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CASE REPORT: XEN Gel Stent as an alternative to trabeculectomy

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Dr Nathan Kerr
MBChB MD FRANZCO
Royal Victorian Eye and Ear Hospital, Centre for Eye Research Australia

Eye Surgery Associates, Melbourne

 

A 57-year-old Caucasian woman with open-angle glaucoma refractory to medical and laser treatment was referred to me by her optometrist for a second opinion and to discuss alternatives to trabeculectomy.

The patient had a history of primary open-angle glaucoma diagnosed seven years previously and had presenting intraocular pressures in the mid 20s. Her central corneal thickness was reduced at 533 microns in her right eye and 540 microns in her left eye. There was a family history of glaucoma affecting her mother who was diagnosed in her late 60s. Her mother was treated with topical medications and reportedly suffered field loss but not blindness.

The patient’s general health was good and she was not regularly taking any medications.

Despite treatment with bilateral selective laser trabeculoplasty (SLT) by her original ophthalmologist and good adherence with three topical ocular hypotensive medications, her intraocular pressures remained in the high teens. Her ophthalmologist noted a Drance haemorrhage in her left eye and advised that trabeculectomy was required.

Having read the information sheet, the patient was worried about the risks, slow recovery and time-off required from her work as a gardener, and was interested in seeking an alternative. Her friend in the United States had undergone the XEN Gel Stent procedure with good results and the patient was interested to know if she was a candidate for the procedure.

Examination

On examination her best-corrected visual acuity was 6/6 in each eye. Her conjunctiva was white and healthy. Both anterior chambers were deep and quiet and her angles were open on gonioscopy. Intraocular pressures measured by Goldmann applanation tonometry were 16 mmHg in her right eye and 18 mmHg in her left eye. There was no pseudoexfoliation or cataract in either eye. Dilated fundoscopy revealed cup-to-disc ratios of 0.9 with thinning of the neuroretinal rim both superiorly and inferiorly in each eye. There was a resolving Drance haemorrhage in her left eye.

 

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Figure 1. OCT shows thinning of the retinal nerve fibre layer

 

Optical coherence tomography (OCT) showed marked thinning of the retinal nerve fibre layer in each eye (Figure 1) and automated perimetry showed early field loss with slow progression in each eye on guided progression analysis (Figures 2A and 2B).

 

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Figure 2A. Humphrey visual field guided progression analysis, right eye

 

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Figure 2B. Humphrey visual field guided progression analysis, left eye

 

We discussed the patient’s diagnosis and our shared goal of preventing vision loss from glaucoma. Given the patient’s age, presenting pressures, reduced corneal thickness, family history of glaucoma, and development of a Drance haemorrhage at 18 mmHg, we discussed the need to achieve an IOP in the low double digits which can realistically be achieved only with subconjunctival filtration surgery.

While trabeculectomy is the current accepted gold standard, we discussed the option of a XEN Gel Stent as an alternative. The XEN has a favourable safety profile and offers a much less invasive operation and faster post-operative recovery. For many patients it can delay or prevent the need for invasive surgery. The patient was carefully counselled on the risks and benefits and elected to proceed with the XEN Gel Stent.

Surgical course

In the operating room under a peribulbar block, I marked the planned exit point for the XEN Gel Stent. To control subconjunctival fibrosis, I injected mitomycin C posteriorly and swept it away from the limbus to prevent the development of an avascular bleb. I made a 1.5 mm clear corneal incision and a single side port to stabilise the eye.  I injected acetylcholine to constrict the pupil and protect her crystalline lens. Then I filled the anterior chamber with viscoelastic before checking and hydrating the XEN before implantation.

The injector was passed across the anterior chamber and through the sclera into the subconjunctival space at exactly my markings. I rotated the bevel of the needle toward 12 o’clock to ensure a superior bleb. I then deployed the stent carefully into the subconjunctival space before checking for correct length and position using a gonioprism.

Lastly, I removed the viscoelastic with bimanual irrigation and aspiration, checked for the development of a bleb, and hydrated the wounds before administering intracameral antibiotic to prevent infection. At the end of the procedure I placed a pad and shield over the eye and prescribed topical steroids every two hours and antibiotics four times a day.

The patient was instructed to discontinue glaucoma medications in the operated eye, to avoid heavy lifting or straining, keep the eye dry, and wear a shield at night for the first week. 

An appointment was scheduled for the following day and the patient was given my mobile number to call in case of emergency.

 

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Figure 3A. Slitlamp photography of the XEN Gel Stent in position

 

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Figure 3B. Low diffuse bleb associated with the XEN Gel Stent

 

Outcome

At the day 1 post-operative visit, the patient’s visual acuity was 6/9 in the operated eye and her intraocular pressure was 7 mmHg without sequelae. Her anterior chamber was deep and there were no macular folds or choroidal effusions. The XEN was well-positioned and there was a low diffuse bleb and no leak (Figures 3A and 3B).

At one week post-operatively, her visual acuity had returned to 6/6 and her intraocular pressure was 10 mmHg. Antibiotics were discontinued at one week and steroids tapered over the next three months. At three months the patient is off all eye-drops and her visual acuity is 6/6 and IOP 9 mmHg. The fellow eye has been scheduled for surgery.

Discussion

The XEN Gel Stent represents a major advancement in the treatment of refractory glaucoma. It provides intraocular pressure levels approaching those of trabeculectomy, in a fast, minimally-invasive operation with a good safety profile and rapid post-operative recovery.1 Unlikely trabeculectomy there are no conjunctival incisions or suturing required, which is appealing from a patient perspective.

While numerically low pressures are common, hypotony is rare.2 Accordingly, its favourable safety profile enables the XEN Gel Stent to be offered at an earlier stage of disease and in many patients it can avert or delay the need for invasive surgery.3 If additional pressure reduction is required, medical therapy can be restarted and the procedure does not preclude further operations such as trabeculectomy or glaucoma drainage device insertion from being performed.

Patients should be monitored closely post-operatively. Optimal outcomes require bleb management including needling and therefore the procedure is best performed by surgeons experienced in bleb management.

As with all subconjunctival procedures that form a bleb, there is a small risk of bleb-related complications. However, compared to trabeculectomy, the morphology of the XEN bleb is different, tending to be low and diffuse. Like any stent, there is a small risk of occlusion or exposure; however, this is rare and can generally be averted with proper technique and placement.

 

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Dr Nathan Kerr

 

Dr Nathan Kerr specialises in minimally-invasive glaucoma surgery (MIGS) and completed a Glaucoma Fellowship at Moorfields Eye Hospital in London. He was the first Australian surgeon to be accredited in the use of the XEN Gel Implant and is co-editor of MIGS.org, a source of patient information on glaucoma surgery. Dr Kerr is a consultant ophthalmologist at the Royal Victorian Eye and Ear Hospital, and consults privately at Eye Surgery Associates. 

 

  1. Schlenker MB, Gulamhusein H, Conrad-Hengerer I, et al. Efficacy, safety, and risk factors for failure of standalone ab interno gelatin microstent implantation versus standalone trabeculectomy. Ophthalmology 2017. doi: 10.1016/j.ophtha.2017.05.004.
  2. Sheybani A, Dick HB, Ahmed IIK. Early clinical results of a novel ab interno gel stent for the surgical treatment of open-angle glaucoma. J Glaucoma 2016; 25: e691–696.
  3. Kerr NM, Wang J, Barton K. Minimally invasive glaucoma surgery as primary stand-alone surgery for glaucoma. Clin Exp Ophthalmol 2017; 45: 393-400.


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