IntraLASIK and LASIK for myopia correction (comparative analysis)

Purpose. Comparison of quality of a formed corneal flap, refractive results, corneal biomechanical properties changes after IntraLASIK and LASIK in patients with myopia.
Materials and methods. 54 patients (96 eyes) were investigated, they were divided into two groups. Patients after IntraLASIK were in the first group, patients after LASIK — in the second group. Patients of both groups were divided into three subgroups according to cornea thickness (<520 µm, 520-580 µm, >580 µm). Keratopachimetry map with «Visante OCT» optic coherent tomograph (Carl Zeiss, Germany) was made for all patients, biomechanical properties of cornea were examined with ORA (Reichert Int., USA).
IntraLASIK was made in two stages. First, corneal flap was formed with IntraLase FS (USA) 60 kHz femtosecond laser, then eximer laser ablation was performed with «Microscan-2000» (Troizk, Russia). LASIK was rendered according to standard method at «Microscan-2000» unit with corneal flap formation with the help of «LSK Evolution M2» (Moria, France) automated microkeratome.
Results. Thickness of superficial corneal flap made with mechanic microkeratome was not even not only at the beginning and end of a cut, but also in central zone (with 110 µm planned thickness flap was 116,2±18,5 µm in the center, at the beginning of flap cut 150,1±22,9 µm, and at the end of cut 136,2±24,7 µm). Flap thickness with femtosecond laser was even and differed within ± 8 µm of the planned, mean deviation of diameter was within 0,1±0,08 mm. According to corneal biomechanical properties analyzer (ORA) data statistically significant (p<0,05) decrease of corneal hysteresis and corneal resistance factor indices was noted in all groups in postoperative period. The degree of decrease of these indices was different and depended on initial corneal thickness, method of corneal flap forming and amount of laser influence.
Conclusions.
1. IntraLase FS femtosecond laser forms corneal flap of uniform thickness along the whole flap, it corresponds precisely to the diameter prognosed. A corneal flap cut by mechanical keratome is maximally thick at the beginning of cut, becomes thinner to the end and is maximally thin in center.
2. There are no obvious advantages of IntraLASIK over LASIK according to refractive results.
3. Decrease of corneal hysteresis and corneal resistance factor can be considered a universal reaction of cornea after IntraLASIK and LASIK surgeries, the degree of biomechanical properties decrease is less after IntraLASIK than LASIK. The degree of corneal biomechanical properties change depends on initial corneal thickness, way of corneal flap forming and amount of laser influence.