Combined Cataract and Nonpenetrating Glaucoma Surgery

Introduction

Glaucoma and cataract frequently develop in the same patient. This is in large part because the two are age-related illnesses. Moreover, glaucoma medications may have a role in cataract progression.

While combined phacotrabeculectomy surgery is currently the standard procedure for many surgeons, trabeculectomy is associated with substantial potential short- and long-term complications, including hypotony, with or without maculopathy, a shallow or flat anterior chamber, serous or hemorrhagic choroidal effusions, hyphema, and anterior chamber inflammation. Long-term risks related to blebs include leakage, blebitis, and endophthalmitis. Because of these potentially vision-threatening complications, the timing of surgery is delayed in many cases.

Alternative techniques such as non-penetrating glaucoma surgeries (NPGS) and ab interno trabecular surgery attempt to lower intraocular pressure with bleb-less procedures.

NPGS generally refers to deep sclerectomy (DS) and viscocanalostomy (VC) as well as canaloplasty. The main advantage of NPGS is the increased safety profile. Avoidance of sudden decompression prevents most serious complications associated with standard trabeculectomy. Other advantages associated with DS are the low rate of postoperative anterior chamber inflammation, and minimal corneal refractive changes, which may explain the improved visual acuity (VA) within the first postoperative days. This surgical approach may simplify ambulatory care. Eyes tend to remain quiet with good vision and a well-formed chamber on the first postoperative day ( Fig. 107-1 ).

Bleb appearance after DS is more diffuse and shallow compared with blebs after trabeculectomy, and long-term complications associated with thin and ischemic blebs may be largely avoided ( Fig. 107-2 [online]).

However, NPGS has not yet achieved wide acceptance because of its technically challenging nature requiring a relatively long learning curve. There is also still debate about its efficacy. Compared to trabeculectomy, all randomized trials agree that the complication rate is lower with NPGS, but the IOP-lowering efficacy is the same or less depending on the study. This disagreement in the literature might reflect differences in surgical techniques. Adjunctive space-maintaining devices, ab externo trabeculectomy, antimetabolites, and Nd : YAG laser goniopuncture enhance the success rates and reduce postoperative IOP.

Adding cataract surgery to a planned trabeculectomy might diminish the IOP-lowering effect of trabeculectomy by an average of 2–4 mmHg. In contrast to trabeculectomy, the IOP-lowering effect or success rate of DS does not appear to be compromised by simultaneous phacoemulsification.

Although there have been few comparative studies, phacoemulsification combined with NPGS has been shown to result in a similar IOP reduction, with the same visual outcome and a lower complication rate than phacotrabeculectomy.

Indications

The goals of combined glaucoma and cataract surgery are to reduce IOP and improve VA in a single procedure. One argument for combined surgery is the difficulty of evaluating the visual fields of patients with both glaucoma and cataract. The cataract affects the reliability of the visual field test, which affects the decision to continue medical management or consider surgery.

Combined surgery requires only one operation, and visual rehabilitation is not delayed or threatened by postoperative IOP elevations.

The choice of surgery depends on several patient factors, e.g. target IOP, stage of glaucoma, and individual risk factors, as well as the surgeon's experience with different surgical approaches.

As newer and safer therapies develop, the debate on how to best manage concurrent glaucoma and cataract is evolving. Generally, combined surgery is indicated in patients with visually disabling cataract and medically uncontrolled glaucoma. However, many surgeons who treat patients with cataract and well-controlled glaucoma choose to perform cataract surgery alone. This decision is influenced by the potentially sight-threatening complications of trabeculectomy.

With NPGS perceived to be a safer procedure, indications for combined cataract and glaucoma surgery are increasing. As a result, there are good arguments for performing phaco-DS or phaco-VC in patients with well-controlled open-angle glaucoma irrespective of the number of medications. This approach has been extended to patients with ocular hypertension; in a recent study by Park et al., 14.7% of patients who underwent planned phaco-VC had ocular hypertension.

Phacoemulsification combined with NPGS should be indicated in situations in which the potential complications associated with trabeculectomy are unacceptably high, such as in a patient with a hemorrhagic choroidal detachment in the opposite eye. Moreover, phacoemulsification combined with NPGS could be indicated in eyes with good VA and pseudoexfoliation to reduce intraoperative complications that are more common in more advanced cataract with pseudoexfoliative glaucoma.

High myopia and a previous vitrectomy also have been associated with an increased risk of postoperative choroidal hemorrhage after trabeculectomy. If combined surgery is indicated, NPGS is preferable to trabeculectomy to avoid sudden ocular decompression. In these cases, scleral thickness is often decreased and scleral flap dissection may be more difficult.

Eyes at increased risk of postoperative inflammation, such as those with uveitic or traumatic glaucoma, may benefit from NPGS, because it is less likely to induce postoperative inflammation.

Contraindications for combined phaco-DS include eyes with extensive primary or secondary angle closure, diffuse conjunctival scarring, primary and secondary closed-angle glaucoma, specifically neovascular glaucoma.

Preoperative Considerations

Preoperative gonioscopy is mandatory to confirm that the anterior chamber angle is open. If the angle is very narrow or closed, NPGS alone is contraindicated. Sometimes, angles that are narrow can open after phacoemulsification, and adding NPGS to cataract surgery could be considered in selected cases.

If anterior peripheral synechiae are present in the superior quadrant, another synechia-free location must be chosen to perform the NPGS, taking into consideration complications associated with inferiorly placed blebs after trabeculectomy.

Risk factors for surgical failure are the same as those for trabeculectomy and include young age, black race, active intraocular inflammation, previous surgical failure, and conjunctival scarring. In these cases, adding intraoperative mitomycin C (MMC) to combined surgery should be considered. In addition, in eyes with advanced glaucomatous damage or those requiring a lower target IOP, adding intraoperative MMC is advised. Care must be taken in patients with high myopia, because hypotony and other MMC-related complications are not uncommon ( Fig. 107-3 ).

Eyes that have undergone argon laser trabeculoplasty (ALT) may have cellular sheets growing over the trabecular meshwork. These membranes are impermeable to aqueous egress through the trabeculo-Descemet's membrane (TDM), and some authors have suggested that eyes that underwent a previous ALT may be better managed with conventional trabeculectomy. This is controversial and patients who have undergone a previous ALT have been included in several studies as candidates for combined phaco-NPGS.

There is a great diversity in current practice with regard to the management of anticoagulant therapy prior to glaucoma surgery. Recently, chronic anticoagulation or antiplatelet therapy has been associated with a statistically significant increase in the rate of hemorrhagic complications during and after glaucoma surgery. It could be advisable to stop these therapies in order to minimize the risks of untoward bleeding.

Eyes with pseudoexfoliative glaucoma have weak zonules, and more precise and careful maneuvers should be used during phacoemulsification to prevent dehiscence. A wide capsulorrhexis is preferable to prevent retraction over time. A small pupil can be surgically enlarged by positioning hooks in the anterior chamber through peripheral corneal stab incisions. No difference in the success rates has been found between primary open-angle glaucoma and pseudoexfoliation glaucoma after phaco-DS and phaco-VC.

Anesthetic Considerations

Phacoemulsification combined with NPGS is commonly performed under peribulbar or retrobulbar anesthesia. A small volume of anesthesia is recommended to facilitate visualization during NPGS dissection and to reduce optic nerve trauma.

Topical anesthesia (cocaine drops, lidocaine drops or lidocaine gel) supplemented or not with intracameral or subconjunctival anesthesia is an effective alternative to retrobulbar anesthesia for phacotrabeculectomy, eliminating the vision-threatening and systemic complications of regional anesthesia. Moreover, topical anesthesia does not increase the orbital pressure either directly from a volume effect or indirectly related to the Honan balloon. This is especially important for patients with advanced glaucoma whose optic nerve may be damaged further by external pressure.

Other advantages of topical anesthesia are the ability to facilitate surgical field exposure in the operated eye, less cost, patching is unnecessary, and topical eyedrops can be instilled earlier in the postoperative period.

The preferred approach by the authors is a superior peri­bulbar anesthesia to block the superior rectus-levator complex preventing Bell's phenomenon. The inferior muscle is not blocked allowing the patient to look down, providing a large exposition area without any suture to fix the eye.

With these considerations in mind, phacoemulsification and NPGS under topical or subconjunctival anesthesia or both should be performed only in highly cooperative patients, and by experienced surgeons.

Operative Technique and Potential Modifications

The goal of NPGS is to reduce resistance in the zone where the aqueous humor outflow is impeded by removing the juxtacanalicular trabecular meshwork and the inner wall of Schlemm's canal without opening the anterior chamber. Common to all techniques is the creation of a TDM by removing a deep block of scleral tissue and deroofing Schlemm's canal ( Video 107-1 ).

Both share an initial surgical pathway. A superior rectus muscle, or a superior intracorneal traction can be used. Alternatively, as previously mentioned, surgery can be performed without any suture of fixation.

Conjunctival dissection is performed in a limbus- or fornix-based fashion. A fornix-based flap is the preference of the authors because it facilitates better visualization during surgery. Moreover, considering the size of the outer scleral flap (5 × 5 mm), a conjunctival limbus-based flap has to be made too near the superior rectus muscle insertion.

The sclera is exposed and careful hemostasis is made. This is followed by the creation of a one-third thickness outer scleral flap measuring 5 × 5 mm extending 1–2 mm into the clear cornea. An inner scleral flap measuring 4 × 4 mm is dissected to 90% thickness, so that Schlemm's canal is entered. The critical landmark is the scleral spur. This structure is easily recognized, because the scleral fibers are brilliant white and arranged in a parallel fashion to limbus. Immediately after it, Schlemm's canal is found and the dissection is extended to the level of the Descemet's membrane. Although the canal itself does not require dissection, the lateral edges of the flap overlying the canal require relaxing incisions. Great care must be taken when cutting this tissue to avoid perforating the underlying TDM.

A thin layer consisting of the inner wall of Schlemm's canal and adjacent trabecula remains. This thin layer is commonly referred to as the TDM. Anterior is the corneal contribution from Descemet's membrane.

After dissection a wide TDM window the inner scleral flap is removed by cutting along its hinge using a diamond knife or a sharp knife and completed with microscissors. The cut has to be performed as near as possible to the hinge to avoid reducing the size of the TDM.

At this point, the DS and VC procedures diverge. DS continues with the removal of the inner wall of Schlemm's canal, the site at which most glaucomatous outflow resistance is thought to reside. The most popular technique uses a forceps in a peeling maneuver ( Fig. 107-4 [online only]). Successful removal generally results in a marked increase in aqueous humor diffusion through the TDM.

Various implants (AquaFlow ^TM , Collagen Draining Device, STAAR Surgical, Monrovia, CA; T-Flux implant ^TM , IOLTECH, la Rochelle, France; Esnoper ^TM , AJL Ophthalmics, Alava, Spain, HEALAflow ^TM , Anteis, Switzerland) can be placed in the scleral space.

Viscocanalostomy involves the additional step of injecting high-viscosity sodium hyaluronate into the cut ends of Schlemm's canal using a very fine cannula (AlconGrieshaber, Switzerland) and then firmly suturing the scleral flap to encourage aqueous egress by methods other than subconjunctival filtration. Instead of an implant, a high-viscosity viscoelastic is injected under the superficial scleral flap.

Deep Sclerectomy and Phacoemulsification

When a combined surgery is performed, phacoemulsification is performed through a clear temporal or horizontal corneal incision, and the DS is performed in the superior quadrant. If the patient underwent a previous failed trabeculectomy superiorly, DS can be carried out in the superonasal or superotemporal quadrant ( Fig. 107-5 ).

Phacoemulsification and intraocular lens (IOL) implantation should be done first before entering Schlemm's canal, because high IOP during phacoemulsification and hydrodissection may rupture the fragile TDM.

The technique preferred by the authors is to begin DS in the same manner as described previously, stopping just before entering Schlemm's canal. Phacoemulsification and foldable IOL implantation are performed in a standard fashion and the viscoelastic is removed. DS is then completed by entering Schlemm's canal ( Fig. 107-6 [online only]).

Alternatively, standard clear corneal phacoemulsification is performed first. The viscoelastic is not removed and an NPGS is initiated superiorly. The viscoelastic makes the globe rigid and facilitates creation of the outer scleral flap. The viscoelastic must be manually removed with an irrigating syringe to avoid elevating the IOP and rupturing the TDM. One advantage to this approach is that if intraoperative complications develop, such as zonular rupture or vitreous loss, the glaucoma surgery can be deferred.