The presentation 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. After surface ablation, eyes with clear corneas that are overcorrected may benefit from a reduction in topical corticosteroids, which may lead to regression of the overcorrection.
Figure 6-7 Stromal infiltrates after use of a bandage contact lens following photorefractive keratectomy.
(Courtesy of Jayne S. Weiss, MD.)
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.
Persistent severe haze is usually associated with greater amounts of correction or smaller ablation zones. Animal studies have demonstrated that ultraviolet B exposure after PRK prolongs the stromal healing process, with an increase in subepithelial haze. Clinical cases of haze after high ultraviolet exposure (such as at high altitude) corroborate these studies.
If clinically unacceptable haze persists, a superficial keratectomy or phototherapeutic keratectomy (PTK) may be performed. In addition, topical mitomycin C (0.02%), with PTK or debridement, may be used to prevent recurrence of subepithelial fibrosis. Because haze is known to resolve spontaneously with normal wound remodeling, re-ablation should be delayed for at least 6–12 months. The clinician should be aware that, in the presence of haze, refraction is often inaccurate, typically with an overestimation of the amount of myopia.
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Figure 6-8 Corneal haze after photorefractive keratectomy (PRK). A, Severe haze 5 months after PRK. The reticular pattern is characteristic of PRK-induced haze. B, Haze has improved to a moderate level by 13 months postoperatively.
(Courtesy of Roger F. Steinert, MD.)
Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.