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Corneal Trabeculectomy
Ayman Nassar, Abdalla Al Sawi, Mohamed Al Deeh, Hani Salem, and
Mohamed Abd Rabo.
Puropse: To evaluate a modified trabeculectomy technique for glaucoma
filtering surgery through a clear corneal flap without performing a conjunctival
incision.
Methods: The procedure was performed on 27 glaucomatous eyes with
uncontrolled TOP. A corneal flap 2 x 3 mm was raised and a sclera! pocket was
dissected 2 to 3 mm posteriorly . The subconjunctival space was entered with a
cystitome and a fragment of the floor of the scleral pocket was excised using a
Kelly Descemet s membrane punch. The anterior chamber was entered at a
limbal incision and iridectomy was performed. Corneal flap was closed with two
separate 10-0 nylon sutures.
Results: At 6 month the mean TOP decreased from 32.65mm Hg
preoperatively to 12.93 mmHg. 88% of the eyes had an TOP less than or equal to
18 mm Hg without medication.
Conclusion: Corneal trabeculectomy showed as a relatively as a traumatic
filteration procedure producing diffuse persistent conjunctival blebs and adequate
control of TOP.
BULL. OPHTHALMOL. SOC. EGYPT, 1999; VOL. 92, NUMBER 3, 657-660
Success of glaucoma filtering surgery depends
on the maintenance of a patent fistula connecting the
anterior chamber of the eye and the subconjunctival
space. Scarring at the conjunctiva-episclera interface
represents the most common cause of filteration
failure and subsequent elevation of the TOP .
Minimizing surgical trauma is believed to decrease
postoperative scarring .
Cairns in 1985 described a trabeculectomy
technique through a clear corneal incision avoiding
the conjunctiva and Tenon s capsule. Inspite of
reporting initially good results, poor results have
been obtained by other authors who used his
technique ( Keiler and Moltino, 1985, Ali et al., 1990
, and Taha, 1990 ). The technique did not entail a
direct communication between the created internal
fistula and the conjunctival space but relied upon the
ostia of the scleral perforating vessels to provide
access to subconjunctival space .
Van Buskirk, (1992) and later Cioffi and Van
Buskirk, (1993) described a modification to Cairns
technique by creating an external fistula that
communicates directly to the subconjunctival space.
In this article, we review the results of 27 glaucoma
eyes who were operated upon by the modified
technique for corneal trabeculectomy.
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Subject and methods
The study was conducted on 27 eyes of 18
glaucoma patients ( 8 men and 10 women) who were
submitted for glaucoma surgery due to uncontrolled
TOP or deteriorating visual field loss despite maximal
tolerated medical treatment. As regards the type of
glaucoma, 14 eyes had chronic angle closure
glaucoma, 11 eyes had chronic open angle glaucoma
and 2 eyes had pseudoexfoliation s yndrome
associated with glaucoma. Mean age of the patients
was 54.13 years (range 29 to 73 years).
Technique :
Fixation suture was taken through superior rectus
muscle to rotate the eye downwards, the upper nasal
or upper temporal quadrant was chosen for surgery,
only in two cases the operation site was at 6 o'clock
meridian. A partial-thickness trapezoidal flap 2 mm
in wide at the corneal side and 3 mm at the limbal
base was made using a super blade. A spatula blade
was then used to dissect the flap at approximately
1/3-1/2 corneal thickness. Dissection was continued
Corneal Trabeculectomy, Ayman Nassar et al
posteriorly 2-3 mm beyond the cornea-scleral
junction to fashion an intrastromal scleral pocket .
An irrigating cystitome formed by a 27-gauge needle
bent over its tip and mounted on a syringe containing
normal saline was introduced into the intrascleral
pocket till it reaches its posterior end, then rotated
90° superiorly so that the bevelled tip pierces the
roof of the sclera] pocket and enters the
subconjunctival space. Saline was then injected to
raise the conjunctiva and form a subconjunctival
bleb. The incision was then enlarged by a horizontal
side-to side movement of the cystitome. At the
anterior end of the scleral pocket, a fragment
approximately 1.5 x 1.0 mm of the its floor was
excised using the Kelley Descemet membrane punch,
this creates an external fistula from the
subconjunctival space to the intrascleral pocket. An
ab-externo stab incision, 2 mm in length, was made
to enter the anterior chamber at the anterior extent of
the surgical blue zone under the corneal flap. Two
bites were taken from the posterior lip of the incision
using the Kelly Descemet membrane punch to create
the inner part of the fistula. Peripheral iridectorny
was then performed and the corneal flap closed by
two 10-0 nylon sutures at its anterior end. Sometimes
two additional sutures were needed to secure the flap
at its base. The anterior chamber was formed by
injecting saline through a previously made limbal
stab incision. Postoperatively the patients were given
a combination of neomycin, polymyxin, and
dexamethasone (Maxitrol eye drop four times daily,
and cycloplegic two times daily . Topical steroids
were continued for approximately six weeks during
which the dose was tapered gradually
Examinations were carrided on the immediate
postoperative day and for the next two days to
evaluate the inflammatory reaction of the eye,
anterior chamber depth, filteration bleb, lop, and
fundus examination . Visual acuity was measured at
later follow-up visits . Further examinations were
done at weekly intervals during first month
postoperatively , and monthly intervals later.
Results
All cases received a minimum follow-up of 3
months, 15 cases showed up to 6 months. The
surgery was considered successful if the TOP was 18
mm Hg or less at 3 month visit without antiglaucoma
medication The mean [OP preoperatively was
32.65±7.24 mmHg. At one week lOP ranged from 414 trim Hg with a mean of 7.51±2.9 mmHg. At 2
weeks, the mean TOP was 10.29±2.41 mmHg. At 1,3
and 6 months the mean lOP remained almost stable
at approximately 12 mmHg .
Table (1) shows the mean TOP at the successive
follow-up visits . Eighty-eight percent of the eyes had
10P less than or equal to 18 mmHg without
medication at the end of three month postoperatively.
Three cases (3/27) failed to achieve the desired TOP
level throughout the follow-up period .
Table (1) : Comparing preoperative and postoperative lOP
KW
10P
Range (mmHg)
Mean ± SD
No. of eyes
Preoper. [OP
27
22-64
32.65 ± 7.25
One week
27
0-14
7.51 ± 2.94
2 weeks
27
4-16
10.29 ± 2.41
1 month
27
9-27
12.16 ± 2.11
3 month
27
10-22
12.26 ± 2.43
6 month
15
10-16
12.93 ± 1.91
One case was controlled medically with single
topical medication (Timolol) and 10P was reduced to
approximately 15 mmHg and remained so thereafter.
The other case did not respond to reinstitution of
medical therapy and digital pressure, and underwent
a revision of the corneal trabeculectomy at the same
site, by removing adequate episcleral tissue to
enhance filteration through the originally made
658
fistula. The TOP after two months was 10 mmHg
without medication. The third case was complicated
by an infected bleb 4 months after surgery.
Clinically the filteration blebs were typically low
and diffuse covering one to two quadrants. The blebs
were seen well formed throughout follow-up period
with occasionally apparent cystic changes. No
BULL. OPHTHALMOL. SOC. EGYPT, 1999; VOL. 92, NUMBER 3
Table (2) : Summerizes the operative and postoperative complications.
Complication
Number
Perecent
Operative :
2
8
1- Tandvertent injury to corneal flap.
2
8
1- Hypherna .
7
26
2- Shallow A.C.
16
59
3- Flat A.C.
2
8
4- Hypotony.
2
8
5- Choroidal effusion.
2
8
6- Anterior uveitis.
3
11
7- Wound leak .
-
0
8- TOP increase.
2
8
1- Infected bleb
1
4
2- TOP increase .
3- Persistent hypotony
1
4
1
4
2- Iandequate excision of sclera] tissue .
Early postoperative :
Late postoperative :
encapsulated blebs have developed. Transient
corneal edema, at the site of the corneal flap was
commonly seen in the early postoperative period and
tend to resolve subsequently. Epithelial defect over
the corneal flap was noticed in one case which was
complicated with inadvertant damage to the corneal
flap during surgical manipulations.
As regards the encountered complications,
bleeding from the sclera] bed at the time of dissecting
the sclera] pocket or when rotating the cystitome was
the main distressing problem during surgery, this was
managed by gentle compression. Mild hyphema seen
in the first day following surgery occurred in seven
cases and resolved spontaneously over few days.
Shallow anterior chamber on the first postoperative
day was commonly observed in nearly all cases and
reformed within 2-3 days with simple patching and
routine postoperative treatment. Two cases, however,
remained shallow for 3-4 weeks due to visible
choroidal detachment. The latter managed
conservatively and disappeared after 4 weeks. No
wound leak was observed in any case. Persistant
hypotony was encountered in one case and was
attributed to an over functioning bleb that encircled
the entire limbus, causing bogginess of the bulbar
conjunctiva and ocular discomfort. This case, despite
persistent low TOP had a final visual acuity of 6/12,
unchanged from his preoperative examination. In
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general, keratometric readings obtained for all cases
before and after surgery did not show significant
changes.
Discussion
Corneal trabeculectomy, using Van Buskirk
technique, showed in our study a successful control
of TOP in 88.8% at the end of the 3 and 6 months
follow-up. The reported success rate for conventional
trabeculectomy when performed as initial surgery
range from 50-98% (Watson et al., 1981).
Van Buskirk (1992) in his series of 5 glaucoma
patients at high risk for failure of glaucoma filtering
surgery achieved a 100% control of TOP, three of this
cases, however, were treated postoperatively with
subconjunctival 5-FU in divided doses. Cioffi and
V a n B u s k i r k , ( 1 9 9 3 ) p e r fo r m e d c o r n e a l
trabeculectomy on 20 eyes and reported success rate
of 85% (17 of 20 eyes) at 3 month follow-up
examination. The mean TOP at 3 month was 13.9
mmHg compared to 12.26 mmHg in our series,
whereas at 6 months the mean IOP was 11,0 mmHg
compared to 12.93 mmHg in our study .
Lerner,
(1997) described
a modified
trabeculectomy technique different from that of
Corneal Trabeculectomy, Ayman Nassar et al
Cairns, (1985) and Van Buskirk (1992) in that he did
not dissect a corneal flap, instead he preformed a 2.5
mm conjunctival periotomy without cutting the
Tenon s capsule, followed by partial thickness limbal
incision and then dissected a sclera) pocket for 2 -3
mm posteriorly. As in the Buskirk technique, the
subconjunctival space was entered with a cystitome
passed through the scleral pocket. He reported a 90%
success rate (27 of 30 eyes) in his series at 6 month
postoperatively without medication .
Filtering blebs were typically low and diffuse
and were seen formed in all successful case throught
the follow-up period. They developed a hypovascular
appearance with multiple microcystic changes of
filteration. No encapsulated blebs were seen. Similar
findings were reported by Cioffi and Van Buskirk
(1993) and Lerner (1997) .
Hypotony with flat anterior chamber was
ob s e r ve d in 2 c a s e s c omp lic a te d b y c hor oid a l
detachment in our study. Both cases regaind normal
d e p th c ha mb e r a nd s how e d a b s or p tion of the
suprachoroidal fluid within 4-6 weeks
postoperatively without specific treatment apart from
usual postoperative regimen .
However, pers istent hyp otony w ith a n over
functioning bleb was noticed in one case without
adverse sequelae. Van Buskirk, (1992) reported flat
a nte r i or c ha mb e r in one c a s e a s s oc ia ted w i th
choroidal detachment. This patient had received 5 FU postoperatively. Cioffi andVan Buskirk (1993)
reported one case of shallow AC that, persisted for 3
months a nd thr e e ca se s with vis ib le c hor oid a l
detachment that resolved spontaneously .
Under manipulation of the corneal flap may lead
to epithelial defects. Transient corneal epithelial
defect over the corneal flap was observed in one case
in the present study and it healed during the first
week postoperatively. Corneal edema from
manipulation of the corneal flap lead to transient
e p ithe lia l d e fe c t. Va n Buskir k (1992) rep or ted
transient corneal epithelial defects in all five patients
in his first study . The epithelial defects healed
promptly in four of the five patients but persisted for
two weeks in one patient who was treated
adjunctively with 5-FU that necessitated the use of a
bandage soft contact lens.
•
Bleb infection was encounteres in a single case
four months p ostoper ative ly in our study. T his
particular case was one of two cas es who were
operated upon at 6 o clock position. The latter site
has the disadvantage of an unprotected bleb that is
continuously irritated by the lower lid movements.
The procedure however, is technically easier to
perform at 6 o clock since the instruments are hold
660
conforming with the usual position, unlike the upper
meridian where the instruments are hold facing the
surgeon, opposite to the usual position.
Corneal trabeculectomy presents no doubt a
significant modification of the original
trabeculectomy technique, since it offers the great
advantage of sparing the conjunctiva intact avoiding
excessive surgical trauma that stimulates
postoperative conjunctival scarring. The clinical
appear ance of the oper ated eyes w i th minima l
infla mma tor y r eac tion, together w ith p r evious
histological studies on rabbit eyes (Cioffi et al.,
1993), suggest that corneal trabeculectomy incites
less subconjunctival inflammation than conventional
trabeculectomy. Meanwhile, the technique has the
disadvantage of dissecting a corneal flap, working in
a small surgical field and difficulty in obtaining
adequate exposure.
References
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a new method. Am J. Ophthalmol. 1965, 66: 6739
2. Cairns JE: Clear-cornea trabeculectomy. Trans.
Ophthalmol. Soc. UK. 1985.
3. C i o f f i G A a n d V a n B u s k i r k E M : C o r n e a l
trabeculectomy without conjunctival incision.
Extended follow-up and histological findings.
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Taha AM: Clear ornea versus subscleral
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