Delayed Onset Keratectasia After LASIK

We read with not just great interest but also major concern the recent article on delayed onset keratectasia following laser in situ keratomileusis (LASIK).1 A review of the 5 cases reported indicates 3 possible explanations for this phenomenon: Performing LASIK in patients with high myopia and a thin cornea resulted in posterior stromal bed thickness less than 250 μm. The occurrence of posterior keratectasia in this situation has been documented by Wang and coauthors.2 The keratectasia is probably due to the action of intraocular pressure (IOP) on the weakened cornea. Corneal topography in posterior keratoconus reveals corneal steepening at the site of pathology. This steepening appears to be greater in older patients3 and provides further evidence of the ability of IOP to produce ectasia in a thinned cornea. Performing LASIK in keratoconic eyes can produce keratectasia, possibly because of the altered corneal biomechanics. Progression of keratoconus has been reported after LASIK and photorefractive keratectomy (PRK) in such eyes.4 The patient reported by Geggel and Talley1 does not fit into either of the above categories. Corneal thickness 1 year after LASIK treatment and enhancement was 449 μm in the right eye and 460 μm in the left. Since the corneal thinning increased rapidly in only the right eye in the next 5 months (corneal thickness in the left eye remained stable, 466 μm), it is unlikely that the corneal changes in the right eye were related to posterior stromal bed thickness. The rapidity of corneal thinning is similar to that described in the patient who developed keratectasia after LASIK in an eye with forme fruste keratoconus.3 The preoperative topography in the patient reported by Geggel and Talley1 does not suggest keratoconus. However, there is a disparity in the refractive (0.50 diopter [D]), keratometric (1.12 D), and topographic (1.62 D) astigmatism, and the axis of the steeper corneal meridian in the 3 methods is 85 degrees, 66 degrees, and 46 degrees, respectively. The patient discontinued rigid gas-permeable contact lens use 3 weeks before examination, and this may have masked a forme fruste keratoconus. However, if we consider this an unlikely explanation, we have to accept that the patient with normal corneal thickness may develop keratectasia after LASIK for a correction of only 6.5 D due to an idiopathic, poorly understood mechanism. Other reports of significant late-onset regression after myopic keratomileusis for high to severe myopia5 raise concern that these 5 patients may represent the visible end of a larger spectrum of such patients. Newer complications such as displacement of the LASIK flap during vitrectomy and the occurrence of an oculocardiac reflex during LASIK continue to be reported with LASIK. Intraoperative and postoperative complications are reported in about 5% of LASIK procedures6 and are probably higher during the learning curve of the LASIK surgeon. Although LASIK causes less postoperative pain and allows rapid recovery of vision, the potential for keratectasia caused by an unexplained mechanism, resulting in the need for penetrating keratoplasty, should not be taken lightly. A recent study7 comparing PRK and LASIK in the treatment of −2.5 to −8.0 D of myopia found no significant differences between the 2 treatment groups in refractive outcomes, predictability, and induced cylinder. Uncorrected visual acuity of 20/20 or better was achieved in 25% more LASIK eyes at 2 years. Uncorrected visual acuity of 20/40 or better was achieved in 100% of LASIK eyes and 96% of PRK eyes at 2 years. In 1 LASIK-treated eye with a flap displacement and 1 PRK-treated eye with regression and haze, final visual outcome was unsatisfactory. We therefore believe that in eyes with <−6.0 D of myopia, in which visual outcomes after PRK are excellent, a case can be made to reduce the usage of LASIK. In eyes with myopia greater than −6.0 to −8.0 D, the safety and predictability of PRK are less satisfactory,8 and LASIK can be considered in these eyes. However, careful preoperative ocular evaluation, corneal pachymetry, and stability of preoperative topography, particularly in contact lens users, are essential. During surgery, 250 to 300 μm of posterior stromal bed must be retained. In the treatment of myopia above −10 to −12 D, LASIK has limitations in predictability and stability.9 In these eyes, clear lens extraction with intraocular lens (IOL) implantation yields better predictability and visual quality outcome and faster visual recovery. The correction is achieved at the level of the crystalline lens and, therefore, the magnification is better than with correction at the corneal plane. Complications resulting from decentration of a deep corneal ablation, seen in LASIK, do not occur. The surgical process does not involve creating high IOP with its possible deleterious effects on the macula in this group of patients with myopic macular degeneration. With modern phacoemulsification techniques, cataract surgery is performed in a closed chamber and allows capsular IOL implantation with a very small limbal or scleral tunnel incision. The rate of complications arising from the lens extraction and IOL implantation is decreasing.10 The use of an acrylic IOL with increased biocompatibility has reduced the occurrence of postoperative posterior capsule opacification and this reduces the need for neodymium:YAG capsulotomy. However, the incidence of retinal detachment in highly myopic patients with aphakia or pseudophakia is related to age, and the procedure should be used very carefully or even avoided in patients under 30 years of age.11 A careful retinal examination, with scleral depression, and prophylactic treatment of any peripheral pathology is mandatory prior to cataract extraction. We concur with Koch12 that surgeons must report cases of keratectasia after corneal refractive surgery to help understand the mechanism of corneal changes in these eyes. The use of newer imaging modalities, such as high-frequency ultrasound, may help by allowing evaluation of corneal changes in vivo.13 We believe that the refractive surgeon must have a balanced approach toward the surgical treatment of myopia and offer our guidelines for the same. Alfred T.S. Leung FRCS, FRCOphth Srinivas K. Rao MD Dennis S.C. Lam FRCS, FRCOphth aMadras, India bShatin, Hong Kong