In their case series, Teus and de Benito-Llopis found that LASEK+MMC to treat post-LASIK myopic regression led to the development of unacceptable overcorrection. The authors reported that of the 4 eyes treated with LASEK+MMC, 3 developed overcorrection (spherical equivalent [SE] range +1.00 to +2.75 D). There was no haze development or other complications.
The major consideration in flap relifting in the treatment of post-LASIK myopic regression is the excessive ablation of the corneal stroma that may lead to corneal ectasia.1 Studies evaluating surface ablation after LASIK reveal varying results in haze development and refractive outcomes.2,3 Carones et al.2 report dense haze formation that led to myopic regression and a best corrected visual acuity loss in 82.3% of eyes after photorefractive keratectomy retreatment for post-LASIK myopic regression. In our study, LASEK retreatments in eyes with myopic regression after LASIK resulted in good visual and refractive outcomes.3 However, an attempted SE correction greater than −2.00 D led to haze development that could lead to a loss in best corrected visual acuity.3 Considering the success of MMC in the treatment of complicated LASIK procedures such as buttonholed or transected flaps,4 we suggest the use of MMC to prevent haze formation, particularly in at-risk eyes (eyes with an attempted SE correction greater than −2.00 D).
The cases reported by Teus and de Benito-Llopis provide valuable information about the use of MMC in LASEK retreatment of post-LASIK myopic regression. Development of overcorrection in 3 of 4 treated eyes is an ominous sign that necessitates great caution and must be appreciated. The authors proposed 2 explanations for the overcorrection: different response to surface ablation of a cornea treated with LASIK than a virgin cornea or alteration of the wound-healing response by the use of MMC. We think the first explanation is inappropriate because in the previous studies evaluating the role of surface ablation in the treatment of post-LASIK myopic regression, the major concern was haze development and consequent myopic regression.2,3,5,6 No study has reported significant overcorrection affecting visual acuity results. Mitomycin-C alters the stromal wound-healing response by inhibiting rapidly proliferating cells, particularly the keratocytes.7 This property accounts for its ability to prevent haze formation and successive myopic regression. In a recent study evaluating the affect of MMC in myopic LASEK, Camellin8 found that early and late overcorrection and an increase in higher-order aberrations developed in the MMC group. In addition to the MMC, the epithelial flap in LASEK also had the potential to modify the wound-healing response. When LASEK application is combined with MMC, an unexpected wound-healing response may produce overcorrection.
In our study, we found that with an attempted SE correction less than −2.00 D, LASEK retreatments in eyes with myopic regression after LASIK resulted in a significant improvement in the uncorrected visual acuity comparable to the results of flap lifting. In the series of Teus and de Benito-Llopis, the attempted SE correction for LASEK retreatment was less than −2.00 D in all cases. We do not think MMC was needed in these cases. Either MMC should be reserved for eyes with an attempted SE correction greater than −2.00 D or it should be avoided, as the cases of Teus and de Benito-Llopis imply.
In conclusion, there may be no need to use MMC with LASEK to treat post-LASIK myopic regression in eyes with an attempted SE correction less than −2.00 D. Further studies are necessary to reveal the role of MMC in surface ablations to treat post-LASIK myopic regression.
1. Andreassen TT, Simonsen AH, Oxlund H. Biomechanical properties of keratoconus and normal corneas. Exp Eye Res. 1980;31:435-441.
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. 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.
4. Muller LT, Candal EM, Epstein RJ, et al. Transepithelial phototherapeutic keratectomy/photorefractive keratectomy with adjunctive mitomycin-C for complicated LASIK flaps. J Cataract Refract Surg. 2005;31:291-296.
5. Li Y, Li JH, Zhou F., 2005. [LASEK for the correction of residual myopia and astigmatism after LASIK] [Chinese], Zhonghua Yan Ke Za Zhi, 41, 981-985.
6. 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.
7. Gambato C, Ghirlando A, Moretto E, et al. Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes. 2005; 112:208–218; discussion by RS Rubinfeld, 219
8. Camellin M. Laser epithelial keratomileusis with mitomycin C: indications and limits. J Refract Surg. 2004;20:S693-S698.