What are the advantages of deep sclerectomy over ab externo trabeculectomy in open-angle glaucoma?
Maria da Luz Freitas, MD, FEBOS Glaucoma
A esclerectomia profunda é uma cirurgia filtrante, cuja vantagem sobre a trabeculectomia é baixar a pressão intra-ocular no período intra-operatório de forma gradual e progressiva, através da passagem controlada do humor aquoso entre a câmara anterior e o espaço subconjuntival. Com esta técnica cirúrgica não há abertura da câmara anterior, nem saída abrupta de humor aquoso ou perda de profundidade daquela. Este facto reduz para quase zero as atalamias e os descolamentos coroideus e, a inflamação intra- e pós-operatória é bastante menor. Esta realidade associada à não aplicação de atropina no pós-operatório faz com que o olho no dia seguinte à cirurgia esteja calmo, com recuperação visual e restituição da vida activa bastante rápida. O aumento de segurança faz com que este procedimento seja feito em regime de ambulatório. A passagem controlada e progressiva do humor aquoso é conseguida com a abertura do canal de Schlemm, a criação de uma janela trabeculo-descemética e o “peeling” da face interna do canal de Schlemm que muitas vezes se associa a microperfurações da malha justacanalicular. J. Vaudaux e A. Rossier1,2, após terem realizado estudos em olhos enucleados chegaram à conclusão de que a velocidade de saída humor aquoso e descompressão da câmara anterior é 5,5 vezes menor na esclerectomia profunda, havendo também um aumento da área de drenagem nesta técnica cirúrgica, permitindo uma saída sustentada ao longo do tempo.
Therefore, notwithstanding the initial purpose – aqueous humor drainage, deep sclerectomy:
- does not enter the anterior chamber;
- allows controlled outflow of aqueous humor;
- does not cause athalamia or severe intra-operative hypotony (avoiding choroidal detachment and macular or papillary changes);
- does not require iridectomy (decreasing inflammation and keeping flow dynamics unchanged);
- decreases the triggering of inflammatory factors;
- no vitreous prolapse (rare, but can occur in trabeculectomy);
- does not require post-operative atropine.
Consequently, there are fewer peri-operative complications, fewer immediate post-operative complications and the recovery is faster. Deep sclerectomy can be performed in outpatient clinics and surgical indications have increased.
Sometimes, goniopuncture is required in the immediate or late post-operative period. Goniopuncture is an adjunctive deep sclerectomy procedure, such as YAG capsulotomy in cataract surgery or needling in trabeculectomy. It is a safe, effective procedure and does not increase the risk of infection or the need to use the operating room, such as in bleb needling.
Furthermore, and importantly, the cataractogenic effect is lower. There are several contributing factors: slow decompression, absence of athalamia, less inflammation, absence of iridectomy. According to the Advanced Glaucoma Intervention Tria3, 78% of eyes undergoing primary trabeculectomy developed cataracts after 5 years, and that the risk of developing cataracts doubles with the presence of shallow anterior chambers and major inflammation in the post-operative period. Shaarawy et al.4 reported that the 64-month progression of senile cataract was 25% in patients undergoing deep sclerectomy.
There is a widespread notion that deep sclerectomy is less effective than trabeculectomy. Several factors contribute to this notion. One of the most important is that deep sclerectomy has a longer learning curve than trabeculectomy, requiring an effective opening of Schlemm's canal and full peeling. This perception requires training. I became aware of this myself when comparing two identical groups I had operated on – one during the learning curve and another at 10 years: not only did I find a greater percentage decrease in tension (36.7% vs. 40.4%), but also a lower 12-month mean IOP (18.6 mmHg vs. 15.7 mmHg)5.
Another factor is patient selection: open angles have to be at least Shaffer classification Grade 3. In narrower angles without peripheral anterior synechiae, this technique can be used in combined surgery (deep sclerectomy plus cataract phacoemulsification).
Many studies include the learning curve, but the point is that there is in fact no randomized study comparing both techniques, using identical populations and performed by the same surgeons.
However, I cannot fail to mention a paper published by Bissig et al.6 which assesses 10-year results in the first 105 eyes undergoing deep sclerectomy with collagen implants conducted by André Mermoud. This paper reported that the qualified 10-year success was 89%, with a mean pre-operative IOP decrease of 26.8 ± 7.7 mmHg to a mean post-operative IOP of 12.2 ± 4.7 mmHg. Corrected visual acuity dropped from 0.71 ± 0.33 to 0.53 ± 0.25 on the first day after surgery, recovering within one month and maintaining this for 10 years (10-year cataract surgery rate of 40%). During this time (from month 1 to month 119), goniopuncture was conducted in 61 eyes, with an average of 29 months between sclerectomy and goniopuncture. No major complication was described.
As there are fewer inflammatory processes, fibrosis mechanisms also decrease, and in glaucoma secondary to uveitis surgical efficacy increases substantially.
Opening the Schlemm's canal, the creation of a trabeculo-Descemet’s window and the peeling of the inner wall of Schlemm's canal, which is often associated of juxtacanalicular meshwork microperforation, allow a slow outflow of the aqueous humor. Besides, creating this space, combined with the creation of the intrascleral space, increases the filtration area both at the time of surgery and permanently over time, also allowing for complementary drainage routes (Schlemm's canal, ciliary body). Besides improving results with goniopuncture, this also provides more flattened filtering blebs, which do not interfere as much in lacrimal film dynamics and consequently in patient comfort.
3. Increased indications
Generic surgical indications for glaucoma are: non-medically controlled glaucoma, glaucoma or ocular hypertension intolerant to medical therapy and therapy non-compliance. Non-medically controlled glaucoma is the glaucoma with signs of disease progression, as proven by perimetry or focal or general increase of the cup-to-disk ratio.
Deep sclerectomy can be performed alone or in combination with phacoemulsification in all situations with an intact camerular angle of at least Schaffer classification Grade 3.
Therefore, it is indicated in: primary open-angle glaucoma; pseudoexfoliation glaucoma; pigmentary glaucoma; steroid-induced glaucoma; glaucoma in pseudophakic or phakic eyes; other secondary open-angle glaucoma.
Since deep sclerectomy is much less pro-inflammatory and there is no fast decompression, it is preferentially indicated in glaucoma secondary to uveitis, glaucoma in high myopia, and glaucoma associated with Sturge-Weber syndrome or nanophthalmos.
Another group in which trabeculectomy poses an increased surgical risk is in terminal open-angle glaucoma. Due to the safety and efficacy of deep sclerectomy, this should be the preferential technique for this patient group7.
4. Possible use of premium lenses
Glaucoma patients are an exclusion factor for every project aimed at launching or studying premium lenses. There are different reasons for the exclusion when considering multifocal premium lenses and toric monofocal premium lenses. Multifocal lenses alone can cause scotopic and mesopic contrast sensitivity changes, in addition to photopic and glare phenomena8,9,10,11. In spite of the reduced changes with latest generation diffractive aspheric multifocal lenses12,13, it is consensus that they should not be used, even in initial glaucoma. Using this type of lenses in these patients may solve the problem of using glasses, however it affects the already debilitated quality of vision in glaucoma patients even more. According to Korth et al.14 in his synopsis of several electrophysiological tests – color, spatial and temporal contrast sensitivity studies, initial glaucoma shows reduced contrast sensitivity, especially in mesopic conditions, which can be correlated with perimetric changes, interfering in daily activities.
Toric monofocal premium lenses raise other issues: if patients with a toric monofocal lens require glaucoma surgery, what is the astigmatism or spherical error induced? Or, when performing a combined surgery, is the astigmatism induced by the combination of both surgeries distinct from the astigmatism induced by cataract surgery alone? Once again, there are few published papers to help us assess refractive changes caused by different glaucoma surgeries. Furthermore, existing papers analyze a very small number of eyes. In 2004, Egrilmez et al.15 published a comparative study on keratometric changes induced by trabeculectomy, T-flux deep sclerectomy and viscocanaloplasty. He concluded that trabeculectomy induced astigmatism the most: 1.24 ± 0.96 Diopters (D) versus 0.88 ± 0.47 D with deep sclerectomy versus 0.42 ± 0.22 D with viscocanaloplasty. Another study16 showed that 47.4% of deep sclerectomy cases induced with-the-rule astigmatism (0.03 ± 1.67 D). In 2013, I started a prospective study of changes I had induced when performing deep sclerectomy with an Aquaflow implant, alone or as a combined procedure. Although the sample included 50 eyes, the astigmatic changes induced in 90% of the cases in deep sclerectomy alone were < 0.5 D, with an axis variation of 1.6º ± 6.1º; in the combined procedure, the magnitude of the induced astigmatism was similar, but axis variations ranged between 20º and 25º.
Despite samples being small in all of these studies and the need to increase the number of eyes, it seems that astigmatic changes caused by non-penetrating procedures (deep sclerectomy and viscocanalostomy) are reduced and compatible with toric monofocal premium lenses. However, it should be recognized that, as in phacoemulsification, induced changes are surgeon-specific, so each surgeon should conduct their own astigmatism induction study and lens estimation tables should include this factor in combined surgery
The advantages of deep sclerectomy over trabeculectomy in open-angle glaucoma are: safety, without loss of efficacy. Consequently , this surgical procedure can be performed in an outpatient setting, with fewer complications, a fast recovery and return to active life. Moreover, it is also clinically indicated in previously very high risk situations.