Drug-induced glaucomas: mechanism and management

Glaucoma comprises a heterogeneous group of diseases that have in common a characteristic optic neuropathy and visual field defects, for which elevated intraocular pressure is the major risk factor. The level of intraocular pressure within the eye depends on the steady state of formation and drainage of the clear watery fluid, called the aqueous humour, in the anterior chamber of the eye. An obstruction in the circulatory pathway of aqueous humour causes an elevation in intraocular pressure. Because intraocular pressure is the most modifiable parameter, therapeutic measures (medical and surgical) are aimed at reducing the pressure to protect against optic nerve damage. Glaucomatous optic neuropathy results from degeneration of the axonal nerve fibres in the optic nerve and death of their cell bodies, the retinal ganglion cells. Clinical examination of the optic nerve head or disc and the peripapillary nerve fibre layer of the retina reveals specific changes, and the resulting visual field defects can be documented by perimetry. Glaucoma can be classified into four main groups: primary open-angle glaucoma; angle-closure glaucoma; secondary glaucoma; and developmental glaucoma. Drug-induced glaucoma should be considered as a form of secondary glaucoma because it is brought about by specific systemic or topical medications. Although there is a high prevalence of glaucoma worldwide, the incidence of drug-induced glaucoma is uncertain. Drugs that cause or exacerbate open-angle glaucoma are mostly glucocorticoids. Several classes of drugs, including adrenergic agonists, cholinergics, anticholinergics, sulpha-based drugs, selective serotonin reuptake inhibitors, tricyclic and tetracyclic antidepressants, anticoagulants and histamine H(1) and H(2) receptor antagonists, have been reported to induce or precipitate acute angle-closure glaucoma, especially in individuals predisposed with narrow angles of the anterior chamber. In some instances, bilateral involvement and even blindness have occurred. In this article, the mechanism and management of drug-induced glaucomatous disease of the eye are emphasised. Although the product package insert may mention glaucoma as a contraindication or as an adverse effect, the type of glaucoma is usually not specified. Clinicians should be mindful of the possibility of drug-induced glaucoma, whether or not it is listed as a contraindication and, if in doubt, consult an ophthalmologist.