Drug-induced and toxic disorders in neuro-ophthalmology

Abstract

Signal processing in the retinal photoreceptors, as well as in the cells and synapses of the afferent visual pathways, is controlled by a group of neurotransmitters, proteins, enzymes, and their metabolites that arise in complex cascades of chemical reactions to produce all the necessary functions of normal visual perception. Neurotropic drugs, toxins and some foods can interfere with these processes and their underlying structural components, thereby disturbing visual perception. In addition, there are non-neural metabolic processes that are needed to maintain the integrity of the visual system. For example, pigment epithelial cells, glial cells, and vascular components of the afferent visual pathway are all susceptible to the effects of drugs, toxins, and some foods. This mechanism is often responsible for subjective alterations in visual perception that are either expressed symptomatically by the patient or detected by specific visual function tests. Since a very large number of substances can specifically damage vision, we can discuss only the general principles of the diagnosis and management of toxic visual disorders. For individual cases of known or suspected toxic damage to vision, standard sources of reference should be consulted (see "Further Reading" at the end of the chapter). This chapter describes the cell-specific disturbances of visual function, providing a rational basis for understanding toxic visual disorders, and outlines the typical symptoms of drug side effects that affect vision. This is meant to give the clinician a rational basis for diagnostic testing in cases of suspected toxic damage to the visual system.