Dr Abdelwahhab Azzawi

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In recent decades, safety concerns have fuelled progress in glaucoma surgery techniques. Standard trabeculectomy (TE) has well-known complications such as hypotony; choroidal detachment; flat anterior chamber; hyphema; acute or late endophthalmitis; and, in some cases, surgery-induced cataract.

Many new methods, including non-penetrating surgical procedures, have been developed in the search for an alternative approach. Deep sclerectomy (DS) has become one of the most widely used non-penetrating surgeries in primary open-angle glaucoma (POAG), and there is good evidence as to its efficacy and safety.

In DS, removing the inner wall of Schlemm’s canal and the juxta-canalicular trabecular meshwork enhances aqueous outflow. The trabeculo-Descemet’s membrane (TDM) remains intact to control and prevent excessive aqueous outflow, which offers an advantage in comparison with TE.

The low complication rates of DS offer an opportunity to perform the surgery at an earlier stage of glaucoma, and it can be considered as first-line therapy in cases when eye drops are not enough to control the IOP or if laser treatment is unavailable.

 DS can also be considered if the compliance of the patient is uncertain.

Furthermore, DS is preferred in uveitic glaucoma with open angle as it causes less inflammation than penetrating procedures.

 Another indication with which DS is the more appropriate choice of procedure is high myopia, which has a higher risk of choroidal detachment.

In the presence of risk factors for inflammation such as chronic blepharitis, or for patients with dementia, DS could be considered to reduce the risk of endophthalmitis. Cataract surgery in glaucoma patients is a good indication to reduce the IOP through combined surgery (phaco with DS).

 On the other hand, neovascular glaucoma is considered as a contraindication to DS, since the TDM filtration can be decreased or stopped by the fibrovascular membrane over the irido-corneal angle.

Similarly, cases of iridocorneal endothelial syndrome are contraindicated for DS. A narrow angle is considered as a relative contraindication because of possible anterior synechia formation or iris incarceration following surgery.

 Eyes with damaged trabeculae (e.g., post-traumatic angle recession, post-laser trabeculoplasty) are also relatively contraindicated for DS, as surgical success depends on the integrity of angle structures.

The different biometric changes following TE and DS, which may be important in cases such as combined surgery, are discussed as follows.

Claridge et al. studied and controlled 29 patients admitted for TE.

 Subjective and automatedrefraction, manual keratometry and corneal topography were assessed pre- and postoperatively, and the results confirm that glaucoma surgery has an influence on astigmatism.

After TE there was an increase in vertical keratometry producing with-the-rule (WTR) astigmatism. Moreover, the topographic changes lasted for at least 12 months after surgery. These changes could have a significant effect on visual function in some patients.

Rosen et al. used corneal topography preoperatively and at 12 weeks postoperatively to show a WTR shift of 1.5–2.5 D of cylinder, which was underestimated by keratometry.

 This was thought to relate to tight sutures, excessive cautery or a large drainage bleb.

 This change in astigmatism would interfere with precise measurement of the IOL in combined surgery.

On the other hand, in a report by Corcosteguiet al. reviewing 38 eyes of 35 patients, there was no clinically significant refractive change following phaco-DS surgery.

 This could be down to the flat bleb after DS. Moreover, the sutures in DS should not be tight like those in TE. A recent review by Chan et al. suggests that the astigmatism change stabilises at 3 months after TE.

Anterior chamber depth (ACD) is another variable after glaucoma surgery. Husain et al. analysed 122 patients over 5 years after TE and found that the mean decrease in ACD from baseline was 0.11 mm at all postoperative visits.

However, Bouhéraouaet al.evaluated parameters including ACD in 20 eyes of 20 patients who underwent DS for POAG. Measurements were taken 1 day pre-op, then on days 1, 7 and 30 post-op, and surgery was not found to affect ACD.

 This could be a result of the controlled filtration through TDM in DS.

Husain et al. reported that, 5 years after TE, axial length (AL) was shorter by about 0.16 mm compared with the value before surgery.

 This has an effect of about 0.4 D, which is sometimes significant visually.

On the other hand, García et al., who studied 22 patients who had undergone DS, reported that the decrease in AL 1 year after DS was 0.08 mm.

 The difference is thought to be related to the amount of filtration after glaucoma surgery.

Phaco surgery can result in damage to the endothelium in the cornea.

 Glaucoma surgery is another well-known cause of endothelial cell loss (ECL), but it occurs less with DS than with TE.

Arnavielleet al. studied 62 eyes of 62 patients and reported ECL values of 7% after TE and 2.6% after DS 3 months after surgery, then, 12 months after surgery, 9.6% with TE and 4.5% with DS.

 Some surgeons prefer to include paracentesis in DS surgery to reduce the aqueous humour in the anterior chamber, which reduces the chances of perforating the TDM. This may be the cause of more ECL in DS.

Reduced endothelial cell count may lead to corneal decompensation in the long term and this should be considered in combined surgery: it is wise to measure the endothelial cell count before surgery. Regardless of this, DS offers an advantage to the patient with reduced endothelial cell count.

Overall, DS has many advantages that may make glaucoma surgery or combined surgery in many patients safer and more successful. This is particularly relevant in developing countries, where minimally-invasive glaucoma surgery (MIGS) might be difficult to afford or unavailable; also, MIGS might not reduce the IOP enough to reach the target pressure.

Abdelwahhab Azzawi, MD, FEBO, MRCPS (Glasg)

Dr Azzawi is head of the Azzawi clinic in Grossenhain in Sachsen, Germany (https://azzawi-augenpraxis.com). He has no financial disclosures.

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, et al. Longitudinal changes in anterior chamber depth and axial length in Asian subjects after trabeculectomy surgery. 

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Articles

Comparisons of deep sclerectomy and trabeculectomy show the former to have better outcomes and fewer complications in cases where it is indicated. 

Biometric changes and endothelial cell loss after deep sclerectomy and trabeculectomy

Gonioscopy forms an essential part of the glaucoma evaluation, enabling the structure of the iridocorneal angle to be seen, which is important in diagnosing and monitoring eye conditions associated with glaucoma. However, Schlemm’s canal (SC) can be poorly visible in the angle, especially in excessively pigmented eyes.

Blood reflux from episcleral veins to the SC is a well-known sign that helps one to visualise the SC

 and can be caused by the pressure of the goniolens on the episcleral veins, reduced intraocular pressure (IOP) or both.

 Three quarters of outflow resistance of the aqueous humour in normal eyes comes from the trabecular meshwork (TM), while 25% of the resistance comes from SC.

 The juxtacanalicular meshwork is responsible for normal outflow resistance in the TM.

Many glaucoma surgeries aim to overcome this resistance of outflow, which may reduce the IOP. The trabecular micro-bypass implant iStent inject (Glaukos Corporation), which received CE Mark clearance in Europe in 2010 for the treatment of open-angle glaucoma,

 aims to connect the anterior chamber directly with SC, thus overcoming the resistance of the TM.

In one study, blood reflux was seen in nearly all (91%) of eyes immediately after implanting iStent,

 but there are few case reports about the late hyphaema that can occur through the implant following surgery.

 We evaluated blood reflux during gonioscopy 3 to 6 months following implantation of either the trabecular micro-bypass devices iStent inject or the newer-generation device, iStent Inject W, to evaluate the effectiveness of the implantation and adjust the drugs therapies patients were on if necessary.

In a case series, 22 eyes from 20 patients who had been diagnosed with either early primary open-angle glaucoma (POAG) or ocular hypertension (OHT), and who also had cataracts and prior difficulties with eyedrops, received implants of either iStent inject or iStent inject W combined with their cataract surgeries. All procedures were carried out by the same surgeon at the department of ophthalmology in Staedisches Klinikum Dresden hospital in Dresden, Germany.

Two stents were implanted in each eye nasally. 14 eyes received iStent inject and eight eyes were implanted with iStent inject W. Patients were treated with at least one hypotensive eye drop before the surgery.

The patients were controlled regularly after the surgery and the IOP was measured at each visit. The required drugs therapy was reduced in most cases and adjusted to reach the target pressure according to the guidelines of European Glaucoma Society, with consideration of the IOP before the surgery.

There were no significant complications intraoperatively or after the surgery. Gonioscopies with Goldmann 3 mirror classic contact lens 903 was performed on the eyes 3-6 months after surgery to evaluate the blood reflux through the devices.

The gonioscopy lasted about 1 minute with light pressure applied to the lens and slightly greater pressure applied nasally, before the pressure was eased off and evidence sought of possible blood reflux from the lumina of either of the stents.

Following the surgeries, patients had a mean IOP of 18 mmHg and a mean of 1.25 glaucoma eye drops was used. The patients did not require any further interventions and there were no complications observed intraoperatively or postoperatively.

Three of the patients who had an IOP of less than 15 mmHg had blood reflux through one of the two iStents during gonioscopy, but this was not visible in the other 19 eyes.

An 82-year-old woman with POAG had an IOP of 13 mm Hg. She was prescribed brinzolamide (Azopt, Alcon Laboratories) eyedrops with a dosing schedule of twice a day.

Gonioscopy was performed 3 months following the surgery. The iStent inject w was implanted. The results can be seen in Figure 1.

An 85-year-old male with POAG had an IOP of 12 mmHg. He was provided with derzolamide plus timolol eyedrops (Cosopt, Merck & Co) for twice-daily use.

A gonioscopy was performed 5.5 months after the surgery. iStent inject was implanted (see Figure 2).

A 72-year-old male with POAG had an IOP of 15 mmHg. He was prescribed tafluprost (Taflotan, Santen Pharmaceutical) eyedrops to be taken once a day.

Gonioscopy was performed 3.5 months following his surgery. iStent inject W was implanted. Results can be seen in Figure 3.

From the findings of these three cases, we can see that all the patients who had late blood reflux had an IOP under 15 mmHg, whereas other patients with higher IOPs did not. It is well known that the IOP following iStent implantation should not be lower than the pressure in the episcleral veins, which is usually 6-9 mmHg, but it can be elevated in glaucoma patients.

Moreover, it is widely accepted that blood reflux in SC is more likely to occur in eyes with low IOP2 since lowering the IOP reportedly facilitates blood movement into SC.

The blood reflux has been classified into three patterns:

No filling, suggesting the collapse of SC and atrophy of collector channels;

Patchy filling of SC suggesting the partial collapse of SC; and

Full filling of SC with blood indicating patent SC and healthy collector channels.

It is important to note that the diameter of SC is between 50.8 μm and 393.5 μm,

 and this diameter is smaller in older patients in comparison with children. Moreover, the diameter of SC is smaller in glaucoma patients compared with those who do not have glaucoma.

We know that the central outlet in iStent inject and iStent inject W is 80 μm and that the side flow outlet is 50 μm. This may lead to the ineffective implantation of the device in some cases, such as where the diameter of SC is small, which may obstruct the outflow.

This could be the explanation for observing blood reflux just from one stent in our three patients and not in both stents, but it could also be related to the IOP and the amount of blood in SC. These considerations may also explain the minimal blood reflux seen in the third patient, which does not obscure the vision of the angle.

On the other hand, the excessive treatment of IOP in glaucoma patients following implantation of the stent may lead to a spontaneous recurrent microhyphaema in the anterior chamber. In these patients, reducing the therapy would be more reasonable and IOP phasing may offer a better view to optimise it. 

In conclusion, gonioscopy may offer a cost-effective method of evaluating the function of iStent after implanting it and could help in adjusting the therapy after the surgery.

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Abdelwahhab Azzawi, MD, FEBO, MRCPS (Glasg)


E: Abdelwahhab.Azzawi@klinikum-dresden.de


Dr Azzawi is an ophthalmic consultant based at Department of Ophthalmology, 

Staedtisches Klinikum Dresden, Dresden, Germany

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Gonioscopy may offer a reasonable and cost-effective method to evaluate the function of the trabecular micro-bypass device post-implantation and it could help in adjusting the therapy after the surgery.

Author | Dr Abdelwahhab Azzawi

Articles

Biometric changes and endothelial cell loss after deep sclerectomy and trabeculectomy

Monitoring blood reflux during gonioscopy in glaucoma