Neurophysiological investigation in optic nerve disease: combined assessment of the visual evoked response and electroretinogram.

Abstract

The electroretinogram (ERG) and the pattern visual evoked responses (VER) obtained from patients with suspected primary optic nerve lesions were analyzed. Patients with hereditary optic atrophy or optic nerve lesions with retinal disease or with systemic disorders were excluded from the analysis. According to the results of the ERG functions and VER, 83 patients with suspected primary optic nerve lesion could be classified into 3 categories. Normal ERG functions, VER with normal amplitude but with delayed peak or with significant interocular difference in the peak time, suggesting a lesion in the myelin sheath of the optic nerve. Subnormal ERG functions, VER with subnormal amplitude and with delayed peak or with significant interocular difference in the peak time, suggesting axonal as well as myelin involvement, leading to orthograde and retrograde transneuronal degeneration. Subnormal ERG functions, VER with subnormal amplitude but without a delayed peak and without interocular difference in the peak time, suggesting a generalized cellular and axonal involvement. Patients classified into the above 3 groups were then correlated with clinical findings. The 1st group of patients (category 1), showed either a number of neurological symptoms to suggest multiple sclerosis without any visual deficit or a sudden transient loss of vision accompanied by pain in the affected eye. They were finally diagnosed as multiple sclerosis with optic neuritis. The 2nd group of patients (category 2), had similar case histories to those of category 1 but showed a more severe, permanent loss of vision, commonly with temporal pallor and pupillary defects. The final diagnoses of these patients were either multiple sclerosis or compressive or ischemic optic neuropathies. The 3rd group of patients all showed bilateral, gradual, painless loss of vision but were subdivided into 2 distinct clinical diagnostic categories: toxic amblyopia (category 3), and bilateral optic atrophy of unknown cause (category 4).