Clinical application of mfERG/VEP in assessing superior altitudinal hemifield loss

Multifocal ERG (mfERG) and multifocal VEP (mfVEP) have been used widely in the investigation of pathological changes or functional variations in the visual system. Altitudinal hemifield loss is a visual field defect that is usually found in patients with ischaemic optic neuropathy (ION). Anterior ischaemic optic neuropathy (AION) is a complex multi-factorial disease and it is difficult to diagnose according to clinical symptoms and signs alone. AION is believed to be caused by an infarction of the optic nerve due to the occlusion of the posterior ciliary arteries. The current report presents a patient diagnosed with non-arteritic AION. In this report, the mfERG findings did not match the results of the visual field test but those of the mfVEP did. After consideration of the visual electrophysiological and visual field results, the defect arises from neither the retina nor the visual pathway behind the optic chiasma. Hence, the optic nerve is the most likely location of the lesion, causing the superior altitudinal hemi-field loss. This report shows that the mfERG and mfVEP techniques can be used for objective visual field assessment to supplement the conventional visual field testing.