Metabolic disorders involving metals

Several metals such as zinc, copper, and iron are essential for normal cellular functions and tissue metabolism. However, the accumulation of excessive amounts of these essential metals in cells, as a result of metabolic disorders or abnormal exposure, can cause tissue damage. The eye is a potential target organ for many chemicals including metals. Foreign bodies composed of iron or copper can produce marked degenerative changes in the eye and excessive amounts of cobalt can result in cataractous lens changes in laboratory animals (1). Fumes and salts of metals can act as external irritants giving rise to conjunctivitis and corneal ulceration. In addition, exposure to nonessential metals like gold, silver, and mercury can result in characteristic discoloration of the cornea or lens. Nevertheless, since the eye is protected by two physiological barriers, the blood-retinal and bloodaqueous barriers, the toxicity of metals depends not only on the exposure levels but also on the permeability of these barriers. Certain metabolic disorders either inherited or acquired, can affect the deposition of metals in the eye and cause damage. This chapter will describe ocular disorders caused by either deficiencies or increased amounts of the essential metals.