Fundamentally, glaucoma is a neurodegenerative disease and from experimental models we know that alpha2 agonists are neuroprotective agents. As such, the Low-pressure Glaucoma Treatment Study (LoGTS) was conceived to examine the possibility of other therapeutic measures being useful in the management of glaucoma other than a simple intraocular pressure (IOP)-lowering medication.

I have been involved in the LoGTS for some years to examine the effiacy of glaucoma treatments in preserving visual function. Recently, in the American Journal of Ophthalmology, my colleagues and I published results of the randomized, doublemasked, multicentre clinical trial comparing the alpha2-adrenergic agonist brimonidine tartrate 0.2% to the beta-adrenergic antagonist timolol maleate 0.5%, two medications with similar IOP effectiveness, in preserving visual function in low-pressure (normaltension) glaucoma.¹ These results have further added to our previous published papers on the study design and baseline characteristics,² and the visual field and intraocular pressure asymmetry.³

An important trial

LoGTS is an important trial for various reasons. It is the first randomized clinical trial to demonstrate the possibility of a pressure-independent treatment effect in patients with low-pressure glaucoma. It is also the first prospective randomized clinical trial to compare the impact of topical therapy on visual function by using a trend analysis approach to detect visual field (VF) progression. By enrolling patients with low baseline IOP, it demonstrates the power of having an enriched study population that minimizes the impact of IOP on glaucoma progression and may serve as a model for future neuroprotection trial.

To ensure we had an appropriate study group we set out certain exclusion parameters, which were untreated IOP > 21 mmHg, VF mean deviation worse than –16 decibels, or contraindications to study medications. To allow for a higher patient attrition in the brimonidine group to an expected ocular allergy, both eyes received twice-daily monotherapy in blocks of 7 (4 brimonidine, 3 timolol) by an independent pharmacy in new white bottles.

We determined the efficacy of the treatments mainly on the VF progression in either of the patient's eyes, but it had to be defined as the same three or more points with a negative slope {≥–1 db/year on three consecutive tests, which was assessed by pointwise linear regression. We also examined the level of our study groups' progression on glaucoma change probability maps (GCPM) of pattern deviation and the 3omitting method for pointwise linear regression as a secondary outcome of the treatment efficacy.