LASIK operations with the Ziemer FEMTO LDV femtosecond laser flap creation after previous photorefractive keratometry or laser-assisted sub-epithelial keratomileusis

Abstract

Editor, Enhancement procedures may be needed after previous refractive surgery in the cases of under or over correction and regression. Enhancement procedures can be performed by photorefractive keratometry (PRK) or laser-assisted in situ keratomileusis (LASIK). LASIK is an attractive option for retreatment after previous surface ablations such as PRK or laser-assisted sub-epithelial keratomileusis (LASEK). Main reasons for choosing LASIK are a quick recovery and the absence of haze. Previously, in LASIK, corneal flaps have been recreated using various microkeratomes (Comaish et al. 2002; Pitkänen et al. 2010). In recent years, femtosecond lasers have emerged as alternatives to the traditional microkeratome-based LASIK. Femtosecond laser technology has some advantages, such as less variation in flap thickness and a more uniform flap thickness throughout the whole flap, compared to microkeratome-based flaps. However, reports published on reoperations performed with the femtosecond laser technology after previous refractive surgery are still scarce and limited to Intralase (Tran et al. 2008). This study presents the outcomes of the first 89 consecutive reoperated eyes of 71 patients, previously treated with PRK (87 eyes) or LASEK (two eyes), which now underwent LASIK flap creation with the FEMTO LDV (Ziemer Ophthalmic Systems, Port, Switzerland) femtosecond laser and excimer laser treatment with the Allegretto Wave Concerto 500 Hz excimer laser (Wavelight AG, Erlangen, Germany). The patients were operated in the two Finnish Mehiläinen Hospitals, in Tampere and in Helsinki. In all the eyes operated, a superior hinge was used and the intended flap thickness was 90 μm. The diameter of the suction ring was chosen according to the preoperative keratometric K1 value measured before the primary operation. The study included 64 myopic eyes (residual spherical equivalent of refraction, SE, range −6.63 D to −0.25 D, mean SE −1.45 ± 1.01 D) and 25 hyperopic eyes (range SE +0.00 D to +2.88 D, mean SE +1.31 ± 0.91 D). Flap dimensions and the best-corrected visual acuities were measured and intra- and postoperative complications recorded. Mean flap thickness was 90.5 ± 5.4 μm (range, 74–104; Fig. 1) and mean flap diameter was 9.1 ± 0.2 mm (range, 8.8–9.7). Flap thickness was positively correlated with corneal thickness both in myopic (r = 0.33, P < 0.01) and in hyperopic previously surface-ablated eyes (r = 0.51, P < 0.01). The distribution of flap thickness in 89 previously surface-ablated eyes now reoperated with the FEMTO LDV using the intended flap thickness of 90 μm. Complications occurred in six eyes (5.9%). They all were observed in the previously PRK-treated eyes. Most of the complications were very mild, and none of them prevented further treatment with excimer laser. There were no changes in the Snellen lines of BSCVA in 73 eyes (94.8%), and one line was gained in four eyes (5.2%). The mean flap thickness in the previously surface-ablated eyes was equivalent to the one we obtained in our previous study evaluating 787 primary operations with the FEMTO LDV (Pietilä et al. 2010). In this study, flap thickness was affected by corneal thickness just as in our previous study (Pietilä et al. 2010). Although the reason for this positive correlation is unknown, it is, if anything, a clinically advantageous phenomenon. Corneal changes in the previously PRK- or LASEK-treated eyes are mainly ultrastructural (changes in keratocytes in anterior stroma, absence of Bowman’s membrane, subclinical haze in wound healing process). LASIK revision in these eyes poses potentially more risks, and the previously operated corneal tissue is likely to behave in a different way than in the primary LASIK procedure. It is, however, evident that LASIK revisions with the femtosecond technology can be safely performed in most of these cases. Although in general retreatment of previously operated eyes offers greater risks in refractive surgery, the FEMTO LDV femtosecond laser can be successfully used for corneal flap creation in previously surface-ablated eyes.