Why switch from conventional trabeculectomy to the modified Moorfields Safer Surgery (MSS) trabeculectomy?
Fernando Trancoso Vaz, MD
The trabeculectomy is the most frequent glaucoma surgery in the world. Despite its effectiveness, conventional trabeculectomy is often linked with a high rate of complications associated with excessive drainage of aqueous humor.1,2 Several surgical techniques have been developed with the aim of reducing these complications, such as the modified Moorfields Safer Surgery (MSS) trabeculectomy. In general terms, the main advantages associated with these modifications are improved reproducibility and safety of the trabeculectomy, which results in improved intra- and postoperative intraocular pressure (IOP) control and a lower rate of immediate postoperative complications.1,2 This chapter aims to describe these factors. Table 1 summarizes the comparison between the two techniques (conventional vs. MSS), considering the changes adopted by the authors in the transition between the two techniques.
· Main disadvantages of the conventional technique:
1. Less IOP intraoperative control, with a higher risk of hypotony and athalamia during surgery and associated postoperative complications, such as choroidal hemorrhage, macular edema and corneal decompensation.1,2 Although many surgeons use viscoelastic in the anterior chamber, it frequently suffers fluctuations and, consequently, IOP fluctuations, which may be associated with a greater risk of decompression.
2. Variability of the postoperative filtration rate. Despite its efficacy, conventional trabeculectomy is associated with a relatively high complication rate, sometimes secondary to excessive drainage of the aqueous humor (hypotony, athalamia, hypotony maculopathy, choroidal detachment, suprachoroidal hemorrhage, malignant glaucoma, and cataract). This hyperfiltration is more difficult to control (difficult to control the degree of tightening of the scleral sutures).1-4
Main advantages of the MSS technique:
1. Increased safety of the procedure associated with:
1.1. Improved IOP control during surgery by maintaining the anterior chamber stability and preventing the abrupt reduction of IOP, by using an anterior chamber stabilizer with continuous infusion of balanced saline solution (Balanced Salt Solution BSS). This factor was also demonstrated in the study performed at our hospital in 2015 regarding the analysis of possible changes in the anterior chamber observed with a Scheimpflug chamber (Oculus - Pentacam®), the study having indicated the presence of small changes in the parameters of the anterior chamber, without repercussion on its stability.1,2,5
1.2. Increased reproducibility and drainage control by tightening the adjustable/removable sclera sutures under a constant BSS flow and adjusting the tightness according to the latter. After surgery, if IOP is high, it is possible to adjust and/or remove the extra sutures to increase the drainage which, meanwhile, has been controlled. This factor was demonstrated in the study by Minwen et al.3 that compared the trabeculectomy with and without absorbable sutures. 1-4
1.3. Subconjunctival debridement/larger and more diffuse Tenon and diffuse application of Mitomycin C (MMC, when necessary) underneath the flap to allow the obtainment of a large non-cystic filtration bleb, with fewer complications. This factor was demonstrated in the study by Wells et al.6 on the formation of cystic blebs and associated late complications after trabeculectomy with application of MMC.1,2,6
2. Increased reproducibility of the procedure associated with:
2.1. Use of 0.5 mm punch, with the creation of a sclerotomy always of the same size and not variable as in conventional trabeculectomy.1,2
2.2. Standardized intraoperative tightening, under continuous infusion of BSS, of the extra scleral sutures (adjustable/removable).1.2
3. Simplicity of the technique, being easy to implement:
3.1. Need for little additional equipment
3.2. Short learning curve2
|Steps||Conventional Trabeculectomy||MSS Trabeculectomy||Advantages|
|Conjunctival incision||Limbus base||Fornix Base||Larger filtration area|
|Antifibrotics||Under and over the flap||Under and over the flap and in an extensive and quite posterior area||Broad and diffuse bubbles, with fewer risks than the cystic|
|Paracentesis||Without AC Maintainer||With AC stabilizer||Safety|
|Sclerotomy||With 15º knife/
|With 0.5mm punch||Reproducibility|
|Scleral flap suture||2 fixed sutures||2 fixed sutures + ≥2 adjustable sutures||Safety and reproducibility|
Table 1 – Comparison of the two techniques (conventional vs. MSS), considering the changes adopted by the authors in the transition between techniques.
Unfortunately, there are no comparative studies between the two techniques and, as a consequence, we have to rely on studies in which the surgical techniques are evaluated individually. On the other hand, it is difficult to establish a complete comparison between the existing studies, even with respect to complications, since the populations, the type of glaucoma and the success rate criteria are not always identical. The retrospective study by Shigeeda et al. 7 on conventional trabeculectomy reports a success rate of 74% at 6.8 years, with bleb fluid leakage in 7.9 ± 2.6% of the eyes, prolonged hypotony in 8.3 ± 2.5% and blebitis in 5.9 ± 2.4%. The study by Khaw et al.1 on MSS trabeculectomy reports a success rate of 98.7% at 3 years, with a lower rate of complications: blebitis, endophthalmitis and hypotony maculopathy in 0.2%, each, and no cases of suprachoroidal hemorrhage. The Stalmans et al.2 study also refers a low rate of complications (hypotony in 1.5% up to the 3rd week, athalamia in 1.8%, choroidal detachment in 8.9% up to the 12th postoperative month and no cases of bleb leakage). This study also highlights the stability of IOP at levels below 12 mmHg throughout the follow-up, from the 1st day to the 21st postoperative month. The preliminary study performed at our hospital in 2011,8 presented at the 4th World Glaucoma Congress (2011, Paris), with the first 32 operated eyes (28 patients), showed an average IOP at the first month of 10.75 ± 4.15 mmHg and at the third month of 10.83 ± 2.5 mmHg, and also infrequent postoperative complications (bleb fluid leakage in 3%, hypotony by week 2 in 3% and choroidal detachment during follow-up in 6%).5 Other studies using the same technique corroborate these data.
Why switch from Conventional Trabeculectomy to the Modified Moorfields Safer Surgery (MSS) Trabeculectomy? Because a more reproducible, safer technique is obtained, with greater IOP control, with fewer complications and, because of its short learning curve, an easy transition without major costs or the need to resort to implants or devices. To summarize, the changes that occur with the MSS technique that result in these characteristics are: extensive dissection of the conjunctiva, wide area of application of MMC (if necessary), use of an anterior chamber Maintainer with continuous infusion of BSS, standardized sclerostomy with punch and combination of fixed and adjustable/removable scleral sutures.1,2,5