Figure 6-8 Corneal haze after PRK. A, Severe haze 5 months after PRK. The reticular pattern is characteristic of PRKinduced haze. B, Haze has improved to a moderate level by 13 months postoperatively. (Courtesy of Roger F. Steinert, MD.)

Persistent severe haze is usually associated with greater amounts of correction or smaller ablation zones. Animal studies have demonstrated that ultraviolet (UV) B exposure after PRK prolongs the stromal healing process, with an increase in subepithelial haze. Clinical cases of haze after high UV 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.

Ayres BD, Hammersmith KM, Laibson PR, Rapuano CJ. Phototherapeutic keratectomy with intraoperative mitocmycin C to prevent recurrent anterior corneal pathology. Am J Ophthalmol. 2006;142:490–492.

Donnenfeld ED, O’Brien TP, Solomon R, Perry HD, Speaker MG, Wittpenn J. Infectious keratitis after photorefractive keratectomy. Ophthalmology. 2003;110(4):743–747.

Hofmeister EM, Bishop FM, Kaupp SE, Schallborn SC. Randomized dose-response analysis of mitomycin-C to prevent haze after photorefractive keratectomy for high myopia [published online ahead of print July 3, 2013]. J Cataract Refract Surg. doi:10.1016/j.jcrs.2013.03.029.

Krueger RR, Saedy NF, McDonnell PJ. Clinical analysis of steep central islands after excimer laser photorefractive keratectomy. Arch Ophthalmol. 1996;114(4):377–381.

Moller-Pedersen T, Cavanagh HD, Petroll WM, Jester JV. Stromal wound healing explains refractive instability and haze development after photorefractive keratectomy: a 1-year confocal microscopic study. Ophthalmology. 2000;107(7):1235–1245.

Complications Unique to LASIK

The complications associated with LASIK are primarily related to flap creation, postoperative flap positioning, or interface problems.

Microkeratome Complications

In the past, the more severe complications associated with LASIK were related to problems with the microkeratome, which caused the planned LASIK procedure to be abandoned in 0.6%–1.6% of cases. In current practice, advances in microkeratome technology and the advent of femtosecond laser use for creating the LASIK flap have substantially reduced the incidence of severe, sight-threatening

complications.

When using the microkeratome, meticulous care must still be taken in the cleaning and assembly of the microkeratome to ensure a smooth, uninterrupted keratectomy. Defects in the blade, poor suction, or uneven progression of the microkeratome across the cornea can produce an irregular, thin, or buttonhole flap (Fig 6-9), which can result in irregular astigmatism with loss of CDVA. Steep corneal curvature is a risk factor for the development of some intraoperative flap complications. If a thin or buttonhole flap is created, or if an incomplete flap does not provide a sufficiently large corneal stromal surface to perform the laser ablation, the flap should be replaced and the ablation should not be performed. Substantial loss of vision can be prevented if, under such circumstances, the ablation is not performed and the flap is allowed to heal before another refractive procedure is attempted months later. In such cases, a bandage soft contact lens is applied to stabilize the flap, typically for several days to a week. Although a new flap can usually be cut safely using a deeper cut after at least 3 months of healing, most surgeons prefer to use a surface ablation technique.

Figure 6-9 LASIK flap with buttonhole. (Reproduced with permission from Feder RS, Rapuano CJ. The LASIK Handbook: A Case-Based Approach. Philadelphia: Lippincott Williams & Wilkins; 2007:95, fig 5.1. Photograph courtesy of Christopher J. Rapuano, MD.)

Occasionally, a free cap is created instead of a hinged flap (Fig 6-10). In these cases, if the stromal bed is large enough to accommodate the laser treatment, the corneal cap is placed in a moist chamber while the ablation is performed. It is important to replace the cap with the epithelial side up and to position it properly using the previously placed radial marks. A temporary 10-0 nylon suture can be placed to create an artificial hinge, but the physiologic dehydration of the stroma by the endothelial pump will generally keep the cap secured in proper position. A bandage soft contact lens can help protect the cap. A flat corneal curvature (<40.00 D) is a risk factor for creating a free cap because the flap diameter is often smaller than average in flat corneas.

Figure 6-10 A free cap resulting from transection of the hinge. The cap is being lifted from the microkeratome with forceps (arrow), and care is being taken to maintain the orientation of the epithelial external layer to prevent accidental inversion of the

cap when it is replaced. (Courtesy of Roger F. Steinert, MD.)

Corneal perforation is a rare but devastating intraoperative complication that can occur if the microkeratome is not properly assembled or if the depth plate in an older-model microkeratome is not properly placed. It is imperative for the surgeon to double-check that the microkeratome has been properly assembled before beginning the procedure. All microkeratomes made after the 1990s are constructed with a prefixed depth plate, which eliminates this source of error. Corneal perforation can also occur when LASIK is performed on an excessively thin cornea. Corneal thickness must be measured with pachymetry prior to the LASIK procedure, especially in patients who are undergoing re-treatment.

Jacobs JM, Taravella MJ. Incidence of intraoperative flap complications in laser in situ keratomileusis. J Cataract Refract Surg. 2002;28(1):23–28. Lee JK, Nkyekyer EW, Chuck RS. Microkeratome complications. Curr Opin Ophthalmol. 2009; 20(4):260–263.

Nakano K, Nakano E, Oliveira M, Portellinha W, Alvarenga L. Intraoperative microkeratome complications in 47,094 laser in situ keratomileusis surgeries. J Refract Surg. 2004; 20(Suppl 5):S723–726.

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