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LASIK has become the single most common elective operation. The ﬁrst phase of LASIK, the creation of a corneal ﬂap, is the most critical step of LASIK and it affects the visual outcome of the whole procedure. The technological evolution of ﬂap creation has emerged from manually guided mechanical microkeratomes to automated microkeratomes, single-use microkeratomes, and most recently to femtosecond laser technology. Since the early femtosecond laser models were introduced, considerable progress has been made in improving flap geometry and limiting complications of LASIK performed with femtosecond laser. This has led to increasing popularity of LASIK performed with the femtosecond laser.
Small-incision lenticule extraction (SMILE) is a new method for surgical correction of myopia and myopic astigmatism. The procedure does not involve a flap, and the length of the side cut that is used for lenticule extraction is shorter when compared with the side cut of a standard LASIK flap. In addition, the lamellar cut area, which is only 1 mm larger than the lenticule diameter, is smaller when compared with a standard LASIK flap. A smaller side cut length and a smaller lamellar cut area in SMILE surgery may lead to better preservation of anterior corneal nerves and reduce the incidence of dry eye findings.
Sixty eyes with simple myopia or myopic astigmatism were recruited in this study. All patients underwent assessment of uncorrected and best corrected visual acuity, refraction, slit lamp examination, measurement of intraocular pressure, fundus examination, measurement of tear breakup time, Schirmer test, corneal sensation, corneal tomography and measurement of corneal biomechanics. These eyes were randomly assigned into two equal groups: FS-LASIK group: included 30 eyes in which femtosecond laser was used for flap creation (WaveLight® FS 200) then underwent excimer laser ablation (WaveLight® EX 500), SMILE group: included 30 eyes in which femtosecond laser was used for intrastromal lenticule creation (Visumax®) then underwent mechanical removal of the lenticule. There was no significant difference in any parameter preoperatively between both groups.
Patients were examined at postoperative day 1 and week 1 for assessment of flap or cap alignment and measurement of uncorrected visual acuity, then at months 1, 3 and 6 regarding uncorrected and best corrected visual acuity, refraction, tear breakup time, Schirmer test and corneal sensation. Corneal biomechanics were measured at 6th month visit only.
After analysis of the results, we found that there was significant improvement in both groups in uncorrected visual acuity, spherical equivalent and cylindrical error compared to preoperative values. Both groups showed significant decrease in tear breakup time, Schirmer test, corneal sensation, corneal hysteresis and corneal resistance factor compared to preoperative values.
Regarding comparison of both groups postoperatively, uncorrected visual acuity and best corrected visual acuity were not significantly different between both groups. Comparison regarding refractive correction showed that spherical equivalent and spherical error were not significantly different between both groups throughout the follow up period, but cylindrical error was significantly higher in SMILE group than FS-LASIK group throughout the follow up period. Tear breakup time was significantly better in SMILE group than FS-LASIK group at 1st month, but this difference disappeared at 3rd and 6th month. Schirmer test was not significantly different between both techniques through the follow up period. Corneal sensation was significantly better in SMILE group than FS-LASIK group at 1st month and 3rd month, but this difference disappeared at 6th month. Corneal hysteresis and corneal resistance factor were significantly higher in SMILE group than FS-LASIK group at the end of follow up period.