Article Date: 3/1/2010

Working Together: Glaucoma Specialist/Retinal Surgeon Cooperation

Working Together: Glaucoma Specialist/Retinal Surgeon Cooperation

Communication is vital to successful patient care.

NATHAN RADCLIFFE, MD • R.V. PAUL CHAN, MD

Any specialist who manages complicated eye diseases knows that a sick eye will often mimic the human body's condition of multiple organ failure. Patients with retinal disease may develop glaucoma through a variety of mechanisms. On the other side of this cycle, the management of glaucoma and its surgical complications will often require the skills of a retinal surgeon. As such, good communication and cooperation between retinal and glaucoma surgeons is vital to the care of patients with these two comorbidities.

Given the high prevalence of diabetic retinopathy and open-angle glaucoma alone, it is not surprising that a large number of patients have both glaucoma and retinal disease. Glaucoma is the second leading cause of vision loss and affects 2.22 million US citizens.1 Diabetes afflicts 10.2 million adults in the United States, and 40% of those pa tients have some retinopathy.2 Patients with other conditions often treated by retinal physicians are also likely to develop glaucoma. For example, patients with primary open-angle glaucoma can develop retinal disease secondary to myopia, a known risk factor for the disease. Age and hypertension predispose patients to both glaucoma and macular degeneration. In this review, we will discuss the comanagement of patients with retinal disease and glaucoma, particularly as it relates to surgical management.

CAUSES OF COMORBIDITIES

Some retinal diseases specifically predispose the patient to glaucoma and vice versa. Pigment dispersion syndrome (PDS) and pigmentary glaucoma are characterized by dispersion of pigment granules throughout the anterior segment, and these disorders occur mainly in myopic patients. In addition to the classic clinical triad of corneal pigmentation (Krukenberg spindle), radial, slit-like, midperipheral iris transillumination defects and dense trabecular pigmentation, pigmentary glaucoma is associated with a 6% to 8% incidence of retinal detachment.3

Furthermore, the incidence of lattice degeneration is higher for all degrees of myopia in patients with PDS than in the general population.4 Exfoliation syndrome is associated with secondary open-angle glaucoma from the production of a fibrillar extracellular material that is deposited throughout the anterior segment, including the iris, lens capsule, trabecular meshwork, and the lens zonules. The accumulation of fibrillar material on the zonules predisposes to ectopia lentis, which can result in posterior dislocation of the phakic crystalline lens or can alternatively lead to delayed “in-the bag” intraocular lens dislocation.5

The treatment of retinal diseases can lead to glaucoma, particularly with the use of steroids. For certain conditions, such as macular edema secondary to branch retinal vein occlusion, intravitreal steroid use may be decreasing due to the availability of newer anti-VEGF therapies. However, intravitreal steroids are still frequently used and glaucoma may occur. For example, after intravitreal triamcinolone acetonide injection, the cumulative incidence of intraocular pressure elevation over two years was 45%.6 With the use of fluocinolone acetonide intravitreal implant for refractory uveitis, up to 75% of patients required IOP-lowering therapy.7 While anti-VEGF therapy has reduced the use of intraocular steroids for a variety of conditions, there are anecdotal reports of both transient and long-term IOP elevation after anti-VEGF medications having been injected, and this possibility is under investigation.

RETINAL COMPLICATIONS FROM GLAUCOMA SURGERY

Glaucoma surgery can lead to complications that will often require retinal surgery. Today, trabeculectomy with mitomycin C (MMC) is preferred by glaucoma surgeons in the United States as the initial procedure of choice, though the three-year data from the tube vs trabeculectomy study has been published and will likely support an expanding role for tube placement in glaucoma.8,9 An early complication of trabeculectomy is hypotony (low IOP) and choroidal detachment, the latter of which, along with a shallow or flat anterior chamber, occurred in around 10% of patients after trabeculectomy in the Collaborative Initial Glaucoma Treatment Study (CIGTS) study.10

Fortunately, choroidal hemorrhage was much more rare, occurring after only 0.7% of trabeculectomies in this study. Depending upon the clinical situation, chronic serous choroidal detachments may require drainage, which in some cases is performed by the retinal surgeon. Choroidal hemorrhages can be devastating and painful, and they occasionally require drainage with or without vitrectomy. Late complications of trabeculectomy can require retinal surgical management as well.

With the use of MMC, the vision-threatening complication of bleb-related endophthalmitis can occur in up to 7.5% of cases after five years of follow-up.11 Bleb-related endophthalmitis requires either a tap and inject or pars plana vitrectomy (PPV), depending on the visual acuity and the management preference of the surgeon.

Because of these complications and the high rate of failure of trabeculectomy, glaucoma tube-shunt surgery is gaining in popularity among glaucoma surgeons.12 The prospective tube vs trabeculectomy study is an ongoing multicenter, randomized clinical trial comparing trabeculectomy with MMC to Baerveldt glaucoma implant in patients who had previous trabeculectomy or cataract extraction. This study recently reported that, at three years, tube-shunt surgery had a higher success rate (85%) compared to trabeculectomy with MMC (69%).9

With tube-shunt surgery, the majority of early complications are attributable to hypotony in the postoperative period.13,14 This complication arises because nonvalved tubeshunt surgery (Molteno or Baerveldt) requires the formation of a fibrotic capsule around the extraocular reservoir for proper function. The tube is typically ligated with an absorbable (Vicryl, Ethicon, Inc., Somerville, NJ) suture that will dissolve after capsular formation has occurred. If the tube is open prior to the formation of this capsule (which takes around four to six weeks to form), ocular hypotony and its associated complications may occur.

The Ahmed valve is capable of providing acceptable IOP control with a lower rate of hypotony within the early postoperative period. However, over a longer period of follow-up (22 months), it may be less effective at lowering IOP than the Baerveldt or Molteno, though other studies suggest the two devices may be equally effective.15-19 The ongoing prospective Ahmed vs Baerveldt Comparison (ABC) Study has completed recruitment and should provide some valuable evidence in the near future.

DIABETES AS A PRECURSOR

Diabetes can predispose patients to glaucoma through proliferative diabetic retinopathy and neovascular glaucoma (Figure 1) and also through postvitrectomy open-angle glaucoma. For example, nonclearing vitreous hemorrhage from diabetes may require vitrectomy, and Stanley Chang, MD, has shown that there is an increased risk of open-angle glaucoma after PPV.20

Figure 1. A superotemporal drainage tube has been placed in an eye with florid rubeosis iridis and neovascular glaucoma.

Neovascular glaucoma (NVG) is the term given to synechial angle closure from anterior-segment neovascular membrane formation. Secondary open-angle glaucoma (caused by new vessels obstructing the trabecular meshwork) may precede the contraction of the fibrovascular membrane with secondary angle closure. Overall, NVG is most commonly caused by intraocular vascular occlusions (which themselves may be precipitated by elevated IOP).

Secondary (steroid response) glaucoma may occur after triamcinolone injections and possibly from anti-VEGF agents, though these agents are invaluable in the treatment and prevention of neovascular glaucoma, and we are probably seeing less need for shunt placement for NVG due to early and aggressive anti-VEGF treatment in these patients.

INTRAOPERATIVE CONSIDERATIONS

While instrumentation and surgical techniques are quite distinct between the two subspecialties, both glaucoma and retinal surgeons typically begin their surgeries by incising the conjunctiva. Since prior conjunctival surgery has been shown to be a risk factor for trabeculectomy failure, proper handling of the conjunctiva is important for future successful glaucoma surgeries, and occasionally this territory serves as a battleground between retinal and glaucoma surgeons.

Glaucoma surgeons prefer that the conjunctiva and Tenon's be incised as anteriorly as possible and that meticulous care be used in precisely reapproximating the conjunctiva to the limbus at the end of surgery. While newer techniques, such as 23- or 25-gauge vitrectomy, may not require a complete conjunctival peritomy, this is not always preferable in a glaucoma patient.

Since the introduction of 25-gauge PPV in 2002, most vitreoretinal surgeons have trended away from the use of conventional 20-gauge PPV.21 Transconjunctival sutureless vitrectomy (TSV) with 25- and 23-gauge instruments potentially offers the advantages of reduced postoperative inflammation, decreased convalescence period, improved patient comfort, and decreased operative times.22 Although initially, 25-gauge was limited secondarily to instrument flexibility, decreased flow, and poor globe manipulation, TSV evolved to 23-gauge, providing the vitreoretinal surgeon with surgical performance closer to 20-gauge. And with improvements to 25-gauge instrumentation, vitreo-retinal surgeons have a variety of options with TSV in handling most surgical conditions, from macular pucker to complicated retinal detachment. However, although small-gauge instrumentation may be used for most surgeries, a transconjunctival approach may not be the ideal choice when dealing with a patient who may potentially need glaucoma surgery.

While a transconjunctival approach may seem minimalistic, it is essentially guaranteed to create a scleral-conjunctival adhesion. In this case, it is preferable to just perform a peritomy at the limbus, which can be reapproximated as a sheet of tissue with minimal adhesions. Even a 360° limbal peritomy will cause less conjunctival scarring than three small 2-mm incisions above the vitrectomy port. Finally, if relaxing incisions are required, the best place for such incisions is at 3 o'clock or 9 o'clock, where the conjunctiva is unlikely to be involved in filtration or bleb formation. When performing combined glaucoma and retinal surgery, we typically have the glaucoma surgeon begin the case by making the agreed-upon conjunctival incisions.

Several new surgical techniques under development promise to avoid conjunctival filtration in glaucoma and may provide more leeway for the retinal surgeon in terms of conjunctiva management. One such procedure is the Trabectome (NeoMedix Corp., San Juan Capistrano, CA), which is essentially an irrigation/aspiration unit with a microelectrocautery tip that can ablate the trabecular meshwork and the inner wall of Schlemm's canal through a corneal paracentesis incision, lowering resistance to aqueous outflow without a conjunctival incision. Another such possible sutureless glaucoma surgery system is the iStent (Glaukos Corporation, Laguna Hills, CA; not available in the United Sates), a 1.0-mm heparin-coated titanium microtube that is placed in Schlemm's canal, again through a corneal paracentesis wound. The iStent pierces the trabecular meshwork, lowering the aqueous outflow resistance.

Retinal surgeons may be called upon at the time of glaucoma surgery to aid in ideal tube placement. The most common invitation calls for the removal of vitreous prior to placement of a pars plana seton or in relation to complications of pars plana valve placement, eg, retinal detachment or choroidal hemorrhage. For a variety of reasons, tubeshunt placement in the vitreous cavity may be indicated, and a PPV dedicated for this purpose is typically required. Corneal disease is one indication. In particular, patients who have poor endothelial function prior to glaucoma drainage device are poor candidates for anterior-chamber tube placement. In patients for whom an anteriorly placed tube may have led to corneal decompensation, posterior tube relocation, either into the vitreous cavity or into the iridociliary sulcus, is indicated.

Descemet's stripping automated endothelial keratoplasty (DSAEK) is becoming increasingly common and, in most cases of DSAEK in patients with anterior-segment tubes, tube repositioning will be indicated, usually into the vitreous cavity. Finally, in glaucoma with severe conjunctival disease where bleb formation is impossible, endoscopic cyclophotocoagulation can be performed through a PPV or anterior approach. For example, in postkeratoprosthesis patients (Figure 2), the anterior chamber is essentially nonexistent, and we prefer that this intervention be performed through the pars plana.

Figure 2. In this postkeratoprosthesis patient with extensive conjunctival scarring due to a chemical burn, filtration surgery was not possible and endocylophotoablation was performed through a pars plana approach.

COOPERATING IN VITRECTOMIES

One area of common miscommunication between glaucoma and retinal surgeons is the approach to vitrectomy in patients requiring a pars plana valve. For example, when pars plana tube placement is required, a complete vitrectomy is indicated. It is our experience that, in prior vitrectomized eyes, unless the original vitrectomy was performed with valve placement in mind, an additional vitrectomy should be planned for at the time of valve placement.

Specifically, the retinal surgeon will want to be sure to remove the anterior hyaloid membrane, an event that is unnecessary in most vitrectomy surgeries (particularly in phakic patients). Furthermore, the retinal surgeon will want to perform a very close vitreous shave in the quadrant of anticipated tube placement. In certain cases, endoscopic vitrectomy may be useful. As compared to conventional wide-angle viewing systems, endoscopy has the potential for better visualization of the vitreous. This may prove especially useful when there is vitreous incarceration in glaucoma implant tubes (Figure 3).

Figure 3. An inferotemporal pars plana glaucoma drainage tube is noted to have vitreous incarceration.

When performing concurrent vitrectomy and tube placement at our institution, we prefer to first perform the conjunctival dissection (usually by the glaucoma surgeon) and to place the tube plate in the appropriate quadrant. Since this maneuver requires extensive globe manipulation (eg, placement of muscle hooks in preparation for Baerveldt placement behind the recti muscles), it is better if the eye is firm and does not yet have any vitrectomy or irrigation ports that may restrict globe duction, be at risk of dislodgement, or leak aqueous humor. After the valve plate is placed, the vitrectomy can be performed through bare sclera. Finally, the tube is inserted and is inspected for appropriate placement and to be sure there is no visible vitreous incarceration. Triamcinolone as diluted as 1 mg/mL is used to stain the vitreous if there is any question. It is the authors' preference for nonvalved glaucoma drainage devices (Baerveldt or Molteno) for placement in the vitreous cavity since there is less risk of permanent failure if vitreous incarceration occurs, though the risk of early hypotony, long-term failure, and vitreous incarceration must be carefully balanced for each patient's particular situation.

For example, should vitreous obstruct the tube ostium, YAG vitreolysis is significantly more effective in a nonvalved device, as releasing vitreous into the tube will usually doom an Ahmed valve to failure. Suturing of the sclerotomy ports is at the discretion of the surgeons, but it is our experience that, after 25-gauge or 23-gauge sutureless vitrectomy, IOP will be lower for weeks to months after vitrectomy alone. When ligated nonvalved glaucoma implants (Baerveldt or Molteno) are used, sutureless vitrectomy ports may allow for some short-term IOP control prior to suture dissolution and tube opening, though the risk of hypotony must also be considered.

One situation in which minimal-to-no conjunctival dissection may be preferred is the case of vitrectomy in an eye with a functioning glaucoma filter, particularly the often fragile trabeculectomy. Here it is typically best to discuss the placement of each vitrectomy port with the glaucoma surgeon, and in some cases the retinal surgeon may wish to sit temporally in order to avoid port placement in an area of filtering conjunctiva. Antifibrosis agents such as 5-fluorouracil (typically 5 to 10 mg) may be injected adjacent to the filter intraoperatively or in the office setting in the early postoperative period. Advances in trocar design for transconjunctival sutureless vitrectomy may also improve our ability to preserve the conjunctiva. Compared to older designs, new trocar blades (eg, Edgeplus, Alcon) produce a more linear incision, which may allow for better wound closure and may be less traumatic on the sclera and conjunctiva.

While the management of retinal detachment surgery has shifted somewhat over the past several decades away from primary scleral buckle placement, the glaucoma surgeon will still en counter many eyes with previously placed scleral buckles and significant conjunctival scarring. Several approaches are available for these patients. If minimal scarring is present, trabeculectomy with MMC may still be the initial procedure. Nonconjunctival filtering procedures, as discussed above, may be indicated as well. Glaucoma drainage devices may be placed with the plate placed superficially to the buckle. In some cases, it may be difficult to place the wings of the Baerveldt 350-mm shunt beneath the recti muscles when a scleral buckle is in place. In this case, either the tube plate can be trimmed, a 250-mm plate can be used, or the valve can be placed superficial to the muscles.

Finally, a Schocket procedure may be performed. In this technique, a simple tube (such as a Crawford tube) or the amputated tube from a commercially available drainage device is placed proximally into the capsule surrounding the scleral buckle and distally into the anterior chamber.23 A patch graft will then cover the tube's insertion into the anterior chamber. The capsule surrounding the scleral buckle serves as the reservoir and provides resistance to aqueous outflow.

Malignant glaucoma is a postop complication of cataract extraction or trabeculectomy that may often require a special approach to vitrectomy. The mechanism behind malignant glaucoma, also called aqueous misdirection syndrome, is not fully understood. This condition is a rotational angle closure that may be caused by ciliochoroidal effusions that rotate the ciliary body anteriorly or by positive pressure originating at the level of the posterior capsule and anterior hyaloid face. Cycloplegics, aqueous suppressants, and/or YAG capsulotomy/hyaloidotomy may be successful in resolving this condition, but if not, then vitrectomy may be required.

If the vitrectomy is not performed with a specific goal in mind, recurrence of malignant glaucoma is common. In this situation, the key is for the surgeon to create a single-chambered eye. In order to accomplish this, a complete PPV with anterior hyaloidectomy is performed and, upon its completion, the vitrector is brought into the anterior chamber, removing a portion of the lens zonules, lens capsule, peripheral iris, and any inflammatory debris that may have led to the rotational angle closure.

SUMMARY

Glaucoma and retinal disease are often interrelated and it is critical that the bridge of communication between the glaucoma and vitreoretinal surgeons remains strong. With advances in pharmacotherapy and new surgical techniques/instrumentation, we have been able to improve patient outcomes. Although care must be taken in choosing transconjunctival sutureless vitrectomy for patients prior to glaucoma surgery, TSV using trocars and 25-gauge or 23-gauge instrumentation may improve healing and patient comfort post–glaucoma-filtering surgery. Also, with advent of the anti-VEGF era for various retinal diseases, glaucoma secondary to steroid use may become less prevalent. RP

Nathan Radcliffe, MD, is an assistant professor of ophthalmology and director of the Glaucoma Service at Weill Cornell Medical College and New York-Presbyterian Hospital in New York. R.V. Paul Chan, MD, is St. Giles Assistant Professor of Pediatric Retina and assistant professor of ophthalmology at Weill Cornell. The authors report no financial interests in any product mentioned in this article. Dr. Chan can be reached via e-mail at roc9013@med.cornell.edu.

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Retinal Physician, Issue: March 2010