Comparison of outflow facility before and after the microhook ab interno trabeculotomy.

Purposes: To elucidate the mechanism of intraocular pressure (IOP) reduction by microhook ab interno trabeculotomy (μLOT), the aqueous humour outflow facility was compared preoperatively and post-operatively.

Methods

Fifty-one eyes (37 patients; mean age, 67.2 ± 11.8 years) were included. The IOP, number of medications and outflow facility coefficient (C) estimated by pneumatonography were compared preoperatively and post-operatively using the paired t test. Linear regression analysis was performed to identify possible correlations between the C value and IOP or number of medications. To adjust for biases from including both eyes of a patient and differences in background, the preoperative and post-operative C values were compared using a mixed effects regression model.

Results

The mean preoperative IOP (18.2 mmHg) and mean number of medications (2.8) decreased significantly post-operatively by 26% and 18%, respectively, to 13.5 mmHg and 2.3 (p < 0.0001, for both comparisons). The preoperative C value of 0.27 µl/min/mmHg increased significantly (p < 0.0001) by 89% to 0.51 µl/min/mmHg post-operatively. Linear regression analysis indicated that higher IOP was associated with lower C values (estimate, -0.01/mmHg, p = 0.0107); medication numbers were not associated with the C value (estimate, -0.04/medication, p = 0.1739). Mixed effects regression analysis showed that the post-operative measurement (estimate, 0.11/preoperative measurement, p < 0.0001) was associated with a higher C value, while age, sex, µLOT procedure, IOP and medication numbers were not.

Conclusion

Outflow facility assessed by the tonographic C value increased significantly after µLOT. Increased conventional outflow by elimination of the outflow resistance at the trabecular meshwork is the main mechanism of IOP reduction after µLOT.