Combined phacoemulsification and trabeculectomy surgeries tend to amount
to less than the sum of their parts in terms of intraocular pressure
reduction. A better option is to perform the cataract surgery first and
then, around six months later, perform the trabeculectomy if necessary,
said Thierry Zeyen MD, University Hospitals, Leuven, Belgium, at the
XXIX Congress of the ESCRS.
Prof Zeyen noted that phacoemulsification on its own can lower IOP by around 6.0 mmHg in eyes with angle-closure glaucoma, and by 1.0 to 3.0 mmHg in eyes with primary open-angle glaucoma (POAG), as it does in eyes with no glaucoma at all, even after two years.
"We don't really know for sure what the mechanism of action is behind this IOP reduction. Probably it's the deepening of the anterior chamber, the opening of the angle and the stretching of the trabeculum via the contraction of the capsular bag," Prof Zeyen said. On the other hand, combined phacoemulsification and trabeculectomy procedures reduce IOP less than trabeculectomy alone, he pointed out. That is, a phaco-trabeculectomy procedure achieves an IOP reduction of only 5.0 to 7.0 mmHg, compared to an average IOP reduction of 9.0 to 12 mmHg following trabeculectomy alone, he noted.
"Trabeculectomies work less well in combined procedures simply because of the long-lasting (often subclinical) inflammation. Phacoemulsification also compromises the function of pre-existing blebs, even with small incision clear corneal procedures, usually resulting in an increase of 1-2 mmHg. Phacoemulsification also makes blebs flatter and a little bit more vascularised, probably due to a prolonged subclinical inflammation after phaco," Prof Zeyen said.
Phacoemulsification is generally more difficult in glaucoma patients because of such features common to eyes with the disease, such as small pupils and pseudoexfoliation. In addition, the postoperative refraction is less predictable in combined surgery because of unforeseeable anterior chamber depth, especially early after surgery or after needling procedures resulting in a (temporary) myopic shift. Finally, a postoperative shallow anterior chamber may result in a subluxation of the IOL.
Prof Zeyen noted that the European Glaucoma Society's current guidelines state that, "the success rate of combined phacoemulsification and filtration surgery is not as favourable as filtration surgery alone," and that "there is no evidence to support a generalised switch from sequential to combined surgery." He added that his own recommendation is to perform phacoemulsification first, to avoid damaging a filtering bleb, and then wait for six months, by which time the inflammation will have largely dissipated, before performing the trabeculectomy. He noted that in some cases, particularly those with angle-closure glaucoma, further IOP reductions may not be necessary after phacoemulsification. Furthermore, among eyes in which IOP remains elevated, trabeculectomy may not be necessary because the cataract procedure will have greatly facilitated the performance of laser trabeculoplasty procedures, and some eyes may obtain an adequate response from topical medications.
At the same time, there remain some cataract patients within whom trabeculectomy should be performed first, Prof Zeyen maintained. Those cases include patients whose visual function is threatened by such factors as extreme IOP elevation, advanced optic disc cupping or visual field defects close to the point of fixation. Phacoemulsification should then be postponed for at least six months in order to protect the filtration bleb. However, a phaco-trabeculectomy is a valid option in patients who insist on undergoing only one surgical procedure. In those patients, it is advisable to spare one quadrant of conjunctiva in case a second trabeculectomy is necessary in the future, he added.
Prof Zeyen noted that studies have shown that in eyes with angle-closure glaucoma and <180° of goniosynechiae, phacoemulsification reduces IOP, by around 6.0mm while laser iridotomy reduces IOP by only 3.0 mmHg on average. He added that a prospective randomised clinical trial (RCT), called the EAGLE study, is currently carried out to evaluate whether early phacoemulsification of the crystalline lens will provide better results than conventional stepped approach (peripheral iridotomy -> medical treatment -> glaucoma surgery) in the treatment of primary angle-closure glaucoma.
New combined procedures
Novel ab interno glaucoma procedures can easily be combined with small incision phacoemulsification. iStent (Glaukos) and Trabectome (Neomedix) combined with phacoemulsification can decrease the IOP with 3 to 5 mmHg. This can be enough to control the pressure in some patients and to reduce the need for postoperative medication. A third generation iStent is currently under study and it might be that more than one stent needs to be implanted to improve the results, Prof Zeyen said.
The combination of Cypass (Transcend Medical), a micro-stent introduced gonioscopically to promote uveo-scleral outflow, or Hydrus (Ivantis), a new Schlemm's canal scaffold, with phaco-surgery may have a more significant IOP lowering effect but long-term results are not yet published, he added. Canaloplasty (iScience) can be combined with phacoemulsification as well but is a more challenging surgery, needing a separate conjunctival and scleral dissection. However, if a tension suture can be placed, a considerable IOP decrease (around 10mmHg) might be expected. Late onset cheese wiring has been described, causing the suture to become exposed in the anterior chamber, according to Prof Zeyen.
Endoscopic photocoagulation is another procedure that can produce good IOP reductions when used in combination with phacoemulsification. It can be performed directly after completion of cataract removal. However, since it is a procedure which blocks aqueous inflow, it is inherently less preferable than procedures that enhance aqueous outflow, Prof Zeyen added. Those above mentioned new combined procedures are promising but RCT's, conducted independently from the manufacturers, and comparing combined phacoemulsification and novel procedures with phaco-trabeculectomy or trabeculectomy alone are necessary to assess their long-term safety and efficacy, Prof Zeyen concluded.