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Editors Selection IGR 9-3

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Comment by Robert Ritch & David Greenfield & Jeffrey Liebmann & Stuart Gardiner & Theodore Krupin 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 Low-pressure Glaucoma Treatment Study Group is pleased to see our April 2011 AJO publication that presented results of our randomized trial of brimonidine versus timolol in preserving visual function in patients with low-pressure glaucoma reviewed in International Glaucoma Review. We thank the five glaucoma specialists for their comments.

LoGTS is an important trial for various reasons. It is the first randomized clinical trial to demonstrate the possibility of a pressureindependent treatment effect in patients with glaucoma.

LOGTS is the first randomized clinical trial to demonstrate the possibility of a pressureindependent treatment effect in patients with glaucoma

It is also the first prospective RCT to compare the impact of topical therapy on visual function by using a trend analysis approach to detect progression. By enrolling patients with very low baseline IOP, it demonstrates the power of having an enriched study population that minimizes the impact of IOP on disease progression and may serve as a model for future neuroprotection trials. Lastly, direct comparisons between drugs may be necessary in the future in order to demonstrate cost effectiveness of new therapies.

Direct comparisons to other studies is problematic. For example, we do not think our results should compared ti the EMGT study which enrolled a different population, used a different treatment protocol, and used a different method for assessment of progression. Our four-year rate of progression in the timolol patients (45.7%) is similar to the reported 36%-50% three- to five-year rates in low-pressure glaucoma as referenced in our paper.

The magnitude of IOP lowering in LoGTS was relatively low (10- 12.5%), but consistent with what typically occurs in patients with very low untreated baseline IOP. A recent meta-analysis of medical treatment in patients with low pressure glaucoma (Cheng et al., Ophthalmology 2009; 116: 1243-1249) demonstrated that less IOP reduction occurs in these patients compared to those with higher IOP enrolled in phase 3w clinical trials. The minimal IOP reduction in LoGTS may have enhanced our ability to detect a pressure-independent effect.

The minimal IOP reduction in LoGTS may have enhanced our ability to detect a pressureindependent effect

It is also possible that less progression could have occurred in LoGTS if IOP reduction was more aggressive, but this is not relevant to the interpretation of our results.

LoGTS enrolled patients with glaucomatous optic neuropathy and corresponding visual field defects. We agree that structure and function are often poorly correlated in glaucoma, but that this relationship is usually more apparent in eyes with established visual field loss. The visual fields in LoGTS were analyzed using both trend and event analyses, all of which were consistent in their outcomes. There are many ways to further analyze the data and we look forward to doing so. Dropouts during the course of the study were a limitation of LoGTS, and as highlighted in the paper were considerably higher in the brimonidine-treated eyes and was expected from the inception of the study. This is consistent with clinical experience using brimonidine tartrate 0.2%.

Our results demonstrate that brimonidine preserves visual function better than timolol when used as monotherapy in eyes that do not develop ocular allergy in this cohort. The mechanism could be related to either a beneficial effect associated with brimonidine and/ or a detrimental effect associated with timolol. As described in the paper, 24-hour IOP control, ocular perfusion pressure, compliance and other unknown and unmeasured variables may have contributed to the study outcome.

The LoGTS trial emphasizes the need for further research in the field of neuroprotection.

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