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Editors Selection IGR 13-4

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Comment by Chris Johnson 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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The proportion of patients with visual field progression in the timolol group (39%) was surprisingly high

An agent that has 'neuroprotective' properties, other than IOP-lowering, is the 'holy grail' in glaucoma. While many compounds have shown promise in experimental glaucoma models, clinical efficacy in human patients have not been shown so far. This was thus a fascinating randomized controlled trial evaluating visual field progression in 178 patients with low-pressure glaucoma, with the major findings being fewer brimonidine 0.2%-treated patients (9.1%) having visual field progression by pointwise liner regression compared to timolol 0.5% -treated patients (39.2%) over four years. A large proportion (36/99, 36.4%) of brominidine-treated patients dropped out within one year, mostly due to allergy, while the corresponding figure for the timolol group was 8/79 (10.1%). These figures were higher than the anticipated 25% attrition rate planned by the authors prior to the study start, and raises the question of internal validity of the results. The reported decrease in IOP was not significantly different between groups, but diurnal (or 24-hour) IOP measurements were not performed. The proportion of patients with visual field progression in the timolol group (39%) was surprisingly high, considering the short follow-up period and that these were patients with low pressure glaucoma. In addition to pointwise linear regression analysis measured by Progressor software (Medisoft Inc, Leeds, UK), secondary analyses with glaucoma change probability maps (and post-hoc analysis) were performed. Interestingly, progression criteria did not require the progressing locations to be contiguous by either method. Only five patients in the brimonidine and 18 patients in the timolol group were found to be progressing by all three methods. While statistically robust, the clinical or real life significance of such visual field progression on patients' visual function is unknown. It would be interesting to know the optic disc and/or RNFL changes in this cohort and to see if there are corresponding structural differences in the two groups.

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