Combined Phacoemulsification and Canaloplasty
Canaloplasty is an ab externo procedure during which Schlemm's canal is cannulated with a fiber optic probe (iScience International, Menlo Park, California, USA), and a suture is then introduced 360° and tightened until the trabecular meshwork is put on adequate stretch to improve aqueous humor outflow. Ideally, high-resolution ultrasound is used to confirm that the tissues of interest are properly stretched. The procedure is technically more difficult than those previously described and has the additional disadvantage of causing conjunctival scarring, which makes subsequent glaucoma surgery less successful and technically more difficult. An additional disadvantage is the expense of the equipment that is needed to perform the operation.
Efficacy
Combined phacoemulsification–canaloplasty was shown to lower IOP by approximately 40% in three studies. The remarkably similar results of these studies may be because of pooling of data from the same patients in all three reports. None of the studies used a comparison group of phacoemulsification alone. A more recent small independent study by Matlach et al., also without a comparison group of phacoemulsification alone patients, found an average 55% drop in IOP after 12 months. In the only study to date comparing phacoemulsification–canaloplasty to phacoemulsification alone, Arthur et al. have reported a more profound IOP-lowering effect of the combined procedure throughout 24 months, although half to two-thirds of patients were lost to follow-up. The study was retrospective, so there was no randomization and the starting IOPs were relatively low in each group (16.2 in the phacoemulsification group and 18.2 in the phacoemulsification–canaloplasty group). In addition, the phacoemulsification–canaloplasty group started with mean baseline IOPs that were 2 mmHg higher than in the phacoemulsification group. Although there was no statistically significant difference in IOP at baseline or 24 months, patients in the combined group were on fewer medications and were less likely to fail by the standard criteria as outlined in the Tube vs. Trabeculectomy Study (Table 4).
Complications
Transient hyphema, inadvertent filtering bleb, Descemet's detachment, and suture erosion through the trabecular meshwork may be seen after phacoemulsification–canaloplasty. In addition, suture placement within the canal may not be possible in approximately 15–25% of patients.
Conclusion
Phacoemulsification–canaloplasty appears to be more effective at lowering IOP than phacoemulsification alone and may be an effective and well tolerated alternative to phacoemulsification–trabeculectomy. Negative aspects of this procedure include its technical difficulty and the creation of conjunctival scarring which could limit the success of subsequent trabeculectomy. Although rare so far, there is also concern over possible long-term erosion of the suture used in canaloplasty into the anterior chamber because of constant tension on the trabecular meshwork.