One-site Combined Surgery/Two-site Combined Surgery

Introduction

The coexistence of cataracts and glaucoma is a relatively common finding. This is not surprising since the prevalence of both diseases increases with age. In addition the treatment of glaucoma, both medical and surgical, has been associated with the accelerated development of cataract. The Collaborative Normal Tension Glaucoma Study found a significantly higher incidence of cataract in the treated compared to control group (38% vs. 14%, p = 0.001). In the treated group the rate of cataract formation was 48% in those treated with trabeculectomy, 25% in those treated with medications and/or trabeculoplasty and 14% in the untreated controls. The Advanced Glaucoma Intervention Study reported a 78% increased risk of cataract following trabeculectomy. In the Collaborative Initial Glaucoma Treatment Study the rate of cataract surgery was three times greater in the surgery group as compared to the initial medical treatment group (p = 0.0001). A recent evidence-based review graded the evidence as strong that trabeculectomy is associated with an increased rate of cataract formation.

Despite the frequency of coexisting cataracts and glaucoma there is no consensus on management. There are several surgical strategies: cataract surgery alone, glaucoma surgery alone (including trabeculectomy, glaucoma drainage implant, non-penetrating glaucoma surgery, ExPRESS shunt, gold shunt, iStent) and combined cataract and glaucoma surgery. The surgical decision is influenced by numerous factors including target intraocular pressure (IOP), number of glaucoma medications, severity of glaucoma damage, degree of cataract, type of glaucoma, number of previous operations and surgeon experience.

Indications

Although there is no consensus on when to combine or not to combine cataract and glaucoma surgery, a review of the current literature provides evidence to assist with management decisions. According to a systematic review there is weak evidence suggesting that phacoemulsification alone may result in a 2–4 mmHg IOP decrease at 1–2 years and there is strong evidence that trabeculectomy surgery alone results in a 2–4 mmHg additional IOP lowering compared to combined surgery. Possible explanations for poorer efficacy with combined surgery versus trabeculectomy surgery alone include a larger wound area with combined surgery resulting in higher levels of growth factors such as transforming growth factor-beta and longer surgical time resulting in an increased breakdown of the blood–aqueous barrier.

There is increasing evidence that phacoemulsification alone may lower IOP in cases of chronic angle-closure glaucoma. A study from East Asia compared phacoemulsification alone to combined phacotrabeculectomy in medically controlled chronic angle closure. The mean IOP postoperatively beyond 6 months was not statistically significantly different, with the phacotrabeculectomy group less than 1.5 mmHg lower than the phaco alone group. However, the phacotrabeculectomy group also required 0.8 fewer glaucoma drops (p < 0.001). In contrast, in medically uncontrolled chronic narrow angle glaucoma, patients who had phacotrabeculectomy had lower IOP at all time points compared to those who had phaco alone by between 1.2–3.0 mmHg, but this difference was only statistically significant at 3 and 18 months postoperatively (p = 0.01). The phacotrabeculectomy group required significantly fewer glaucoma medications at all time points (1.25, p < 0.001). At 24 months, 7 of 27 subjects (25%) who had phaco alone did not require medication compared with 17 out of 24 (71%) in the combined phacotrabeculectomy group.

In addition to angle-closure glaucoma, other scenarios where phacoemulsification alone may lower IOP include pseudoexfoliation glaucoma, aqueous misdirection, phacomorphic glaucoma, phacolytic glaucoma and glaucoma secondary to spherophakia.

The Canadian Ophthalmological Society evidence-based guidelines for the management of coexisting cataract and glaucoma recommend the following algorithm: (1) mild glaucoma controlled with 1 or 2 glaucoma medications and a visually significant cataract – phacoemulsification alone; (2) visually significant cataract in the presence of moderate to advanced glaucoma, with a preoperative IOP within or near the target range – combined phacotrabeculectomy; (3) visually significant cataract with uncontrolled preoperative IOP – consider trabeculectomy first, followed by cataract surgery at least 6 months later. This latter recommendation should specifically be considered in cases of advanced glaucoma with mild cataract where a very low target IOP is required or markedly elevated IOP where there is increased risk of a suprachoroidal hemorrhage following rapid IOP lowering.

There are several advantages associated with combined surgery over staged procedures including decreased surgical and anesthetic risk with one procedure, decreased costs to both the healthcare system and patient, faster visual rehabilitation and decreased risk of postoperative IOP spikes compared to phacoemulsification alone.

Combined cataract and trabeculectomy surgery may be performed using a one-site single incision for both the cataract and glaucoma surgery, or two-site separate incisions (one incision for the cataract and a separate location for the trabeculectomy). The indications, technique and outcomes will be compared below.

Preoperative Considerations

Several factors such as target IOP, surgical site access, orbit shape, surgeon experience, ergonomic comfort, and time may influence the choice between one- versus two-site phacotrabeculectomy. As detailed later there is limited evidence that final IOP, number of glaucoma medications, visual acuity or complications are affected by the choice of one- versus two-site surgery. In cases of conjunctival scarring limiting the location of the trabeculectomy to a site that would make phacoemulsification through the same incision difficult, one should consider separating the incisions. A deep orbit may also favor two-site surgery with a temporal approach to phacoemulsification and a superior trabeculectomy. Surgeon experience with temporal phaco­emulsification should also be considered. Finally two-site surgery takes significantly more time than one-site surgery and this may be important if operating room time is at a premium.