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Ahmed® Glaucoma Valve for Treatment of Refractory Glaucoma

Introduction
Intraocular pressure is the single modifiable risk factor resulting in progression of various subtypes of glaucoma. Intraocular pressure control is often achieved with topical medications, outpatient laser procedures, or minimally-invasive glaucoma surgery (MIGS). This patient is a 63-year-old with traumatic glaucoma in the right eye with elevated intraocular pressure sub-optimally controlled despite maximum medical therapy (29 mmHg). His intraocular pressure must be controlled with incisional glaucoma surgery – in this case, with placement of an Ahmed Model FP7 glaucoma valve. An advantage of valved glaucoma shunts is lower risk of postoperative hypotony-related complications compared to non-valved glaucoma shunts.

Methods
The 10 and 12 o’clock meridians are marked with a marking pen to define the borders of the conjunctival peritomy. A limbal traction 6-0 Vicryl suture is placed superotemporally in the cornea at the limbus. The conjunctival peritomy is then completed using Westcott scissors along the predetermined marks. The peritomy is extended posteriorly with blunt dissection using Stevens tenotomy scissors. Wet field cautery is used to achieve hemostasis of the scleral bed. A Stevens tenotomy hook is used to identify the superior rectus muscle and a marking pen is used to mark its border. The Ahmed Model FP7 tube shunt is then introduced onto the surgical field. Balanced salt solution is injected into the tip of the tube using a 30-gauge cannula to ensure adequate patency of the valve. The Ahmed plate is then sutured to the sclera approximately 8 mm posterior to the limbus using 5-0 Nylon suture. A corneal paracentesis is made at the 8 o’clock position, and viscoelastic is injected to deepen the anterior chamber. A 23-gauge needle attached to the Healon syringe is then used to tunnel from a point 2.0 mm posterior to the limbus into the anterior chamber. The needle tract is anterior and parallel to the plane of the iris and the surgeon must ensure that the tube does not contact the iris or corneal endothelium after insertion. The implant tube is then laid flush with the cornea and shortened with Westcott scissors with an oblique cut, bevel up. Healon is injected as the needle is withdrawn. Non-toothed forceps are then used to insert the tube into the anterior chamber. A single 8-0 Vicryl suture is used to secure the tube to the underlying sclera. A corneal patch graft is cut to fit the site of tube implantation and secured with a single 8-0 Vicryl horizontal cross mattress suture. The conjunctival peritomy is then closed with a running 8-0 Vicryl suture on a BV needle. Anchoring sutures incorporating the conjunctiva and the episclera to firmly secure the corners of the peritomy to the limbus. A 9-0 Nylon suture is used to re-approximate the limbal conjunctiva. At the conclusion of the case, the eye is returned to a neutral position, the traction suture is removed, and satisfactory intraocular pressure is confirmed by palpation.

Results
No complications arose during the procedure. Postoperatively, the patient had subconjunctival hemorrhage, injection, and mild pain that decreased over the following week. Prednisolone acetate drops were applied six times daily to prevent inflammation and moxifloxacin drops were applied four times daily to prevent infection. At the three-month follow up, the eye was quiet and intraocular pressure was measured to be 9 mmHg.

Conclusion
Implantation of an Ahmed glaucoma tube shunt is a safe procedure that can effectively treat various subtypes of glaucoma with sub-optimally controlled intraocular pressure despite maximum medical therapy.

Joseph W. Fong, MD
Jones Eye Institute, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA
JFong@uams.edu

Ahmed A. Sallam, MD, PhD
Jones Eye Institute, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA
ASallam@uams.edu

Surgery was performed at University of Arkansas for Medical Sciences, Little Rock, AR, USA.

The 10 and 12 o'clock meridians are marked with a marking pen to define the borders of the conjunctival peritomy. A limbal traction 6-0 Vicryl suture is placed superotemporally in the cornea at the limbus. The conjunctival peritomy is then completed using Westcott scissors along the predetermined marks. The peritomy is extended posteriorly with blunt dissection using Stevens tenotomy scissors. Wet field cautery is used to achieve hemostasis of the scleral bed. A Stevens tenotomy hook is used to identify the superior rectus muscle and a marking pen is used to mark its border. The Ahmed Model FP7 tube shunt is then introduced onto the surgical field. Balanced salt solution is injected into the tip of the tube using a 30-gauge cannula to ensure adequate patency of the valve. The Ahmed plate is then sutured to the sclera approximately 8 mm posterior to the limbus using 5-0 Nylon suture. A corneal paracentesis is made at the 8 o'clock position, and viscoelastic is injected to deepen the anterior chamber. A 23-gauge needle attached to the Healon syringe is then used to tunnel from a point 2.0 mm posterior to the limbus into the anterior chamber. The needle tract is anterior and parallel to the plane of the iris and the surgeon must ensure that the tube does not contact the iris or corneal endothelium after insertion. The implant tube is then laid flush with the cornea and shortened with Westcott scissors with an oblique cut, bevel up. Healon is injected as the needle is withdrawn. Non-toothed forceps are then used to insert the tube into the anterior chamber. A single 8-0 Vicryl suture is used to secure the tube to the underlying sclera. A corneal patch graft is cut to fit the site of tube implantation and secured with a single 8-0 Vicryl horizontal cross mattress suture. The conjunctival peritomy is then closed with a running 8-0 Vicryl suture on a BV needle. Anchoring sutures incorporating the conjunctiva and the episclera to firmly secure the corners of the peritomy to the limbus. A 9-0 Nylon suture is used to re-approximate the limbal conjunctiva. At the conclusion of the case, the eye is returned to a neutral position, the traction suture is removed, and satisfactory intraocular pressure is confirmed by palpation.
Glaucoma tube shunt placement is indicated when more conservative therapies, including pressure-lowering eye drops, outpatient laser procedures such as selective laser trabeculoplasty and micropulse transscleral cyclophotocoagulation, and minimally invasive glaucoma surgery (MIGS) can no longer adequately control a patient’s intraocular pressure to a degree that prevents accelerated optic nerve damage in various subtypes of glaucoma.
There are no known absolute contraindications for Ahmed valve implantation. Relative contraindications anterior chamber tube placement in eyes with borderline corneal endothelial function or shallow anterior chamber, known intraocular tumors, and active uveitis. Thin conjunctiva can result in increased risk of tube or plate exposure and thin sclera can result in scleral perforation during surgery. In addition, careful consideration should be given to patients who are unable to comply with the extensive postoperative medications and follow-up required following Ahmed valve implantation.
The patient was placed under monitored anesthesia care in the supine position in the operating room. Proparacaine hydrochloride 0.5% eyedrops and betadine (povidone-iodine 5%) antiseptic drops were applied to the operative eye. A 2% lidocaine retrobulbar block was administered. Sterile drapes were placed over the face and head in the usual fashion for intraocular surgery. A Lieberman eyelid speculum was placed in the eye to keep the eyelids open during the procedure.
The surgeon reviews the patient’s intraocular pressure control and serial glaucoma studies including visual fields, optical coherence tomography of the retinal nerve fiber layer, and gonioscopy to determine the degree and rate of disease progression. The surgeon also reviews a detailed history of present illness, complete ocular history, medical history, dilated physical examination of the eyes, and neuropsychiatric evaluation to assess the patient’s ability to follow commands. It is important to assess the patient’s adherence to medical therapy, including access to care and ability to afford glaucoma medications. The surgeon should note the health of the conjunctiva and sclera at the proposed valve placement site.
Intraocular pressure is determined by the balance between secretion of aqueous humor by the ciliary body and its drainage through two independent pathways—the trabecular meshwork and uveoscleral outflow pathway.1 The Ahmed glaucoma valve provides a bypass to these pathways by shunting aqueous humor to the posterior subconjunctival space.
Implantation of an Ahmed glaucoma valve is a safe procedure that can effectively treat various subtypes of glaucoma with sub-optimally controlled intraocular pressure despite maximum medical therapy.2 An advantage of valved glaucoma shunts such as the Ahmed valve is lower risk of postoperative hypotony-related complications compared to non-valved glaucoma shunts. The Tube Versus Trabeculectomy (TVT) Study found that tube shunt surgery was more likely to maintain intraocular pressure control and avoid persistent hypotony, reoperation for glaucoma, or loss of light perception vision when compared to trabeculectomy with mitomycin C, the previous “gold standard” for surgical glaucoma management, during the first year of follow-up. The incidence of postoperative complications was higher after trabeculectomy with MMC relative to tube shunt surgery.3
Complications of Ahmed valve implantation include immediate and late hypotony after surgery, excessive capsule fibrosis and clinical failure, erosion of the tube or plate edge, and, in rare cases, vision-threatening infection.4
The authors have no financial disclosures or conflicts of interest.
None
1. Weinreb RN, Aung T, Medeiros FA. The pathophysiology and treatment of glaucoma: a review. JAMA. 2014;311(18):1901-1911. doi:10.1001/jama.2014.3192 2. Riva I, Roberti G, Oddone F, Konstas AG, Quaranta L. Ahmed glaucoma valve implant: surgical technique and complications. Clin Ophthalmol. 2017 Feb 17;11:357-367. doi: 10.2147/OPTH.S104220. PMID: 28255226; PMCID: PMC5322839. 3. Gedde SJ, Schiffman JC, Feuer WJ, et al. Treatment outcomes in the Tube Versus Trabeculectomy Study after one year of follow-up. Am J Ophthalmol. 2007;143(1):9–22. 4. Minckler DS, Francis BA, Hodapp EA, et al. Aqueous shunts in glaucoma: a report by the American Academy of Ophthalmology. Ophthalmology. 2008;115(6):1089–1098.

Review Ahmed® Glaucoma Valve for Treatment of Refractory Glaucoma.

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