Complications Unique to Surface Ablation

Persistent Epithelial Defects

Usually, the epithelial defect created during surface ablation heals within 3–4 days with the aid of a bandage soft contact lens or pressure patching. A frequent cause of delayed re-epithelialization is keratoconjunctivitis sicca, which may be treated with increased lubrication, cyclosporine, and/or temporary punctal occlusion. Patients who have undiagnosed autoimmune connective tissue disease or diabetes mellitus or who smoke may also have poor epithelial healing. Topical nonsteroidal antiinflammatory drugs (NSAIDs) should be discontinued in patients with delayed re-epithelialization. Oral tetracycline-family antibiotics may be beneficial for persistent epithelial defects. Temporary discontinuation of other potentially toxic topical medications, such as glaucoma drops, may also help in re-epithelialization. The importance of closely monitoring patients until re-epithelialization occurs cannot be overemphasized, as a persistent epithelial defect increases the risk of corneal haze, irregular astigmatism, refractive instability, delayed recovery of vision, and infectious keratitis.

Sterile Infiltrates

The use of bandage contact lenses to aid epithelial healing is associated with sterile infiltrates, which may occur more frequently in patients using topical NSAIDs for longer than 24 hours without concomitant topical corticosteroids. The infiltrates, which have been reported in approximately 1 in 300 cases, are secondary to an immune reaction (Fig 6-7). They are treated with institution of topical steroids, tapering and discontinuation of topical NSAIDs, and close follow-up. It must be kept in mind that any infiltrate may be infectious and should be managed appropriately. If infectious keratitis is suspected, the cornea should be scraped and cultured for suspected organisms.

Figure 6-7 Stromal infiltrates after use of a bandage soft contact lens following PRK. (Courtesy of Jayne S. Weiss, MD.)

Corneal Haze

The manner of wound healing after surface ablation is important in determining postoperative topical corticosteroid management. Eyes that have haze and are undercorrected may benefit from increased corticosteroid use. Eyes with clear corneas following surface ablation and that are overcorrected may benefit from a reduction in topical corticosteroids, which may lead to regression of the overcorrection.

When present, subepithelial corneal haze typically appears several weeks after surface ablation, peaks in intensity at 1–2 months, and gradually diminishes or disappears over the following 6–12 months (Fig 6-8). Late-onset corneal haze may occur several months or even a year or more postoperatively after a period in which the patient had a relatively clear cornea. Histologic studies in animals with corneal haze after PRK demonstrate abnormal glycosaminoglycans and/or nonlamellar collagen deposited in the anterior stroma as a consequence of epithelial–stromal wound healing. Most histologic studies from animals and humans show an increase in the number and activity of stromal keratocytes, which suggests that increased keratocyte activity may be the source of the extracellular deposits.