ABSTRACT
The retina and the optic nerve are susceptible to numerous nutritional deficiencies, toxicities, and pharmacologic effects. The electrophysiologic findings of the more commonly encountered conditions in this group of disorders are discussed in this chapter, and electrophysiologic testing is of value in some of these conditions. The topics covered are:
Vitamin A deficiency Nutritional optic neuropathy Metallic intraocular foreign bodies-ocular siderosis Methanol poisoning Synthetic retinoids-isotretinoin (Accutane) Chloroquine=hydroxychloroquine Thioridazine (Mellaril), chlorpromazine, and other phenothiazines
Quinine Deferoxamine (Desferrioxamine) Vigabatrin Sildenafil (Viagra)
Gentamicin Ethambutol Cisplatin Indomethacin
VITAMIN A DEFICIENCY
Vitamin A is a fat-soluble vitamin that is absorbed by the small intestine and transported to the liver where it is stored as vitamin A ester. Vitamin A is delivered to the target tissues by retinol binding protein, a transport protein produced by the liver, as vitamin A alcohol (retinol). In the retina, retinol is stored in the retinal pigment epithelium and enters the outer segments of the photoreceptors as 11-cis retinol where it is transformed to 11-cis retinaldehyde (retinal) and combined with the protein opsin to form the light sensitive rhodopsin. Therefore, vitamin A deficiency may arise from inadequate nutritional intake, poor intestinal absorption, impaired liver storage, ineffective retinol binding protein transport, or impaired conversion of retinol to retinaldehyde.
