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Editors Selection IGR 16-1

Surgical Treatment: Outflow parameters for canaloplasty

Comment by Leon Herndon on:

25214 Clinical evaluation of the aqueous outflow system in primary open-angle glaucoma for canaloplasty, Grieshaber MC; Pienaar A; Olivier J et al., Investigative Ophthalmology and Visual Science, 2010; 51: 1498-1504

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Grieshaber et al. (526) randomly selected one eye from 28 consecutive black African primary open-angle glaucoma (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 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.

A multinomial regression model showed that higher intraocular pressure (IOP) was strongly associated with poor blood reflux. Mean IOP before surgery and episcleral venous egress correlated significantly with blood reflux, suggesting that a collapsed SC, probably secondary to high IOP, may be an underestimated sign in black African patients with POAG. These findings are in keeping with those in previous clinical studies indicating an inverse relationship between IOP and blood reflux. Experimental studies further show that the canal becomes much narrower as the trabecular meshwork (TM) expands into the lumen of the canal with increasing IOP. Canaloplasty is performed with the intent of increasing the natural flow of aqueous from the anterior chamber, through the TM into SC, and out through the collector channels. The combination of provocative gonioscopy and channelography may be helpful in determining the overall status of the individual case before surgical intervention. Absence of both blood reflux into the canal and episcleral filling suggests collapse of the canal and closure of the ostia of the collector channels. Canaloplasty was least successful in these cases, as the IOP after surgery was the highest in this group.

Provocative gonioscopy and channelography may becomediagnostic tools in routine canaloplasty

This study has practical clinical implications as provocative gonioscopy and channelography may become diagnostic tools in routine canaloplasty, as the outcome depends on the integrity of the distal outflow system. Should this distal outflow system be found to be inadequate on diagnostic testing, then the surgeon might choose to convert to another procedure, such as trabeculectomy, that bypasses the distal outflow pathway.

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