Deferring PI in filtering surgery does not increase
By Cheryl Guttman
ORLANDO, FL - With small modifications in filtering surgery technique,
both trabeculectomy and phacotrabeculectomy can be performed safely
and effectively in many eyes without routine peripheral iridectomy
In a retrospective study, researchers at the John Moran Eye Centre,
University of Utah, Salt Lake City, US reviewed all cases of trabeculectomy
and phacotrabeculectomy performed by three glaucoma surgeons between
January 1998 and August 2000.
They extracted data on patients' eyes aged 40 years and older diagnosed
with primary open angle glaucoma, pseudoexfoliation glaucoma or
primary angle closure glaucoma and a minimum postoperative follow-up
of six months.
The investigators divided the eyes that underwent filtering surgery
alone or combined with phacoemulsification into two groups according
to whether or not a PI was performed. They then compared the data
for development of complications and intraocular pressure (IOP)
In the phacotrabeculectomy group, PI was performed only if there
was significant iris prolapse. There were 38 eyes in the series
with a PI and 120 eyes without.
Among eyes undergoing trabeculectomy alone, PI was performed routinely
in the presence of angle closure glaucoma, hyperopia, a short axial
length (less than 22.5 mm) or if there was significant iris prolapse.
The study included 36 eyes that had trabeculectomy with a PI and
76 eyes that had the filtering surgery without a PI.
A 24-month follow-up analysis showed that safety and efficacy in
both the trabeculectomy and phacotrabeculectomy groups was as good
or better in eyes not undergoing PI.
There were no complications potentially related to lack of a PI,
for example pupillary block or iris incarceration to the internal
Moreover, avoiding a PI reduced the risk of postoperative hyphaema
and in the phacotrabeculectomy group was associated with less postoperative
IOP control over time was generally comparable in eyes with as opposed
to without a PI, although there was a trend for the filtering surgery
success rate to be higher in eyes without a PI, Ike K. Ahmed MD
Dr Ahmed reiterated that a PI has been considered an essential part
of filtering surgery because it can relieve and even prevent pupillary
block as well as prevent iris incarceration into the internal ostium
of the trabeculectomy.
Furthermore, it was felt to be mandatory when filtering surgery
was combined with cataract removal using intracapsular or extracapsular
However, PI can potentially be associated with a number of complications
and the question has been raised that it might even reduce the success
rate of trabeculectomy and increase the risk of posterior capsule
opacification (PCO) after phacotrabeculectomy secondary to disruption
of the blood-aqueous barrier and induction of inflammation and flare.
"Our preliminary findings suggest that it may not be necessary
to perform a PI routinely in eyes undergoing filtering surgery alone
or combined with phacoemulsification and that it may in fact be
beneficial to defer the PI in selected low risk eyes," he reported.
he cautioned that this study did not address eyes with secondary
glaucoma. He said that a PI is likely to be needed when performing
trabeculectomy for phakic eyes with angle closure glaucoma and in
hyperopes with a shorter axial length.
In addition, Dr Ahmed emphasised that it behoved the surgeon to
perform an iridectomy if significant iris prolapse occurs intraoperatively,
if there is premature entry into the anterior chamber and in nanophthalmic
Rates of postoperative hyphaema and increased inflammation in the
PI group were significantly higher than among eyes undergoing trabeculectomy
without a PI.
Shallow anterior chamber was encountered more often in the non-PI
group compared to eyes having surgery with a PI, although the difference
was not statistically significant.
Dr Ahmed emphasised that when a PI is deferred, the approach to
surgery must be modified using strategies that will increase the
distance of the ostium from the iris and reduce the chance of early
postoperative shallowing of the anterior chamber.
Those principles are illustrated by the technique used by the Moran
Eye Centre surgeons.
The procedures were performed under topical or retrobulbar anaesthesia
and began with the creation of a fornix-based conjunctival flap.
Then a 4.0 mm x 3.0 mm rectangular or trapezoidal scleral flap was
fashioned with the dissection taken relatively far anteriorly into
clear cornea, past the vascular arcades.
If indicated, an antimetabolite soaked sponge was then applied under
the scleral and conjunctival flaps. After irrigation with a balanced
salt solution, the anterior chamber was entered.
"Creation of a fistula anteriorly in clear cornea increases
the distance between the ostium and the iris and creates a valve-like
effect, reducing the likelihood of anterior chamber shallowing,"
Dr Ahmed explained.
Next, a Crozafon punch was used to create a 1.0 mm x 2.0 mm sclerostomy.
Two 10-0 nylon sutures were placed as slipknots and their tension
was adjusted to allow a slow ooze from the scleral flap.
Careful intraoperative titration of aqueous flow through the scleral
flap helps avoid early postoperative shallowing of the anterior
chamber, and that goal can also be facilitated with the use of early
suture lysis or releasable sutures, he noted.
Additional sutures were used if needed and the conjunctiva was closed
with a running horizontal mattress suture using 10-0 Vicryl. Some
patients were prescribed cycloplegics to use postoperatively for
In eyes undergoing combined surgery, a two-site approach was used
with implantation of a polyacrylic foldable posterior chamber IOL.
Viscoelastic was removed from the anterior chamber after the scleral
sutures were placed.