The wound-healing process remains the greatest determinant of success in glaucoma filtration surgery, as complications occurring during this process may impair IOP control, worsen the prognosis and/or cause progression of disc cupping and visual field loss . Eyes in which trabeculectomy has failed have a higher risk of further failure with subsequent filtering surgeries, including drainage devices [8,9,10,11, 15]. The use of mitomycin C and 5-fluorouracil improves the success rate, but also increases the risk of complications [10, 15,16,17].
Unlike classic trabeculectomy, our surgical procedure has the advantage of using two different drainage pathways to lower the IOP: the anterior chamber to subconjunctival space fistula and the uveoscleral drainage through the SCS. If the filtration bleb becomes increasingly vascularized and/or excessive capsular fibrosis appears, the uveoscleral pathway may be still patent.
The pathophysiological basis of bleb scarring appears to be related to exposure to aqueous humor that contains a higher concentration of inflammatory mediators, which in turn can activate a fibrotic response after contact with vascular Tenon tissue [18, 19]. In our technique, the intrascleral pathway does not come into contact with vascular Tenon tissue, raising the expectation that a fibrotic response will not be activated and indeed may remain patent. Another point to consider in the generation of fibrosis is the location of the drainage route. Previous studies suggest that the SCS may have a lower frequency of fibrosis compared to the subconjunctival space due to differences in cell proliferation .
The suprachoroidal surgical approach has other factors that led us to select it, such as the clinically relevant choroidal resorptive function, the negative difference in hydrostatic pressure and the natural counterpressure of the SCS. Our search of the literature found evidence that these factors may counteract the appearance of hypotony while maintaining aqueous drainage [14, 21, 22]. Also, the SCS is an attractive route of drug delivery, bypassing the sclera and diffusing rapidly into the posterior segment . This may be specially useful in patients with uveitic glaucoma and retinal diseases associated with macular edema for whom it is hard to maintain therapeutic drug concentrations .
Our intervention is not the only one that has used the SCS as a filtration pathway; a number of previous studies have used this approach with varying degrees of success. These interventions use different devices, such as modified tubes or complex devices, that are inserted into the SCS, such as, for example, the Gold Micro Shunt (SOLX Ltd, Boston, MA, USA) and the CyPass Micro-Stent (Alcon, Fort Worth, TX, USA). Compared to standard trabeculectomy, the success rate of some of these procedures has been shown to be higher than that of trabeculectomy, with differences varying between 10 and 30%. Also, the frequency of complications appears to be approximately 20% lower [14, 15, 25,26,27,28]. When we evaluated the intervention against other procedures employing suprachoroidal devices, we observed that those surgeries present a success rate of approximately 70–90% compared to nearly 100% in our technique.
The present intervention has unique characteristics because it uses the SCS without resorting to devices designed to maintain it. One important advantage is that it uses only scleral tissue from the patient’s own eye. Another important advantage is the long follow-up and evidence of the maintenance of the mentioned space over time. A complete success rate, defined as controlled IOP without additional medications remained high during the follow-up (80.65%) as compared to other interventions [14, 15, 25,26,27,28].
The procedure described in our study offers multiple advantages. By using autologous scleral tissue, there is a tendency to avoid rejection as well as the risk of fibrotic reaction consecutive to the presence of a foreign body. The location of the suprachoroidal incision, above the pars plana, may tend to decrease the risk of cyclodialysis, as well as that of severe intraoperative and postoperative hemorrhages. During the follow-up period we did not observe any bleb-related complications or surgical failure secondary to subconjunctival fibrosis . The use of an aqueous conductive channel totally formed by sclera may have some advantages over the episcleral devices, including the lack of conjunctival erosions, lower risk of endophthalmitis secondary to explant exposition and absence of damage to the extraocular muscles [24, 30].
In addition, as this procedure does not depend exclusively on the filtrating bleb it can be performed in eyes in which the conjunctival scarring would not allow a conventional filtration surgery . Another advantage is that in our procedure there are no foreign bodies in the anterior chamber, thereby avoiding contact complications such as corneal decompensation and cataracts .
The report of surgical complications is quite heterogeneous among studies. Despite these differences, the overall frequency of complications is higher in standard trabeculectomy than in interventions using suprachoroidal devices [8, 11, 18]. In our study, the frequency of complications was low, even in comparison with similar interventions [9, 25,26,27,28], with no serious complications or challenging situations, such as infections or prolonged hypotony.
We found that the IOP was significantly reduced in all patients and that most patients were able to stop glaucoma medication usage after the 24 months of follow-up. In patients who required medical treatment, the number of different medications decreased significantly, the majority ultimately only using a single drug. Patients’ visual acuity was not affected by the procedure, and no permanent or severe complications were observed.
We have included some operated cases of both eyes with this technique. It can be argued that the fellow eyes are not independent because they may share success/failure factors. We acknowledge this point as a potential limitation.
A limitation of the procedure is its long learning curve, due to the complexity of performing the two scleral flaps and creating a patent tunnel. Despite this, we believe that the advantages of the procedure far outweigh this limitation. Despite having a significant loss of follow-up, we do not believe that this has affected the end results of the study. The follow-up at 12 months did not present losses and had comparable results. Also, the demographic characteristics of the patients at the beginning and end of the study were similar. While the number of participants in this study is higher than those used in similar studies, it is still insufficient to obtain definitive results.