Clinical Evaluation of the Aqueous Outflow System in Primary Open-Angle Glaucoma for Canaloplasty

Abstract

To assess the aqueous outflow pathway in primary open-angle glaucoma (POAG) through provocative gonioscopy and channelography with a flexible microcatheter and fluorescein tracer during canaloplasty. One eye each was randomly selected from 28 consecutive black African POAG patients undergoing canaloplasty. Provocative gonioscopy was performed at the beginning of surgery, and blood reflux from collector channels into Schlemm's canal (SC) was semiquantitatively evaluated. During canaloplasty, a flexible microcatheter injected fluorescein tracer stepwise into SC. The outflow pathway parameters of interest were blood reflux, transtrabecular passage of fluorescein, and episcleral vein filling. Mean age, intraocular pressure (IOP), and cup-to-disc ratio were 45.9 years (SD +/- 13.3), 41.0 mm Hg (SD +/- 11.9), and 0.78 (SD +/- 0.22), respectively. Mean IOP (P < 0.001) and episcleral venous egress (P = 0.01) correlated significantly with blood reflux, but cup-to-disc ratio (P = 0.71), age (P = 0.70), and fluorescein diffusion (P = 0.90) did not. A multinomial regression model showed that higher IOP (P < 0.001, OR, 1.687; 95% CI, 1.151-2.472) was strongly associated with poor blood reflux, independent of the patient's age (P = 0.383, OR, 0.942; 95% CI, 0.823-1.078). No correlation was found between preoperative IOP, transtrabecular passage, episcleral venous egress, and cup-to-disc ratio. The mean IOP was 17.5 mm Hg (SD +/- 3.7) 6 months after surgery. The level of IOP after surgery correlated with the grade of blood reflux and episcleral venous egress (P < 0.001). High mean IOP may be associated with poor blood reflux and filling of SC. A collapsed canal, probably secondary to high IOP, may be an underestimated sign in black African patients with POAG. The quality of blood reflux and episcleral venous egress may both be predictive of the level of IOP after surgery. Provocative gonioscopy and channelography may reflect the function of the outflow pathway and may be helpful in assessing the surgical outcome of canaloplasty.