Study of efficacy and timing of laser suture lysis in reducing intraocular pressure after trabeculectomy with mitomycin-C

Abstract

Context:

Laser suture lysis is used to enhance filtration after trabeculectomy.

Aims:

The aim of this is to evaluate the change in intraocular pressure (IOP) after laser suture lysis after trabeculectomy with mitomycin-C and to correlate the efficacy of suture lysis in relation to the time of lysis.

Settings and Design:

Prospective interventional study of seventy eyes of seventy patients.

Subjects and Methods:

Trabeculectomy with mitomycin-C was performed for 352 patients with glaucoma. Laser suture lysis was carried out when indicated for seventy patients during 2^nd–8^th week posttrabeculectomy. Primary outcome measures were IOP at immediate postsuture lysis, 1, 2, 4, 6, and 8 weeks, 3 and 6 months following laser suture lysis. For the purpose of statistical analysis, patients were divided into three groups depending on the week of suture lysis as <3 weeks, 3^rd–5^th week, and >5 weeks posttrabeculectomy and 21 mmHg was used as the cutoff for the achievement of target IOP.

Statistical Analysis Used:

Descriptive statistical analysis has been carried out. Significance is assessed at 5% level of significance. Student's t-test (two-tailed, independent) has been used to find the significance of study parameters on continuous scale between two groups. Chi-square/Fisher exact test has been used to find the significance of study parameters on categorical scale between two or more groups.

Results:

On immediate postsuture lysis, 62 patients (88.6%) had IOP of <21 mmHg which increased to 68 patients (98.6%) at the end of 6 months postsuture lysis. When laser suture lysis was performed during 3^rd–5^th week posttrabeculectomy, 34 patients (73.9%) achieved the target IOP.

Conclusions:

Laser suture lysis during 3^rd–5^th week posttrabeculectomy with mitomycin-C is an effective and safe technique for reducing IOP.

Introduction

Trabeculectomy aims to promote a filtering conjunctival bleb where a scleral flap must be loose enough to permit aqueous outflow, but taut enough to prevent postsurgical ocular hypotony and shallow or flat anterior chambers. Failure of bleb formation in the immediate postoperative period in the presence of a high intraocular pressure (IOP), deep anterior chamber, and patent internal ostium on gonioscopy may be due to an over tight sclera flap. Titration of filtration in the postoperative period is currently attempted with laser[1,2] or a releasable suture technique.[3]

Laser suture lysis has the advantage of being a simple technique which can be performed as an outpatient procedure which does not require the acquisition of new surgical skills unlike releasable sutures,[4] with prolonged surgical time. Other complications of releasable sutures are windshield wiper keratopathy, discomfort to patient, suture track infection, and need for meticulous follow-up.

Hence, this study was undertaken to evaluate the outcomes of eyes that underwent laser suture lysis following trabeculectomy with mitomycin-C and to correlate the efficacy of suture lysis in relation to the time of lysis.

Subjects and Methods

Prospective interventional study of seventy eyes of seventy patients was conducted.

Fornix-based trabeculectomy with intraoperative use of mitomycin-C (0.4 mg/ml for 3 min) was performed for 352 patients with glaucoma. All the surgeries were done by a single surgeon. The triangular partial thickness scleral flap of trabeculectomy was sutured with only one apical suture, using nylon 10–0 suture material.

Laser suture lysis was done in seventy eyes during 2^nd- 8^th week posttrabeculectomy. The indication for the procedure was the presence of over tight sclera flap with failing filtration bleb-associated with high IOP (22 mmHg or more for mild glaucoma, 17 mmHg or more for moderate glaucoma, and 12 mmHg or more for severe glaucoma), deep anterior chamber, and patent internal ostium on gonioscopy. Informed written consent was taken from these patients. After anesthetizing the eye with topical proparacaine, the apical scleral flap suture was visualized through the conjunctiva over the bleb using Blumenthal laser suture lysis lens [Figure 1]. Gentle pressure on the conjunctiva by overlying lens caused thinning and blanching of conjunctival vessels allowing the sutures to be easily brought into focus even in the presence of subconjunctival hemorrhage and conjunctival edema. The suture was cut [Figures 2 and 3] using diode laser. Laser parameters used were energy 200–400 mW, spot size 50 micron, duration 0.1 s.

Figure 1.

Volk Blumenthal laser suture lysis lens

Figure 2.

Suture as seen through Volk Blumenthal lens

Figure 3.

Suture cut as seen through lens

Primary outcome measures were IOP at immediate postsuture lysis (within 5 min of suture lysis), 1, 2, 4, 6, and 8 weeks, 3 and 6 months following laser suture lysis.

For the purpose of statistical analysis, patients were subgrouped into three groups depending upon the week of laser suture lysis as <3 weeks, 3^rd–5^th week, and >5 weeks posttrabeculectomy and 21 mmHg was used as the cutoff for the achievement of target IOP in this particular study.

Results

The age distribution of the patients is shown in Graph 1.

Graph 1.

Age distribution of patients in the study group

The percentage of patients in the various subtypes of glaucoma is depicted in Graph 2.

Graph 2.

Subtypes of glaucoma in the study group

Mean presuture lysis IOP was 19.87 ± 3.18 mmHg and immediate postsuture lysis IOP was 13.68 ± 3.97 mmHg across all the study groups [Table 1 and Graph 3].

Table 1.

Pattern of intraocular pressure according to weeks of laser suture lysis

Graph 3.

Intraocular pressure at each study point in the three subgroups. Pretrab = Pretrabeculectomy, Prelysis = Prelaser suture lysis, Immd post lysis = Immediate post laser suture lysis

On immediate postsuture lysis, 62 patients (88.6%) had IOP of <21 mmHg which increased to 68 patients (98.6%) at the end of 6 months postsuture lysis [Graph 4].

Graph 4.

Comparison of percentage of patients who had Intraocular pressure of <21 or >21 mmHg at each study point. Pretrab = Pretrabeculectomy, Prelysis = Prelaser suture lysis, Immd post lysis = Immediate post laser suture lysis

After a mean follow-up of 6 months, 48 patients (68.6%) had successfully controlled IOP without antiglaucoma medication.

We could achieve about 30% reduction in the IOP by performing laser suture lysis following trabeculectomy with mitomycin-C [Graph 5].

Graph 5.

Percentage change in intraocular pressure when compared to prelysis intraocular pressure at each study point in the three subgroups. Pretrab = Pretrabeculectomy, Prelysis = Prelaser suture lysis, Immd post lysis = Immediate post laser suture lysis

Six patients (75.0%) achieved target IOP in the subgroup of patients for whom laser suture lysis was done earlier than 3 weeks posttrabeculectomy with mitomycin-C.

Target IOP was reached in 34 patients (73.9%) when laser suture lysis was performed during 3^rd–5^th week.

Only in eight patients of 16 patients (50.0%), target IOP was reached in the subgroup of suture lysis after 5 weeks of trabeculectomy [Graphs 6 and 7].

Graph 6.

Percentage of patients in the three subgroups

Graph 7.

Percentage of patients in whom target was achieved in each subgroup

Target IOP achieved is positively correlated to lower week of lysis with P = 0.234.

Complications such as shallow anterior chamber and hypotony occurred in 3 (0.04%) eyes in the subgroup wherein laser suture lysis was performed earlier than 3 weeks posttrabeculectomy.

Statistical methods

Descriptive statistical analysis has been carried out in the present study. Significance is assessed at 5% level of significance. Student's t-test (two-tailed, independent) has been used to find the significance of study parameters on continuous scale between two groups. Chi-square/Fisher exact test has been used to find the significance of study parameters on categorical scale between two or more groups.

Discussion

The technique of suture lysis was first described by Leiberman with a Goldmann goniolens in 1983. More recently, new lenses have been designed to facilitate the procedure and laser suture lysis has become an established procedure to titrate filtration and in the management of failing blebs.[5]

Laser suture lysis is an effective alternate method to releasable sutures of decreasing scleral resistance to aqueous outflow and lowering IOP. Suture lysis remains effective before healing of the tissues, which can vary based on the use of mitomycin-C, its concentration and the timing of exposure, tightness of the sutures among other factors. It can also depend on factors such as tendency to fibrosis, which can vary from patient to patient.

We could achieve successful control of IOP in 48 patients (68.6%) with a mean of 12.97 ± 2.81 mmHg without antiglaucoma medication after follow-up of 6 months after laser suture lysis.

In a similar study conducted by Singh et al., 18 patients (90%) had successfully controlled IOP (mean 14.1 ± 3.6 mmHg) without medication after a mean follow-up of 6 months.[4]

The difference in percentage of patients who achieved target IOP between these two studies is due to the difference in timing of suture lysis. Laser suture lysis was performed for 29 patients (41.4%) during 3^rd–5^th week and for 38 patients (51.3%) after 5 weeks posttrabeculectomy in our study, whereas Singh et al. did the procedure for most of their cases 2–3 days after drainage surgery, which could account for their higher rate of success. Another difference between these two studies is intraoperative use of antimetabolite during trabeculectomy: We used mitomycin-C for all our cases, whereas 5-fluorouracil was used only for three cases in their study.

According to our study, laser suture lysis is more safe and effective during 3^rd–5^th week posttrabeculectomy with mitomycin-C. Target IOP achieved is positively correlated to lower week of suture lysis with P = 0.234. The percentage of target IOP achieved was less in the subgroup wherein suture lysis was done after 5 weeks of trabeculectomy. A longer time interval between surgery and laser suture lysis may result in both a lesser degree of IOP reduction and a lower incidence of subsequent hypotony.[6]

Although the incidence of complications was less in our study, we noticed shallow anterior chamber and hypotony in three (0.04%) eyes when laser suture lysis was done earlier than 3^rd week posttrabeculectomy. One patient with shallow anterior chamber was managed conservatively whereas the other patient with shallow anterior chamber and another patient with hypotony required surgical intervention.

Bardak et al. in their study of ocular hypotony after laser suture lysis following trabeculectomy with mitomycin-C have also mentioned that early application of laser suture lysis results in lower final IOPs, but has a higher risk of hypotony.[7]

According to Kolker et al., laser suture lysis has the following limitations: Failure of laser suture lysis due to thick overlying Tenon's capsule, postoperative inflammation, and subconjunctival hemorrhage.[8] We did not face these complications in our study, and we could cut the suture using laser energy in all our patients. This was accomplished due to excellent visualization of the suture using Blumenthal suture lysis lens.

The target IOP of 21 mmHg was not achieved in 22 eyes (31.4%) even after successful laser suture lysis. This could be attributed to scarring at the episcleral surface causing bleb failure and other patient related factors such as very advanced glaucoma. We tried to salvage the failing bleb with 5-fluorouracil subconjunctival injections with or without needling of the bleb depending on the extent of the scarring as advised by Vijaya et al.[9]

Antiglaucoma medications were started depending on the clinical condition of the patient when all the above said measures failed to achieve the target IOP.

The limitation of our study was that proper subgroup analysis depending on the type and severity of glaucoma was not possible due to inadequate sample size which would make calculation of statistical significance irrelevant.

Conclusions

Laser suture lysis is a simple technique which can be performed as an outpatient procedure to reduce IOP posttrabeculectomy. It is more safe and effective when it is done during 3^rd–5^th week posttrabeculectomy with mitomycin-C.

Financial support and sponsorship

This study was supported by the Nethradhama Superspeciality Eye Hospital, Bengaluru.

Conflicts of interest

There are no conflicts of interest.