Several new ab interno and ab externo approaches to angle surgery in adults and children with open-angle glaucoma show promise for improving the control of intraocular pressure (IOP) less invasively and with fewer complications than current ab externo filtering procedures. These include the Trabectome®, iScience canaloplasty, Glaukos®, laser goniopuncture, and Solx—a new translimbal shunt into the suprachoroidal space. Updates on all these procedures have recently been presented in the US at major meetings of the American Academy of Ophthalmology (AAO), the American Glaucoma Society (AGS), the Association for Research in Vision and Ophthalmology (ARVO), and the American Association of Cataract and Refractive Surgeons (ASCRS).
The Trabectome (see Figure 1), approved by the US Food and Drug Administration (FDA), permits ab interno trabeculotomy—including ablation of a strip of trabecular meshwork and the inner wall of Schlemm’s canal— with simultaneous aspiration and irrigation to remove tissue debris while maintaining a stable anterior chamber.1,2 The device includes a ceramiccoated insulated footplate that acts as a glide within Schlemm’s, and also protects adjacent tissues from heat or mechanical injury.3
This procedure is performed through a clear 1.6mm near-limbal temporal corneal incision under direct gonioscopic control via a modified Swan-Jacob goniolens (see Figure 2). The goal is to unroof a 90–120º arc of Schlemm’s by removing the meshwork, juxtacanalicular connective tissue, and inner wall of the canal, allowing direct aqueous access to collector channels in the posterior canal wall. A foot-pedal control maintains aspiration and ablation at constant levels. An infusion sleeve allows continuous or intermittent inflow of fluid. Ablation power and aspiration rates are adjustable.
The most useful anatomical landmarks for identifying Schlemm’s intra-operatively include the scleral spur and pigmented meshwork, if present. Alternatively, blood in Schlemm’s canal after installation of viscoelastic into the anterior chamber often clearly marks the location of Schlemm’s. The inferior nasal quadrant is specifically targeted as collector channels are thought to be most numerous there. As ablation proceeds, the back wall of Schlemm’s appears as a white band in the trail of the instrument’s footplate.
Back bleeding from exposed collector channels or Schlemm’s typically occurs during the latter part of canal opening or when IOP drops as the instrument is removed. Back bleeding typically stops spontaneously over several minutes, or when an internal tamponade is installed via fluid or an air bubble. Only rarely among the more than 400 procedures performed and reported so far has the resulting hyphema been more than 10–20%, persisted for more than a few days, or been associated with a postoperative IOP spike. Intra-operative back bleeding may be decreased by pre-operative use of apraclonidine. Ocucoat® has proved to be a satisfactory viscoelastic when required, and seems to be relatively easily cleared from the anterior chamber. A single 10-0 nylon or polyglactin suture has been routinely placed across the corneal wound. Post-operatively, most eyes have been treated with 1% pilocarpine twice daily for two weeks, and pre-operative medications resumed temporarily pending IOP results over ensuing weeks. Overall, topical medications have been reduced from a pre-operative mean of 2.7 to a post-operative mean of 0.8 (see Figure 3). Reduction of IOP in an ongoing prospective case series has averaged 40% (mean pre-operative IOP of 24mmHg) to mid-teen levels (mean post-operative IOP of 16mmHg) persisting for at least 40 months in 15 patients (see Figure 4).
To date, disadvantages of the Trabectome include the handpiece being only single-use and IOP outcomes generally in the mid-teens, limiting its use to patients with mid-teen IOP goal ranges. Advantages include short surgical times, simplified post-operative follow-up, no bleb formation or late infection risk, and no damage to conjunctiva that would preclude any necessary standard surgery thereafter. Thus far, progression of cataract in phakic eyes has been minimal, which also contrasts sharply with standard filtering procedures. Other than the expected back bleeding, in general complications have been minimal and non-vision-threatening.
In theory, this procedure should improve outcomes in children compared with ab externo trabeculotomy or goniotomy, but the clinical experience to date has been too minimal for comparative assessment. The Trabectome procedure has been combined with cataract extraction (phacoemulsification and intraocular lens (IOL) placement) in approximately 100 cases with reasonable IOP improvement. Skill transfer has been easy among the approximately 25 surgeons involved so far. This procedure probably ranks between laser trabeculoplasty and standard filtering procedures in relation to the efficacy of other current management schemes for open-angle glaucoma. No prospective trials comparing Trabectome with standard filtering surgery or with medicine and laser have yet been reported.
Dr Minckler is a paid consultant for NeoMedix, manufacturer of the Trabectome™.