were investigated for the pattern visual evoked cortical potential (VECP) and the pattern electroretinogram (ERG). In 21 of the eyes the disappearance VECP responses were not detectable. In the other 20 eyes the peak latency and amplitude of the disappearance VECP were delayed and decreased significantly compared with normal eyes. The recovery of the peak latency of the disappearance VECP in ethambutol optic neuropathy was faster than that of the amplitude. Twelve eyes in six patients were studied by pattern reversal ERG. Though the mean peak latency of the pattern ERG was within normal limits, the mean amplitude was decreased significantly. Our investigations indicated that ethambutol optic neuropathy disturbed not only the optic nerve but also the retina.

Pattern evoked potentials were recorded simultaneously with an electrode placed on the skin of the lower eyelid, gold foil electrodes hooked on the right and left eyelids, and a skin electrode at Oz in normal subjects and in patients with optic nerve and macular diseases. Peak latencies and amplitudes of the pattern electroretinogram (PERG) were compared between the two electrodes. In both records, the peak latency showed no difference at 56.7 +/- 2.9 ms (mean +/- S.D.), while the amplitude of the PERG with the lid skin electrode was at 1.2 +/- 0.3 microV, approximately one-third of that obtained with the gold foil electrode. Although the skin electrode did not always record responses as well as the gold foil, its advantages recommend its use in clinical cases.

Visually evoked cortical potentials in response to pattern-appearance, -disappearance, and -reversal stimuli were studied in normal subjects and in patients suffering from optic neuritis. It was found in normal subjects that pattern disappearance VECPs were as reliable as the pattern reversal ones. On the other hand, the appearance response showed interindividual differences which made its evaluation rather difficult. The same was true in the records of the patients. Both the mean peak latencies of the disappearance responses and those of the pattern reversal ones were prolonged significantly in optic neuritis, compared with those obtained from normal subjects. We concluded that the peak latencies of the disappearance response could be more confidently used than those of the appearance response for diagnosing optic neuritis.

Scalp profiles of steady-state pattern visual evoked cortical potentials (VECPs) along the horizontal line at Pz (for upper field stimuli) and Oz (for lower field stimuli) were studied in 12 normal subjects by simultaneous five channel recordings from electrode positions 3 cm and 6 cm laterally on either side of, and at, Oz or Pz. Each electrode was referred to Fz or to the right earlobe. The amplitude and phase of the averaged VECPs (n = 20) were calculated by means of Fast Fourier Transform. With smaller check size the amplitude data verified that the scalp profile of the lower visual field peaked at the hemisphere contralateral to the quadrant stimulated. With larger check size the peak shifted to the ipsilateral hemisphere. With upper field quadrant stimulation, position of the reference electrode at Fz was found to be unsuitable since the VECP amplitude at the level of Pz was greatly reduced. Phase and apparent latency also varied with the field stimulated as well as with the position of electrodes.

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