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Comment by Harry Quigley on:

27800 A Randomized Trial of Brimonidine Versus Timolol in Preserving Visual Function: Results From the Low-pressure Glaucoma Treatment Study, Krupin T; Liebmann JM; Greenfield DS et al., American Journal of Ophthalmology, 2011; 151: 671-681

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Dr Krupin and colleagues recently published the results of the Low Tension Glaucoma Treatment study which was a randomized multicenter trial comparing the efficacy of topical timilol to brimonidine in retarding progression of open-angle glaucoma. 99 patients were randomized to brimonidine with 77 to timilol. The unequal study groups were designed to counteract the expected loss in the brimonidine group due to topical allergy, which was largely responsible for the high discontinuation rate seen with brimonidine in the study. While similar levels of IOP reduction were seen in each group there was significantly lower rates of visual field progression by both pointwise linear regression and change probability approaches in the brimonidine group compared to those taking timilol (9.1 vs. 39.6%). These results, as discussed by the authors, could have resulted from a protective effect of brimonidine or a deleterious effect from the timilol. The high rates of visual field progression (over a third in 2.5 years) suggest the later may be a possibility. Perhaps as speculated by the authors, the systemic effects of beta-blockers might play a role, however, recent evidence that brimonidine may have greater effects on nocturnal blood pressure call this into question and more research is required. Additionally, since diurnal variation in IOP was not tightly measured, variation in IOP could have been missed between groups, which could possibly account for some of the differences. Although it is doubtful that twice daily dosing of brimonidine would provide a more stable 24-hour IOP. The study findings are intriguing and more work on clinical efficacy and basic mechanisms would assist in determining if true IOP-independent neuroprotection would favor brimonidine treatment.

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