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Editors Selection IGR 12-1

Surgical Treatment: Ab-externo Schlemm's-canal surgery

Comment by Thomas Samuelson on:

25114 Pneumatic trabecular bypass (PTB): pilot study, Eldaly MA, Journal of Glaucoma, 2010; 19: 31-34

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In this case series report, Eldaly (521) describes a novel, low cost, ab-externo approach to Schlemm's-canal surgery. The technique is quite straightforward utilizing a standard vertical cutdown to the canal beneath a partial thickness scleral flap. The canal is then canulated in each direction with a blunt 27-gauge needle connected to the filtered air pump of a vitrectomy machine. Once the blunt-tipped needle is inside the canal, the air pressure is incrementally increased from 10 mmHg until pneumatic canal rupture occurs as determined by air bubble entry into the anterior chamber. The same procedure was accomplished on the opposite side of the cutdown.

The study population included tem eyes of ten patients with end-stage open-angle glaucoma with 'hand-motions' vision or worse. All eyes had cup-to-disc ratios of greater than 0.9. Two eyes had a previous trabeculectomy, while no study eyes had prior laser trabeculoplasty. All eyes were phakic. The preoperative IOP, determined by the mean of three daily pressure measurements (9AM, 12 noon, and 3PM), was 30.9 mmHg (SD 3.78) while taking 2.6 glaucoma medications. The IOP lowering results utilizing this technique were impressive. At the six-month follow visit the mean IOP was 16.6 mmHg (SD 4.43) on 0.5 medications (SD 0.97). Complications were few, primarily transient hyphema. In seven of ten eyes, two canal pneumatic rupture sites were identified gonioscopically, one on each side of the cutdown. In the remaining three eyes, only one rupture site was noted. No bleb was noted in any patient.

We may be moving ever closer to clinically significant surgical IOP reduction without the hazards of a filtration bleb

While the sample size in this paper limits it's clinical utility, the authors describe encouraging short term results in a difficult patient population with a mean IOP reduction of 43.5% (SD 13.92) at six months. Clearly, longer follow-up is needed to better understand the feasibility of this technique in the management of open-angle glaucoma. However, the authors provide encouraging results in this pilot series and additional research regarding this technique seems warranted. Intuitively one might suspect that the pneumatic bypass sites would scar over with time. Moreover, it is unclear why this procedure would enjoy such marked reduction in IOP when other similar procedures such as the iStent or Trabectome result in much more modest IOP reduction. Despite these questions, the authors add to the mounting evidence that we may be moving ever closer to clinically significant surgical IOP reduction without the hazards of a filtration bleb.

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