Viscocanalostomy, a prospective two year follow-up study
S Abd El Wahab,MD. A El Shayeb,MD. H El Gazar, MD.
Aim: To prospectively study the success rate and complications of the non-penetrating glaucoma surgery ,
viscocanalostomy.
Methods: 31eyes of 31 patients who had medically uncontrolled primary open angle glaucoma were enrolled in this
prospective study, in which viscocanalostomy was performed on all patients with injection of viscoelastic (HEALON) in
the surgically de-roofed Schlemm's canal and in the scleral bed, the superficial scleral flap was sutured and the
conjunctiva tightly closed. Intraocular pressure, visual acuity, and visual field analysis were performed post operatively
and recorded
Results: The Patients in this study were followed–up for a mean period of 21.2 months. The mean preoperative
intraocular pressure (IOP) was 26.4 mmHg and the mean lOP on the first postoperative day was 8.4 mm Hg and 18.5
mmHg at the end of follow-up period (24 months). 67% of patients in this study achieved an lOP below 20 mmHg
without medication ( complete success ), seven patients , 22.5% required medical treatment to achieve an IOP of <
20mmHg ,while 3 patients,9.6% required further surgical intervention to control their IOP.
Conclusion: Viscocanalostomy may be a good and promising surgical approach for glaucoma patients.
INTRODUCTION
Trabeculectomy. with or without antimetabolite has a well documented complication rate ranging from flat anterior
chambers with marked hypotony and even choroidal detachment to mild hypotony with leaking blebs (Watson et al
1990) .Viscocanalostomy is a non-penetrating filtration procedure for the surgical treatment of open angle glaucoma it
was first described by Stegman in 1994, the procedure was designed in an attempt to lower the risk and incidence of
complications with classic trabeculectomy, This study was conducted at the Department of Ophthalmology Benha
Faculty of Medicine in the period between January 2000 and January 2001, all surgeons sharing in this study passed
through a learning curve prior to the start of the study.
PATIENTS AND METHODS
Inclusion Criteria
31 eyes of 31 patients with medically uncontrolled primary open angle glaucoma were consecutively enrolled in
this study and followed up prospectively (Chart 1). Medically uncontrolled glaucoma was defined as documented
progression of glaucomatous visual field defects and glaucomatous optic nerve morphology under maximal tolerable
medical treatment.
30
20
10
0
Series1
26.4
17
14
Mean Preop.
IOP
No. Of Males
No.Of
Females
26.4
17
14
2.5
0.71
Mean No Of
Mean
Preop.medicat Preop.BCVA
2.5
0.71
Chart (1) Patient data
1
Exclusion criteria
These were, advanced cataract, previous eye surgery or laser , and patients with other ocular pathologic
conditions such as diabetic retinopathy or age related macular degeneration.
Preoperative data
Prior to surgery, patients underwent best corrected visual acuity assessment (Snellen chart ), lOP measurement using a
Haag-Streit Goldmann applanation tonometer biomicroscopy, gonioscopy.and visual field testing and fundus
biomicroscopy.
Postoperative data
After surgery, all the previously mentioned examinations, except for visual field assessment, were conducted on the first
and the seventh day as well as at 1,3,6,9, 12, 18, 24, months. Visual field examination was repeated every 6 months.
Complications have been defined as follows: hyphaema was considered present when erythrocytes were seen in the
anterior chamber. Hypotony was defined as a postoperative lOP < 4 mm Hg. Anterior chamber depth was clinically
assessed in comparison with the fellow eye. Anterior chamber was considered shallow when there was an irido-corneal
touch in the periphery, and flat when there was a lens-corneal touch, as seen on biomicroscopy. Choroidal detachment
was considered present when seen in the peripheral retina, using an indirect ophthalmoscope and by ultrasonography.
Surgical Technique
All surgeries were performed by under GA. A superior rectus muscle bridle traction suture was placed. A fornix based
conjunctival incision was made and Tenon's capsule was opened and dissected and the sclera in the upper fornix was
exposed. Careful haemostasis using wet field cautery was performed. A one third scleral thickness limbus based scleral
flap measuring 5 x 5 mm was dissected (Fig I).This superficial scleral flap was further dissected 1 mm into clear cornea.
A doom shaped part of the deep sclera was then dissected and removed (Fig 2) Dissection was carried out using a square
edged diamond knife, leaving a thin layer of deep sclera over the choroids, posteriorly. Anteriorly, the dissection was
done reaching Schlemm's canal, which was unroofed and the dissection was continued anteriorly into the corneal stroma
which was excised down to the level of Descemt’s membrane (Fig3). When aqueous humour was seen to percolate
through the remaining thin Trabeculo-Descemet’s membrane (TDM), Na hyaluronate (HEALON) was injected in the
two surgically created ostia of Schlemm's canal (Fig 4), aiming at dilating both the ostia and the canal, Healon was also
placed in the scleral bed. The superficial scleral flap was secured with two single lO-O Nylon sutures, and the knots
buried. The conjunctiva and Tenon capsule were carefully closed with another two single lO-O Nylon sutures.
Postoperatively, patients were treated with topical 0.1% dexamethasone, 0.35% neomycin and 6000 µ/ml
poly1myxin (Maxitrol) three times daily for 2 weeks, and then with topical fluoromethonole three times a day for 3-6
months.
When a perforation of the thin TDM occurred during the corneal stroma dissection, the surgery was converted into a
standard trabeculectomy, with a rectangular resection of the trabeculum, followed by a basal iridectomy, and the case
was excluded from the study.
Surgery was considered a complete success when lOP was < 20 mm Hg without glaucoma medication and a qualified
success when IOP was < 20 mm Hg with glaucoma medication at the end of the follow up period. It was considered a
failure when IOP was > 20 mmHg with progressive field changes and optic nerve head damage.
Figure 1
(dissection of superficial flap)
Figure 2
(dissection of deep flap)
2
Figure 3
(excision of deep flap)
Figure 4
(injection of healon in Schlemme’s Canal)
REULTS
Mean follow up period was 21.2 months. The mean preoperative lOP was 26.4mm Hg The mean lOP at the first
postoperative day was 8.4 mmHg. The Mean IOP at 12 months was 15.8mm Hg versus 26.4 mm Hg preoperatively with
a reduction of 40% and at 24 months the mean lOP was 18.8 mmHg with a reduction of 26% ( chart2).
Complete success rate, defined as lOP lower than 20 mm Hg without medication, was 67% (21/31 patients) at 24
months. Patients with an lOP lower than 20 mm Hg with medication (Qualified success) represented 22% (7/31 patients)
, while the total success rate which included both groups (Complete and qualified success groups) was 89% (28/31
patients) at 24 months. Three patients in this study failed to achieve the criteria of qualified success (IOP < 20 mmHg
with or without medication.), and showed progressive field changes requiring further surgical intervention in the form of
classic trabeculectomy which was done after six months in tow patients and after 11 months in the third patient, their
IOP and field changes were monitored for the rest of the follow-up period , one of them was controlled with out medical
treatment and two needed medication to control their glaucoma.
The mean number of medications per patient was reduced from 2.5 to 0.5 after viscocanalostomy. The best corrected
visual acuity (BCVA) dropped on the first postoperative day from a mean of 0.71 preoperatively, to a mean of 0.48.
Visual acuity returned to preoperative levels 2 week after surgery and remained stable over the next 2 years achieving a
mean BCVA of 0.69 at 24 months (Chart 2)
Pre and Post operative IOP & BCVA
30
26.4
25
18.4
20
15.8
IOP
15
BCVA
10
5
0.71
0.48
0.69
Preop
Day One
24 months
IOP
26.4
15.8
18.4
BCVA
0.71
0.48
0.69
0
Chart (2) pre and post operative IOP and BCVA
3
There were no significant operative complications recorded in this series. Postoperative complications that occurred
are given in (chart no.3). There were no shallow or flat anterior chambers, no bleb related endophthalmitis, and no
surgery induced cataracts were observed. However, mild hyphaema was seen in six patients (19.3%), hypotony was
recorded in one patient in the early postoperative period (3.2%), and three patients needed a second surgical intervention.
As mentioned before, cases that were turned into a classic trabeculectomy were excluded from the study.
% of complications
25
20
19.3
15
9.6
10
3.2
5
0
%
%
hyphaema
hypotony
failure
19.3
3.2
9.6
Chart (3) % of complications
DISCUSSION
Most surgeons prefer to delay surgery because of the potential vision threatening complications of classic
trabeculectomy, with or without antimetabolites. Complications include hypotony, hyphaema, flat anterior chamber,
choroidal effusion or haemorrhage, surgery induced cataract, and bleb failure (Watson PG et al 1990)
Yet surgical intervention remains a very effective way of lowering IOP (Shaarawy etal 2003).Bylsma mentioned in
1999 that increasing the safety margin of glaucoma surgery, significantly without sacrificing its efficacy would allow
surgeons to take the decision of surgical intervention at a much earlier time.
In an attempt to avoid the numerous postoperative complications of trabeculectomy, some authors (Savage et al11988)
proposed a tight closure of the scleral flap with secondary suture lysis using argon laser. More recently, for the same
reason, several techniques of non-perforating filtration surgery have been described. Zimmerman et al 1984 reported
positive results of non-penetrating trabeculectomy in phakic and aphakic patients. Stegmann in 1995was the first to
describe viscocanalostomy, in which the scleral space was filled with a viscoelastic substance, and reported complete
success of 82.7% and qualified success in 89.0% of patients at 35 months of follow up.
The major advantage of viscocanalostomy is that it precludes the sudden hypotony that occurs following trabeculectomy by creating progressive filtration of aqueous humour from the anterior chamber to the subconjunctival space,
thus avoiding sudden decompression of the eye ball (shaarawy et al 2003)
In 1999 Stegmann published his results of performing viscocanalostomy on patients suffering from open angle
glaucoma. His prospective study was performed on 214 patients who were poorly controlled by medical therapy and he
reported an lOP of 22 mm Hg or less in 82.7% of eyes without medical therapy (complete success rate). His total
success rate was 89.0%. With a mean follow up of 35 months, this study showed that lOP could, be satisfactorily
controlled with the non penetrating glaucoma surgery, viscocanalostomy.
In a prospective study by Carrassa, in 1998 in which he compared two groups each of 25 randomized patients, one
group had trabeculectomy and the other viscocanalostomy. Viscocanalostomy was found to have a less significant rate of
complications, yet classic trabeculectomy was found to achieve a lower mean lOP.
In 2003 Shaarawy et al published the results of a five year follow-up study on visicocanalostomy on a non-randomized
series of 57 patients. They reported a complete success rate of 60% and a qualified success rate of 30%, their total
success rate was 90% at the end of the follow-up period which extended up to 60months.they also mentioned that 37% of
their patients needed laser goniopuncture to control their IOP.
Luke et al in 2003 also published the results of a prospective randomized trial of visicocanalostomy with and without a
reticulated hyaluronic implant (SKGEL) in open angle glaucoma. They concluded that both surgical techniques had an
equal complete success rate of 40% at the end of the one year follow-up period and that specific intraoperative and
postoperative complications of non-penetrating surgery were lower than those encountered in classic trabeculectomy.
4
Our complete success rate of 67% compares to the complete success rate of shaarawy et al (60%), the slight difference
may be attributed to our shorter follow-up period. Our total success rate (compromising both complete and qualified
success rates) was 89% which compared to that of Stegman (89 %) and Shaarawy (90%) .
Except for the first week after surgery, visual acuity was unaffected by viscocanalostomy. This phenomenon may be
explained by the non-perforation of the eye, which avoids inflammation, use of mydriatics, and sudden hypotony.
Furthermore, visual acuity remained stable because no surgery related cataracts developed after viscocanalostomy.
In our series,the early postoperative complications included the presence of subtle hyphaema in 7 of our cases. The
very small amount of blood in the anterior chamber can be explained by a probable blood reflux from the scleral bed
through the anterior trabeculum, or by undetected micro perforations. (Lachkar et al 2002). We had one case which
developed a choroidal detachment and hypotony on the first postoperative day and continued so for 12 days, after which
the choridal detachment resolved and the hypotony improved , this may again be attributed to microperforations in the
TDM and /or to loose closure of the scleral flap.
In conclusion, viscocanalostomy appears to be a promising non-perforating filtration procedure. In our experience, the
success rate after 2 years of follow up was satisfactory for open angle glaucoma. The immediate postoperative
complication rate was low, and visual acuity was almost unaffected.
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