Purpose:
To compare changes in subbasal nerve density and corneal sensitivity in eyes randomized to LASIK performed with a microkeratome or LASIK performed with a femtosecond laser (bladeless).
Methods:
Twenty patients received LASIK for myopia or myopic astigmatism. One eye of each patient was randomized to flap creation by using a microkeratome (Hansatome, Bausch & Lomb, Rochester, NY) with intended flap thickness of 180 µm, and the fellow eye to flap creation with a femtosecond laser (IntraLase FS, IntraLase Corp., Irvine, CA) with intended flap thickness of 120 µm. Corneas were examined by using confocal microscopy in vivo before and at 1, 3, and 6 months after surgery. Subbasal nerves were measured and nerve density was calculated as the total visible length of nerves per area (µm/mm2). Corneal sensitivity was determined at each visit by using a Belmonte esthesiometer that measured the threshold to mechanical stimulation by a 2–second puff of air (ml/min). Differences between pre– and post–operative nerve densities and corneal sensitivities were compared by using signed–rank tests.
Results:
Nerve density did not differ between treatments at any time (Table), but was decreased at 1, 3, and 6 months after both treatments (P<0.001) compared to before LASIK. Corneal sensitivity also did not differ between treatments at any time (Table). The mean sensitivity threshold was elevated a nonsignificant 30–31% at 1 month after both treatments compared to preoperative (P>0.14, minimum detectable differences = 29 [microkeratome] and 55 [bladeless], α =0.05, ß=0.20).
Conclusions:
Subbasal nerve density is significantly reduced for up to 6 months after LASIK whether the flap is created by using a microkeratome or a femtosecond laser. The anatomical loss of subbasal nerves does not correspond to changes in mechanical corneal sensitivity.
Keywords: refractive surgery: LASIK • clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials • refractive surgery: comparative studies