Sir,

We appreciate the thoughtful comments made by Dr Wishart1 and his interest in our review article.2 There is no way to compare non-medication-induced angle closure from other factors, nor are we suggesting that it is a more common event. The important issue is that physicians need to be aware of the potential of certain drugs to provoke an angle-closure attack in high-risk patients. Gonioscopy helps to identify high-risk patients, especially the hyperopic middle-aged or older patient, and would help physicians in advising their patients of the relative risk. Most cases of pharmacologically induced angle closure have reportedly been due to a pupillary block mechanism, with fewer cases being secondary to plateau iris configuration and choroidal effusions.3, 4 Therefore, a prophylactic laser peripheral iridotomy would be expected to be protective. The decision as to whether that would be appropriate given the risks of angle-closure glaucoma is weighed against the risks of the laser procedure. Dr Wishart noted the prevalence of a narrow angle in the Caucasian population to be relatively low. We suggest that it would be important to identify this population by gonioscopy so that appropriate counseling could be offered. The prevalence of narrow angles in other ethnic groups, especially Asians, is significantly higher.5

The reference for the statement ‘at least one third of acute closed angle glaucoma cases are related to over-the-counter or prescription drugs’ was the third reference4 of our manuscript, but had been cited in error.

The patients studied by Mapstone6 had experienced an acute attack in one of their eyes, and their contralateral eye that had had no sign of glaucoma or had been cases of intermittent angle-closure glaucoma underwent a tropicamide challenge test. In fact, not all the studied eyes had glaucoma but had occludable angle. The point that the risk of tropicamide causing angle closure is 0 is a curious comment, as this point certainly is not substantiated by any large trial in a large high-risk population. Provocative testing is known to be of limited predictive value. Although it is agreed that even in narrow angles dilation may not precipitate angle closure in every case, the obligation of physicians is to (1) recognize which patients may be at risk, (2) advise the patients of a potential risk with pharmacological dilation, and (3) offer a preventive treatment like prophylactic laser iridotomy with risks and benefits reviewed when deemed appropriate.