Combined cataract and glaucoma surgery, both filtering and non-penetrating, has increasingly obtained interest due to the frequent coincidence of both conditions in the elderly population and the frequent occurrence of cataract progression after glaucoma surgery
[1–3]. Canaloplasty is a relatively new non-penetrating surgical procedure which aims for restoring the natural aqueous drainage pathway by circumferentially dilating Schlemm canal using a microcatheter to viscodilate and insert a suture into Schlemm canal to keep it permanently open. The major advantage of this non-penetrating surgical method compared to trabeculectomy is that it avoids serious complications associated with filtering blebs. Combining canaloplasty with clear corneal phacoemulsification seems to allow further improvement of the aqueous outflow and provides higher IOP reduction than performed separately due to alterations of the architecture of the angle resulting in a more open configuration
This clinical trial analyzed one-year results of phacotrabeculectomy and phacocanaloplasty. The data did not reveal statistically significant differences in IOP control between both groups. Nevertheless, postsurgical complications were more frequent seen after phacotrabeculectomy.
It is well known that cataract surgery alone can provide a reduction of IOP, although the effect is generally small
[6, 7]. IOP reduction after clear corneal phacoemulsification is considered to be a consequence of increased outflow of aqueous humor due to an increased angle width and tensioning of the trabecular meshwork. Shingleton and coworkers
 found that IOP reduction was maintained 5 years after cataract surgery. In contrast, IOP is often increased in the early postoperative period in glaucomatous eyes after cataract surgery
Interestingly, several comparative studies on trabeculectomy and phacotrabeculectomy found a higher incidence of postoperative adverse events with the combined procedure. These were mostly induced by an inflammatory response that would limit the efficacy on IOP reduction
[2, 19, 20]. Lochhead et al.
 reported that phacotrabeculectomy was not as effective as trabeculectomy alone in reducing IOP. A possible mechanism that leads to a smaller IOP reduction following phacotrabeculectomy may be the prolonged anterior chamber inflammation due to an altered blood-aqueous barrier
In contrast to outcomes of combined filtering glaucoma surgeries, studies on non-penetrating glaucoma surgery combined with cataract surgery showed a better IOP-lowering effect of combined techniques
[12, 13, 16]. Bull et al.
 examined clinical outcomes of canaloplasty compared to phacocanaloplasty and found better results on IOP reduction in combined surgical cases than in cases with canaloplasty alone. In a multicenter-study conducted by Lewis and co-authors
, 3-year results of canaloplasty and phacocanaloplasty were reported. They concluded that both methods led to a significant and sustained IOP reduction with a low incidence of postoperative complications. Additionally, other clinical trials found a conjunctive effect of non-penetrating glaucoma surgery such as viscocanalostomy
[13, 14] or deep sclerectomy
[11, 12], when performed in combination with cataract surgery.
In our study, we found a 12-month IOP of 11.7 ± 3.5 mmHg for eyes undergoing phacotrabeculectomy, which was lower than in patients treated with phacocanaloplasty (12.6 ± 2.1 mmHg), although this difference was not statistically significant (P = .357). Additionally, the phacotrabeculectomy group needed fewer glaucoma medications (0.2 ± 0.4) compared to the phacocanaloplasty group (1.0 ± 1.5) at 1 year (P = .228). These results might be taken into the surgeon´s considerations, if a higher IOP reduction is necessary in patients with advanced glaucoma or if topical glaucoma drugs are not tolerated. Recently, a study by Ayyala et al.
, comparing surgical outcomes of canaloplasty and trabeculectomy without simultaneous cataract surgery, also found lower IOP with a lower percentage of patients needing postoperative anti-glaucomatous medications for the trabeculectomy group.
In general, studies on combined glaucoma surgeries report a postoperative IOP for phacotrabeculectomy comparable to our results
[11, 14, 20]. For phacocanaloplasty, 1-year outcomes of IOP ranging from 13.7 mmHg to 14.0 mmHg were also comparable to our results
[15–17]. Additionally, non-penetrating surgical methods such as deep sclerectomy
[11, 12] and viscocanalostomy
[13, 14] in combination with cataract surgery led to similar 1-year results of IOP reduction.
In fact, it is difficult to compare the incidence of complications between a penetrating and a non-penetrating glaucoma procedure. Nevertheless, severe hypotony-related complications are more frequent seen after trabeculectomy. In our study, hypotony (15.0%), choroidal detachment (10.0%) and shallow anterior chamber (5.0%) were seen in the phacotrabeculectomy group whereas in none of the patients in the phacocanaloplasty group. In literature, studies report an incidence of hypotony ranging from 18.5% to 20%, choroidal detachment in the range of 9.3% to 20% and a flattening of the anterior chamber in 0% to 10% following phacotrabeculectomy during 1 to 3 years of follow-up
Several studies comparing non-penetrating with traditional incisional glaucoma surgery with or without cataract surgery confirmed lower rates of severe postoperative complications for non-penetrating procedures
[8–11, 14]. In our study, hyphema was seen in 21.1% of patients with phacocanaloplasty and is a common event after canaloplasty. Hyphema seems to be a positive prognostic value regarding IOP development, since postsurgical interventions to reach target IOP became significantly fewer necessary in patients with a microhyphema
. Grieshaber and co-authors concluded that a hyphema may indicate a patent physiologic aqueous drainage system
. While dilating Schlemm canal with viscoelastics, a detachment of Descemet membrane may occur. An intracorneal hematoma is a rare complication following Descemet detachment and can be removed by partial-thickness paracentesis
. Descemet detachment was not encountered in our study. Overall, complication rate for phacocanaloplasty in our study was low and is comparable to previously published studies
[10, 15–17]. Bull and coauthors
 reported a 12.8% incidence of microhyphema, hyphema in 5.5% and Descemet detachment in 3.7%. No hypotony or shallow anterior chamber was seen after canaloplasty and phacocanaloplasty during the early postoperative period
Postoperative bleb manipulation to enhance flow such as focal massage, laser suture lysis, subconjunctival application of antimetabolites and bleb needling is often required after trabeculectomy. Since canaloplasty is a non-filtering, bleb-independent surgical approach, this might be a beneficial advantage compared to trabeculectomy.
Several limitations of this study have to be discussed. This trial was a retrospective and non-randomized; comparison of two separate series commonly having more sources of error due to confounding and selection bias than prospective studies. Additionally, phacotrabeculectomy and phacocanaloplasty were performed by more than one surgeon, though in the same surgical center. Despite the limitation imposed by inclusion of surgical data of different surgeons, both groups had similar preoperative demographic characteristics and the postoperative care was identical for all included patients. Individual predictive factors influencing the long-term outcomes of both combined surgical approaches are needed to decide whether a filtering or non-filtering methods lead to better results.