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Editors Selection IGR 13-4

Surgical Treatment: Trabeculectomy after failed trabectome

Comment by Brian Francis on:

28101 Effect of a failed trabectome on subsequent trabeculectomy, Jea SY; Mosaed S; Vold SD et al., Journal of Glaucoma, 2011; Epub ahead of print

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The most common angle-based or minimally invasive surgeries for openangle glaucoma include ab interno trabeculotomy with the Trabectome, trabecular bypass stent with the iStent, and viscodilation of Schlemm's canal with suture tension, or canaloplasty. These procedures have been developed to eliminate or reduce complications associated with a filtering bleb as seen in trabeculectomy and to some extent, aqueous tube shunts. It is important to establish, however, that these procedures do not adversely affect the outcomes of external filtering surgery performed at a later date.

Jea et al. (415) have examined the success rates of trabeculectomy performed as an initial surgery (control) or after failed Trabectome procedure (study group) in open-angle glaucoma. This was a retrospective analysis of patients with open-angle glaucoma including uveitic glaucoma if no anterior synechiae were present, with uncontrolled glaucoma on maximal tolerated medical therapy. Those undergoing combined procedures were excluded. The failure criteria used were modified from the Tube versus Trabeculectomy Study (TVT): IOP > 21 mmHg or less than 20% reduction from baseline on two consecutive follow ups after one month, additional glaucoma surgery, or loss of light perception. Comparisons were made between the groups with regards to age, sex, race, history of hypertension or diabetes, visual acuity, IOP, corneal thickness, type of glaucoma, previous laser trabeculoplasty, lens status, angle grade and number of glaucoma medications.

A total of 76 eyes were included; 34 in the study group and 42 in the control group. The mean interval between Trabectome and trabeculectomy was 4.9 months. As expected, both groups showed a significant drop in IOP after trabeculectomy, with a baseline of 27.6 ± 11.8 mmHg in the study group decreasing to 10.6 ± 2.6 at 24 months. The control group had a baseline IOP of 29.2 ± 11.4 decreasing to 11.0 ± 5.4 at 24 months. The number of glaucoma medications similarly decreased from 3.2 ± 1.1 to 0.8 ± 1.8, and from 3.6 ± 1.1 to 0.7 ± 1.1 in the study and control groups, respectively. The success rates at one year after surgery were 77.2% in the study group and 73.3% in the control group. There were no significant differences in the occurrence of complications between groups. The reasons for failure and additional procedures were also similar between groups. A history of systemic hypertension and the mean number of glaucoma medications were statistically significant risk factors for trabeculectomy failure, whereas a previous trabectome surgery did not have an effect on failure (P = 0.899). This study addresses an important issue facing newer, angle-based glaucoma surgeries: the question as to whether subsequent standard filtering surgery is adversely affected by prior internal filtration surgery. Proponents of Trabectome and other internal approach angle-based procedures state that the procedures do not cause conjunctival scarring and therefore allow future trabeculectomy. However, this assertion has not yet been analyzed. This paper, although limited by a retrospective design and modest sample sizes, is the first attempt to do so.

It is reasonable to perform Trabectome as an initial procedure, and expect no ill effects on future trabeculectomy

The design is a retrospective, comparative case series of trabeculectomy after trabectome compared to initial trabeculectomy. The two groups are comparable except for a higher baseline IOP in the trabeculectomy only group. Although no difference in success is seen between groups, the study is not designed with a power calculation for group size, but simply uses the numbers available. The analysis is complete and the comparison includes Kaplan-Meier survival curves and success rates as well as comparison of mean IOP and medications between groups. The authors also include an overall analysis of risk factors for failure, which concludes that number of preoperative glaucoma medications and systemic hypertension are significant factors.

In conclusion, this retrospective, comparative case series did not show any difference in the success rates for trabeculectomy as a primary glaucoma procedure, or following prior failed Trabectome. Although the evidence is not absolutely conclusive (due to study design), the data suggest that is reasonable to perform Trabectome as an initial procedure, and expect no ill effects on future trabeculectomy.

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