Unusual sequelae of staphyloma following Ahmed glaucoma valve explantation and its management

Abstract

We report a case of a 7-year-old boy, who presented with plate exposure after Ahmed glaucoma valve (AGV) implantation in the eye with secondary glaucoma following penetrating trauma. He underwent AGV explantation with scleral patch graft and conjunctival limbal autograft and started on topical and oral antiglaucoma medication (AGM) for intraocular pressure (IOP) control. Two months later, he presented to us with high intraocular pressure and uveal tissue prolapse at the site of previous tube entry displacing the scleral and conjunctival grafts posteriorly. The defect was closed with corneal patch graft. Patient underwent limited transscleral cyclophotocoagulation and was maintained on topical AGM for IOP control. Our case highlights that explantation is a definitive management in such cases of plate exposure. Tube entry site is a potential weak area and there is risk of uveal prolapse through this area with high IOP. Corneal patch graft helps in successfully managing such defects involving the sclero-limbal region.

Background

Uveal tissue prolapse through the tube entry site has not been reported so far to the best of our knowledge. As the area of prolapse was involving the sclero-limbal area, we used corneal patch graft though major surface area covered was involving the previous recipient sclera. We could successfully repair the area of uveal prolapse without any leak. We would like to present the management of this unusual sequelae following the Ahmed glaucoma valve (AGV) explantation.

Case presentation

A 7-year-old boy presented to us with redness in left eye (LE) for 3 months. He had a history of penetrating injury at the age of 3 years for which he had undergone corneal tear repair. At the age of 4 years, he developed secondary glaucoma and complicated cataract. He underwent cataract extraction and intraocular lens implantation, twice trabeculectomy prior to AGV implantation. AGV implantation was done 1 year ago (at the age of 6 years). As he developed hypertensive phase with high intraocular pressure (IOP) 6 months after AGV implantation, he had undergone bleb wall excision with conjunctival autograft for hypertensive phase of AGV.

On examination, his right eye’s anterior and posterior segments were normal with a visual acuity of 20/20 and IOP of 12 mm Hg. Best-corrected visual acuity in the LE was 20/160 and IOP was 14 mm Hg. Clinical examination of LE revealed conjunctival erosion and anterior migration of AGV plate with plate exposure in the supero-temporal quadrant 5 mm from limbus. Cornea was clear centrally, with a healed pigmented horizontal scar in the inferior half signifying the past corneal tear repair. Anterior chamber (AC) was deep with a long tube at 2 o’clock. Fundus showed a pale disc and attached retina.

With the diagnosis of AGV plate exposure, AGV explantation with scleral patch graft and conjunctival limbal autograft (CLAG) in the LE under general anaesthesia was planned.

Intraoperatively, a large conjunctival defect with AGV plate exposure was confirmed (figure 1A). AGV was explanted in toto. No leak from the tube-entry site was noted (figure 1B), and one 10-0 nylon suture was put to close the wound. A scleral patch graft of 4×4 mm was used to cover the tube entry site (figure 1C) and a CLAG from the infero-nasal quadrant was taken and placed over the scleral patch graft (figure 1D).

Figure 1.

Intraoperative pictures of left eye showing explantation of the exposed plate of Ahmed glaucoma valve (shown in dotted white lines in (A)), tube entry site (pointed with yellow arrow in (B)), a scleral patch graft covering the tube entry site (C) and conjunctivallimbal autograft taken from the infero-nasal quadrant which is placed over the scleral patch graft (D).

On postoperative day 1, IOP in LE was 35 mm Hg with intact scleral and conjunctival grafts. Wound was well apposed. He was started on topical steroids, cycloplegics and antibiotics along with topical and short course of oral antiglaucoma medication (AGM). A bandage contact lens (BCL) was placed in order to avoid foreign body sensation and irritation due to multiple sutures. Patient had uneventful postoperative visit at 1 month with an intact scleral patch graft, well-healed CLAG and controlled IOP with topical AGM in LE.

After 2 months, there was a spike in the IOP of 35 mm Hg in the LE. On examination, uveal prolapse (figure 2) in the area of previous tube entry (2 mm from the limbus) beyond the edge of the BCL was noted with posterior displacement of both scleral patch graft and conjunctival autograft. As the uveal prolapse was a potential site for infection, with risk of sympathetic ophthalmitis in the other eye and location was sclero-limbal, a corneal patch graft was planned.

Figure 2.

Two months postoperative slit lamp picture of the left eye showing an intact bandage contact lens and uveal prolapse in the area of previous tube entry shifting the scleral patch graft and conjunctival autograft posteriorly.

After trephining the recipient bed size of 5.5 mm which included the area of prolapse, a corneal patch graft of 6.5 mm was placed and secured with 12 interrupted 10-0 nylon sutures. Limited transscleral cyclophotocoagulation (TSCPC) was performed subsequently in the infero-nasal and supero-nasal quadrants and started on topical AGM for IOP control.

In the last visit, 3 months post TSCPC, the visual acuity was 20/200, N36 with a borderline IOP of 20 mm Hg in LE and an intact corneal patch graft (figure 3). Fundus showed a disc of 0.7 CDR (cup-to-disc ratio) with diffuse pallor. AGM was continued and the patient was maintained on low-dose, low-potency steroids in the LE and was asked to review after 3 months.

Figure 3.

Slit lamp picture of the left eye showing intact corneal patch graft 4 months after repair of the weak area of sclera where uveal tissue has prolapsed.

Investigations

B scan of the LE was performed to rule out any infections but no infection was found.

Differential diagnosis

The only differential diagnosis in our case considered was scleral melt secondary to any connective tissue disorder, but since the IOP was high and the uveal tissue has prolapsed through the pre-existing weak area, the diagnosis was quite straight forward and we ruled out scleral melt.

Outcome and follow-up

Patient was followed up for 3 months post TSCPC. In the last visit, the visual acuity was 20/200, N36 with a borderline IOP of 20 mm Hg in LE and an intact corneal patch graft (figure 3). Fundus showed a disc of 0.7 CDR with diffuse pallor. AGM was continued and the patient was maintained on low-dose, low-potency steroids in the LE and was asked to review after 3 months

Discussion

AGV implant (New World Medical, Rancho Cucamonga, California, USA) is a valved device with unidirectional flow, and is increasingly becoming popular in the management of refractory glaucomas.^1–3 Typically, implants are indicated in eyes with conjunctival scarring from previous surgeries and also as a primary choice in certain types of secondary glaucomas where the success of filtering surgeries would be less. Among the various complications related to AGV implantation, exposure of a part of a glaucoma drainage device implant is known to occur in 2%–7% of cases⁴ and can be potentially sight-threatening due to the propensity to cause infection in view of its direct communication to the AC.

Ayyala et al⁵ retrospectively looked at the various risk factors for implant exposure and showed that the OR of exposure was nine times higher with one prior intraocular surgery. They hypothesised that previous ocular surgery may induce conjunctival scarring or thinning, and hence fail to preserve the device. Our case had five prior surgeries (one corneal tear repair, one lens explantation and two failed trabeculectomies, AGV implantation, AGV bleb wall excision with conjunctival autograft) which posed a high risk for plate exposure. Chronic use of multiple AGM and mitomycin C application in previous surgeries could also have possibly affected the conjunctival health. Duration between plate exposure and bleb wall excision in our case was 5 months. Ischaemic necrosis from microvascular compression as well as immunological reactions of the overlying conjunctiva has been proposed to be the pathology behind the plate exposure.⁵

Explantation of the implant² is the management of choice in cases of plate exposure, as major part of the implant would be exposed and chances of conjunctival necrosis and re-exposure would be high if attempt is made to close it. Roy and Senthil² reported a series of 6 cases with plate exposure following AGV implantation and all six eyes had explantation of the AGV with 3 of them having re-implantation in a different quadrant at a later date and the other three eyes being managed medically. All six cases were reported to have good IOP control post operatively. Explantation of the AGV was performed in our patient as there was plate exposure in order to prevent infection.

Tube entry site can be closed by various methods as described in the literature.^{2 6} Roy and Senthil² used a corneal patch graft to seal the defect following the explantation of AGV. Yoo et al⁶ described the use of pericardium (tutoplast) plug to seal the corneo-scleral defect instead of sutures as the use of sutures can induce astigmatism. But since in our case the visual potential was guarded and astigmatism was not of concern, we used a 10-0 nylon suture to close the defect and no leak was noted following it and to reinforce the scleral stability, we additionally used a scleral patch graft to cover the defect along with a CLAG to cover the conjunctival defect. Previous published case reports have described various methods of closure to prevent leak-related complications and hypotony.^7–9 Though there was no leak or hypotony related complication in our case intraoperatively or postoperatively, there was uveal prolapse through the fistula site after 2 months due to increased IOP. Thus, one stitch with 10-0 nylon might not be sufficient to close the fistula site and thicker sutures like 8-0 nylon or tissue replacement with pericardium or scleral patch is required to prevent complications like hypotony or high IOP.

Reported complications following the revision surgery in the past include re-exposure of the plate, recurrent erosions of the conjunctiva over the tube or the scleral patch graft melt, phthisis, tube migration towards corneal endothelium and cystoid macular oedema.^{4 10} Uveal tissue prolapse through the tube entry site has not been reported so far to the best of our knowledge. It is possible that young age, repeated microtrauma by possible eye rubbing in child, poor conjunctival status due to multiple previous surgeries involving conjunctiva and chronic low-grade inflammation along with a sudden spike in the IOP postoperatively, all could have contributed to the prolapse of the uveal tissue through an already weak area due to previous tube entry.

Currently, most of the surgeons prefer to cover defects in sclera with a preserved human donor scleral patch graft^{2 11} and defects in cornea with donor corneas obtained from the eye bank due to its easy availability and affordability.^{4 10} Mansoori reported a case of recurrent sclera patch graft shrinkage and melting for which usage of another scleral patch graft was done.¹¹ But the decision of donor tissue has to be taken on case-to-case basis. As in our case the area of prolapse was involving the sclero-limbal area, we used corneal patch graft though major surface area covered was involving the previous recipient sclera. We could successfully repair the area of uveal prolapse without any leak. To prevent recurrences, we performed limited TSCPC for IOP control.

Patient’s perspective.

I am very happy that my son’s eye pressure is under control and he can see well with both eyes now.

Learning points.

• Plate exposure after Ahmed glaucoma valve implantation though uncommon can occur specially in eyes with multiple previous intraocular surgery. Explantation of the implant should be considered as definitive management.

• Tube entry site (fistulous track) is a potential weak area through which uveal prolapse may occur in cases of high intraocular pressure.

• One stitch with 10-0 is not adequate for such fistula repair. Thicker sutures like 8-0 nylon or tissue replacement with pericardium or scleral patch is required to prevent complications like hypotony or uveal prolapse.

• Corneal patch graft helps in successful management of uveal prolapse through sclero-limbal defects due to high intraocular pressure thus preventing serious sight-threatening complications.