Five-year follow-up results from the Primary Tube Versus Trabeculectomy Study indicate that trabeculectomy surgery led to lower failure rates than tube surgery in patients with glaucoma.
Study design
The Primary Tube Versus Trabeculectomy Study was a nonblinded, randomized, prospective clinical trial that compared the efficacy and safety of tube shunt surgery and trabeculectomy (with mitomycin C) in 242 patients with primary open-angle glaucoma who had no prior ocular surgeries. The primary outcome measure was the cumulative rate of surgical failure at 1 year, defined as: IOP >21 mmHg or reduced <20% below baseline on 2 consecutive follow-up visits after 3 months; IOP ≤5 mmHg on 2 consecutive follow-up visits after 3 months, no light perception vision, or reoperation for glaucoma.
Outcomes
The 5-year follow-up visit completion rate was 90.3%. At that time point, 48% of patients in the tube surgery group and 39% in the trabeculectomy group had surgical failure. The probability of failure at 5 years was 42% in the tube surgery group and 35% in the trabeculectomy group, with higher baseline IOP and inadequate IOP reduction being key causes of failure. At 5 years, IOP reduction and visual acuity were similar between the treatment populations; however, those who underwent tube surgery were taking significantly more medications.
Limitations
A standardized measurement of visual field function and/or nerve fiber layer thickness, widely used as measures of disease progression, would have been useful in this study. The initial definition of success as IOP ≤21 mmHg may have been too generous, as most surgeons would consider this level too high for the average patient with disease severe enough to warrant major incisional surgery. The advent of new surgical options, including minimally invasive glaucoma surgeries (MIGS), were also not within the scope of this study. As MIGS are now often employed in early and moderate glaucoma, the fact that eyes with a history of prior incisional surgery were excluded limits the ability to extrapolate the study results to the current glaucoma patient population.
Clinical significance
This study shows no significant difference in failure rates or IOP between tube surgeries and trabeculectomies at 5 years, but eyes receiving trabeculectomies had a significantly higher rate of complete success and a significantly lower number of medications. To make the most of these results, it would have been interesting to examine rates of other major complications/failures, including traumatic ruptures and endophthalmitis. Ultimately, the choice between performing tube surgeries vs. trabeculectomies is likely to remain dependent on patient risk profiles, disease characteristics, and surgeon preference. The growing popularity of MIGS is also likely to shift the current landscape in glaucoma surgery.
Financial Disclosures: Dr. Lynn Sun discloses no financial relationships.