Eyedrops are often considered a benign treatment, and their side-effects on the rest of the body are vastly underappreciated.

Over 40 per cent of patients using brimonidine have side-effects in the rest of their body, and more than half of those using betaxolol complain of eye irritation. AZOPT can cause hair loss, chest pain, dizziness, dry mouth, stomach and breathing problems, kidney pain, nausea and throat infections. Some physicians suggest constant monitoring of patients taking a topical beta-blocker for glaucoma (Br J Ophthalmol, 2000; 84: 710-3).

The biggest risk is that the cause of the symptoms is never found. All but the most sleuth-like of GPs may miss the link between these seemingly unrelated side-effects and the eyedrops.

Eyedrops also interact with other drugs. For example, brimonidine should not be taken with MAO inhibitors, tricyclic antidepressants, CNS depressants, beta-blockers, antihypertensives or digitalis. As for AZOPT, in rare cases, it can interact with high doses of salicylates (aspirin).

If latanoprost is taken with another containing the preservative thimerosal, the interaction can cause the other solution to crystallise in the eye.

All eyedrops can cause bacterial keratitis, or corneal infection, which can easily be passed on to and by the container.