Combined Surgical Approach Depends on Patient Characteristics
As the population ages and lifespans increase worldwide, a rising number of patients will present with concomitant cataract and glaucoma. These patients face special visual challenges, as their central vision is clouded by cataract and their peripheral vision is relentlessly eroded by glaucoma.
When these patients with concomitant disease require surgery, it is important for the ophthalmologist to make an informed choice regarding the most appropriate surgical approach for each case. This article reviews surgical options available to ophthalmologists for their patients with both cataract and glaucoma, along with some of the factors to consider when deciding which to choose.
RATIONALE FOR COMBINED APPROACH
In patients with both cataract and glaucoma, there are four basic approaches to surgical management: (1) perform cataract surgery only, (2) perform glaucoma surgery followed by cataract surgery, (3) perform cataract surgery followed by glaucoma surgery, or (4) perform a combined cataract and glaucoma surgical procedure. The choice of approach depends on the patient's clinical factors—the degree of glaucomatous damage, the intraocular pressure (IOP), the response to previous medical or laser therapy, the density of the cataract—and the surgeon's level of experience and surgical preference.
Cataract surgery alone can lower IOP by 2 to 4 mm Hg.1,2 In some patients with cataract and mild glaucoma, this option may offer enough IOP control to eliminate some or all of the patient's glaucoma medication regimen. If greater reduction is needed, a combined procedure can lower IOP by 6 to 8 mm Hg.3,4
Additionally, IOP spikes, which may occur after cataract surgery alone, should be avoided as much as possible in eyes with glaucomatous damage. The same risk for IOP spikes applies if cataract surgery is performed first, followed by glaucoma surgery. A combined procedure can reduce the risk of postoperative IOP spikes.
Glaucoma surgery can be performed first, followed by cataract surgery 3 to 6 months after bleb stabilization, to address both diseases; however, visual rehabilitation is delayed, and both risk and cost are increased by returning to the operating room a second time. Also there is the possibility of compromising the working bleb as a result of the second surgery.
Performing glaucoma and cataract surgeries at the same time is the preferable option for many patients.5,6 It combines the advantages of both procedures and avoids many of the risks of performing them separately. It lowers IOP and restores visual function at the same time, provides long-term IOP control, avoids the risk of postoperative IOP spike after cataract surgery, and reduces the risks engendered by performing two separate operations. The disadvantages are that combined procedures are slightly more difficult to perform than individual surgeries and require a longer surgical time.
COMBINATION OPTIONS
Once the surgeon has weighed the advantages and disadvantages and elected to perform combined glaucoma and cataract surgery, he still has a range of options to consider. Again, the choice depends on the patient's clinical factors and the surgeon's comfort level with the different surgical approaches.
For cataract extraction, phacoemulsification is the preferred procedure because it is performed in a closed chamber, minimizing the risk of expulsive hemorrhage or choroidal effusion. For the glaucoma portion of the procedure, there are many choices, including simple iridectomy, traditional trabeculectomy, and newer nonpenetrating filtering procedures.
Peripheral iridectomy. Performed at the time of phacoemulsification, this procedure can be sufficient to lower IOP in some patients with angle-closure glaucoma.
Trabeculectomy. This procedure can be performed with phacoemulsification with a one- or two-site approach.7 In the one-site approach, cataract extraction and IOL implantation are performed through conjunctival and scleral flaps, and the scleral flap is then converted into a filter by sclerectomy and iridectomy. In the two-site approach, superior conjunctival and scleral flaps are created at the beginning of the case, then phaco is carried out through a temporal clear corneal incision, and the filter is completed at the end of surgery (Figures 1 and 2).
Trabeculectomy can also be combined with a microincision cataract surgery technique, such as microphakonit.8 In this procedure, a 0.7-mm phaco probe, irrigating chopper, and instruments for irrigation and aspiration are used to perform the cataract extraction, which is followed by trabeculectomy as described previously (Figure 3).
The use of antimetabolites, particularly mitomycin C (MMC), in conjunction with combined phaco and trabeculectomy is controversial. MMC may prolong the IOP-lowering effect of combined surgery,9,10 and adjunctive MMC use in trabeculectomy has been associated with bleb-related endophthalmitis, hypotonic maculopathy, and late-onset bleb leaks.11-14 These factors should be considered.
Viscocanalostomy. Combined with phacoemulsification, viscocanalostomy can again be performed with either a one- or two-site approach.15 Viscocanalostomy is a blebless, nonpenetrating procedure that facilitates aqueous outflow through Schlemm's canal and collector channels. In this procedure, under retrobulbar or peribulbar anesthesia, a conjunctival flap is created, followed by two scleral flaps, one superficial and one deeper. The 5 x 5-mm superficial flap is approximately 200 µm thick, and the inner 4 x 4-mm flap approaches the level of the choroid. The inner flap dissection is advanced toward the limbus to expose Schlemm's canal, which is then deroofed, and the flap is further advanced 1 mm into the clear cornea with blunt dissection. The flap then excised. A Descemet's window is created, allowing aqueous egress into the intrascleral space. A special cannula is used to inject high-viscosity viscoelastic into the openings in Schlemm's canal in each direction, opening up the canal and preventing its collapse and scarring postoperatively. When the flow of aqueous through the Descemet's window into the intrascleral lake has been confirmed, the superficial flap is sutured tight, and viscoelastic is injected under the flap to prevent collapse of the space.
THROUGH A SUPERIOR SCLERAL TUNNEL
When this procedure is combined with cataract surgery in a single-site approach, the cataract surgery is performed through a superior scleral tunnel, and the scleral flaps are subsequently created at that site. In the two-site approach, cataract surgery is performed temporally.
Deep sclerectomy. Another blebless, nonpenetrating procedure, deep sclerectomy can be combined with phacoemulsification.15 The procedure is similar to viscocanalostomy, with creation of superficial and deep scleral flaps and the excision of the deeper flap to create an intrascleral space and a Descemet's window. Differences include the use of a smaller superficial flap (4 x 4 mm) and less watertight closure of the flap to allow fluid to flow into the sub-Tenon's space. Some surgeons insert collagen or hyaluronic acid implants into the scleral lake or inject high-viscosity viscoelastic into the lake to maintain the space and delay healing.
In this nonpenetrating procedure, antimetabolites can also be applied to delay healing and prolong the IOP-lowering effect. If additional lowering of IOP is desired after deep sclerectomy, the Descemet's window can be perforated ab interno using a Nd:YAG laser.
The one- and two-site approaches to combining deep sclerectomy with cataract surgery are similar to those with viscocanalostomy.
Each of these procedures has advantages and disadvantages that must be considered when selecting the best choice for the patient. Penetrating procedures tend to have a greater pressure-lowering effect than nonpenetrating procedures. On the other hand, nonpenetrating procedures have an added degree of safety because they avoid postoperative complications, such as hypotony, uveitis, and endophthalmitis. Additionally, bleb-related complications, such as scarring, patient discomfort, and blebitis, are avoided.
SELECTING THE PROCEDURE
The cataract and refractive surgeon should keep these factors in mind when deciding what procedure to select for a patient with concomitant cataract and glaucoma or whether to refer that patient to a subspecialist colleague for a procedure outside of his comfort zone. With the many variations of combined techniques available to surgeons, it is possible to achieve optimal visual and IOP-lowering results simultaneously for our patients with cataract and glaucoma.
Amar Agarwal, MS, FRCOphth, FRCS, is the Director of Dr. Agarwal's Group of Eye Hospitals, Chennai, India. Dr. Agarwal may be reached at tel: +91 44 2811 2811; fax: +91 44 2811 5871.
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