Coincident cataract and glaucoma surgery

Published on 08/03/2015 by admin

Filed under Opthalmology

Last modified 08/03/2015

Print this page

rate 1 star rate 2 star rate 3 star rate 4 star rate 5 star
Your rating: none, Average: 0 (0 votes)

This article have been viewed 1959 times

CHAPTER 36 Coincident cataract and glaucoma surgery

Introduction

The management of coincident cataract and glaucoma presents common and challenging decisions for the ophthalmic surgeon. Emerging data and technological advances continue to shape the approach to coexisting cataract and glaucoma13. Historically this generally involved sequential surgery with initial glaucoma surgery followed by cataract extraction months later when the intraocular pressure (IOP) was controlled and the bleb had matured. The rationale for the sequential approach was based on the poor success rate of combined extracapsular cataract extraction (10 mm scleral incision) and glaucoma filtration surgery. While the advantage of the sequential approach is the high success rate of primary filtration surgery, the disadvantages are that the patient undergoes at least two operations, prolonged poor vision, and the risk of bleb failure after the cataract operation. As techniques improved with clear cornea small incision phacoemulsification and guarded filtration surgery with anti-metabolites, glaucoma surgeons began to reconsider combined rather than sequential surgery4,5. As new procedures such as canaloplasty, ab interno trabeculectomy (Trabectome), endoscopic cyclophotocoagulation, and trabecular meshwork stents evolve, there may be a decreased need to perform traditional filtering procedures including glaucoma drainage devices. Modern techniques of clear cornea small incision cataract surgery alone lower IOP and may be the preferred initial step to manage most cases of coexisting glaucoma and cataract68. However, combined surgery remains an important option for select cases with advanced glaucoma or markedly elevated IOP. We describe techniques for the surgical treatment of coexisting cataracts and glaucoma.

Indications

Traditional indications for combined cataract and glaucoma surgery are uncontrolled glaucoma that requires surgery in a patient with visually significant cataract, or the need for cataract extraction in a patient with advanced or poorly controlled glaucoma. The mere coexistence of glaucoma and cataract is not in itself an indication for combined cataract and glaucoma surgery9. Mild to moderate glaucoma that is controlled well on medication is usually best managed by cataract extraction alone. In these instances, it is best to perform the cataract extraction with a conjunctival sparing approach such as a clear corneal incision. If the glaucoma later becomes uncontrolled, a glaucoma procedure can be performed readily. Small incision cataract extraction techniques have made the ‘cataract extraction first, glaucoma surgery later if necessary’ approach more feasible. (Table 36.1)7.

Table 36.1 Options for surgical management of coincident cataract and glaucoma*

Trabeculectomy first; cataract extraction later Combined cataract extraction–trabeculectomy/tube shunt Cataract extraction first; glaucoma surgery later if needed
Consider if employing large incision 10–11 mm extracapsular cataract extraction   Mild to moderate glaucoma, well-controlled intraocular pressure with additional medical options available
  Far advanced glaucoma Untreated or medically controlled ocular hypertension with additional medical options available
  Patients on MTMT or patients intolerant to medications
Patients poorly compliant with medications
Low target intraocular pressure
 

MTMT = maximally tolerated medical therapy.

* Assumes visually significant cataract.

Small incision approach.

Conjunctival sparing technique – preferably clear cornea.

The goals of combined cataract and glaucoma surgery vary from patient to patient depending on both the severity of the cataract and that of the glaucoma. For example, a patient with advanced, but non-progressive glaucoma whose IOP is well controlled with minimal medication may require only careful observation or additional short-term medications following cataract extraction. In such patients, it is possible to avoid the problems associated with glaucoma surgery and still get the patient through the surgery without further visual loss. Conversely, a patient with progressive glaucoma and poorly controlled IOP often requires more aggressive pressure lowering and a long-term solution to achieve optimal IOP. Although rare in developed countries, extremely dense, brunescent cataracts that cannot be removed with standard clear cornea phacoemulsification techniques may require extracapsular cataract extraction. In these cases surgeons should place extracapsular incisions strategically to allow for future glaucoma procedures. Management of individual patients differs according to the specific goals of treatment and likely outlook for each eye.

Anesthesia

Combined cataract and glaucoma procedures can be performed with retrobulbar, peribulbar/subTenon’s, or topical anesthesia. Topical anesthesia with subconjunctival supplementation is adequate for the majority of cases. While local subconjunctival injection of anesthetic is adequate for most cases, if additional anesthesia or akinesia is needed a small incision can be made in the conjunctiva and large bore blunt tip cannula can be passed along the sclera posteriorly into the muscle cone to perform an intraoperative ‘subTenon’s’ block. Prior to administering anesthesia, intravenous sedation may be employed. A combination of agents with ultra-short-acting sedative and amnesiac properties such as methohexital 20–30 mg (Brevitol, Jones Medical), midazolam HCl 1 mg (Versed, Roche Laboratories), or alfentanil 250 µg (Alfenta, Janssen Pharmaceutica Inc.) may be given intravenously to reduce anxiety and pain. This combination of medications provides several minutes of deep sedation during which the block can be given without pain or patient awareness. The block consists of 2% xylocaine (Lidocaine, Astra) without epinephrine. Hyaluronidase (Wydase, Wyeth-Ayerst) is generally not necessary but can be used. In most cases, bupivacaine HCL (Marcaine, Sanofi Winthrop) 0.75 is not needed, but it may be used if the anticipated surgical time is to be longer than 1 hour. Within minutes after administration of the block, the patient is aware and able to cooperate with the surgeon. During the procedure only light sedation or none at all will be required. It is important to control the patient’s systemic blood pressure during the surgery for many reasons, but primarily to reduce the risk of suprachoroidal hemorrhage. After the peribulbar or retrobulbar block, it may be helpful to apply pressure to the globe for several minutes, using digital compression over a closed eyelid or a mechanical device such as a Honan balloon, or a mercury bag. However, external compression strategies, while common with larger incision extracapsular techniques, are less commonly utilized in the small incision phacoemulsification era and are generally unnecessary.

The theory behind the use of external compression is that the pressure prevents bleeding into the retrobulbar space, facilitates diffusion of the anesthetic solution into the orbital tissues, and softens the eye, making the surgery safer9. As the risk of applying external compression to eyes with badly damaged optic nerves is not clear, it is advisable to limit the magnitude and duration of ocular compression to 20–30 mmHg and 5 to 10 minutes in such patients.

For patients with markedly elevated IOP, preoperative intravenous mannitol will minimize the abrupt change in intraocular pressure following the incision. The need for mannitol to suppress IOP is infrequent, however, and depends on the clinical circumstance and the general health of the patient, especially from a cardiopulmonary perspective. Osmotic agents like mannitol are preferred over aqueous suppressants because they dehydrate the vitreous, thereby reducing vitreous volume and softening the eye. Conversely, aqueous suppressants retard aqueous production during the early perioperative period. At least theoretically, reduced aqueous outflow through the new filter could exacerbate hypotony and later bleb fibrosis.

Preoperative considerations

Preoperative clinical assessment is vital. Gonioscopy should be performed. The conjunctiva should be examined carefully. Topical steroids should be administered if the conjunctiva is inflamed10. The surgeon should carefully examine the eye for the presence of exfoliative material, which can be associated with a more aggressive postoperative inflammatory response, weakened zonular fibers, and poor pharmacologic dilation11,12. It is important to note the pupillary response to pharmacologic dilatation. If dilatation is poor and pupil manipulation is anticipated, the patient should be informed, as such manipulation may result in anisocoria or pupillary distortion. This precaution is particularly important for younger patients with light irides in whom the cosmetic effect of anisocoria or irregular pupil will be more apparent. Depending on the surgical procedure, patients should be educated preoperatively about the specific features of the postoperative period with combined cataract and glaucoma surgery, which may require frequent doctor visits and prolonged visual recovery, beyond that expected for standard cataract surgery in non-glaucomatous eyes.

Surgical technique

Small incision cataract extraction techniques have vastly improved treatment of cataracts in patients with glaucoma. Standard cataract surgery is described in great detail in Chapter 8. Rarely, other techniques, such as extracapsular or intracapsular extraction may be necessary. Surgeons should either be competent in these other techniques or refer specific cases9. When possible, a clear cornea incision is preferable to preserve the conjunctiva and the trabecular meshwork for any future glaucoma procedures. Current techniques for combined glaucoma surgery using small incision phacoemulsification will be described here.

Cataract surgery alone as a glaucoma procedure

Studies following cataract extraction in the 1970s and 1980s demonstrated minimal reduction of IOP1315. However, advances in surgical technique and intraocular lens technology means that these results probably don’t apply today. As extracapsular surgery became the standard, studies began to demonstrate an average lowering of IOP by 2–4 mmHg1618. Studies that stratify patients based on preoperative IOP clearly demonstrated that patients with higher preoperative IOP enjoy the greatest reduction of IOP after cataract surgery and that IOP can be controlled in 20% of patients with cataract surgery alone1,1921. Long-term studies have shown a drop in IOP of about 3 mmHg with 75–85% of patients maintaining an IOP reduction up to 10 years7,8,2225.

The method of cataract extraction may influence the reduction in IOP. Phacoemulsification (particularly clear cornea phacoemulsification) seems to lower IOP more than manual extracapsular cataract extraction16,17,26,27. PXF patients may have an even greater long-term decrease in IOP than POAG patients, even though IOP often rises in the immediate postoperative period2830. Factors that have been identified to be important in the perioperative control of IOP include pressurization of the eye at the time of surgery, immediate postoperative medications, and viscoelastic type3134. The surgeon should remove all viscoelastic carefully and ensure that the eye is not over-pressurized at the time of surgery. Despite limitations, cataract surgery seems to be emerging as a safe way to lower IOP in patients with mild to moderate glaucoma while avoiding the morbidity of traditional glaucoma surgery.

Results of combined cataract extraction and trabeculectomy

Overall, combined phacotrabeculectomy and trabeculectomy alone have similar outcomes. A couple of studies have compared phacotrabeculectomy with trabeculectomy alone. In one retrospective study 85 eyes that underwent trabeculectomy were compared with 105 eyes that had had phacotrabeculectomy. The mean postoperative IOP was similar in both groups at all time points up to 2 years. However, the mean IOP decrease from baseline was higher in the trabeculectomy alone group35. Another study showed a similar success rate of 70% in patients having either combined phacotrabeculectomy or trabeculectomy alone36. In a retrospective study of 60 eyes that underwent phacotrabeculectomy, 95% achieved an IOP of 21 mmHg or less with or without medication, 50% of eyes had an IOP less than 15 mmHg, and 57% of eyes had a 30% reduction in IOP. Best corrected vision of 20/40 or better was maintained in 87% of eyes37.

A prospective study of phacotabeculectomy looked at 304 consecutive eyes over 1 year showing a mean IOP of 15.5 mmHg with nine eyes requiring a reoperation38. Two studies comparing one-site and two-site phacotrabeculectomy showed similarly safety and IOP control over a 3-year follow-up period in patients with POAG and pseudoexfoliative glaucoma (PXFG) with a mean postoperative IOP of 15 mmHg in all groups39,40.

Single-site combined filter and cataract extraction

When performing combined cataract extraction and filtering surgery, a one-site or two-site incision may be used. In a one-site approach the entire procedure can be performed through the conjunctival and scleral incisions used in standard trabeculectomy mimicking a guarded filtration procedure as described in Chapter 354143. Either a limbus-based or fornix c based conjunctival flap can be used and the merits of each technique are discussed in Chapter 219.

Anti-metabolites are typically used in combined cataract and filtration surgery since the goal of the procedure is a long-term functioning bleb. Mitomycin C (MMC) is applied to the proposed filtration site following dissection of the conjunctival flap (Fig. 36.1A) (see Chapter 25) with saturated pledget tips. The conjunctival incision should be protected from MMC exposure (Fig. 36.1B,C; Fig. 36.2). A complete discussion regarding the use of anti-metabolites in filtration surgery can be found elsewhere, but the role of MMC in combined cataract and glaucoma surgery is less clear5,4449. Many surgeons believe the potential benefits of MMC in conjunction with meticulous surgical techniques outweigh the risks; others disagree. 5-fluorouracil can also be used safely for phacotrabeculectomy50.

image

Fig. 36.2 A 3.5 mm scleral flap is dissected. The dissection is carried anteriorly well into clear cornea.

From Samuelson TW. Management of coincident glaucoma and cataract. Curr Opin Ophthalmol 1995;6:14–21. Copyright Rapid Science Publishers.

The scleral flap is identical to that used in standard guarded filtration procedure. Alternatively, some surgeons modify the scleral flap in combined glaucoma surgery to mimic the scleral tunnel approach of standard cataract surgery. The size and shape of the scleral flap are quite varied among surgeons yielding equally effective results (Fig. 36.3). A paracentesis tract is then performed using a no. 75 blade to facilitate two-handed phacoemulsification.

image

Fig. 36.3 If a 5.5 mm polymethyl methacrylate intraocular lens is used, the scleral flap is larger, measuring 5 mm at the limbus.

From Samuelson TW. Management of coincident glaucoma and cataract. Curr Opin Ophthalmol 1995;6:14–21. Copyright Rapid Science Publishers.

Buy Membership for Opthalmology Category to continue reading. Learn more here