Trabeculotomy opening size and IOP reduction after Trabectome® surgery.

BACKGROUND: Trabeculotomy with the Trabectome® is an effective surgical procedure to lower intraocular pressure (IOP). However, in some patients it does not lead to a significant IOP reduction despite a gonioscopically well visible opening of Schlemm's canal. This study investigated whether the size of the trabeculotomy opening and other parameters, including anterior chamber depth (ACD) are related to IOP reduction.

METHODS: Retrospective observational case series with 93 eyes of 93 patients who underwent Trabectome surgery. Trabeculotomy opening and ACD were measured with an anterior segment swept source OCT. IOP was taken pre-operatively and at a single follow-up visit [follow-up time 125 ± 66 days (mean ± SD)]. The relationship between IOP reduction and OCT parameters and possible confounding factors was analyzed in a multiple linear regression model.

RESULTS: The trabeculotomy opening size did not correlate with IOP reduction (slope of regression line = 0.0016; 95% confidence interval of slope: -0.025 to 0.028). The same applied for all other parameters tested, including ACD, which showed a tendency towards better IOP reduction with a deeper AC (slope = -1.9; 95% confidence interval: -5.54 to 1.73). Comparison between the 1st and 4th quartile of the trabeculotomy opening showed a significantly higher ACD in the largest trabeculotomy opening quartile (3.32 ± 0.05 mm vs. 3.16 ± 0.04 mm; p = 0.031).

CONCLUSIONS: The fact that the trabeculotomy opening size did not correlate with IOP reduction points to the poorly understood role of the intrascleral aqueous outflow pathway in glaucomatous IOP elevation. A deeper AC might be a factor promoting a larger trabeculotomy opening.