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  • Toxic chemicals and systemic drugs can affect all parts of the eye, including cornea, iris, ciliary body, lens retina, and optic nerve.
  • Ophthalmologic procedures for evaluating the health of the eye include routine clinical screening evaluations using a slit-lamp biomicroscope and ophthalmoscope, and an examination of the pupillary light reflex.
  • Most electrophysiologic or neurophysiologic procedures for testing visual function after toxicant exposure involve stimulating the eyes with visual stimuli and electrically recording potentials generated by visually responsive neurons.

*This chapter has been reviewed by the National Health and Environmental Effects Research Laboratory, U.S. EPA, and approved for publication.

Environmental and occupational exposure to toxic chemicals, gases, and vapors as well as side effects resulting from therapeutic drugs frequently results in structural and functional alterations in the eye and central visual system. The retina and central visual system are especially vulnerable to toxic insult.

Ocular Pharmacodynamics and Pharmacokinetics

Toxic chemicals and systemic drugs can affect all parts of the eye (Figure 17–1; Table 17–1). Factors determining whether a chemical can reach a particular ocular site of action include physiochemical properties of the chemical, concentration and duration of exposure, and movement across ocular compartments and barriers. The cornea, conjunctiva, and eyelids are often exposed directly to chemicals, gases, and particles. The first site of action is the tear film, a three-layered structure with both hydrophobic and hydrophilic properties. The outermost thin tear film layer is secreted by the meibomian (sebaceous) glands. This superficial lipid layer protects the underlying thicker aqueous layer that is produced by the lacrimal glands. The third layer is the very thin mucoid layer that is secreted by the goblet cells of the conjunctiva and acts as an interface between the hydrophilic layer of the tears and the hydrophobic layer of the corneal epithelial cells.

Figure 17–1

Diagrammatic horizontal cross-section of the eye, with medium-power enlargement of details for the cornea, iris and ciliary body, lens, and retina. The morphologic features, their role in ocular pharmacodynamics, pharmacokinetics, drug metabolism, and the adverse effects of drugs and chemical agents on these sites are discussed in the text.

Table 17–1 Ocular and central visual system sites of action of selected xenobiotics following systemic exposure.

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