Aqueous Outflow Can Predict Pressure Outcomes Following Suture Trabeculotomy

Aqueous outflow resistance at baseline can provide predictive data regarding the reduction in intraocular pressure (IOP) after patients with glaucoma undergo modified 360-degree suture trabeculotomy (ST), according to results of a study published in the Journal of Glaucoma.

This prospective case series evaluated 43 eyes of 32 patients with glaucoma who underwent ST at the Hokkaido University Hospital in Japan between 2017 and 2020. The mechanism of IOP reduction was evaluated using the coefficient of aqueous outflow (C-value) measured at baseline, and at 3 and 6 months postoperatively using an electronic Schiötz tonographer. C-values were calculated using the IOP rate of decay in the supine position during application of a recording probe on the cornea at a weight of 5.5 g for 4 minutes.

The patients were aged mean 58.0 (range, 30-80) years, 43.8% were men, 65.6% of cases were unilateral, 62.8% of eyes had primary open-angle glaucoma (POAG), 16.3% uveitic glaucoma, 13.9% exfoliation glaucoma, 7.0% steroid glaucoma, and 25.6% of eyes also underwent cataract surgery at the time of ST.

Following the procedure, patients decreased the average number of glaucoma medications from 3.8±1.1 at baseline to 0.9±1.3 at 3 months and 1.0±1.1 at 6 months.

At baseline, mean IOP was 19.0±7.3 mmHg and C-value was 0.19±0.09 μl/min/mm Hg, which were correlated with each other (r, -0.40; P <.01).

At follow-up there was a numeric, but not significant, decrease in IOP at 3 months (mean, 15.4 mm Hg; P =.10) and 6 months (mean, 16.1 mm Hg; P =.21), and a significant increase in C-value at both 3 months (mean, 0.24 μl/min/mm Hg; P <.01) and 6 months (mean, 0.27 μl/min/mm Hg; P <.01). Similar to baseline, the rates of change in IOP and C-value correlated at 3 months (r, -0.49; P <.01) and 6 months (r, -0.46; P <.01).

The observed reduction in IOP at 3 months (r, -0.39; P <.05) and 6 months (r, -0.33; P <.05) months correlated with the C-value at baseline.

Stratified by treatment success, defined as IOP lower than 21 mm Hg and IOP reduction of more than 20%, the success rates were higher for eyes with baseline C-values ≤0.17 μl/min/mm Hg (81.3%-86.4%) than for eyes with baseline C-values >0.17 μl/min/mmHg (46.7%-66.7%; P <.05).

Treatment success was associated with both baseline IOP (P <.01) and C-value (P <.05).

Outcomes were similar between the patients who underwent ST alone or in combination with cataract surgery.

Stratified by type of glaucoma, eyes with POAG used fewer topical glaucoma medications at months 3 and 6, had lower IOP at 3 months, and higher mean C-value at 6 months compared with baseline (all P <.01).

The findings in this study may have been biased by the fact that some patients discontinued ripasudil, which is thought to affect conventional outflow pathway.

“Increased conventional outflow by elimination of the aqueous outflow resistance at the trabecular meshwork is the main mechanism of IOP reduction after ST,” according to the researchers. “Preoperative C-value, which shows aqueous outflow resistance, is likely to be useful for predicting the outcomes of ST. Cases with low preoperative C-value, rather than those with high preoperative C-value as seen in POAG, may be suitable for ST.”