Normal fundus and abnormal electroretinogram: differential diagnosis

Abstract

To assess retinal dysfunction when ophthalmoscopy reveals normal features. Ganzfeld electroretinography of the rod and of the cone systems was used to detect congenital or acquired retinal dysfunction. In infants under 5 years of age ERG was performed using inhalational anaesthesia. In addition, multifocal ERG techniques detect discrete local retinal dysfunctions. The ERG results are evaluated in comparison to normative data and to ophthalmoscopic as well as perimetric results. Patient data were selected to demonstrate typical ERG changes and the corresponding differential diagnosis. Abnormalities in ERG results and normal ophthalmoscopic features are shown in 8 typical examples. They were observed in the following conditions: (1) stationary congenital dysfunctions, (2) early stages of the hereditary tapetoretinal degenerations, and (3) toxic or cancer-associated retinopathies. In these disorders the ERG complemented visual field testing by detecting isolated dysfunction of the rod- and cone-systems. In the context of making crucial diagnostic decisions ERG complements ophthalmoscopy and psychophysical testing of the retinal function. This diagnostic test facilitates differential diagnosis, helps to establish prognosis, and provides a basis for genetic counselling.