Postoperative Corneal Dellen Following PreserFlo MicroShunt: A Case Report

Abstract

Patient: Male, 15-year-old

Final Diagnosis: Corneal dellen

Symptoms: Redness • tearing

Clinical Procedure: —

Specialty: Ophthalmology

Objective: Rare coexistence of disease or pathology

Background

The PreserFlo MicroShunt is a subconjunctival drainage device increasingly used to manage open-angle glaucoma. While its safety profile is considered favorable compared with that of trabeculectomy, rare postoperative complications, including corneal surface pathology, can still be encountered. To our knowledge, corneal dellen has not been previously reported following PreserFlo implantation.

Case Report

A 15-year-old boy with pathological myopia and Stickler syndrome underwent PreserFlo MicroShunt implantation for refractory secondary open-angle glaucoma. Two weeks postoperatively, he developed a temporal area of corneal stromal thinning consistent with dellen, located adjacent to an elevated bleb in the horizontal plane. Conservative therapy, including a switch from prednisolone acetate to loteprednol etabonate, intensive preservative-free lubrication, autologous serum drops, and bandage contact lens placement, was initiated. Full corneal re-epithelialization and recovery were achieved within 1 week, without compromising bleb function or intraocular pressure control.

Conclusions

Corneal dellen is a potential, although previously undocumented, complication of PreserFlo MicroShunt surgery, particularly when bleb elevation is prominent in areas not protected by the eyelid. Prompt recognition and targeted conservative therapy may allow for complete recovery while preserving device function and visual outcomes. Surgeons should monitor the ocular surface for this complication and adjust postoperative management accordingly.

Introduction

The Preserflo MicroShunt is a relatively new ab externo subconjunctival drainage device designed to lower intraocular pressure (IOP) in patients with open-angle glaucoma. Made from a bioinert, flexible material (styrene-block-isobutylene-block-styrene) [1], the device is small, easily implantable, and has gained popularity as a simpler and less complication-prone alternative to trabeculectomy [2]. The adoption of the device has become so widespread that it is sometimes informally referred to as the “trab killer”.

Several studies have demonstrated that Preserflo achieves significant early postoperative IOP reduction, often into single digits, with a shorter learning curve for surgeons and fewer postoperative visits [3,4]. However, despite this favorable safety profile, the full spectrum of its complications is still unfolding. Reported complications include hypotony, choroidal effusions, bleb fibrosis, keratitis, and exposure [5,6].

As experience with the device grows, more complications are being reported. Here, we report a rare and, to the best of our knowledge, previously undocumented complication: corneal dellen formation occurring just 2 weeks postoperatively in a patient who underwent uneventful Preserflo implantation.

Case Report

A 15-year-old boy with a history of pathological myopia, heavy eye syndrome, and Stickler syndrome was evaluated for secondary open-angle glaucoma in both eyes (OU).

His left eye had previously undergone multiple retinal surgeries for recurrent retinal detachment. Two months prior to glaucoma surgery, the patient received laser photocoagulation in the right eye (OD).

IOPs were controlled with medical therapy. However, in subsequent visits to the clinic, the right eye started to have persistent elevated IOP despite maximum tolerated medical therapy, including latanoprost 0.005% once daily OU, timolol 5 mg/mL/dorzolamide 20 mg/mL OU twice daily, brimonidine tartrate 0.15% OU twice daily, and oral acetazolamide 250 mg twice daily. Despite maximal tolerated medical therapy, right eye IOP rose to 32 mmHg, as measured by Goldmann applanation tonometry. Central corneal thickness was 580 μm OD and best-corrected visual acuity was OD: 20/250, improving to 20/200 with pinhole, and OS: 2–3/300. Clinical examination revealed a quiet conjunctiva, clear cornea, deep and quiet anterior chamber, clear lens, and open angles on gonioscopy. Fundus examination of the right eye showed a tessellated myopic fundus, tilted optic disc with a cup-to-disc ratio of 0.6, and good retinal attachment.

At a subsequent visit, the IOP in OD increased further to 36 mmHg despite ongoing therapy. Mild conjunctival injection and epithelial corneal edema were noted, along with a hazy fundus view. Given poor pressure control, glaucoma surgery was indicated. Traditional trabeculectomy was considered high-risk due to ocular surface concerns and potential postoperative complications. Micropulse cyclophotocoagulation was also considered but deemed potentially less effective given the patient’s high myopia and altered ciliary anatomy. After considering the patient’s risk factors, PreserFlo MicroShunt implantation was selected as the preferred surgical option. Prior to surgery, panretinal photocoagulation was recommended by the retina specialist due to some peripheral retinal changes caused by Stickler syndrome.

Intraoperatively, a dense avascular conjunctival band extending from the superior temporal to inferior nasal quadrant was observed, with adherent Tenon’s capsule and fibrotic adhesions despite no prior intraocular surgery (except panretinal photocoagulation). Hydrodissection attempts with balanced salt solution failed to elevate the conjunctiva, necessitating a posterior limbal-based peritomy with careful Tenon and conjunctival dissection. An amount of 0.4 mg/mL of mitomycin-C was applied for 4 minutes on a long posterior sponge.

Abnormal tenon adhesion to presumed muscle tissue was dissected to improve exposure. Due to extensive fibrosis, a scleral tunnel was created at the 9 to 10 o’clock position, 3.5 mm posterior to the limbus, with a sharp blade and 25-gauge needle.

The PreserFlo MicroShunt was introduced approximately 2 mm into the anterior chamber, and its position was confirmed by anterior segment optical coherence tomography (AS-OCT). The device was secured with 9-0 nylon sutures, and 9-0 nylon was used as a ripcord inserted inside the tube; the conjunctiva was sutured watertight. Intracameral dexamethasone and antibiotics were administered. No intraoperative complications occurred.

On postoperative day 1, the patient’s visual acuity was approximately hand motion, and IOP was 12 mmHg. The examination revealed a well-covered tube, clear cornea, deep and quiet anterior chamber, clear lens, and flat retina. Postoperative management included topical prednisolone acetate 1% every hour, ofloxacin 4 times daily, lubricating drops 4 times daily, and carbomer gel twice daily.

At the 2-week follow-up (postoperative day 14), the patient’s visual acuity improved to 20/400 OD, with an IOP of 20 mmHg, measured by iCare tonometry. The right eye showed blepharitis, mild conjunctival injection, a well-formed large elevated bleb without leaks, and a temporal area of corneal thinning (approximately 20% of corneal thickness) adjacent to the bleb, with fluorescein uptake and no infiltrates (Figures 1, 2). The anterior chamber remained deep and quiet with occasional pigmented cells; the lens was clear, and the retina appeared grossly flat. The clinical impression was corneal dellen, likely related to the large bleb formation following PreserFlo surgery. AS-OCT demonstrated epithelial thinning with mild focal stromal thinning adjacent to the bleb, corresponding to the corneal Dellen observed at slit-lamp examination (Figure 3).

Figure 1.

Slit-lamp image of the right eye 2 weeks after PreserFlo implantation shows mild injection, with no leak elevated bleb, and adjacent temporal corneal thinning with fluorescein staining and no infiltrates.

Figure 2.

Slit-lamp image of the right eye 2 weeks after PreserFlo implantation shows corneal stromal thinning with slit beam.

Figure 3.

Anterior segment optical coherence tomography image of the right eye 2 weeks after PreserFlo implantation shows epithelial thinning with mild focal stromal thinning adjacent to the bleb.

In response, the topical steroid was switched from prednisolone acetate to loteprednol etabonate 0.5% (Lotemax) twice daily, continuing ofloxacin, adding autologus serum 20% balanced saline solution 4 times daily, lubricating drops (optive fusion UD) were increased to every hour, lubricating gel (carbomer) was increased to 4 times daily, and a bandage contact lens was placed to aid corneal healing

One week after the treatment adjustment (postoperative day 21), the IOP increased to 42 mmHg (iCare). Despite this, slit-lamp examination showed complete resolution of the corneal dellen. AS-OCT findings showed a return to normal corneal contour and thickness, consistent with the complete clinical resolution of the Dellen. Oral acetazolamide 250 mg twice daily was initiated to control IOP, and ripcord removal was planned in two weeks.

Six weeks following ripcord removal, the IOP had stabilized to 17 mmHg. The bleb remained well-formed, and no recurrent corneal complications were observed.

Discussion

Dellen is a recognized complication following filtering or shunt glaucoma surgeries. While typically managed conservatively, early postoperative cases may pose therapeutic challenges due to the need to preserve a functioning bleb while promoting corneal healing in the presence of topical corticosteroids.

Soong and Quigley reported a dellen incidence of up to 9% after trabeculectomy, with lesions commonly located adjacent to large blebs within the horizontal plane, similar to the presentation observed in this case, where the dellen was located temporally around the 9 to 10 o’clock position, just adjacent to the elevated bleb [7].

Fenzl et al reported a case of dellen-like keratopathy with diffuse bilateral involvement occurring seven years after glaucoma drainage device implantation, in contrast to the current case, where dellen developed acutely 2 weeks postoperatively [8].

The PreserFlo MicroShunt is gaining popularity among glaucoma specialists for managing moderate to severe glaucoma, owing to its favorable efficacy and improved safety profile compared to trabeculectomy. Although transient complications such as hypotony and choroidal detachments have been reported, they generally resolve spontaneously, as observed by Barberá et al, Batlle et al, and Beckers et al [9–11].

Saeed et al reported rare corneal complications following PreserFlo MicroShunt surgery, such as keratitis, corneal abrasions, and ulcers. However, based on current knowledge, no case has described dellen formation after PreserFlo implantation [6].

Usually the underlying pathology is believed to be similar to that of dellen formation following trabeculectomy, in which disruption of the tear film by an adjacent large bleb is the primary contributing factor. However, in our case, the patient exhibited unique and challanging features. Patients with Stickler syndrome have underlying connective tissue abnormality, which likely played an important role in the atypical postoperative response the patient experienced. Patients with Stickler syndrome have mutations in COL2A1 and COL11A1, which encode type II and type XI collagen, respectively, and are known to alter the architecture and biomechanical properties of the extracellular matrix, leading to increased tissue laxity and reduced structural resistance [12]. These abnormalities, which are documented in large national cohorts of patients with Stickler syndrome, affect the sclera, conjunctiva, and cornea, predisposing to tissue distensibility and fragility [13]. Consequently, the subconjunctival space may expand more easily, facilitating the formation of a larger and more diffuse bleb than usual. Moreover, the same collagen defects can weaken limbal support, making the ocular surface more susceptible to microdefects and local dehydration, further explaining the development of a focal dellen adjacent to the bleb. Taken together, these factors – along with the wide surgical dissection used in our case to promote a posterior, diffuse bleb – provide a coherent explanation for the unusually elevated bleb and the associated dellen effect. In addition, reports in the literature suggest that blebs located closer to the horizontal plane may carry a higher risk for dellen development. This association was also supported by Soong and Quigley in their analysis of dellen following filtering surgeries [7].

Although there are no comparative data on PreserFlo in Stickler syndrome, the literature shows that patients with Stickler carry a lifelong glaucoma burden (approximately 12%) and a pediatric prevalence of about 10%, often secondary to retinal detachment or cataract surgery [14]. Moreover, collagen type I/II abnormalities have been associated with trabecular meshwork dysfunction, rendering angle-based procedures less predictable [12]. In this context, a subconjunctival bypass approach such as PreserFlo offers a physiologically sound and safer option for achieving sustained IOP control while minimizing intraocular manipulation. This rationale informed the decision to proceed with PreserFlo implantation in this patient.

In this case, once the corneal dellen was identified, topical steroids were immediately switched to loteprednol etabonate (Lotemax); decreasing the strength and frequency of the steroids was done to give time for the cornea to heal, along with the addition of autologous serum balanced salt solution and intensive lubrication. This approach led to complete resolution at the 1-week follow-up. Despite this, the IOP rose to 42 mmHg, presenting another challange in the case. We attributed this increase to early fibrosis that happened after decreasing the frequency and switching to a softer steroid. Prompt management with oral acetazolamide and subsequent ripcord removal normalized the IOP within 6 weeks, without affecting bleb morphology or corneal recovery.

In conclusion, awareness of potential complications associated with PreserFlo implantation is essential, particularly when procedural modifications are required. Recognizing the risks this procedure poses to patients with complex connective tissue disorders is paramount. Anticipating such outcomes enables surgeons to optimize postoperative care and preserve surgical success.

Conclusions

This report is the first documented case of corneal dellen formation following PreserFlo MicroShunt implantation. Although the case presents unique clinical features and its generalizability remains limited, such reports are essential to expanding the literature on potential complications associated with this device. Notably, this complication can theoretically occur in eyes with large blebs located near the palpebral fissure, where tear film disruption is more likely. Conservative medical management, including temporary tapering of topical corticosteroids and intensive ocular surface lubrication, can facilitate complete corneal recovery without compromising bleb function.