Comparative Study of Femtosecond Laser versus Mechanical Microkeratome in Flap Fashioning in LASIK

Abstract

LASIK is the most commonly performed procedure in refractive surgery and the first choice for the correction of refractive errors in the majority of patients.

A crucial step during LASIK is the creation of a hinged corneal flap due to the potential complication that may occur and cause the postponement of the procedure. The precision in reproducing flap thickness is significant when planning and performing LASIK surgery.

Mechanical microkeratome systems produce a meniscus shaped flap, with the flap being thinner in the center and thicker in the periphery. These flaps show variability in both flap thickness and diameter. A flap that is too thin is prone to complications including a free, irregular, incomplete, buttonhole, or lacerated flap. A flap that is too thick increases the likelihood of violating the minimum safe residual stromal bed thickness of 250 μm which can increase the risk of refractive regression and keratectasia. Therefore, it is important to produce a uniform flap with a narrow standard deviation from the attempted thickness.

The femtosecond laser utilizes a 1053 nanometers (nm) wavelength infrared laser pulse in the femtosecond (10-15) duration range to create photodisruption at a predetermined depth in the cornea to cleave the tissue and develop a plane of separation

One hundred eyes with simple myopia or myopic astigmatism (simple and compound) were recruited in this study. These eyes were randomly assigned into two equal groups: MK group: included 50 eyes in which mechanical microkeratome was used for flap creation (Moria M2 automated microkeratome).FS group: included 50 eyes in which femtosecond laser was used for flap creation (FS 200 Wavelight).All eyes then underwent excimer laser ablation using Allegretto 500.

Patients were examined at post-operative-day 1, week 1, months 1, 3 and 6.

After analysis of the results, we found that: there was a highly statistically significant difference between the two groups regarding the central corneal flap thickness deviation with the FS group having more accurate central corneal flap thickness than the MK group. There was no statistically significant difference between the two groups regarding the UCVA and refraction throughout the period of follow up.

We encountered epithelial abrasion in one eye in MK group (2%), three cases of OBL in FS group (6%) and one case of suction loss in FS group. We did not encounter any other intraoperative complications like incomplete cut, free cap, decentered ablation or air bubble in the anterior chamber.

In the follow up visits, DLK occurred in 6 eyes of 4 patients (1 eye in MK group and 5 eyes in FS group) and one case suffered from minimal striae in one eye (MK group). In MK group 16 patients complained of symptoms

of dryness versus 12 patients in FS group. Re-treatment was done for two eyes of two patients (one in each group). In our follow up visits we encountered no other postoperative complications such as epithelial ingrowth, infection or displaced flap.