The pattern electroretinogram: a long-term study in acute optic neuropathy.
We report a 2-year prospective study of the electroretinographic response to reversal of checkerboard patterns (P-ERG) obtained in 63 eyes with acute optic nerve lesions. The aim of the study was to document the value of P-ERG regarding diagnosis and prognosis of four types of optic neuropathy: optic neuritis, compressive or hereditary optic atrophy, and traumatic optic neuropathy. We documented visual loss by neuro-ophthalmologic examination and recorded pattern-reversal visual evoked potentials (P-VEP). The initial P-ERG was normal to large- and medium-sized checks in 89% and the P-VEP abnormal in 94% of eyes with acute optic nerve lesions. Forty-six eyes were followed for up to 2 years. Two groups emerged. Group A (n = 17) gradually and permanently had significant reduction of the P-ERG to three separate check sizes. All 17 had no improvement in acuity better than 20/100, retained centrocecal scotomas, and developed optic atrophy. In group B (n = 29) the P-ERG remained within normal limits to one or more check sizes. Twenty-two of these eyes recovered acuity to 20/25 or better and had resolution of the field defect. The data showed that P-VEP was superior to P-ERG in diagnosis of acute and chronic optic nerve lesions. However, significant reduction of the b-wave of the P-ERG to three separate check sizes correlated closely with failure of visual recovery and the eventual development of severe optic atrophy, suggesting a prognostic value for P-ERG in optic neuropathy.