Nevertheless, drug-induced respiratory side-effects such as breathlessness and increased exercise intolerance are often overlooked or written off by doctors as simply being normal signs of ageing among the elderly (who make up the majority of glaucoma sufferers).

Central nervous system side-effects with beta-blockers include depression, psychosis, hallucinations, confusion, fatigue, insomnia and impotence (J Clin Psychopharmacol, 1987; 7: 264-7; JAMA, 1986; 255: 37-8).

* Prostaglandin analogues such as latanoprost (Xalatan), bimatoprost (Lumigan) and travoprost (Travatan) have toppled beta-blockers off their dominant position in the glaucoma drugs market. They lower eye pressure by increasing the size of the spaces in the drainage system, allowing more fluid to flow out of the eye. The popularity of prostaglandins for glaucoma therapy has been attributed to their superior eye-pressure-lowering effects (Br J Ophthalmol, 2004; 88: 1391-4) and their easy-to-comply-with, once-daily dosing.

Downside: All three types of prostaglandins often cause bizarre changes in eye colour and eyelashes. The eyes may darken due to an increase in melanin (the eye-colouring pigment) in the iris; there may be darkening of the skin on the eyelids and sometimes under the eyes; and the eyelashes may increase in length and thickness (often regarded as a benefit).

Uveitis (inflammation of the nourishing membrane of the eye) is a more serious side-effect commonly seen with latanoprost (Ophthalmology, 1998; 105: 263-8). Glaucoma patients with a history of uveitis were most likely to have a flareup, and a small number of patients with no previous uveitis also developed the condition after using latanoprost eyedrops (Acta Ophthalmol Scand, 1999; 77: 668-72).

Latanoprost can also reactivate the herpes simplex virus and trigger bouts of herpes simplex-related keratitis (Arch Soc Esp Oftalmol, 2000; 75: 775-8; Am J Ophthalmol, 1999; 127: 602-4). In these cases, only stopping latanoprost solved the problem.

Prostaglandin eyedrops can also induce macular swelling, especially in people who have undergone cataract surgery (Am J Ophthalmol, 2002; 133: 403-5), and they may also cause eye pressure to fall too low, resulting in eye damage due to choroidal detachment (Am J Ophthalmol, 2001; 132: 928-9).

Prostaglandins have been hailed by the medical profession as the best tolerated eyedrops with the fewest systemic side-effects. Nevertheless, as WDDTY has uncovered, latanoprost can cause cardiovascular effects as well as headache and facial rash (J Ocul Pharmacol Ther, 2003; 19: 405-15; BMJ, 2001; 323: 783).

A case report from Germany described a young patient using a beta-blocker–latanoprost combo to treat his aniridia and glaucoma enduring heavy sweating over his entire body for up to two hours due to using the drops (Ophthalmologe, 1998; 95: 633-4). A study comparing latanoprost with the alpha-adrenergic brimonidine found that nearly half the patients using latanoprost complained of “hands and feet that became cold easily” (Ophthalmology, 2002; 109: 307-14).

Eyedrops in your lenses In acknowledgement of these drug side-effects, the medical industry is now working on a new generation of treatments for glaucoma as well as for hard-to-treat retinal diseases. These novel ideas include contact lenses that incorporate nanotechnology to deliver drugs directly into the eye.

Medicine understands that 95 per cent of the medication administered via eyedrops drains into the nasal cavity and enters the bloodstream - hence, the adverse systemic effects. The assumption is that, if a drug can be directed to only go where it’s needed, then most of the unwanted effects will disappear.