Drugs in the Treatment of Openangle Glaucoma

There has been a small revolution involving the type of eye drops used for the treatment of glaucoma in recent times. For years, the mainstay of treatment was pilocarpine and the topical beta-blockers, for example timolol, but the potential systemic side effects of these drugs have led to the introduction of other novel types of ocular hypotensive agents. In general, these new agents can be divided into alpha2-adrenergic agonists, carbonic anhydrase inhibitors and prostaglandin analogues.

The production of aqueous humour can be reduced by either blockade of the beta-receptors on the ciliary body epithelial cells (i.e., with a beta-blocker) or by agonism of the alpha2-receptors. Brimonidine and apraclonidine are both alpha2-receptor agonists and show good efficacy compared with timolol. A significant number of patients, however, do develop an allergy to these agents and this has limited their widespread use. Acetazolamide was introduced as a diuretic many years ago; although not a very good diuretic, it has proved to be a potent ocular hypotensive when given orally. Again because of side effects its use has been restricted to short-term treatment. In 1995, dorzolamide was introduced and more recently, brinzolamide has become available. These are also carbonic anhydrase inhibitors but they are available in drop form and are able to penetrate the cornea. Their ocular hypotensive effects are generally not as great as topical beta-blockers but they are useful as adjuvant agents. It has recently been discovered that a second aqueous outflow route exists in the eye - the uveoscleral route. It is known that certain prostaglandins increase the flow of aqueous via this route and a number of topical prostaglandin F2a analogues are now available. Latanoprost, travoprost and bimato-prost have all been shown to as effective as topical beta-blockers with minimal side effects.

All these medications have the problem of compliance. Elderly patients may forget to instill drops on a regular basis. In some cases, even instillation of three different glaucoma drops fails to control the intraocular pressure. In these instances, the only sure way of lowering the pressure is by glaucoma drainage surgery.

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