* argon laser trabeculoplasty (ALT). The most frequently performed laser procedure for open-angle glaucoma, this uses an argon laser to burn 50-100 ‘spots’ in the eye’s drainage system - the trabecular meshwork, the spongy tissue at the front of the eye - to improve eye-fluid flow. The effectiveness of ALT varies but, in general, it controls eye pressure best within the first year of treatment. After that, it becomes less and less effective so that most patients need to either go back to drugs or undergo further laser treatment (Am J Ophthalmol, 1995; 120: 718-31).

* selective laser trabeculoplasty (SLT). This is considered to be gentler than ALT as, instead of creating thermal burns, it targets the melanin pigment in cells of the trabecular meshwork, triggering a cellular reaction that improves fluid drainage. It works as well as ALT, lowering eye pressure in nearly 90 per cent of eyes. And, as SLT is less aggressive, it is more suitable for repeat treatments (Arch Ophthalmol, 2003; 121: 957-60).

* trabeculectomy, or filtrating microsurgery. This is the usual non-laser surgery for glaucoma. It involves removing a piece of tissue from between the sclera (the whites of the eyes) and the trabecular meshwork, thus creating an alternative route for the aqueous fluid to escape. The fluid is then channelled into a reservoir, or ‘bleb’, under the eyelid, from where it is eventually absorbed into blood vessels. This has a high success rate (nearly 95 per cent two years after treatment), but still relies on the use of antimetabolites (in the form of eyedrops) to ensure that the bleb doesn’t heal and close up.

* non-penetrating filtrating surgery. This procedure is less invasive than a trabeculectomy as the surgeon only works on the outermost layer of the eye. However, it is trickier to perform, and has a success rate of only 60 per cent (Chin Med J [Engl], 2004; 117: 1006-10).