A case of resistant scleral thinning following uneventful pterygium surgery: A case report and a literature review

Introduction We describe the management of a scleral thinning after uneventful pterygium surgery, it is an uncommon complication; in addition, we have reviewed similar published cases in the literature. Presentation of case A 48-year-old woman presented with thinning sclera in the first week after pterygium excision surgery. Conservative treatment was the first line in the management. There was no improvement for two weeks, so we decided to do a rotational flap. We put a scleral dellen diagnosis by excluding other etiologies. The condition was successfully managed, the thinning sclera healed completely. Scleral and conjunctival re-surfacing was observed. Clinical discussion Scleral dellen is an early and rare postoperative complication after pterygium surgery. The diagnosis is confirmed after excluding other causes of scleral thinning. The exact pathophysiology of it is not determined yet, many authors described probable explanation in their published cases. We did a comprehensive review of similar cases with their management. Conclusions Scleral dellen is uncommon complication after pterygium surgery, its diagnosis depends on exclusion. The management can be conservative. However, if no progression was detected do not hesitate going for surgical closure.


Introduction
Pterygium is a fibrovascular growth of the conjunctiva on the corneal surface. Several surgical techniques are available for the treatment of pterygium; excising accompanied by adjunctive treatment with mitomycin C or conjunctival autografts is currently the most popular treatment option since it provides the most satisfactory results [1,2].
The condition of scleral defect after pterygium surgery has been reported in many publications as a scleral dellen, scleral melting, scleral thinning and scleral necrotizing defects. In addition, there is not a definitive pathology described for this complication neither guidelines for treatment.
In this case, we present a severe acute scleral defect occurred after an uneventful pterygium surgery. In addition, we reviewed similar published cases and their management. This work has been reported in line with the SCARE criteria [3].

Case report
A 48-year-old Caucasian woman presented to the outpatient clinic with a history of recurrent irritation, redness and foreign body sensation in her right eye. Ophthalmologic examination revealed a primary pterygium on the nasal side of her right eye, measuring 3 mm at the limbus and 4 mm into the cornea. No other abnormalities were detected in the eye. She denied any systemic, ocular or medical histories. The pterygium was excised by a senior resident under topical and subconjunctival anesthesia (lidocaine 2% and epinephrine 1/200,000). A conjunctival autograft was performed to cover the conjunctival defect using sutures without any adjunctive therapies such as intraoperative mitomycin C or cauterization, nor postoperative beta radiation.
The operation ended smoothly. We gave the patient a combination therapy of levofloxacine 0.5% and dexamethasone 0.1% eye drops four times daily after surgery with antibiotic ointment.
The outcome looked satisfactory the day after surgery without any complaints or complications. Three days later, however, the graft shrank Abbreviations: SINS, Surgically Induced Necrotizing Scleritis; SD, Scleral Dellen. and appeared grey and dry. Areas of bare sclera have appeared around the graft with congested conjunctiva. After asking her again, she denied any history for medical, ocular conditions or taking medications. An extensive therapy of topical steroids, antibiotics, and artificial tears was given.
One week later, the patient came to the department complaining of mild discomfort, foreign body sensation and a black dot at the surgical site. Her corrected visual acuity was 20/25 just as before the operation, the intraocular pressure was 16 mm Hg. On slit lamp examination, the conjunctival sutures were no longer in place and a well-demarcated focal area of scleral thinning was visible measuring approximately 2 * 2.5 mm surrounded by congested edematous conjunctiva. The thinned sclera was dry and the uvea was visible through the base of the lesion (Fig. 1). There was no ciliary injection, no papillary or follicular reaction at the palpebral conjunctiva. No cells or flair in the anterior chamber, Bscan was normal. The rest of the eye exam was normal.
The patient was referred to the Internal Medicine Department in order to rule out autoimmune or any infectious diseases. Medical history, physical examination, and laboratory tests (blood count, biochemistry, rheumatoid factor and antinuclear antibody screening) were all in normal ranges.
We made a diagnosis of scleral dellen and continued the mentioned medications with hourly lubrication. After two weeks of conservative treatment, scleral thinning did not decrease in size despite the intensive ocular lubrication in the treatment.
Finally, we decided to do a surgical management with a rotation flap of adjacent conjunctiva.
The medication regime contained levofloxacin 0.5% and dexamethasone 0.1% eye drops four times daily with unpreserved artificial tears 24 times a day after surgery. The outcome was good as the patient symptomatically improved and the thinning area decreased in size. Four weeks after the procedure, the thinned sclera appeared regularly thick and white in color with no more visible uvea (Fig. 2).

Discussion
We are presenting a challenging case of scleral thinning after uneventful pterygium excision with autograft that covered the conjunctival defect without any adjunctive therapies.
Scleral dellen is an early postoperative complication during first two weeks of bare sclera technique owing to delayed conjunctival wound closure [4,5]. The formation of a dry area on the cornea, limbus even sclera is not uncommon which could lead to the formation of dellen. The exact pathophysiology of this complication on sclera is not determined [5,6]. Chen and Noonan [6] in addition to T. Starck et al. [7] suggest that conjunctival edema with raised granulation tissue edges may cause a discontinuity of the tear film leading to exacerbated local desiccation and dellen formation. Tsai et al. [5] added that the delayed conjunctival wound closure should be taken as another factor. In Accorinti et al. case [8], authors assumed that tear film stability disruption and dehydration may also contribute to dellen formation. On the other hand, S. Mitra et al. [9] suggest a contribution of steroids in the pathology of dellen development.
Our first differential diagnosis to rule out was surgically induced necrotizing scleritis (SINS); SINS is a painful condition, patients typically offer history of serious, profound boring pain. In addition, the majority of cases of SINS present within few months of surgery. The managment of the thinned sclera is difficult [10].
Our patient however, was healthy at presentation. She had not any sever pain or symptoms. There are not any conditions predispose to ulceration, poor wound healing or severe tear film. Schirmer-Test was within normal limits. All laboratory studies were normal, no systemic diseases such as autoimmune processes or vasculitis were detected at presentation. Apart from the drying effect produced by the edematous conjunctiva and the loss of the graft, no other etiological factor was found.
We did a comprehensive review of similar cases with their management; we found 12 published articles. All of them, are case reports or case series. The results are concluded in Table 1. Half of the published cases were healed with the conservative treatment along with patching. However, the other half needed a surgical intervention.
A conservative treatment consisting of the use of extensive artificial tears, antibiotic ointment and a patch is a useful management for the major of scleral dellen cases. However, if the case does not respond to the treatment, a surgical approach should be considered. Conjunctival flap and multilayered amniotic membrane transplantation are useful operations with minimum complications. In addition, when the case is associated with an Impending perforation, a lamellar scleral patch graft may be undertaken.
More observational and case-control studies are needed in order to investigate the pathophysiology of this condition and to describe guidelines for the management.

Conclusion
Conservative treatment is an appropriate initial treatment for scleral dellen. In resistant cases, conjunctival flap may be a good management. More studies on the histopathology and pathophysiology should be done to identify the actual ground for this complication.

Consent
Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Provenance and peer review
Not commissioned, externally peer-reviewed.

Ethical approval
Case reports are exempt from ethnical approval in our institution.

Funding
This article does not have funding sources.

Declaration of competing interest
All authors have no conflict of interest to declare.