|Year : 2014 | Volume
| Issue : 2 | Page : 97-105
Modified trabeculectomy with an extended subscleral tunnel: could it be a secure way toward successful glaucoma surgery?
Ahmed M Saeed, Sameh Saleh
Department of Ophthalmology, Benha University, Benha, Egypt
|Date of Web Publication||12-Sep-2014|
Ahmed M Saeed
Benha University, Zayed Tower, Elsouk Eltogary Street, El-Kanater Elkhayria, Elqalyobia, Benha
Source of Support: None, Conflict of Interest: None
The aim of this study was to describe a modified surgical technique of an extended subscleral tunnel (ESST) with adjunctive application of mitomycin-C (MMC) and to evaluate its safety and efficacy in long-term intraocular pressure (IOP) control in glaucoma patients.
Patients and methods
This was a randomized-controlled prospective clinical trial that included 54 eyes of 46 patients diagnosed with primary open-angle glaucoma. They were divided into two equal groups: the 'trabeculectomy with adjunctive MMC' treatment, group A, and the 'modified trabeculectomy with adjunctive MMC and ESST' treatment, group B. Ultrasonic biomicroscopy measurement of the aqueous drainage route was performed at 12 and 24 months postoperatively. The main outcome results included the cumulative probability of surgical success, IOP values, and the number of antiglaucoma drugs needed.
Group B achieved a cumulative probability of complete success of 0.68 and qualified success of 0.96 at the end of the 24-month study period; however, group A achieved a cumulative probability of complete success of 0.44 and qualified success of 0.84. Group B succeeded in achieving lower mean IOP values than group A, with fewer antiglaucoma drugs at all postoperative visits, but this was not statistically significant (P > 0.05). The aqueous drainage route was always larger in group B and there was a statistically significant decrease in its size only in group A (P = 0.036). Group B achieved statistically significant fewer early and late postoperative complications and also required fewer additional interventions compared with group A (P = 0.029). No significant adverse effects were caused by this modified combined technique.
Modified trabeculectomy with ESST combined with adjunctive MMC could be an efficient, safe, familiar, and applicable treatment technique for a successful trabeculectomy. It may provide a favorable long-term outcome, representing a simple novel way of performing successful glaucoma surgery.
Keywords: mitomycin-C, modified trabeculectomy, subscleral tunnel, ultrasonic biomicroscopy
|How to cite this article:|
Saeed AM, Saleh S. Modified trabeculectomy with an extended subscleral tunnel: could it be a secure way toward successful glaucoma surgery?. J Egypt Ophthalmol Soc 2014;107:97-105
|How to cite this URL:|
Saeed AM, Saleh S. Modified trabeculectomy with an extended subscleral tunnel: could it be a secure way toward successful glaucoma surgery?. J Egypt Ophthalmol Soc [serial online] 2014 [cited 2018 Aug 21];107:97-105. Available from: http://www.jeos.eg.net/text.asp?2014/107/2/97/140648
| Introduction|| |
Trabeculectomy is the most frequently applied surgical method to reduce intraocular pressure (IOP) in glaucoma patients. The goal of glaucoma filtering surgery is to establish a permanent flow of aqueous from the AC to the subconjunctival space. However, the procedures tend to fail over time because of fibroblastic proliferation and the biosynthesis of collagen and other extracellular materials that occur during normal healing . Large-scale retrospective studies have suggested that filtering blebs become nonfunctional in at least 50% of patients 5 years after surgery. This clearly indicates the necessity for the development of techniques to reduce postoperative scarring in filtering blebs .
Various methods and different modifications have been investigated over the years to prevent the naturally occurring scarring of the filtering bleb and, subsequently, to reduce the incidence of this detrimental complication.
Mitomycin-C (MMC) has widely been considered as an essential intraoperative adjunctive to trabeculectomy surgery to prevent fibrosis and further failure of trabeculectomy [3,4].
The aim of this study was to describe a modified surgical technique for a trabeculectomy procedure that combined an extended subscleral tunnel (ESST) with adjunctive intraoperative application of MMC and to evaluate its safety and efficacy in long-term IOP control in glaucoma patients in comparison with conventional trabeculectomy with adjunctive MMC.
This was a randomized-controlled prospective clinical trial. It was carried out during the period from March 2010 to July 2013. The postoperative evaluation and follow-up period was 24 months.
This study was carried out at the Ophthalmology Department of Benha University Hospital, Benha, Egypt.
| Patients and methods|| |
This trial included 54 eyes of 46 patients (25 women and 21 men) diagnosed with primary open-angle glaucoma. They were recruited from among those attending the ophthalmology clinics of Benha University Hospital. The indication for filtration surgery was uncontrolled IOP by maximum tolerable antiglaucoma therapy. Two patients were excluded from the study because they missed two subsequent postoperative follow-up visits. The mean age of the 44 patients included was 57.51 ± 8.04 years. The 50 eyes of the 44 patients (24 women and 20 men) were divided randomly into two equal groups: the 'trabeculectomy with adjunctive MMC' treatment, group A, and the 'modified trabeculectomy with adjunctive MMC and ESST' treatment, group B.
There was no statistically significant variation between the groups studied in race, sex, and age (P > 0.05). Informed consents were obtained from all patients after a thorough explanation was provided of the treatment approach and surgical procedures with their possible side effects and potential complications, with the approval of the Research Ethics Committee at Benha faculty of Medicine, Benha University.
Patients with all types of glaucoma other than primary open-angle glaucoma, patients with other ocular pathologies (retinal surgeries, significant cataract, uvietis, corneal pathology), patients who missed two subsequent postoperative visits or did not complete the 24-month follow-up period, and patients who were not willing to provide consent were excluded from the study.
Baseline data included the following:
(1) Baseline IOP, which was recorded as the preoperative IOP with the use of antiglaucoma drugs.
(2) Ocular hypotensive medications - their class, number, duration, and evidence of chronic inflammation were reported.
(3) Visual field test using a Humphrey perimeter (Carl Zeiss Meditec Inc.) using a threshold 24-2 SITA-standard program to obtain the baseline mean deviation (MD) and pattern standard deviation (PSD).
(4) Best-corrected visual acuity (BCVA) in decimal notation using standard Snellen charts.
(5) Central corneal thickness using an ultrasonic pachymeter (Corneo-Gage plus 4s; Sonogage Inc., Cleveland, Ohio USA).
Complete ocular examination was performed: anterior segment slit-lamp examination, gonioscopy using Goldman contact lens, fundus examination (optic nerve head, vertical cup disc ratio, and nerve fiber layer if possible), and assessment of history of systemic diseases (diabetes, hypertension, collagen diseases, hepatitis, etc.). At baseline, systemic hypertension, mean HbA1c levels, HB%, lipid profile as well as prothrombin time and concentration were controlled whenever indicated.
All procedures were performed under local peribulbar anesthesia. A conjunctival incision was made at the limbus to create a fornix-based conjunctival flap. A half-thickness scleral flap (4 × 4 mm) was created and dissected into the clear cornea. A cellulose microsponge soaked in 0.3 mg/ml MMC solution (Mitomycin-C Kyowa; Kyowa Hakko Kogyo, Tokyo, Japan) was applied to the under surface of the scleral flap over a wide posterior area for 3 min, with separation of the conjunctival edge away from direct contact with the soaked microsponge, and with a Tennon capsule as a barrier in between. Then, the sponge was removed and the entire area was lightly and copiously washed with irrigating saline.
In group B: another longitudinal scleral groove was created in the center of the deep scleral bed area under the rotated scleral flap by dissecting a scleral strip extending for 2 mm proximal to the upper margin of the first flap so that it measured about 1.5 × 6 mm. On reaching the surgical limbus, the scleral strip was excised and the AC anterior chamber was entered (Photo 1).
In both groups, standard trabeculectomy of equal size (two bites aside) was created by a Kelly punch; peripheral iridectomy was performed by scissors. Closure of the scleral flap with 10/0 Nylon sutures was performed to achieve controlled seepage of the aqueous to the posterior subconjunctival space.
In group B: a triangular snip was excised from the scleral flap over the tunnel created for deroofing. Tenon's membrane was dissected from the conjunctival flap and excised cautiously in order not to injure the superior rectus muscle sheath.
In all patients, the conjunctival incision was tightly closed with continuous 8/0 Vicryl sutures (Vicryl polyglactin 910; Ethicon Inc., Somerville, New Jersey, USA). Additional mattress suture was used to ensure conjunctival adherence to the superior cornea. Any intraoperative complication was reported.
All patients received prednisolone acetate 1% and gatifloxacin 0.3% (Optipred and Tymer, Jamjoom Pharma, Jeddah, Saudi Arabia); eye drops were administered five times daily for 3 weeks. Cyclopentolate 1.0% (Cicloplejico eye drop; Alcon CUSI, S.A., Barcelona, Spain) was administered three times daily for 2 weeks. Antiglaucoma eye drops were tailored according to IOP values for every patient at each study visit with the aim of maintaining IOP less than 21 mmHg with the least tolerable drugs.
The postoperative study visits were at 1, 3 days, every week for 1 month, 1, 3, 6, 12, 18, and 24 months with documentation of IOP, number of IOP-lowering drugs, BCVA, gonioscopy, fundus examination, complications, and additional maneuvers required to maintain filtration or to handle complications as well as any additional surgical intervention. Efficacy, in terms of postoperative reduction in IOP, was determined on the basis of the Guidelines on Design and Reporting of Glaucoma Surgical Trials .
Ultrasonic biomicroscopy (UBM) measurement of the aqueous drainage route (ADR) was performed at 12 and 24 months postoperatively (mode DICON P45 UBM plus Paradigm Instruments, USA).
Colored photography of the filtering blebs was performed. They had been classified according to the morphologic classification of filtering blebs after glaucoma filtration surgery: the Indiana Bleb Appearance Grading Scale [6,7]. Perimetry was performed at 12 and 24 months. Additional visits and investigations were performed when required.
The program used was SPSS version 16 software (IBM Corporation, Armonk, New York, USA). Quantitative data were analyzed using mean and SD, whereas qualitative data were described a frequency and percentage. The Student's t-test was used to compare the means of different groups, the Fisher exact test to compare frequencies, and the Kaplan-Meier test to determine survival tables. The level of significance considered in this work was 0.05 (P < 0.05 was considered significant).
| Results|| |
The outcome data for all patients were summarized and represented according to the above mentioned definitions of success . The survival curve ([Figure 1]) shows the surgical success and the survival table shows the numbers in each study group analyzed at each postoperative follow-up time point of 1, 6, 12, 18, and 24 months [Table 1].
|Table 1 Surgical success and shows the numbers in each study group analyzed at each follow-up time point at 1, 6, 12, 18, and 24 months postoperatively|
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The survival table shows surgical success in both study groups analyzed at every follow-up postoperative time point. The differences between the two groups were not statistically significant [Table 1].
Scatter plots show the proportions of study participants in both groups who fulfill the criteria for success at 12, 18, and 24 months postoperatively ([Figure 2], [Figure 3], [Figure 4], respectively), with the diagonal lines at 45° (y = x) showing those with a reduction in IOP after surgery (right lower half) from those of an increase in IOP (left upper half) or no change.
The mean and SD values of the IOP in both groups during the entire study period are presented in [Table 2] and [Figure 5].
|Table 2 Mean and SD values of the IOP in the two groups over the entire study period|
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There was a statistically significant decrease in the mean IOP on comparing the baseline value with the postoperative values at all postoperative time points in both groups (P was always < 0.05). On comparing the two groups, the mean IOP values were always lower in group B than A at all postoperative time points (except at 18 months), but not to a statistically significant level.
The percentages of patients receiving IOP-lowering drugs in both patient groups at different time points postoperatively are shown in [Figure 6]. The mean number of IOP-lowering drugs was statistically significantly lower (P < 0.05) on comparing the baseline value with the postoperative values at all follow-up time points in both groups. When comparing the two groups ([Figure 6]), the numbers of IOP-lowering drugs were always lower in group B at all postoperative study visits, but not to the level of statistical significance. (P = 0.23, 0.68, and 0.68, respectively).
When comparing the mean size of the ADR between both groups at 12 and 24 months postoperatively, group B showed larger values (by 0.14 and 0.23 mm, respectively), but not to a statistically significant level (P = 0.1 and 0.07, respectively). When comparing the mean size of the ADR within each group between 12 and 24 months postoperatively, only group A showed a statistically significant decrease (P = 0.036). However, group B showed a relatively larger size at the end of the study period.
|Figure 1: (a) Excised scleral strip and (b) cannula passing through the ESST. ESST, extended subscleral tunnel.|
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|Figure 2: The survival curve that shows the rate of surgical success of the two groups over the entire follow-up period of 24 months.|
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|Figure 3: Scatter plots showing the proportions of study participants in both groups who fulfi ll the criteria for success at 18 months. IOP, intraocular pressure.|
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|Figure 4: Scatter plots showing the proportions of study particiaptns in both groups who fulfi ll the criteria for success at 24 months. IOP, intraocular pressure.|
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|Figure 5: Mean postoperative IOP values in both groups over the entire study period. IOP, intraocular pressure.|
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|Figure 5: Percentages of patients receiving IOP-lowering drugs in both patient groups at different time points of 6, 12, 18, and 24 months postoperatively. IOP, intraocular pressure.|
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The morphological types of bleb in both groups are shown in the following [Table 3].
[Table 4] shows the baseline and the postoperative values at 24 months of BCVA and visual field parameters (MD and PSD in decibels) in both groups.
There were no statistically significant differences in the mean BCVA when comparing the baseline with the 24-month postoperative values either within each group or between both groups. No patients progressed to lose light perception; however, seven eyes (four in the conventional group and three in the modified group) lost less than 2 Snellen lines at the final follow-up.
There were no statistically significant differences in the mean MD and PSD on Humphrey-automated perimetry between the two groups either preoperatively or at 24 months postoperatively. Four eyes in group A (16%) and three eyes in group B (12%) showed VF progression during the 24-month follow-up period. Group A showed more visual field deterioration (higher MD and PSD values) than group B at the end of the study, but not to the level of statistical significance.
|Table 4 Baseline and 24-month visit values of BCVA and visual field parameters (MD and PSD in decibels) in both groups|
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The intraoperative, early, and late postoperative complications of both groups are shown in [Table 5].
|Table 5 Intraoperative, early, and late postoperative complications reported in both groups|
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Intraoperative complications were reported more in group A than B, but with no statistical significance. The early and late postoperative complications were more in group A than B, both with statistical significance.
Additional interventions were required as follows: suturing conjunctival wound leak (in two cases of group A), prophylactic intracameral and intravitreal antibiotic injection (in a case of blebitis in group A), needling of a Tenon's cyst (in two cases of group A), suturelysis (in a case of group B), and trabeculectomy revision surgery (three cases in group A at 12, 18, and 24 months as well as one case in group B at 24 months postoperatively, all with no surgical complications). The maneuvers were needed significantly more marked in group A than B.
| Discussion|| |
Despite various developments in many fields of ophthalmology, the trabeculectomy technique has remained very similar to the original description by Cairns 46 years ago . Since the introduction of intraoperative mitomycin and postoperative subconjunctival injections of 5-fluorouracil, trabeculectomy has not been altered markedly. These facts stand in contrast to the need for a more efficient surgical therapy for OSG as one of the main disadvantages of filtering surgery is the lack of enduring success.
Trabeculectomy is usually the initial filtration surgery performed in Egypt. Considering that scarring at the surgical site is the most common cause of failure of trabeculectomy, the high failure rate in primary cases may be explained in part by the fibrotic conjunctival changes induced by trachoma or by the long duration of medical therapy as well as other underlying inherent racial factors . This clearly shows the need to develop techniques to reduce postoperative scarring in filtering blebs .
To date, no sufficient method has been established to achieve satisfying postoperative long-term surgical results with only minimal or no side effects for the patient. Trabeculectomy has been subjected to some stylistic variations by many surgeons with the introduction of antimitotics and concerns over wound healing.
In the current study, we used a fornix-based conjunctival flap, in agreement with Lanzl et al.  in an effort to encourage more posterior drainage. It is preferable to attempt the creation of a more posterior bleb to minimize the chance of bleb exposure at the limbus and also to minimize the chance of bleb extension on the cornea.
Although none of the other stylistic variations (including the shape, size, thickness, and length of the flap) has been proven to affect longer term outcomes , we used a rectangular, half-thickness, long flap that may promote more posterior drainage and greater flow.
In our modified trabeculectomy technique, an additional small perpendicular strip of sclera is removed extending from the AC to 2 mm beyond the edge of the scleral flap together with an overlying triangular snap excision for its deroofing as well as tenonnectomy, thus creating an ESST facilitating aqueous passage into the posterior subconjunctival space.
Bleb-modifying agents, especially MMC, do represent a major advancement in achieving more desirable outcomes for patients at risk of trabeculectomy failure [3,4].
Anand et al.  reported that MMC application over the area of scleral flap dissection during glaucoma surgery is associated with a high incidence of bleb avascularity, transconjunctival oozing, and delayed bleb leaks (observed in 17 eyes (13.6%) - 15 (24.6%) in their trabeculectomy group). Taking their results into consideration, we applied MMC on the under surface of the flap, at a low dose (0.3 mg/ml), for a short duration (3 min), with separation of the conjunctival edge away from direct contact with the soaked microsponge and with a Tennon capsule as a barrier in between before its excision. All these simple factors could enable minimization of such drawbacks and complications.
Yamamoto et al.  reported that the 5-year cumulative incidence of bleb-related infection was 2.2 ± 0.5% in eyes treated with MMC-augmented trabeculectomy. However, You et al.  reported that MMC application under both the conjunctiva and the scleral flaps improves IOP outcomes, with no further risk of infection. In our study, the use of MMC in lower doses could help achieve better IOP control, with no late-onset bleb leak or bleb-related endophthalmitis reported, supporting the safety of MMC adjunction, especially when applied over a wide posterior area and at a low dose.
The modified technique applied in the current study achieved a cumulative probability of complete success of 0.68 and qualified success of 0.96 at the end of the 24-month study period; however, conventional trabeculectomy with adjunctive MMC only achieved a cumulative probability of complete success of 0.44 and qualified success of 0.84. The cumulative probability of complete success was 0.92 and 0.84 at 6 and 12 months, respectively.
The current study has a certain advantage of adding the effect of ESST to that of MMC in the wound-healing process, aiming to reduce postoperative fibrosis, thereby paving the way toward successful glaucoma surgery.
This combined approach achieved higher success when compared with other studies reporting on conventional glaucoma surgery. Pandit et al.  reported 90% (45 out of 50 cases) success over 5 years using a similar modification for trabeculectomy through removal of a small strip of sclera, but without any antimitotic drugs. However, they defined surgical success as IOP less than 20 mmHg and they included patients with other types of glaucoma in their study (congestive and secondary glaucoma, three and four cases, respectively).
Our results are better than the successful outcomes reported in several trabeculectomy series in which various concentrations of MMC have been used [16-18] and also the average 5-year survival for mixed low and higher risk cases ranges from 60  to 80%.
The results were also comparable with those of Strnad and colleagues who evaluated the long-term efficacy after nonpenetrating deep sclerectomy (DS) using different types of implants. They divided the patients into three groups: DS without implant: 34 eyes, DS with Staar implant: 31 eyes, and DS with T-flux implant: 27 eyes. The complete success rate was 0; 7.1; and 18.2% at 96 months. Qualified success rate was 87.5; 89.5; and 100% at 96 months .
The modified approach used led to a statistically significant decrease in the mean IOP when comparing the baseline value with the postoperative values at all postoperative time points. This should be considered in relation to the mean numbers of IOP-lowering drugs administered, where there was also a statistically significant decrease in the mean number of IOP-lowering drugs on comparing the baseline value with the postoperative values at all postoperative time points. When compared with the values of the conventional trabeculectomy group, it succeeded in achieving lower mean IOP values with fewer antiglaucoma drugs at all postoperative visits.
Trabeculectomy bleb failure is commonly ascribed to the process of fibrosis, gradually contracting the bleb down to and flattening it against the scleral flap . Bleb morphology is not a reliable predictor of IOP reduction, although a higher bleb is more likely to result in a lower pressure . Most surgeons prefer a modestly elevated, diffuse, relatively large, and posterior bleb for reasons of safety. Most observers try to avoid a significantly vascularized bleb.
The morphological classification of the blebs  showed that 92 versus 76% of the blebs were functioning (type 1 and 2 blebs) in the modified trabeculectomy group compared with the conventional group. This was because of the additional beneficial effect of ESST to that of the MMC applied as both interfere with fibroblast and tissue proliferation [3,4].
In agreement with Wells et al. , UBM can be a useful method to study and explain the mechanisms of filtering structures and to evaluate the bleb function. The eyes with good IOP control showed UBM images characterized by better visibility of large ADRs under the scleral flap. A statistical correlation between IOP and measured size of the ADR showed an inverse relationship . The results of the current study supported that our modified technique succeeded in achieving a larger ADR when compared with the conventional technique at 12 and 24 postoperative months by a mean of 0.14 and 0.23 mm, respectively. The actual advantage of our modification was evident when comparing the mean size of the ADR within each group between 12 and 24 months postoperatively, where it showed a relatively larger size at the end of the study period (0.64 ± 0.27 and 0.7 ± 0.54 mm, respectively) in contrast to the conventional group, where it showed a statistically significant decrease (P =0.036).
In the current study, there was no statistically significant difference between both groups in BCVA and VF parameters. There was no significant reduction in the median VA during follow-up after surgery. No patients progressed to lose light perception; however, seven eyes (four in the conventional group and three in the modified group) lost greater than 2 Snellen lines at the final follow-up for various reasons: one eye in each group because of glaucoma progression (on the basis of changes in the Humphrey automated perimetry standard) and others' visual loss may be attributed partly or entirely to the surgery (cataract and corneal edema) as well as to comorbidity (diabetic retinopathy and age-related macular degeneration). Our results are in agreement with those of Pandit et al.  who reported in their study that VA remained the same, with no visual deterioration during follow-up.
We used MD and PSD to study VF progression in this study. There were no statistically significant changes in these parameters, supporting that there was little further visual loss related to glaucoma progression during the follow-up period. The results of this trial may be considered sufficient to prevent any further glaucoma-related visual loss.
Fewer operative complications were reported with the modified technique when compared with the conventional group, with both early and late postoperative complications reaching the level of statistical significance. Moreover, the additional interventions and the maneuvers required were significantly more marked in the conventional group.
The most common cause of severe hypotonous complications is a leaking trabeculectomy bleb, often through inadvertent cutting of a conjunctival button hole or conjunctival wound dehiscence . In the current work, the conjunctival incision was tightly closed with continuous 8/0 Vicryl sutures and an additional mattress suture was used to ensure conjunctival adherence to the superior cornea. Also, protection of the healing conjunctival edges from the MMC applied led to a healthy tight healing without such complications (especially leaky and ischemic avascular blebs). Moreover, the wide posterior drainage of the aqueous achieved by ESST, controlled closure of the flap, and tenonnectomy helped minimize bleb-related complications (especially high bleb with dellen, Tennon cysts). This represents another advantage to our technique in terms of its safety.
| Conclusion|| |
Modified trabeculectomy with ESST combined with adjunctive MMC could represent an efficient, safe, familiar, and applicable treatment technique for successful trabeculectomy. This combined approach may be sufficient to prevent any further glaucoma-related visual loss and should be considered in glaucoma patients requiring surgery, especially those with an increased risk of bleb failure. It may provide a favorable long-term outcome with fewer postoperative complications, representing a secure way to successful glaucoma surgery.
| Acknowledgements|| |
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]