Primary Open-Angle Glaucoma (POAG) is a chronic progressive optic neuropathy with characteristic morphological changes at the optic nerve head and retinal nerve fiber layer, in the absence of other ocular or congenital anomalies. It is the second leading cause of blindness in the world after cataract and the leading cause of permanent blindness. Glaucoma treatment consists of lowering intraocular pressure (IOP), which can be performed by topical eye drops, laser, or surgery. Even with treatment, there is 15.5% blindness per 7.5±5.5 years.
Considering the irreversible nature of the glaucomatous damage, it is fundamental to treat it early and effectively. Surgery is more effective in decreasing IOP (48% mean decrease) than medication (18-35%) and laser (25.6%). Surgery is usually considered when medical therapy is deemed inappropriate, not tolerated, insufficient, and either glaucoma progresses (documented by visual fields, OCT, or other) or has a high risk of progression. Trabeculectomy is a traditional glaucoma surgery modality. Trabeculectomy consists of opening a guarded hole in the eye within the trabeculum, to allow drainage of the aqueous humor and consequently to decrease the IOP. Trabeculectomy is invasive and has a high complication rate.
There are many non-penetrating alternatives to trabeculectomy that aim to have the same effectiveness in decreasing IOP but fewer complications.
The most widely known non-penetrating surgery is deep sclerectomy.
Etiology and risk factors
The etiology of glaucoma is unknown. However, several of glaucoma's risk factors are known:
- Ethnicity: The Afro-Americans and Afro-Caribbeans have a higher prevalence of PAOG than Caucasians.
In Latinos, the prevalence is higher than Caucasians but inferior than the prevalence in Afro-Americans and Afro-Caribbeans.
- Pseudoexfoliation syndrome increases the risk of POAG.
- Pigment dispersion syndrome
- Moderate to high myopia (greater than three diopters)
- Low ocular perfusion pressure 
The pathophysiology of glaucoma is not yet fully understood. However, two leading theories are usually put forward to explain the apoptosis of the retinal ganglion cells (RGC).
The first theory is the mechanical theory; it explains apoptosis as a consequence of a break in the axonal transport of RGC at the lamina cribrosa, secondary to high intraocular pressure (IOP). Various studies have shown IOP as a risk factor for glaucoma. However, this theory does not fully explain the pathophysiology of glaucoma: intraocular hypertension is insufficient to make a glaucoma diagnosis, and there is glaucoma even within normal ranges of IOP (normal-tension glaucoma).
The second theory is the vascular theory, which proposes the apoptosis of RGC as a result of a decrease in local vascular flow, due to mechanical effects such as IOP, or systemic effects such as cardiovascular risk factors. This decrease in blood flow is associated with a vaso-regulatory dysfunction. The resulting hypoperfusion and loss of vascular self-regulation lead to ischemia and a cascade of oxidative stress, which leads to the apoptosis of RGC.
In 1856, Albrecht von Graefe proposed an iridectomy to treat acute angle-closure glaucoma. In 1867 (1879), Wecker performed the first filtering surgery; later, Lagrange reported a sclerecto-iridectomy and Elliot, the trephining operation. These were full-thickness procedures: the aqueous humor left directly from the anterior chamber to the sub-conjunctival space, through a limbal scleral wound. They carried a high risk of complications, namely infection, hypotony, cataract, and leak.
In 1964, Krasnov created the first non-penetrating filtering surgery: the sinusotomy. In 1968, Cairns reported the first trabeculectomy. He dissected a corneoscleral flap, excised a segment of the trabeculum and Schlemm's canal, and sutured the flap. The trabeculectomy had significantly reduced the risk of hypotony, leaks, and infections. Later, it was found that mitomycin-C extended bleb survival, as well as 5-Fluorouracil.
In 1989, Kozlov and Fyodorov described the deep sclerectomy. They unroofed the Schlemm's canal, reducing the resistance of the remaining trabeculum to the aqueous flow. IOP was reduced with fewer complications. In 1999, Stegmann reported the viscocanalostomy; later, canaloplasty was proposed.
More recently, new approaches have been developed in micro-invasive glaucoma surgery (MIGS). MIGS aims to have: small ocular trauma, fast recovery with a better quality of life, good security profile, and internal implantation. A recent systematic review compared several MIGS devices, and it concluded they seem to be effective and safe, but more studies are needed.
A glaucoma surgeon should be familiar with different surgical techniques and use the indications and advantages of each to improve the patient's outcome.
Knowledge of anatomy is fundamental for performing a successful deep sclerectomy.
This surgery is highly technical, has a steep learning curve, and depends on the understanding of the anatomy to identify the surgical limbus and the Schlemm's canal.
a) Iridocorneal angle
The iridocorneal angle is limited by the cornea, anteriorly, and the iris, posteriorly. Figure 1 illustrates the iridocorneal angle structures. Figure 2 illustrates them with an OCT. In an open-angle, the visible structures are, from anterior to posterior:
1. Schwalbe's line. The most anterior structure is Schwalbe's line, a pigmented line that shows the transition between the Descemet membrane and the trabeculum. Its width is of 50-150 µm. The corneal wedge can be useful to identify a less pigmented Schwalbe's line: the two linear light reflexes that arise with a narrow slit of light, cross each other in the Schwalbe's line.
2. Non pigmented trabeculum, adjacent to the Schwalbe's line; the first part of the trabeculum.
3. Pigmented trabeculum. This part of the trabeculum is the functioning, filtering part of the trabeculum (mnemonics: the pigmented trabeculum is the working part of the trabeculum; therefore, it gets pigmented or "dirty" by filtering pigment and residues). It is more pigmented inferiorly (possibly due to gravity) and in dark irises. The trabeculum or trabecular meshwork is responsible for 70 to 90% of the aqueous humor outflow. Its inner face is juxtaposed to the Schlemm's canal, while its external face contacts the aqueous humor. When performing a selective laser trabeculoplasty, the whole trabeculum should be aimed. When performing an argon laser trabeculoplasty, the aim should be between the pigmented and non-pigmented trabeculum. Besides pigmented and non-pigmented trabeculum, there is another important classification for the trabecular meshwork:
3.1 Uveal meshwork. The innermost portion of the trabeculum is adjacent to the aqueous humor, inserting from the iris root to the peripheral cornea. It is formed by ropelike trabeculae with large holes, ranging from 25 to 75 µm. A trabecula is "a meshwork" or "a piece of a spongy substance".
3.2 Corneoscleral meshwork. It extends from the scleral spur to the scleral sulcus and consists of several sheets of trabecula. The trabeculae have increasingly smaller oval holes as they approach the Schlemm's canal, of 50 to 5 µm, offering slightly more resistance to the aqueous humor.
3.3 Juxtacanalicular tissue. The innermost part of the trabecular meshwork, histologically different from the remaining tissues. This endothelial tissue causes the highest resistance to the aqueous humor outflow: the only openings consist of minute pores and giant vacuoles (from 0.5 to 2 µm).
4. Schlemm's canal. Invisible in gonioscopy, except when there is compression to cause reflux of blood from the episcleral veins to the Schlemm's canal. If the pressure of the episcleral veins is higher than intraocular pressure (IOP), a red line of blood is seen in the gonioscopy. This 360° endothelial channel receives the aqueous humor, which then travels to the collector channels (or episcleral veins) and aqueous veins.
5. Scleral spur. Arguably the most straightforward structure to identify in the gonioscopy, the scleral spur is a white, lustrous, dense band. The scleral spur is the most anterior portion of the sclera; it is composed of 75% to 80% collagen and 5% elastic tissue. Longitudinal ciliary muscle fibers insert in the scleral spur. Its identification in deep sclerectomy surgery is fundamental.
6. Ciliary band. The ciliary band is a thick (thicker in myopes) band, rose to dark-brown, which represents the ciliary body. Angle-recession, a relative contraindication for performing deep sclerectomy, is seen as a sectoral deepening of this band.
7. Sometimes iris vessels are seen in the angle, especially in blue irises. Vessels can be physiological if they follow the angle radially. These vessels never cross the trabecular meshwork. Neo-vessels, however, cross the iridocorneal angle structures (namely the trabeculum) and display a random orientation.
8. Sometimes iris processes are seen, for example, in brown irises; they are distinct from peripheral anterior synechia (PAS). PAS constitute a relative contraindication for deep sclerectomy. Iris processes do not cross the trabecular meshwork. PAS cross many structures of the iridocorneal angle; they may distort the angle's anatomy and are thicker than iris processes.
It is crucial to differentiate an open-angle from a narrow-angle before considering a deep sclerectomy.
b) Surgical limbus and surgical anatomy
During surgery, in a fornix-based approach, we encounter the following structures successively (figure 3):
1. Bulbar conjunctiva, inserted at the corneoscleral junction (anatomical limbus), a richly vascularized tissue.
2. Tenon's capsule, a poorly vascularized fibroelastic membrane. Tenon's capsule fuses to the sclera 3 to 5 mm posterior to the corneoscleral junction (anatomical limbus), close to an area known as surgical limbus.
3. Episclera (the outer part of the sclera; it is richly vascularized), and sclera. The sclera is a poorly vascularized fibrous tissue, with disorganized collagen fibers.
4. The surgical limbus is a blue-grey zone, located approximately 3 mm posterior to the anatomical limbus (figure 5), with a width of 1.2 mm, between the white sclera posteriorly and the transparent cornea anteriorly. The surgical limbus corresponds to the internal junction of the cornea and sclera, and deeply, to the area of the trabecular meshwork. Therefore, it is essential to identify it during surgery.
5. When the scleral flap is dissected, there is a relative posterior displacement of the surgical limbus (the blue-gray zone). In the surgical limbus, between the blue zone and the more transparent corneal zone, a white line is present, which corresponds to the scleral spur.
6. Once the scleral spur is identified, the Schlemm's canal can be peeled adjacent to that white line.
Almost all glaucoma subtypes can be operated with a deep sclerectomy. Some examples are specified below:
• Primary open-angle glaucoma
• Pigmentary glaucoma
• Pseudo-exfoliative glaucoma
• Normal-tension glaucoma
• Secondary open-angle glaucoma (for example, uveitic glaucoma may be operated with this technique initially if the angle is open, but not in the presence of a membrane closing the angle)
• Steroid-induced glaucoma
• Aphakic and pseudophakic glaucoma
A non-functioning trabeculum or a narrow-angle will not allow aqueous humor to outflow through the trabeculo-Descemet membrane; therefore, their presence contraindicates the procedure. If the angle is closed, the deep sclerectomy will not be effective. The importance of performing and understanding the gonioscopy before surgery (and during each glaucoma consultation) cannot be overstated.
• Primary angle-closure glaucoma
• Secondary angle-closure glaucoma
• Neovascular glaucoma
• Congenital and juvenile glaucoma
• Narrow-angle glaucoma (a combined sclerectomy and cataract surgery may be performed as the cataract surgery will allow a partial opening of the iridocorneal angle)
• Traumatic glaucoma (deep sclerectomy may still be performed if the area of trabecular damage, angle recession, or another traumatic lesion is small and lies outside the surgery area)
• Glaucoma secondary to increased episcleral venous pressure
A complete preoperative assessment is crucial, for several reasons:
• To assess the rate of glaucoma progression (a "fast progressor" is the patient whose visual field degrades ≥2 dB/year) and consequently, how fast one should operate:
- Urgent intervention: if there is a significant threat to the central vision, or an extremely high IOP with maximal medical treatment
- Fast intervention (<3 months): if progression, or the visual fields affect the central 10° of vision, or in a young patient, or if the IOP is superior to the target-IOP
• Medical history, family history of glaucoma, medications (anticoagulants should be stopped for five days before surgery, however, this is not consensual).
• A complete ophthalmological examination:
- Visual acuity
- IOP (Goldmann applanation tonometry)
- Slit-lamp examination
- Coexisting cataract: opt for combined cataract surgery and sclerectomy
- Conjunctiva: its integrity is crucial for surgery. If there is scarring at 12h, the glaucoma surgery should be performed at another site (for example, at 10h); avoid zones of previous eye surgeries
- Fundus examination (to exclude coexisting retinal pathologies)
• Complementary exams such as
- OCT (we also perform OCT-Angiography, although not mandatory)
- Reliable and recent visual field
- Central corneal thickness
• Topical medication: eyedrops containing conservatives should be withdrawn if possible (while maintaining IOP controlled), topical corticosteroids or NSAIDs can be given a month before surgery to decrease conjunctival inflammation
• Last but not least, it is vital to understand and to tailor patients' expectations and fears, to explain what can be achieved with glaucoma surgery, what are the advantages and risks of each surgery, to tailor the patient expectations, and to explain the importance of close postoperative monitoring.
Either general anesthesia (rarely) or local anesthesia (subconjunctival or sub-Tenon) can be performed.
Ophthalmic Betadine® is used.
Careful should be taken to fully displace the eyelashes from the area of intervention.
A corneal traction suture (e.g., with Vicryl 6-0) allows the globe to be tilted down.
This can be limbal-based or fornix-based.
Fornix-based conjunctival dissection: Opening the conjunctiva and Tenon at the limbus. Then, deep posterior dissection is performed under the Tenon's capsule to promote the posterior flow of the aqueous humor and avoid cystic blebs, as shown by Khaw. It is possible to keep a 1 mm limbic conjunctival collar to allow better water-tightness during closure (figure 4).
Limbal-based approach: the conjunctival-Tenon tissues are opened posteriorly, about 10 mm from the limbus, followed by anterior dissection. It is crucial to avoid damage to the superior rectus muscle.
In practice, both methods have equivalent IOP lowering effects. The fornix-based dissection is more straightforward and obtains a more diffuse bleb, but it is more challenging to obtain watertight conjunctiva. The limbal-based method has an easier to obtain watertight conjunctiva. However, the exposure is more complicated, and there is a higher risk of small and cystic blebs due to the fibrosis linked to the conjunctival suture.
Preparation of the sclera
The remains of the episclera are removed. Diathermy hemostasis is performed if necessary. It should be as gentle as possible to limit an inflammatory reaction and avoid excessive scarring.
The application of antimetabolite reduces the risk of postoperative fibrosis. One of the following agents is used for the procedure:
- 5-fluorouracil (25 to 50 mg/mL; 5 minutes)
- Mitomycin C (0.1-0.5 mg/mL; for 1-5 minutes)
The choice of an antimetabolite agent depends on the presence of the risk factors for scarring: <50 years, Afro-Caribbean / Hispanic patient, inflammatory eye disease,
chronic use of topical medication, aphakia, recent eye surgery (<3 months), previous conjunctival incision, previously failed filtering surgery, and neovascular glaucoma.
The application of the antimetabolite agent to the sclera should be as wide and posterior as possible to promote a posterior extension of the filtration bleb and to minimize the risk of obtaining cystic blebs. The sponges are then removed, and profuse irrigation with balanced salt solution is carried out.
Superficial scleral flap
It represents the roof of the decompression chamber, which will accommodate the aqueous humor. Its shape can be triangular, rectangular or trapezoid; the recommended thickness is usually of 1/3 to ½ of the total scleral thickness. Its size is variable (3 to 5 mm). A 15° knife is useful in the flap edges, while a bevel knife facilitates the dissection of the flap.
Deep scleral flap
Two methods can be used for the dissection of the deep scleral flap; the first is usually preferred:
- A rectangular (or triangular) deep scleral flap is dissected. The flap starts posteriorly in a pre-choroidal deep scleral plane. This depth should be maintained as the dissection plane advances anteriorly, to identify the scleral spur and the Schlemm canal (figure 5).
- The paralimbic area can be directly approached by a radial incision in the area of the trabecular meshwork and the scleral spur.
Dissection along the scleral spur will open the Schlemm canal.
Excision of the deep flap is performed at its base.
Peeling of the internal wall of the Schlemm's canal
The cribriform trabeculum and the Schlemm's canal are peeled with a capsulorhexis or a Bonn forceps (video 1). Avoid compressing the eye; otherwise, inadvertent penetration may occur.
In a deep sclerectomy, the outflow of aqueous humor is facilitated by:
- The increase in uveoscleral and transscleral filtration, by thinning the sclera above the suprachoroidal space (by deep scleral flap excision).
- The increase in trabecular filtration, by removal of the internal wall of the Schlemm's canal and the cribriform trabeculum.
Once in the scleral cavity, aqueous humor is absorbed by several mechanisms:
- The conjunctival filtration bleb
- The uveo-scleral pathway through the sclera.
Installation of a drain/implant
A deep sclerectomy (DS) implant can be added (see below for further description).
Repositioning of the superficial scleral flap
Non-absorbable 10-0 sutures are used. These sutures are not mandatory; their goal is to reposition the flap (differently from the flap sutures of a trabeculectomy, which are crucial to titrate the outflow of the aqueous humor).
The closure of the conjunctiva must be watertight. A 10-0 Vicryl with a round needle is usually used.
The presence of the Tenon underneath the sutures is believed to be useful for postoperative sealing.
In a limbus-based peritomy, interrupted sutures are usually sufficient for conjunctival closure.
In a fornix-based peritomy, the conjunctival closure can be performed by:
- Two interrupted sutures at each edge of the disinserted conjunctiva;
- Mattress sutures (which decrease the probability of aqueous leakage; figure 6)
- Corneal anchoring sutures: two corneal incisions are made with a 30 ° knife on each side. They allow the anchoring of the conjunctiva and Tenon by a U-shaped point, knotted at the bottom of the incision.
Pearls for a successful deep sclerectomy
· Knowledge of the relevant anatomical structures
· High magnification is imperative, in particular during the second flap and for unroofing the Schlemm's canal
· The second/deep flap should almost reach the choroid posteriorly, in order to warrant sufficient depth to allow the identification of the Schlemm's canal
· The corneal traction suture is vital for good visualization, but it should be loosened during the deep flap dissection and Schlemm's peeling
· After deep flap dissection, a paracentesis is sometimes helpful to avoid penetration because it decreases the bulging of the trabeculum.
· To peel the Schlemm's canal, it is crucial to use gentle movements and avoid downward pressure, which might cause a penetration. If a penetration happens, performing a micro-iridectomy usually avoids the iris from obstructing the trabeculo-Descemet membrane (which would cause a failure of the procedure). However, frequently it is possible to rescue it with a laser iridoplasty during the postoperative period, or rarely with reintervention for iris repositioning.
Implants in sclerectomy
The creation of a scleral cavity during a deep sclerectomy allows the drainage of aqueous humor. To ensure that this space is maintained, different implants can be used. There are two groups of implants, absorbable and non-absorbable.
- Non-absorbable implants: This implant class includes T-flux®, with the shape of a T, the lateral branches of which are inserted into the openings of the Schlemm's canal. It consists of poly-Megma®, a highly hydrophilic acrylic synthetic substance. More recently, the Esnoper®, an acrylic polymer implant, has been developed. It is a small tetrahedral plate with grooves allowing the drainage of aqueous humor.
- Absorbable implants: The first device to be commercialized was Aquaflow® (figure 7), a cylindrical collagen implant that triples in volume after hydration. It is digested in 6 to 9 months. Hyaluronic acid can also be used to maintain this space (SK-gel®) or a highly cross-linked hyaluronic acid allowing slow resorption (Healoflow®). It is also possible to use a viscoelastic agent (Healon GV®).
Deep sclerectomy has a favorable safety profile. The complications associated with the procedure are common to other filtering surgeries; they can be minimized if proper surgical technique, postoperative compliance, and regular follow-up are followed. Examples of complications include:
- Hemorrhage: common and mild; avoided by using a wet-field cautery during scleral dissection (which, if not excessive, can avoid the development of late scarring and eventually fibrosis).
- Bleb leakage and hypotony: Leakage of the filtering bleb can be observed under blue cobalt light after fluorescein instillation (positive Seidel sign). It can occur if conjunctival sutures are loose. In most cases, the leakage is minor (consider ointment or a contact lens), but if significant, can be surgically corrected.
- Intraocular inflammation: A common complication but usually milder than with trabeculectomy, as the latter is a more invasive procedure, with a higher release of inflammatory cells and molecular mediators.
- Inability to find Schlemm's canal and
- Trabeculo-Descemet membrane perforation: The two most common intraoperative complications, occurring most frequently during the early phase of the learning curve (i.e., first 20 cases) as the trabeculo-Descemet membrane (TDM) is exceptionally fragile. Non-penetrating glaucoma surgery requires excellent surgical skills, and the long-term results might differ depending on the surgeons' proficiency and experience. There is limited data regarding the sclerectomy-related outcomes performed by trainees. The risk of perforation has been reported to decrease with training from 30% to 3%. While a small perforation without iris prolapse has no consequence, a large perforation may lead to iris incarceration/prolapse. Iris prolapse needs either viscoelastic injection or a peripheral iridectomy (as in a trabeculectomy). With shallow or flat anterior chambers, the external flap should be tightly sutured (consider releasable sutures). The inability to find Schlemm's canal relates to an insufficiently deep dissection of the scleral canal for fear of dissecting too deep into the choroid (consider a third deeper scleral flap).
- Intraocular hemorrhage: It is a rare complication, as the IOP reduction is slower and more predictable. Reflux from the Schlemm's canal is usually caused by an increase in the episcleral veins exceeding IOP. It can be minimized by injection of high-molecular-weight viscoelastic or balanced salt solution into the anterior chamber.
- Intraocular pressure fluctuations:
- Hypotony: very common in the early postoperative period and not always a complication: Shaaraway showed that IOP < 5mmHg in the first postoperative day was a predictive factor for a successful surgery. The hypotony should resolve within 1-2 weeks, and it should not be associated with a positive Seidel sign nor a shallow anterior chamber.
- Ocular hypertension (HTO): HTO is rare. It can occur due to retained viscoelastic, insufficient TDM dissection (consider performing a goniopuncture), blockage of by scleral or corneal tissue (requiring a revision surgery), or iris incarceration. Iris incarceration can be treated with viscoelastic injection, miotics, iridotomy, iridoplasty, or with surgery. Late HTO can be due to a less permeable TDM (perform a goniopuncture) or fibrosis (perform needling with 5FU). A progressive IOP increase occurs in up to 60% of the cases during the first year, especially during the first 6-8 months. It is managed by performing a goniopuncture.
- Descemet membrane detachment: Can arise weeks or months after the surgery and can be seen as bullae under the cornea and cause the corneal stroma to become opalescent. The cause usually resides in a rise in intraocular pressure at the level of an apparent cystic filtering bleb, trauma, or excessive eye massage, and treatment consists of draining the stagnant fluid and resolving the cause of the encysted bleb. A period of observation is recommended before attempting a descemetopexy.
- Malignant glaucoma: Very rare; it is managed medically or surgically.
- Blebitis and endophthalmitis: Extremely rare, with only one case reported in the literature.
Surgical follow up
Postoperative follow-up :
- Day 4-8: to measure visual acuity and IOP, and to detect and manage early complications (endophthalmitis, hyphaema, encysted bleb, choroidal detachment, hypotony maculopathy, anterior uveitis, flat anterior chamber, bleb leak, epithelial defect). If complications arise, the respective management and a closer follow-up should be proposed.
- Day 14, Month 1, Month 3, Month 6, Month 9, Month 12, etc.
Medical treatment :
Postoperative medical treatment aims to decrease the risk of infection and inflammation, which might lead to scarring of the filtering bleb. There is no consensus regarding the exact posology or medications, but high doses of corticosteroid with slow tapering seem to lead to fewer complications and better IOP stabilization. Steroids are better than NSAIDs.
The authors propose the following postoperative regimen: combined dexamethasone-antibiotics (e.g., tobramycin + dexamethasone, six times a day for 1-2 weeks, then 4/day for another 2-4 weeks), lubricant eye drops at will, tropicamide (at night for two days, to decrease inflammation), NSAIDs ( 2-3 times/day for 15 days). The patient must avoid physical efforts, protect the eye (a transparent eyeshield should be provided), and consult if he feels pain or vision decrease.
Deep sclerectomy is a viable option for glaucoma patients earlier in the disease process, as it requires less postoperative anti-inflammatory medication, fewer postoperative examinations, carries a lower complication rate, and provides a more predictable rate of IOP reduction, compared to trabeculectomy. Deep sclerectomy may also be a safer and less invasive option in high-risk eyes in patients who have already lost one eye to glaucoma. However, there is limited data regarding the long-term outcomes from randomized clinical trials evaluating sclerectomy versus trabeculectomy. DS has a steep learning curve, takes up more operative time, and some authors suggest that the IOP reduction achieved is lower to that of trabeculectomy. However, there is a high degree of uncertainty regarding IOP control of trabeculectomy versus sclerectomy, according to a Cochrane Systematic Review. Both procedures are also associated with significant conjunctival scarring, which may limit future surgical options.
1. Efficacy (IOP reduction)
Several studies have been performed evaluating the efficacy of deep sclerectomy:
1.1 Postoperative IOP:
Deep sclerectomy with collagen implant has been reported to bring more satisfactory results over a medium-term follow-up, with a reported mean decrease in IOP to 12.4 ± 3.9 mmHg (55.4% reduction) at three months of follow-up and 13.0 ± 3.8 mmHg (53,2% reduction) at three years of follow-up.
A meta-analysis evaluating the efficacy and safety of non-penetrating surgeries (NPS) versus trabeculectomy showed no differences between the NPS subgroups. The NPS subgroup compared deep sclerectomy, canaloplasty, or viscocanaloplasty with trabeculectomy. Adding mitomycin-C (MMC) to trabeculectomy and deep sclerectomy decreased the difference in IOP reduction: trabeculectomy and deep sclerectomy without MMC: −2.65 mmHg [95% confidence interval (CI), −3.90 to −1.39]; trabeculectomy and deep sclerectomy with MMC: −0.83 mmHg [95% CI, −2.40 to 0.74].
1.2 Success rate:
Shaarawy et al. presented a complete success rate (IOP ≤ 21 mmHg without medication) of 62% and 57% 5 and 7 years after surgery, respectively. A study comparing DS performed in one eye and trabeculectomy in the other, reported a complete success at two years of 45% with trabeculectomy and 40% with DS. If an eye fails a previous trabeculectomy, a deep sclerectomy with mitomycin-C is viable, with a 65% complete success rate (IOP <21mmHg under no topical medication). However, for a lower IOP goal or a more longstanding reduction, trabeculectomy may provide better outcomes. Khairy et al. confirmed that DS reduced the IOP and minimized the risk of complications versus trabeculectomy. However, the success rate at 30 months was 18.9%.
The efficacy of deep sclerectomy in congenital glaucoma is excellent, with a reported qualified and total success rate of about 80% after three years of follow-up.
In uveitic eyes, DS with MMC has been reported safe and effective (>80% complete success rate at three years) to lower IOP, with a low rate of complications.
2. Number of medications:
A meta-analysis revealed no significant difference between trabeculectomy and deep sclerectomy with regards to the number of anti-glaucomatous medications (weighted mean difference = 0, 95% CI: −0.12 to−0.13, I = 61.6%, P = 0.004).
3. Failure of Sclerectomy and Outcomes following Goniopuncture
Insufficient filtration of the trabeculo-Descemet membrane in the postoperative period is one of the main causes for DS failure, which can be improved by the laser goniopuncture. Goniopuncture is successful in more than 87% of patients.
4. Adverse Effects and Safety Profile
A meta-analysis assessed the risk of complications (hypotony, choroidal effusion, cataract, and flat or shallow anterior chamber) of trabeculectomy and DS. Trabeculectomy had a higher risk of complications, and the addition of MMC to both surgical procedures reduced the risk ratios of all complications, except for cataract progression. A more recent meta-analysis (which included 7 studies comparing DS to trabeculectomy and viscocanaloplasty) revealed that trabeculectomy had a higher risk of all complications. The odds ratio (OR) was increased for hypotony (OR = 2.7 to 4.3), choroidal detachment (OR = 7.6 to 17.4), flat or shallow anterior chamber (OR = 12.3 to 37.7), and hyphema (OR = 6.7 to 7.2) when both surgeries were performed without MMC; and for hypotony (OR = 2.7 to 6.7) choroidal detachment (OR = 7.6 to 29.1), flat or shallow anterior chamber (OR = 12.3 to 13.4), and cataract formation or progression (OR = 5.7 to 12.2) when MMC was added to deep sclerectomy. When MMC was added to both surgeries, there were fewer trabeculectomy complications: hypotony (OR = 2.7 to 2.1), choroidal detachment (OR = 7.6 to 2.2), flat or shallow anterior chamber (OR = 12.3 to 4.6), and hyphema (OR = 6.7 to 2.7). However, the OR was higher for cataract (OR = 5.7 to 5.9).
Another systematic review concluded that induced astigmatism might account for a reduction in unaided visual acuity in the early postoperative period following a successful trabeculectomy, with less astigmatism for deep sclerectomy. These changes appear to stabilize at three months: it would be prudent to defer the prescription of new glasses until this time. If sequential cataract surgery is to be performed, toric intraocular lenses can be a useful option for astigmatic correction.
5. Graft Survival Post-Penetrating Keratoplasty
Graft survival was reported in a retrospective case series to be higher in eyes with DS than trabeculectomy. Deep sclerectomy seems as efficient, but safer than, trabeculectomy and could be performed as a first-choice treatment in the absence of major peripheral anterior synechiae.
Laser goniopuncture (LGP) may be used post-operatively to reduce the IOP. It is safe, efficient, and non-invasive.
After a deep sclerectomy, the primary determinant of aqueous outflow is the trabeculo-Descemet membrane (TDM). The resistance to the aqueous flow through the TDM may increase over time, inducing a rise in IOP. If the target IOP is not achieved after a DS, a LGP can be performed, instead of adding IOP-lowering medication. LGP creates full-thickness holes in the TDM, allowing the direct outflow of the aqueous humor into the sub-conjunctival space. Before performing a goniopuncture, other causes of ocular hypertension must be ruled out. Inspect the conjunctiva to exclude subconjunctival fibrosis, and perform a gonioscopy to exclude iris incarceration. Goniopuncture is often discouraged within three months after DS, because of the subsequent risk of hypotony. Penaud and al. reported more iris incarceration after LGP within 3 months compared to the group LGP after 3 months, of 25,4% and 11,4% respectively; Di Matteo et al. reported similar results.
Laser goniopuncture procedure and follow-up
- Apply pilocarpine 2% and topical anesthesia (e.g., oxybuprocaine)
- The angle is visualized using a single-mirror contact-lens (e.g., CGAL gonioscopy lens), with coupling gel (illustrated by figure 8). This lens reduces the laser spot by a factor of 1.44, as compared to Goldmann three-mirror contact lens or Latina SLT Gonio laser lens (which can be used in alternative but create a wider spot).
- LGP is performed using Nd:Yag laser (Q-switched mode, single-shot), with the initial energy level of 2mJ, gradually increased until micro blebs appear, and 1-2 micro-perforations occur. The laser beam is aimed at the anterior edge of the TDM, on either side of the scleral window, to reduce the risk of iris incarceration. The TDM has the appearance of a semitransparent membrane that is often depressed outward.
- Perforation may be difficult to confirm if the remained trabeculum is not pigmented. Slight pressure is applied to the eye to observe the movement of micro-blebs through the holes in TDM (figures 9 and 10).
- After LGP, pilocarpine 2% is instilled 3 times a day for 7-14 days, sometimes in combination with steroids or NSAIDs twice a day, for 1-4 weeks. No evidence to date exists to support the use of either or both of the anti-inflammatory medications after goniopuncture.
- The patient should return to follow-up care in 1 to 3 weeks, depending on the IOP, the risk of complications, and the time after deep sclerectomy.
- LGP can be repeated if no punctures are visible in the TDM during follow-up, and the IOP remains high.
Complications of goniopuncture
LGP is a safe procedure to reduce IOP. The occurrence of severe complications is rare. The most frequent complications are iris prolapse/incarceration, occurring in up to 17,6% of cases, and bleeding.
Iris incarceration: Di Matteo et al. observed less iris incarceration after LGP if a prophylactic iridoplasty and iridotomy were previously performed. Therefore, iridoplasty should be performed prior to goniopuncture in convex peripheral irises, shallow peripheral anterior chambers, and in eyes with high IOP. The application of IOP lowering medication before goniopuncture decreases the risk of iris incarceration and hemorrhage.
In the case of iris prolapse, iris retraction is attempted with repeated argon laser, associated with lowering IOP eyedrops and pilocarpine 2%. If these procedures fail, surgery may be needed for iris repositioning (often with an iridectomy).
If hemorrhage occurs during LGP, the procedure should be discontinued, and pressure should be applied to the eye. In case of shallow or flat anterior chamber appearing after LGP, add cycloplegia (if persistent, reform the anterior chamber with viscoelastic). Other rare complications include IOP spike, iritis, peripheral synechia, hypotony, blebitis, and inefficacy to decrease the IOP.
After a DS, LGP is often performed: 35,7% to 67% of cases, usually in the first year after surgery. Harju et al. reported up to 100% of LGP after a DS with a long term follow up of 9 years. LGP is associated with a significant and persistent reduction of IOP, from 27% to 58%.
Deep sclerectomy is an effective option in glaucoma surgery.
It decreases IOP durably, with probably less complications than trabeculectomy.
Anatomical knowledge is the key to succeed in performing this surgery (table 1).
We suggest the following additional resources:
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