Cagıl et al.1 evaluated laser-assisted subepithelial keratectomy (LASEK) in the treatment of post-laser in situ keratomileusis (LASIK) residual refraction. Surface ablation could theoretically be the ideal procedure in cases of post-LASIK regression when in-the-bed enhancement is not advisable, but it has been associated with the development of dense haze.2 Although later reports did not find a high incidence of haze,3,4 the study by Cagıl et al.1 shows that it is an important issue. The authors found haze when ablations greater than −2.00 diopters (D) were performed and suggested that the use of mitomycin-C (MMC) could possibly avoid this complication.
We have treated 4 eyes with post-LASIK regression using LASEK and MMC 0.02% for 30 seconds over the ablated stroma, programming an undercorrection of 10% of the intended correction. The ablation was performed with the Esiris excimer laser (Schwind Eye Tech Solutions) using a photorefractive keratectomy nomogram and a conventional ablation. The optical zone was 6.0 mm with a transition zone of 1.0 mm.
A 35-year-old woman had uneventful LASIK using a 6.0 mm optical zone to correct refractive defects (right eye, +0.50 −1.75 × 180; left eye, −0.75 −2.00 × 10). The preoperative central corneal thickness (CCT) was 503 μm in both eyes. Six months postoperatively, there was regression, with no signs of ectasia (right eye, +0.50 −1.00 × 180; left eye, −0.25 −1.00 × 15). The patient had LASEK+MMC in both eyes. Six months postoperatively, there was an overcorrection in the left eye (right eye, −0.50 D; left eye, +1.00 D). No haze was detected.
A 45-year-old woman came to our clinic because of regression of the myopic defect in the left eye after LASIK performed at another center. She had no data regarding the initial surgery. Refraction in the left eye was −1.25 D, and the CCT was 394 μm. Topography showed no signs of corneal ectasia. Three months after LASEK+MMC, the left eye appeared considerably overcorrected: +2.75 D.
A 55-year-old man had successful LASIK using a 6.0 mm optical zone to correct a myopic defect (right eye, −5.25 −1.75 × 165). The preoperative CCT was 505 μm. One year postoperatively, the patient showed regression (−1.00 sphere), with normal topography and a clear lens. Three months after LASEK+MMC, there was an overcorrection: +2.50 −0.50 × 155.
There are 2 possible causes of our unpredictable results, which seem to contradict the results obtained by Cagıl et al.1 One is that the cornea treated with LASIK responds differently than a virgin cornea to surface ablation.5 The superficial corneal lamellae treated with surface ablation after a previous LASIK flap may be less strongly attached to the peripheral cornea than lamellae in which no flap was made in a primary surface ablation. Therefore, the biomechanical response of those lamellae to laser ablation may be completely different. The nomograms used for primary surface ablation are probably not adequate for retreatment over a stromal flap. The second explanation is that the use of MMC in these cases altered the wound-healing response and was responsible for the resultant overcorrection.
We recommend caution when treating regression or undercorrection after LASIK with surface ablation and MMC. The unpredictable results obtained in our cases suggest that more studies are needed to establish the predictability of this procedure.
1. Cagıl N, Aydin B, Ozturk S, Hasıripi H. Effectiveness of laser-assisted subepithelial keratectomy to treat residual refractive errors after laser in situ keratomileusis. J Cataract Refract Surg. 2007;33:642-647.
2. Carones F, Vigo L, Carones AV, Brancato R. Evaluation of photorefractive keratectomy retreatments after regressed myopic laser in situ keratomileusis. Ophthalmology. 2001;108:1732-1737.
3. Trattler W, Salz JJ. Surface ablation over LASIK flaps. Int Ophthalmol Clin. 2006;46(3):117-122.
4. Shaikh NM, Wee CE, Kaufman SC. The safety and efficacy of photorefractive keratectomy after laser in situ keratomileusis. J Refract Surg. 2005;21:353-358.
5. Dupps WJ Jr, Wilson SE. Biomechanics and wound healing in the cornea. Exp Eye Res. 2006;83:709-720.