ArticleDonald A. Fox, Ph.D., ATS and ARVO Fellow is the lead author on an updated and expanded chapter in Casarett & Doull’s Toxicology: The Basic Science of Poisons (Chapter #17, 9th Edition, McGraw-Hill Education, 2018). The chapter is entitled “Toxic Responses of the Cornea, Retina and Central Visual System”.
This book, edited by CD Klaassen, is among the most complete and respected references in the field of toxicology.
Introduction to Ocular and Visual System Toxicology
The three overall goals of this chapter are:
- to provide essential information on ocular pharmacodynamics, pharmacokinetics, and drug metabolism;
- to review the procedures for evaluating and testing retinal and visual function; and
- to evaluate and review the structural and functional alterations in the mammalian eye, retina and central visual system produced by environmental and workplace chemicals, toxicants, gases and vapors, nanoparticles, and off-target effects of major therapeutic drugs.
Excerpt from Introduction
For your convenience, we have made an excerpt from this publication available for your review. A complete copy of the 9th Edition can be acquired from Amazon.com and other online retailers in 2018.
Environmental and occupational exposure to toxic chemicals, gases, and vapors, and side effects of systemic and ocular therapeutic drugs may result in structural and functional alterations to the eye and central visual system (Anger and Johnson, 1985; Grant and Schuman, 1993; Otto and Fox, 1993; Fox, 1998; Santaella and Fraunfelder, 2007; Bartlett and Jaanus, 2008). Almost half of all neurotoxic chemicals affect some aspect of sensory function (Crofton and Sheets, 1989). The most frequently reported sensory system alterations occur in the visual system (Anger and Johnson, 1985; Crofton and Sheets, 1989; Fox, 1998; Grant and Schuman, 1993). Approximately 3000 substances are toxic to the eye and visual system (Grant and Schuman, 1993). In many cases, alterations in retinal and visual function are the initial symptoms following chemical exposure (Hanninen et al., 1978; Damstra, 1978; Baker et al., 1984; Anger and Johnson, 1985; Mergler et al., 1987; Iregren et al., 2002). This suggests that sensory systems, and in particular the retina and central visual system, may be especially vulnerable to toxic insult. Alterations in the structure and/or function of the eye or central visual system are among the criteria utilized for setting permissible occupational or environmental exposure levels for many different chemicals in the United States (http://www.cdc.gov/niosh/npg/; http://www.epa.gov/iris/index.html). New or existing drugs may have visual side effects (Grant and Schuman, 1993; Novack, 2003; Brigell et al., 2005; Santaella and Fraunfelder, 2007). Subtle alterations in visual processing of information (eg, visual perceptual, visual motor) can have profound immediate, long term, and delayed effects on the mental, social, and physical health and performance of an individual. Among the elderly, reduced visual function is a major factor contributing to decreased ability to conduct routine activities of daily living, decreased ability to live independently, and increased risk of falls, car crashes, and other hazards. Ocular and visual system impairments can lead to increased occupational injuries, loss of productive work time, costs for providing medical and social services, lost productivity, and a distinct decrease in the overall quality of life.
The adverse effects of these agents on the different compartments of the eye (ie, cornea, lens, retina, and retinal pigment epithelium [RPE]), central visual pathway (ie, optic nerve and optic tract), and the central processing areas (ie, lateral geniculate nucleus [LGN], visual cortex) are addressed (Table 17-1). To further understand the potential effects of these chemicals and drugs on the eye, the distribution of Phase I and Phase II drug metabolizing enzymes in ocular tissues are presented in Table 17-2. Table 17-3 provides examples of common signs, symptoms, and potential pathophysiological mechanisms of visual dysfunction associated with acute or chronic exposure to toxic compounds and selected drugs. Some of the symptoms are very nonspecific (eg, “blurred vision”) whereas others are more definitive.
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Toxicology & Pharmacology Expert
Dr. Fox is a highly credentialed internationally-recognized toxicology researcher, educator and lecturer with broad training, expertise and experience in the disciplines of toxicology, neurotoxicology, ocular and retinal toxicology, environmental and occupational toxicology, pharmacology and neuropharmacology, alcohol and drugs of abuse, and human health assessment. He has spent 35+ years studying and consulting on the adverse effects of chemical, biological and physical agents on living organisms. Dr. Fox applies his expertise towards causation analysis, resolving disputes relating to exposure to chemical, environmental and occupational toxicants; adverse prescription, drug-drug and nutraceutical events; adverse recreational drug events; and adverse alcohol events.