A second tube shunt and cyclophotocoagulation both help to control glaucoma


A prospective randomized study of patients with uncontrolled glaucoma after tube shunt placement evaluated the difference in outcomes between placement of a second tube shunt and transscleral cyclophotocoagulation (CPC).

Study design

Forty-two patients aged 40–85 years were included, and an adaptive block randomization scheme was utilized to evenly spread neovascular glaucoma and non–neovascular glaucoma between the two interventional arms. Failure was defined as a <20% reduction in IOP from baseline or an IOP <5 or >18 mm Hg, need for reoperation, or loss of light perception.


There was no statistically significant difference in the primary outcome between patients who received CPC and patients who received a second shunt, as both groups achieved success in approximately 80% of cases. At the 1-year timepoint, reductions in IOP were 11.6 mm Hg in the second shunt group and 12.3 mm Hg in the CPC group. While not meeting statistical significance, there was a difference in the proportion of patients with initial Ahmed vs Baerveldt shunts between the 2 groups, with more initial Ahmed valves in the CPC group and more Baerveldt shunts in the second shunt group. Three different treatment protocols for CPC were utilized.


Despite a long enrollment period, this study was significantly underpowered. As such, differences between treatment groups in the primary and secondary outcomes were often not able to achieve statistical significance. Furthermore, given the small numbers in both groups and further substratification with multiple interventional strategies in the treatment arms (e.g., multiple tube types, multiple CPC settings), there was less capacity to truly identify any differences.

Clinical significance

The results corroborate other retrospective studies in suggesting that CPC may be as effective as a second surgical procedure with little to no difference in adverse events. There is ample opportunity for a similar study design with tighter controls on treatment parameters and improved enrollment in order to definitively answer this important clinical question.

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