Year : 2001 | Volume
: 49 | Issue : 2 | Page : 91--95
Assessing the role of subconjunctival versus intrascleral application of Mitomycin-C in high-risk trabeculectomies
Harish C Agarwal, Deepali Saigal, Ramanjit Sihota
Glaucoma Service, Dr. R.P. Centre for Ophthalmic Sciences, AIIMS, New Delhi, India
Harish C Agarwal
Glaucoma Service, Dr. R.P. Centre for Ophthalmic Sciences, AIIMS, New Delhi, India
Purpose: To compare the efficacy and safety of subconjunctival and intrascleral applications of mitomycin C (MMC) in trabeculectomy for high-risk glaucomas.
Methodology: A randomized prospective clinical study was conducted on 41 consecutive eyes with a high risk of glaucoma surgery failure. Patients were randomized to trabeculectomy and application of subconjunctival MMC or to trabeculectomy and application of intrascleral MMC. MMC solution 0.2 mg/ml was applied for 3 minutes under the conjunctival flap overlying the proposed site of trabeculectomy in Group 1 (n=21), or intrasclerally under the superficial scleral flap in Group II (n=20)
Results: After a follow-up of one year, the intraocular pressure (IOP) decreased from a mean basal IOP of 33.0 ± 8.4 mm Hg to 12.56 ± 2.54 mm Hg in Group I and from 30.9 ± 6.6 mm Hg to 11.6 ± 2.21 mm Hg in Group II. The IOP was 6 - 21 mmHg, without medication, in 90.5 % of the eyes in Group I and 75 % of the eyes Group II. Ocular hypotony, hypotony maculopathy, choroidal detachment and a shallow anterior chamber were more frequent with the intrascleral application of MMC during trabeculectomy, but the difference was not statistically significant. The overall success of the surgery at one year, i.e., achieving an IOP of 6 - 21 mmHg and a stable vision, (reduction in visual acuity of ≤2 lines), was 90.5% in Group I and 75 % in Group II.
Conclusion: No significant difference was seen in overall success or complication between subconjunctival and intrascleral application of MMC-augmented trabeculectomies in glaucomatous eyes at high risk of surgical failure.
|How to cite this article:|
Agarwal HC, Saigal D, Sihota R. Assessing the role of subconjunctival versus intrascleral application of Mitomycin-C in high-risk trabeculectomies.Indian J Ophthalmol 2001;49:91-95
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Agarwal HC, Saigal D, Sihota R. Assessing the role of subconjunctival versus intrascleral application of Mitomycin-C in high-risk trabeculectomies. Indian J Ophthalmol [serial online] 2001 [cited 2020 Apr 9 ];49:91-95
Available from: http://www.ijo.in/text.asp?2001/49/2/91/22655
The adjunctive use of mitomycin C (MMC) during trabeculectomy is recommended to improve the success of surgery in glaucomatous eyes with poor surgical prognosis.[1-3] There is, however, a risk of developing postoperative complications.[4,5] The incidence of ocular hypotony and hypotony maculopathy has been correlated with the concentration and duration of application of MMC during surgery.[6-8] A prolonged reduction of aqueous humour formation has been reported in human eyes after application of MMC at the time of trabeculectomy.[9,10] A subconjunctival injection of MMC, without filtering surgery, also lowers intraocular pressure (IOP) in rabbits, monkeys, and human eyes.[11-13] This suggests that topical application of MMC in the absence of filtering surgery causes ciliotoxicity and decreased formation of aqueous humour. The intraocular penetration of the drug and its clinical efficacy would be expected to differ in situations where the underlying sclera was altered.[14,15]
This study compares the IOP lowering effect and the complications in MMC-augmented trabeculectomies, where the MMC was applied under the conjunctival flap or beneath a superficial scleral flap.
Materials and Methods
The study was conducted at the Glaucoma Service, Dr Rajendra Prasad Centre for Ophthalmic Sciences, New Delhi, India, on patients seen over a period of 6 months. Patients who presented with uncontrolled IOP, on maximally tolerated topical therapy, and in whom there was a risk of failure of glaucoma filtering surgery were included in this study. No prior glaucoma surgery had been done in any of these eyes. Informed consent was obtained from all patients.
The eyes were randomly assigned either to group I, in which the MMC was applied under the conjunctival flap, or group II where it was placed intrasclerally, beneath a superficial scleral flap. In both groups MMC 0.2 mg/ml was applied for 3 minutes during a standard trabeculectomy.
Trabeculectomies were performed with an 8 mm limbus-based conjunctival flap. MMC solution (0.2 mg/ml) soaked in a cellulose sponge of 6x4x1 mm, dry size, was applied either under the conjunctiva or under a triangular half-thickness scleral flap of 4 x 4 mm size. After 3 minutes the tissue was irrigated with 20 ml of balanced salt solution and the trabeculectomy was completed. The superficial scleral flap was approximated with three interrupted 10-0 monofilament nylon sutures (one on each side and one at the apex). Continuous suturing of the conjunctiva was done with 8-0 vicryl suture. Postoperatively all patients received topical dexamethasone 0.1% with neomycin 1% four times a day for six weeks.
The patients were examined at day 1,3,5,7, at 2 weeks and thereafter at 4-6 week intervals for a year. At each follow-up the patient's visual acuity, IOP, status of the anterior segment and fundus were noted. All patients were followed up for one year.
The surgery was considered successful if the IOP was maintained between 6 - 21 mm Hg without further intervention or medication and there was no visual loss exceeding 2 lines of Snellen acuity. The results were statistically analyzed using the chi-square and Fisher's exact test.
Forty-one eyes of 41 consecutive patients were included in the study. Group I consisted of 21 eyes and Group II, 20 eyes. There was no statistically significant difference in baseline variables [Table:1]. The distribution of risk factors for the failure of filtering surgery in these eyes is detailed in [Table:2]. There was no significant difference in the risk factors among the two groups (p = 0.98).
The preoperative IOP was 33.05 ± 8.46 mm Hg in Group I, where subconjunctival MMC was used, and 30.95 ± 6.66 in Group II, where MMC was used intrasclerally. After an MMC-augmented trabeculectomy the IOP was reduced in both groups as detailed in [Table:3] and in the Figure. The IOP was lower after intrascleral application of MMC at every reading, though the difference was statistically not significant except on the fifth and seventh postoperative days (p = 0.03 and 0.01).
Following the subconjunctival application of MMC in trabeculectomy (Group I ), the IOP was 4.48 ± 3.20 mm Hg, at the end of the first week and 8.48 ± 3.11 mm Hg at 2-4 weeks. It stabilized by 9 - 12 weeks at 10.19 ± 2.2 mm Hg. At one year, the IOP was 12.57 ± 2.54 Hg. The control of IOP at, 6 - 21 mmHg was seen in 19 eyes (90.5 %), at the end of one year of follow up.
With intra-subscleral application of MMC (Group-II), the IOP decreased to 2.3 ± 0.92 mm Hg at the end of first week, 6.6 ± 2.08 mm Hg at 2-4 weeks and 9.45 ± 1.70 mm Hg at 9-12 weeks. The IOP stabilized at around 10 mm Hg between 3-6 months. The IOP was between 6 - 21 mmHg in 15 eyes (75 %) at one year of follow-up.
The complications seen after surgery are tabulated in [Table:4]. There was no statistically significant difference between the two groups in the occurrence of these complications (p-values ranged from 0.21 to 0.96). A three or more line deterioration of visual acuity was found in two eyes which received an intrascleral application of MMC, compared to one eye with subconjunctival application of MMC.
The visual acuity was static, ≤ 2 lines of Snellen's acuity in 20 of 21 eyes where subconjunctival MMC was used, and in 16 of 20 eyes in the intrascleral application group. After intrascleral application of MMC, there was a reduction in vision of 2 lines in two eyes due to progression of a preexisting posterior subcapsular cataract. A macular epiretinal membrane was seen at the last follow-up in one eye from the subconjunctival group and two eyes of the intrascleral group who developed hypotony maculopathy, The overall success of the surgery, i.e., an IOP of 6 - 21 mmHg and a stable vision, (reduction in visual acuity of ≤ 2 lines) was achieved in 19 eyes (90.5%) in Group I and 15 eyes (75 %) in Group II [Table:5].
Mitomycin C is used frequently during trabeculectomy under the conjunctival flap at the proposed site of trabeculectomy or under a superficial scleral flap to improve the success of surgery. The effectiveness and safety of these two sites of application has not been established yet. Decreasing the total dose of Mitomycin C, by using a lower concentration or a shorter duration of application has been shown to lower the occurrence of hypotony maculopathy.[6-8] MMC applied after dissection of a superficial scleral flap possibly enters the eye in greater concentrations than when applied over the full thickness of the sclera. Using the MMC over the full thickness of sclera would also decrease the actual dose received by the eye, and consequently its complications.
Our study shows that there was a statistically significant decrease of IOP with the intrascleral application at the end of one week. The IOP reduction thereafter was similar in both groups till the end of one year. Tressler et al have reported a similar control of IOP. In the short term, Vass et al found a lower pressure in eyes with an episcleral application of MMC. In our study, there were more frequent complications after intrascleral MMC compared to subconjunctival MMC during trabeculectomy, but the difference was not statistically significant. No statistically significant differences in the rate of complications were observed in earlier studies[14,15]
Tressler et al applied MMC 0.2 mg/ml for 5 minutes either subconjunctivally or intrasclerally in 24 eyes undergoing trabeculectomy. It was observed that postoperatively the IOP and number of medications required had decreased significantly with both modalities of MMC application: However, a significantly larger number of postoperative procedures were required to control the IOP in eyes following intrascleral MMC application. This suggests that the success rate of MMC-trabeculectomy was poorer with intrascleral application compared to a subconjunctival application though there was no statistically significant difference in the rate of complications with the two sites of application.
Vass et al compared a combined intrascleral and episcleral exposure of 0.2 mg/ml MMC for 5 minutes to an episcleral application alone, during trabeculectomy. The second postoperative week IOP showed the only statistically significant difference between eyes in the two groups - the IOP was significantly lower in the episcleral group. The authors concluded that intrascleral application of MMC be avoided, even though they did not observe an increased complication rate with the intrascleral application of MMC.
Diestelhorst and Krieglstein have demonstrated a reduction of aqueous humour formation after treatment with MMC during trabeculectomy using anterior chamber fluorophotometry. This is probably due to a direct toxic effect of the drug on the ciliary epithelium. Gass hypothesized that scleral thickness may be a factor in the pathogenesis of this condition, as there is a higher incidence of hypotony maculopathy in myopic patients. This may also explain the higher incidence of hypotony maculopathy and other associated complications when intrascleral applications of MMC over only half thickness of sclera were used.
We conclude that there is no significant difference between subconjunctival and intrascleral applications of MMC in glaucoma filtering surgery with regard to the final control of intraocular pressure or maintenance of visual acuity.
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