Is femtosecond LASIK the best option?
A comparative analysis between manual and automated surgery
Initially, flap creation was performed by means of mechanical microkeratomes, with the inconvenience of the generation of flaps that were thinner in the centre than in the periphery, (meniscus-shaped configuration).2 This meniscus of tissue behaved as an additional optical element of the ocular system, inducing new higher order aberrations and modifying the predictability of the second order correction.3
Improvements in mechanical microkeratomes aimed at providing flaps with a more homogeneous thickness profile (planar flap configuration) and of less thickness to leave a thicker stromal residual bed have been developed and introduced in the clinical setting in the last few years. Likewise, femtosecond lasers for LASIK have been also introduced, which are now considered as a significant advancement for corneal laser refractive surgery.4 This type of photodisruptive laser that uses an infrared Nd:Glass laser beam (wavelength 1053 nm) allows the surgeon to program flap creation at a predetermined depth with a high degree of precision.
Our clinical experience
The clinical histories of all patients that had undergone LASIK surgery in our centre since May 2000 were retrospectively reviewed. A total of 13000 surgical procedures had been performed with the mechanical microkeratome Hansatome (Bausch + Lomb, Rochester, New York, USA) and 2000 procedures with the Amadeus microkeratome (Ziemer Ophthalmic Systems, Port, Switzerland). A total of 800 LASIK procedures had been performed with the IntraLase iFS femtosecond technology (Abbott Medical Optics, Santa Ana, California, USA) since January 2011.
According to the clinical guidelines of our centre, a complete preoperative ophthalmological examination had been performed in all cases to evaluate the viability of the corneal surgical procedure. It included uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA), manifest refraction, slit-lamp biomicroscopy, Goldman tonometry, scotopic pupil size measurement, corneal topography, ultrasound pachymetry, biometry, ocular wavefront aberrometry and funduscopy.
The following conditions were considered as exclusion criteria for surgery: estimated stromal residual bed thickness below 250 μm after programming the laser ablation, significant corneal topographic asymmetry, cataract, glaucoma, previous ocular surgery, keratoconus, and any active ocular disease. We only considered for the analysis those cases in which the target postoperative refraction had been emmetropia.