Scleral thinning a complication after pterygium excision

Surgeons explain how they used a scleral patch graft after a patient experienced postoperative scleral thinning.

Amar Agarwal

The sclera, the outermost coat of the eyeball, comprises a group of collagen fibers that make the ocular coat tough and fibrous. It is opaque and appears white due to the high water content and haphazardly arranged collagen fibers. This provides strength and rigidity to the globe despite its constant movement and the pull exerted by the extraocular muscles.

Scleral pathologies are not uncommon and are usually related to systemic conditions or postsurgical complications. Scleral thinning is one such condition commonly encountered in clinical practice. In this column, we describe a patient with scleral thinning after pterygium surgery with conjunctival autograft and how it may be managed with a patch graft.

Scleral thinning

A literature search shows that scleral thickness varies at different anatomical points. For example, at the corneoscleral limbus, it is about 0.5 mm, decreasing to as little as 0.3 mm at the equator; it is 0.9 mm to 1 mm near the optic nerve. Moreover, muscle insertions have thin sclera.

Scleral thinning can occur in various conditions, including myopic degeneration, chronic scleritis, local scleral pathologies and scleral injury. Scleral thinning can result after excessive use of cautery in the scleral bed or overuse of antimetabolites. Prolonged irradiation, transscleral diode laser cycloablation, strabismus surgery and deep sclerectomy procedures can also predispose the sclera to thinning. Autoimmune conditions or collagen vascular diseases are known to present with scleral pathologies, which can also lead to scleral thinning.

Case summary

A 54-year-old female patient came to our outpatient clinic with a history of growth in the left eye for 6 months. She had undergone cataract surgery in both eyes, and her best corrected vision was 20/20. Her IOPs were 10 mm Hg and 12 mm Hg. There was no systemic condition such as rheumatoid arthritis or collagen vascular disorders. She had been diagnosed as having a primary pterygium, and pterygium excision with conjunctival autograft with tissue glue had been performed in her left eye. The patient had been on topical 0.3% gatifloxacin and topical lubricants in the immediate postoperative period.

Figure 1. Acute scleral thinning with uveal show after pterygium removal. Images: Agarwal A

One week later, the patient came to our clinic with severe pain and redness. On ocular examination, there was loss of conjunctival autograft tissue. Scleral thinning was noted with uveal show (Figure 1). Impending perforation was observed. Minimal corneal thinning was also noted at the limbus. Her BCVA was 20/20.

Lamellar scleral patch graft

Scleral patch grafting is one of the best options in the above situation. Donor sclera is harvested from the available enucleated eye bank eyeball, soaked in antibiotic (0.3% gatifloxacin and gentamycin 40 mg/mL) and again cleaned with Betadine (5% povidone-iodine ophthalmic solution, Alcon). The patient is given peribulbar anesthesia. After sterile cleaning and draping, the area of scleral thinning is well-defined and exposed (Figure 2a). The amount of scleral tissue to be replaced is measured with calipers. Donor sclera is placed over the thinned bed area and initially cut in the required size (Figure 2b). Lamellar scleral graft is dissected from the donor sclera. A 10-0 monofilament nylon suture is then used to suture the donor sclera to the bed. The donor size should preferably be larger than the thinned scleral bed. The corneal side of the graft is positioned so that it does not cover the pupillary axis or produce striae. The scleral graft is then covered with the conjunctiva. The conjunctiva is sutured with 6-0 polyglactin sutures (Figure 2c). Subconjunctival antibiotic and steroid injection are given. The postoperative prophylaxis includes antibiotics, topical steroids, lubricants and anti-inflammatory agents. The patient symptomatically improved and showed good graft apposition (Figure 3).

Figure 2. A: Thinned scleral bed area exposed. B: Donor scleral patch graft placed and sutured to the scleral bed and cornea. C: Conjunctiva well apposed.

Figure 3. Day 1 postoperative picture showing good graft apposition.

Scleral complications after pterygium surgery

Scleral dellen is an early postoperative complication of the bare sclera technique with mitomycin C caused by delayed conjunctival wound closure. Treated sclera may become white, or “porcelainized,” due to destroyed vessels and remain so permanently. It has been reported that this is due to the drug’s effect on multipotential cells and the rapidly proliferating cells of vascular endothelium.

MMC is an antimetabolite agent produced by a strain of Streptomyces caespitosus. It inhibits synthesis of DNA, RNA and proteins. This drug is referred to as radiomimetic, as its action mimics that of ionizing radiation. Topical MMC 0.02% eye drops have been known to cause ocular complications such as superficial punctate keratitis, avascularized sclera and pyogenic granuloma. Scleral ulceration was observed in 51 eyes after pterygium excision with bare sclera surgery on long-term follow-up by Tarr et al. Pseudomonas endophthalmitis has been reported in four patients with scleral ulceration after pterygium excision. Tarr et al observed that beta irradiation to prevent recurrence of pterygia is a significant cause of iatrogenic ocular disease. MMC 0.5 mg/mL has also been used after pterygium excision and beta irradiation, which leads to complications such as scleromalacia and scleral ulcer. Excessive intraoperative cautery to the scleral bed should be avoided. Overenthusiastic use of antimetabolites can also lead to scleral complications. Necrotizing scleritis has been reported after conjunctival autograft, and scleral thinning with perforation can also occur.

However, our patient did not have any systemic predisposition or local risk factor for scleral thinning, such as excess cautery, MMC use or irradiation. But the loss of the conjunctival graft might have exposed the underlying scleral bed, making it equivalent to a bare sclera technique. Surgeons can follow simple steps to prevent the loss of autograft: using the correct technique of tissue glue reconstitution, drying the scleral bed before fibrin glue application, harvesting thin conjunctiva without any underlying tenon, and using stay sutures if the graft is unstable on the table.

Alternate therapy

A complete postoperative clinical evaluation for collagen vascular diseases is recommended in these cases. Nevertheless, prompt diagnosis, systemic immunosuppressant use and early surgical closure with a scleral patch graft might prevent further complications. Multilayered amniotic membrane grafting is one alternative in scleral thinning. This helps epithelialization and healing. Fibrin glue can be applied in the defined scleral bed in selected cases of impending perforation. Nevertheless, scleral patch graft is the best choice in severe thinning. Regular follow-up with postoperative anti-inflammatory medications is mandatory in these patients.

The case report shows a patient developing acute scleral thinning after loss of conjunctival autograft with tissue glue. Such a complication can be managed easily with a lamellar scleral patch graft. Thus, regular follow-up and early diagnosis can prevent further complications.

• Amar Agarwal, MS, FRCS, FRCOphth, is director of Dr. Agarwal’s Eye Hospital and Eye Research Centre. Prof. Agarwal is the author of several books published by SLACK Incorporated, publisher of Ocular Surgery News, including Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at 19 Cathedral Road, Chennai 600 086, India; fax: 91-44-28115871; e-mail: dragarwal@vsnl.com; Web site: www.dragarwal.com.