|Year : 2004 | Volume
| Issue : 1 | Page : 23-28
A comparative study of small Incision trabeculectomy avoiding tenon's capsule vis-à-vis trabeculectomy with mitomycin-C
J Das, P Sharma, Z Chaudhuri
Guru Nanak Eye Centre, Maulana Azad Medical College, New Delhi, India
Guru Nanak Eye Centre, Maulana Azad Medical College, New Delhi
Source of Support: None, Conflict of Interest: None
Purpose: To compare the results of small incision trabeculectomy avoiding Tenon's capsule (SIT) vis-à-vis intraoperative use of Mitomycin-C (MMC) in primary chronic angle closure glaucoma.
Methods: A controlled prospective study was conducted on 60 consecutive primary chronic angle closure glaucoma patients requiring glaucoma filtration surgery. Patients were divided into two groups, Group I (n=30): those undergoing SIT and Group II (n=30): those undergoing trabeculectomy with MMC. Patients were followed up serially for 24 months and their intraocular pressure (IOP) was monitored. Success was defined as IOP 22 mm Hg with no additional anti-glaucoma medication or laser/surgical intervention. Success was also defined as a 30% reduction from the initial IOP at which optic disc cupping and/or visual field changes occurred.
Results: The final mean IOP with SIT was 16.80±4.20 mm Hg as against 17.84±3.80 mm Hg with trabeculectomy with MMC. Final success rate of 93.3% was obtained with SIT versus 90% with trabeculectomy with MMC. No major complications were seen with either procedure.
Conclusion: Small incision trabeculectomy safely and effectively reduces the IOP in over 90% cases. The advantages of this procedure over trabeculectomy with MMC are its low cost, use of a small (2.5 mm) limbal incision which obviates the dissection of Tenon's capsule and absence of any major complication.
Keywords: Small incision trabeculectomy, trabeculectomy, mitomycin-C, chronic angle closure glaucoma
|How to cite this article:|
Das J, Sharma P, Chaudhuri Z. A comparative study of small Incision trabeculectomy avoiding tenon's capsule vis-à-vis trabeculectomy with mitomycin-C. Indian J Ophthalmol 2004;52:23-8
|How to cite this URL:|
Das J, Sharma P, Chaudhuri Z. A comparative study of small Incision trabeculectomy avoiding tenon's capsule vis-à-vis trabeculectomy with mitomycin-C. Indian J Ophthalmol [serial online] 2004 [cited 2020 Apr 6];52:23-8. Available from: http://www.ijo.in/text.asp?2004/52/1/23/14636
The goal of any glaucoma filtration surgery is to slow or eliminate pressure-dependent ganglion cell loss by lowering the intraocular pressure (IOP) maximally as higher pressures are more likely to produce further damage. Trabeculectomy has become the filtration procedure of choice because it leads to good IOP control with a lower incidence of postoperative complications as compared to full-thickness filtering surgeries.
Use of adjunctive antimetabolites to decrease fibrosis at the level of conjunctiva, Tenon's capsule and episcleral interface, improves the outcome of filtering surgery in eyes with poor surgical prognosis like young age, black race, aphakes, inflammatory glaucoma, neovascular glaucoma and prior failed filtering surgery. However, the initial enthusiasm was dampened by the associated high risk of complications which includes cataract progression, wound leaks, corneal epithelial toxicity, hypotony maculopathy and endophthalmitis.,
Because filtration failure often relates to subconjunctival fibrosis, creation of filtration fistulas to the subconjunctival space without violating the conjunctiva has been attempted by corneal trabeculectomy,,and transcameral goniopuncture. A recent innovation in this direction is small incision trabeculectomy avoiding Tenon's capsule,,(SIT). This has emerged as a safe and effective alternative to conventional trabeculectomy in patients with primary open angle glaucoma.
The prevalence rate for primary angle closure glaucoma is higher in Asians than Caucasians, and the most common type in Asia, including India, seems to be chronic primary angle closure glaucoma (PACG).
This study seeks to compare the success rate, merits and demerits and incidence of complications of SIT avoiding Tenon's capsule vis-à-vis trabeculectomy with intraoperative mitomycin-C (MMC) application in cases of PACG.
| Materials and Methods|| |
Patients with the diagnosis of primary chronic angle closure glaucoma needing filtering surgery for IOP>22 mm Hg and/or progression of glaucomatous optic neuropathy/ visual field defects in spite of maximum tolerated medical therapy and with patent and functional laser iridotomy were included in the study, conducted at the Glaucoma Services, Guru Nanak Eye Centre, New Delhi. Patients with the diagnosis of open angle glaucoma, secondary glaucomas, congenital/developmental glaucomas, patients needing combined cataract and glaucoma surgery and patients with previous failed glaucoma filtration surgery were excluded.
A total of 60 eyes of 60 primary chronic angle closure glaucoma patients were included in the study and randomly assigned to two groups. Group I underwent trabeculectomy without MMC (30 eyes of 30 patients) and Group II underwent trabeculectomy with MMC (30 eyes of 30 patients).
Documentation of the following information was done for each patient: age, gender, detailed clinical history along with general physical and systemic examination; a comprehensive ocular examination including recording of best corrected visual acuity (BCVA), a thorough anterior and posterior segment examination (especially optic disc evaluation with direct ophthalmoscopy and slitlamp biomicroscopy), IOP measurement with Goldmann applanation tonometer; gonioscopy with a Goldmann single mirror gonioprism and evaluation of the extent of peripheral anterior synechiae by Zeiss indentation gonioscopy, measurement of anterior chamber depth by ultrasound 'A' scan technique using the Humphrey biometer (model 820 REV.G) and recording of visual fields using automated perimetry by Humphrey field analyser (model HFA II 750-5751-A10.1).
Written informed consent was taken prior to surgery which was performed under peribulbar local anaesthesia and O'Brien facial nerve block using 2% xylocaine and 0.5% bupivacaine. A 5-0 polyglactin traction suture was placed under the superior rectus muscle to rotate it downward to expose the superotemporal or superonasal quadrant.
SIT was performed after making a 2.5 mm conjunctival peritomy without cutting Tenon's capsule near the limbus.16 A one-third to one-half partial thickness incision was made at the limbus and a scleral pocket was dissected 2-3 mm posteriorly. The subconjunctival space was entered with an angled crescent knife bevel up (Alcon 1134) and passed through the scleral pocket. Balanced salt solution (BSS) was injected with a cannula through the scleral pocket, forming a subconjunctival bleb. The anterior chamber was entered at the initial limbal incision and Vannas scissors were used to excise a 1.5 x 1.0 mm fragment of the floor of the pocket, followed by a peripheral iridectomy. The scleral wound and the conjunctiva were closed, with separate 10 - 0 running/interrupted nylon sutures.
Trabeculectomy with MMC was performed after raising a limbal-based conjunctival flap and applying a Merocel surgical sponge soaked in 0.2mg/ml MMC to the subconjunctival tissue at the planned trabeculectomy site for 3 minutes followed by thorough irrigation of the site with balanced salt solution.9,20 After raising a half-thickness 4x4 mm rectangular scleral flap, a 2x2 mm block of inner sclerostomy was excised using Vannas scissors and peripheral iridectomy was done. The scleral flap was reapproximated using six 10-0 monofilament nylon interrupted sutures. After closure of conjunctival incision with a running mattress 10-nylon suture, BSS was injected through an inferotemporal beveled paracentesis incision to reform the anterior chamber. No viscoelastic agent was used during the procedure.
Patients with uneventful surgeries were discharged on the first postoperative day and were assessed postoperatively at week one, week six, month three and thereafter at three-monthly intervals till 24 months. At each visit, the examination included a complete anterior and posterior segment evaluation (especially optic disc evaluation with direct ophthalmoscopy and slit-lamp biomicroscopy), IOP measurement using Goldmann applanation tonometer, anterior chamber depth using Humphrey biometer and visual fields by Humphrey automated perimeter. The visual field charting was done every 6 months. In case of any complications, assessment was done more frequently. Assessment of blebs was done according to Migdal and Hitchings21classification of blebs. After surgery, all patients received topical antibiotic-corticosteroid, which were tapered over 4-6 weeks. Antiglaucoma medications were added as indicated by the IOP and clinical status of the patients. Success of the procedure was defined as an IOP 22 mm Hg with no additional antiglaucoma medication or surgery. It was also defined as at least a 30% reduction of IOP from the preoperative measurement. IOP>22 mm Hg with antiglaucoma medications for three consecutive months with or without evidence of progressive glaucomatous optic disc cupping and/or deterioration of visual field status was regarded as failure of the surgery. Qualified success was defined as IOP 22 mmHg with antiglaucoma medications.
The data was compiled and statistically evaluated using the student's 't' test and paired 't' test for quantitative data and Pearsons Chi Square Test for qualitative data as indicated.
| Results|| |
The mean age of the patients in the study was 55.53±11.68 years (range 20-70 years). There were 35 males (58.33%) and 25 females (41.66%). There was no statistically significant difference in age and gender between the two groups. Other preoperative characteristics of the study population are summarised in [Table - 1]. Baseline visual acuity distribution was not significantly different between the two groups.
The mean preoperative IOP of the 60 patients included in the study was 33.84±10.30 mm Hg. There was no statistically significant difference between the two groups regarding the preoperative IOP distribution. The average postoperative IOP at each follow up visit is detailed in [Table - 2] and [Figure - 1].
The final mean IOP achieved with SIT was 16.80±4.20 mm Hg (preoperative mean IOP: 34.50±10.30; P<0.001) as against 17.84±3.80 mm Hg with trabeculectomy with MMC (preoperative mean IOP: 31.18±8.60; P<0.001). The final average IOP at the end of 24 months follow-up was lower in Group I than in Group II but was not statistically significant (P=0.319). There was no statistically significant difference in the postoperative IOP between the two groups except at three months postoperatively. The final average percentage postoperative IOP reduction from preoperative levels was 51.30% and 42.78% in Group I and II respectively.
At the end of 24 months' follow-up, a success rate of 28 (93.33%) of 30 cases was obtained with SIT. Qualified success was recorded in 29 (96.66%) of 30 cases (IOP controlled on antiglaucoma medications). On the other hand, trabeculectomy with MMC had a success rate of 27(90%) of 30 cases and qualified success rate of 28 (93.33%) of 30 cases.
Argon laser suture lysis of one/two scleral flap sutures was performed in five (16.6%) of 30 patients who underwent trabeculectomy with MMC within three days to two weeks postoperatively to titrate aqueous flow and thus achieve the target IOP for each individual case.
In each case regarded as a qualified success, the IOP was well controlled during the first week postoperatively but at week six, appropriate antiglaucoma drugs had to be started when IOP increased to more than 22 mm Hg. The characteristics of the one failed case in Group I and two failed cases in Group II are shown in [Table - 3]. It is noteworthy that all failed cases had advanced glaucomatous optic neuropathy and almost 360° synechial angle closure.
At the end of 24 months' follow-up, the average number of antiglaucoma drugs decreased significantly from their preoperative values ( P<0.05). It was 0.37±0.60 for Group I and 0.25±0.80 for Group II postoperatively (P I-II = 0.514).
The blebs following SIT were qualified as a pale diffusely elevated conjunctiva (Grade 5) in 27 (90%) of 30 eyes and cystic blebs (Grade 6) in 3 (10%) of 30 eyes. The blebs formed following trabeculectomy with MMC were of Grade 4 in 24 (80%) of 30 eyes, and cystic blebs were observed in 6(20%) of 30 eyes of Group II cases. No definite correlation was observed between the appearance of blebs and the final IOP.
The mean postoperative central anterior chamber depth (CACD) values were 2.28±0.35 mm (preoperative 2.40±0.21mm; P=0.114) for Group I and 2.01±0.20 mm for Group II (preoperative 2.30±0.28 mm; P<0.0001) at one week postoperatively (PI-II=0.002). The mean CACD values showed no significant change in either group till the last follow-up. No case of flat anterior chambers (corneolenticular touch) was observed although mild shallowing of anterior chamber (peripheral iridocorneal touch) was seen in 2 (6.6%) of 30 cases in Group I and 6 (20.0%) of 30 cases in Group II on the first postoperative day. This resolved spontaneously at the end of first postoperative week.
Cataract progression was seen in 2 eyes (6.6%) of Group I and 6 eyes (20%) of Group II as assessed by slitlamp examination and visual acuity. None of the other patients in either group had a decrease of more than one line on Snellen's visual acuity.
No major complications were seen during the course of the study [Table - 4]. The visual field loss and optic disc neuropathy did not progress during the course of this study.
| Discussion|| |
Wound healing following glaucoma filtration surgery limits its success because of scarring of the conjunctiva, Tenon's capsule and episcleral interface. Use of adjunctive antimetabolites to decrease subconjunctival fibrosis has become a standard practice to improve the outcome of filtering surgery in eyes with poor surgical prognosis. However, the higher ocular morbidity, caused by them still remains a formidable drawback.
The method of small incision trabeculectomy avoiding Tenon's capsule,,minimises trauma to the subconjunctival tissues and decreases subconjunctival and episcleral fibrosis without using intraoperative anti-metabolites. This has been reported to obviate the chances of failure of the limbal fistula and provide good IOP control (<22 mm Hg). In the present study, 93.33% of the cases undergoing this procedure had the required IOP control without additional antiglaucoma medication at 24 months of follow-up.
Postoperative blebs following SIT were pale, diffuse and low lying. No flat anterior chambers were observed with the exception of mild peripheral iridocorneal touch seen in 2 (6.6%) of 30 eyes.
The advantage of SIT, lies in its low cost and high efficacy without the use of sophisticated instruments or pharmacological wound modulators. Other potential advantages over trabeculectomy with adjunctive antimetabolites includes the use of a small incision avoiding Tenon's capsule dissection and minimal use of cauterization which induces scarring and subsequent fistula failure.
Although a more rigorously controlled study with a longer follow-up and larger sample size is desirable, the present study demonstrates the efficacy and safety of SIT in primary chronic angle closure glaucoma. The results compare favourably with standard trabeculectomy with intraoperative use of Mitomycin C.
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[Figure - 1]
[Table - 1], [Table - 2], [Table - 3], [Table - 4]
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