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.
Phaco first
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.
