Epithelial Sloughing or Defects
The friction of microkeratome passage across the pressurized cornea may loosen a sheet of epithelium (termed epithelial slough) or cause a frank epithelial defect. Although patients with epithelial basement membrane dystrophy are at particular risk—in which case surface ablation rather than LASIK is advisable—other patients show no preoperative epithelial abnormalities. The risk of epithelial abnormality during LASIK correlates with older age. Also, in bilateral LASIK procedures with mechanical microkeratomes, the second eye has a greater likelihood of sustaining an epithelial defect (57%) if an intraoperative epithelial defect developed in the first eye. Techniques suggested to decrease the rate of epithelial defects include limiting medications to avoid toxicity, using chilled proparacaine, minimizing use of topical anesthetic, using nonpreserved drops until just before performing the skin prep or starting the procedure, having patients keep their eyes closed after topical anesthetic is administered, frequent use of corneal lubricating drops, meticulous microkeratome maintenance, and shutting off suction on the microkeratome reverse pass. The femtosecond laser is associated with a reduced incidence of epithelial defects because there is no microkeratome movement across the epithelium.
In cases of significant epithelial defects, a bandage contact lens is often applied immediately postoperatively and retained until stable reepithelialization occurs, with subsequent use of intensive lubricants and, occasionally, punctal occlusion. Persistent abnormal epithelium with recurrent erosions or loss of BCVA may require debridement and even superficial PTK using the technique employed for treatment of recurrent erosions (see BCSC Section 8, External Disease and Cornea). Epithelial defects are associated with an increased incidence of postoperative diffuse lamellar keratitis, infectious keratitis, flap striae, and epithelial ingrowth, and surgeons should watch closely for these conditions.
Chen S, Feng Y, Stojanovic A, Jankov MR II, Wang Q. IntraLase femtosecond laser vs mechanical microkeratomes in LASIK for myopia: a systematic review and meta-analysis. J RefractSurg. 2012;28(1):15–24.
Tekwani NH, Huang D. Risk factors for intraoperative epithelial defect in laser in-situ keratomileusis. Am J Ophthalmol. 2002;134(3):311–316.
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.