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New techniques, variations on old procedures broaden options for glaucoma patients
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Surgical innovations continually improve our ability to manage nerve damage secondary to increased intraocular pressure (IOP). Novel procedures are under development that may revolutionize the way patients with progressive glaucoma are treated. The decision to refer a patient for glaucoma surgery is a complicated one and has been affected by the availability of more anti-glaucoma agents than ever before.
The indications for glaucoma surgery have not changed: patients with subjective visual field loss, progressive visual field changes or glaucomatous optic nerve damage should be considered for surgery. Poor response to medical management can include insufficient response to medications, significant adverse reactions or even the inability to instill medications due to financial hardship or physical limitation.
Hattenhauer and colleagues showed that there is a significant probability of progression of open-angle glaucoma or ocular hypertension even under treatment (Hattenhauer MG, Johnson DH, Ing HH et al. The probability of blindness from open-angle glaucoma. Ophthalmology. 1998;105:2099-2104.). Therefore, there exists a functional risk to our patients if IOP is not adequately controlled. The Moorefield Primary Treatment Trial proposed that primary surgical intervention might produce better long-term outcomes for pressure control (Migdal C, Gregory W, Hitchings R. Long-term functional outcome after early surgery compared with laser and medicine in open-angle glaucoma.Ophthalmology. 1994;101:1651-1657.). The ongoing Collaborative Initial Glaucoma Treatment Study will help us decide whether primary trabeculectomy is an appropriate option when considering IOP, visual function and lifestyle issues (Musch DC, Lichter PR, Guire KE et al. The Collaborative Initial Glaucoma Treatment Study. Ophthalmology. 1999;106:653-662.).
As new surgical techniques, such as deep sclerectomy with collagen implant (DSCI) and viscocanalostomy, are being developed, optometrists need to familiarize themselves with the relative advantages and disadvantages of these procedures as compared to currently available treatment options. Each glaucoma patient we treat is an individual with a multitude of factors that will guide us in recommending the intervention that is most appropriate.
Laser surgery vs. filtration surgery
Patients who do not respond to medical therapy should be counseled about other options, including laser trabeculoplasty (LTP). Results from the Glaucoma Laser Trial have indicated that argon laser trabeculoplasty is a good initial treatment for certain patients with open-angle glaucoma in comparison to medical treatment, but cautioned against extrapolating these results to other glaucoma populations, specifically those with secondary open-angle glaucoma (Glaucoma Laser Trial Research Group. The Glaucoma Laser Trial and Glaucoma Laser Trial Follow-up Study: 7. Results. Am J Ophthalmol. 1995;120:718-731.).
Patients with advanced stages of glaucoma and high IOPs are poor candidates for LTP because the pressure reduction achieved with this procedure may still exceed the level required to prevent further nerve damage. But LTP is a good option for early to moderate stages of glaucoma with significant pigmentation of the trabecular meshwork, as is seen in pigmentary or pseudoexfoliative glaucoma. Patients with lower pre-laser pressure readings (e.g., normal tension glaucoma) may benefit from laser treatment, although the effect is generally more limited. LTP is not recommended for patients with inflammatory causes for open-angle glaucoma because the trabeculitis induced by the laser energy may precipitate episodes of ocular inflammation.
The most recent advances in LTP involve the frequency-doubled Q-switched Nd:YAG laser (532 nm). This procedure has been called selective laser trabeculoplasty and refers to the ability of this laser energy to precisely target pigmented trabecular meshwork cells with minimal photocoagulative damage to surrounding untreated tissue or nonpigmented trabeculum.
Clinical studies using this technique have suggested that selective LTP can be as effective in reducing IOP as argon laser trabeculoplasty (ALT), although more information is needed about long-term efficacy. Damji and colleagues found that SLT decreased IOP as effectively as ALT in the first 6 months after treatment and had greater effect than ALT in patients with failed ALT (Damji KF, Shah KC, Rock WJ, Bains HS, Hodge WG. Selective laser trabeculoplasty v argon laser trabeculoplasty: a prospective randomized clinical trial. Br J Ophthalmol. 1999;83:718-722.).
Trabeculectomy as an alternative
---Collagen implant placement: The Aqua-Flow collagen drainage device is placed radially in the scleral bed to prevent fibrotic closure of this outflow passageway. (Photo courtesy of Staar Surgical AG.) If laser procedures are not suitable treatment options for your patient, alternative interventions such as filtering surgery should be considered. Since Cairns described the trabeculectomy procedure in 1968, numerous variations have been suggested to improve the success rate of surgery. These modifications include the use of antimetabolites to retard fibrosis within the scleral flap and releasable sutures to titrate the postoperative IOP. Newer developments include nonpenetrating filtration surgery, such as deep sclerectomy with collagen implant, as well as viscocanalostomy.
Antimetabolites, such as mitomycin-C (MMC) and 5-fluorouracil (5-FU), have been used intraoperatively or postoperatively to reduce fibroblast proliferation, especially in eyes with significant risk factors for failure. These risk factors include history of ocular surgery, concomitant vitrectomy, black race, age, uveitis, aphakia and neovascular glaucoma and angle recession. The use of antimetabolites has been particularly effective for cases associated with ocular inflammation and with angle recession.
Trabeculectomy with MMC results in similar or lower IOP and fewer postoperative medications than trabeculectomy with 5-FU. Complications following surgery are similar with the exception of corneal epithelial defects associated with postoperative 5-fluorouracil injections. Wound leaks occur more frequently after trabeculectomy with antimetabolites and are more often associated with MMC.
Other surgical modifications include scleral flap sutures that titrate the IOP in the immediate and early postoperative period. The frequency of ocular hypotony and flat anterior chamber can be reduced. Interrupted or releasable sutures are generally placed at the time of surgery according to various methods. If the IOP increases in the postoperative period, then suture release or laser suture lysis can decrease the IOP to safer levels.
Deep sclerectomy, collagen implant
Deep sclerectomy with collagen implant (DSCI) is a nonpenetrating trabecular surgery undergoing clinical trials. In this procedure, a scleral flap is anteriorly dissected into the peripheral cornea. A second scleral flap is created and is amputated at its base. This technique exposes a scleral bed that allows aqueous to flow directly into the suprachoroidal space through Descemet’s membrane. A collagen implant is placed radially in the scleral bed to prevent fibrotic closure of this outflow passageway. Over a period of about 6 months, the collagen implant is absorbed.
Mermoud and colleagues compared this procedure to trabeculectomy surgery and found that DSCI was as effective as trabeculectomy in reducing IOP (Mermoud A, Schnyder CC, Sickenberg M et al. Comparison of deep sclerectomy with collagen implant. Ophthalmic Surg Lasers. 1999;30:120-125.). Postoperative 5-FU injections or Nd:YAG goniopuncture could improve success rates. Complications following DSCI occurred less frequently than following trabeculectomy, and less ocular inflammation was observed. Significant complications included hyphema, wound leak, choroidal detachment, cataract and failure to reach acceptable IOP, requiring surgical revision.
Viscocanalostomy
Like DSCI, viscocanalostomy is a nonpenetrating trabecular surgery. It was first described by Stegmann and colleagues as an alternative to trabeculectomy. This procedure is somewhat similar to DSCI, but in lieu of a collagen implant maintaining an intrascleral reservoir, a high molecular-weight viscoelastic material is injected into the free ends of Schlemm’s canal to prevent its closure. As the viscoelastic material is absorbed, aqueous can access the outflow pathway. The superficial scleral flap is tightly sutured, and the conjunctival wound is closed.
Recovery from viscocanalostomy occurs more quickly than from trabeculectomy surgery, because there is no penetration into the anterior chamber. Complications following this technique include Descemet’s rupture, iris prolapse, choroidal deroofing, hyphema, filtering bleb and limited hypotony. Whether or not these procedures will demonstrate long-term control of IOP remains to be seen, and further studies are underway.
If there is significant external scarring due to previous ocular surgeries (which may include antimetabolite trabeculectomy), then alternative procedures should be considered. These would include the use of a drainage implant or seton in the case of eyes with poorly controlled IOP but reasonable visual potential. In eyes with poor visual potential (i.e., light perception vision), a cyclodestructive procedure might be more appropriate when other interventions do not adequately reduce IOP.
Postop management of filtering surgery
Optometrists can become actively involved in postoperative management of patients following filtering surgery. It is important to be familiar with the normal postoperative course to determine whether or not complications are serious or expected.
After the first postoperative visit, follow-up of these patients is customized based on the patient’s healing response. Due to this dynamic process, postoperative visits after trabeculectomy surgery are generally more frequent than following cataract surgery. Usually, the patient will be seen at least weekly for the first month and biweekly for the first 3 months. If the IOP and vision are stable, then monthly visits would be indicated for the first 3 to 6 months, and then the patient should be seen every 3 to 4 months thereafter.
Patients should be counseled that vision fluctuation and unstable refraction are normal. Most often, the refraction will stabilize by postop week 8, but recovery of best-corrected visual acuity can be prolonged.
The corneal epithelium may demonstrate defects caused by foreign body tracking (sutures), toxicity to postoperative medications including adjunctive antimetabolite injections or surface irregularities such as dellen. Microcystic edema may be present if IOP is sufficiently elevated, and stromal folds are common. Infolding of the cornea can occur with ocular hypotony. Subconjunctival hemorrhages can cause intra-flap fibrosis and bleb failure if they occur adjacent to the scleral flap. Conjunctival injection is common following surgery and gradually resolves. Telangiectatic vessels over or adjacent to the bleb are a sign of inflammation and often precede loss of bleb function or development of a Tenon cyst.
Evaluating the bleb
The bleb should be evaluated for a number of features. These characteristics should be noted whether they occur on the first postoperative day or in the years following. The extent and location of the bleb can be specified in terms of clock hours (e.g., from 10 to 12 o’clock).
Blebs may be focal, localized or diffuse. Elevation or height can be described as flat, moderately elevated or high. The thickness of the bleb wall can vary from gossamer or transparent to opalescent. Thinner blebs occur more frequently following full-thickness procedures and may exhibit grape-like lobules or a macrocystic appearance. Pallor occurs more frequently in blebs following the application of an antimetabolite and will increase through the normal postoperative course. Minimal vascularity of the bleb is preferred, because pale, avascular blebs tend to be ischemic and vulnerable to wound leaks. Conjunctival microcysts can often be seen on the surface of a well-functioning bleb and represent transconjunctival fluid movement. Pinpoint areas of aqueous leakage indicate transudation or ooze and are rarely problematic.
A full-thickness conjunctival defect will produce a Seidel sign that is most easily observed with the application of 2% sodium fluorescein or a moistened fluorescein strip. Commercial preparations of sodium fluorescein-anesthetic are too viscous and may produce a false-negative result. If the pressure is very low (e.g., 0 or 1 mm Hg), it may be necessary to perform a ‘pressure Seidel’ by exerting mild pressure against the globe to express aqueous through a wound leak. The presence of white cells within the bleb can be a sign of localized bleb infection.
Evaluating the anterior chamber
The anterior chamber should be evaluated for cells and flare. Hyphema is not uncommon and generally resolves without sequelae. Exaggerated inflammatory response in the form of a hypopyon requires immediate referral when associated with other signs of intraocular infection. The central and peripheral anterior chamber depth should be checked and compared to the fellow eye.
An isolated clinical finding of a shallow anterior chamber (i.e., midperipheral iris and corneal touch) can be monitored without intervention, although anterior chamber reformation should be considered if this condition persists longer than 2 weeks. Touch between the crystalline lens or lens implant and the cornea following trabeculectomy surgery constitutes an ocular emergency, requiring immediate referral for anterior chamber reformation before permanent corneal decompensation.
The iris should be evaluated for regularity, for contour and for the patency of the peripheral iridotomy. Lens and vitreous clarity should be noted. The retina should be evaluated for choroidal or retinal detachment in addition to macular edema, retinal folds or striae. Decompression or rebound retinopathy due to the acute decrease of IOP appears as scattered dot and blot hemorrhages in the midperiphery or posterior pole.
Postop manipulation of the bleb
---Trabeculectomy: This patient underwent trabeculectomy with releasable sutures. Postoperative manipulation of the bleb can help maintain bleb function by disrupting fibrosis and can assist in the timing of suture release. The “Traverso maneuver” involves the use of a cotton swab adjacent to the flap to deform the flap and allow fluid to escape. This method is in direct contrast to ocular massage, which involves direct compression against the globe 180° from the flap location.
The bleb should be evaluated quantitatively and qualitatively after performing the Traverso maneuver. If the IOP decreases to an appropriate level, then suture release can be considered; however, if the eye becomes hypotonous, then the bleb is immature, and suture release should be deferred to a follow-up visit.
Postoperative manipulation of the bleb may also be required if an encapsulated bleb or Tenon’s cyst develops within the first few weeks after filtering surgery. The bleb appears to be highly elevated, with a tense dome-like appearance. Conjunctival telangiectasia and vascularization may overlie the Tenon cyst. Topical corticosteroids can inhibit further fibrosis, but with minimal effect.
Ocular massage can be suggested in an effort to stretch the fibrotic wall of the Tenon’s cyst. Aqueous suppressants are also recommended to treat elevated IOP. These therapies can be successfully used to manage an encapsulated bleb and reduce the need for needle revision or surgical intervention.
Bleb-related endophthalmitis
---Macrocystic thin-walled bleb: Thinner blebs occur more frequently after full-thickness procedures and may exhibit grape-like lobules or a macrocystic appearance. Long-term follow-up of filtering surgery requires that comanaging optometrists remain vigilant about late postoperative complications.
The most serious complication of glaucoma filtering surgery is bleb-related endophthalmitis. This condition can develop at any point following surgery. Risk factors for bleb infection include the use of antimetabolites, blepharitis, poor eyelid hygiene, conjunctivitis, bleb leak, cystic thin-walled blebs, inferior filtering bleb and contact lens wear. Systemic conditions, such as diabetes, malnutrition or immunocompromise, have also been implicated.
When the infection is limited to the anterior segment, the condition is called blebitis. As the infection spreads to the vitreous and posterior segment, the condition is called bleb-related endophthalmitis.
Related symptoms
---Tenon cyst: Note the highly elevated, tense, dome-like appearance. Postoperative manipulation of the bleb may be required if this develops within the first few weeks after filtering surgery. The symptoms related to blebitis are milder than those reported with endophthalmitis. Injection, photophobia and discharge gradually increase over a few days. The conjunctival vessels overlying the bleb appear injected, and the bleb may be opalescent with conjunctival epithelial defects. The anterior chamber reaction is minimal, and no vitreous cells are observed. Blebitis is usually related to a limited infection by S. epidermidis or S. aureus. This condition responds well to topical or systemic antibiotic therapy and has a good visual prognosis.