1. Treatment using laser trabeculoplasty and topical betaxolol hydrochloride to reduce intraocular pressure (IOP) is associated with delayed progression of glaucoma
2. Treatment to decrease IOP was associated with an increase in nuclear lens opacity grading indicative of cataract formation
Original Date of Publication: October 2002
Study Rundown: Previous epidemiological studies had suggested that few patients with elevated IOP actually developed glaucoma when left untreated. This challenged two assumptions at the time: firstly, the belief that glaucoma was caused by elevated IOP, and secondly, the thought that reducing IOP was a means of treating glaucoma. The Early Manifest Glaucoma Trial (EMGT), which commenced in 1992, was the first adequately powered, randomized trial that assessed the effectiveness of reducing IOP in the treatment of patients with previously untreated glaucoma. Its results showed that reduction of IOP through laser trabeculoplasty and topical betaxolol significantly delayed the onset of disease progression by a median of 18 months compared to the untreated control group. The benefits of treatment remained when participants were stratified according to IOP level, degree of visual damage, age, and presence of exfoliative glaucoma. However, IOP reduction was also associated with a significant increase in cataract formation based on nuclear opacity measurements.
Limitations of the trial include the study’s homogeneous patient population, consisting predominantly of white patients. Study participants were also required to have an IOP ≤30 mm Hg, which precluded the study from assessing the effect of IOP reduction in patients with higher initial IOP levels. Also, for ethical reasons, participants in the control group were monitored only until the onset of disease progression, at which point participants were then given appropriate treatment at the time. This design prevented the study from observing the natural history of glaucoma for an extended period of time. In summary, while the results of the EMGT do not conclusively show that elevated IOP causes glaucoma, it does confirm that elevated IOP is an important component of glaucoma’s pathophysiology, and that reducing IOP can help slow the progression of glaucoma in patients of various age, IOP level, and other characteristics. This finding supports efforts to improve early-detection of elevated IOP in patients.
In-Depth [randomized controlled trial]: The EMGT was a randomized trial that enrolled 255 patients from two Swedish cities. Eligible patients had to have had a diagnosis of newly detected, previously untreated open-angle glaucoma, reproducible visual deficits, and be between 50 and 80 years of age. Exclusion criteria included having severe visual field defects, a mean IOP >30 mm Hg, and significant cataractous lens changes. A total of 129 participants were randomized to receive treatment to reduce IOP through laser trabeculoplasty and topical betaxolol, while 126 participants were randomized to receive no treatment. All patients were monitored until the moment of disease progression, whereupon appropriate treatment was administered for all patients. Progression of glaucoma was assessed via measurements of visual field defects and optic disc cupping. All graders for these measurements were blinded.
Median follow-up was 6 years (range 51-102 months). The study demonstrated that treatment to reduce IOP was associated with a significantly lower frequency of glaucoma progression when compared with no treatment (45% vs. 62%, p = 0.007). This benefit of reducing IOP remained when patients were stratified according IOP level, degree of visual damage, age, and presence of exfoliation. The median time to progression for the treatment group was 18 months longer than for the control group. The study also found that treatment to reduce IOP levels was associated with a significant increase in nuclear opacities, when compared with no treatment (p = 0.002).
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