Visual electrophysiology in the assessment of toxicity and deficiency states affecting the visual system

Abstract

Visual disturbance or visual failure due to toxicity of an ingested substance or a severe nutritional deficiency can present significant challenges for diagnosis and management, for instance, where an adverse reaction to a prescribed medicine is suspected. Objective assessment of visual function is important, particularly where structural changes in the retina or optic nerve have not yet occurred, as there may be a window of opportunity to mitigate or reverse visual loss. This paper reviews a number of clinical presentations where visual electrophysiological assessment has an important role in early diagnosis or management alongside clinical assessment and ocular imaging modalities. We highlight the importance of vitamin A deficiency as an easily detected marker for severe combined micronutrient deficiency.

Fig. 1. Multifocal ERG responses from one eye in a patient taking hydroxychloquine for 7.5 years who had no visible fundus abnormality.

A concentric paracentral depression of the P1 component amplitude is seen in the trace array (A) and the three-dimensional scalar product plot (B). There is also mild prolongation of the P1 implicit time in the same area (C). From Maturi RK, Yu M, Weleber RG. Multifocal electroretinographic evaluation of long-term hydroxychloroquine users. Arch Ophthalmol. 2004;122: 973–81.

Fig. 2. Full-field ERG responses from a patient with Vitamin A deficiency before, and after replacement treatment showing full recovery of the dark adapted ERG.

The use of a red flash under dark adapted conditions (‘Red’) demonstrates that the residual dark adapted ERG response prior to Vitamin A replacement originates wholly from the cone system. From McBain, V., Egan, C., Pieris, S. et al. Functional observations in vitamin A deficiency: diagnosis and time course of recovery. Eye. 2007;21:367–76.