الفهرس 
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Abstract
R
efractive errors and consequent spectacles wear have always been cumbersome for many persons. Development of refractive surgeries in the last decades was established in response to patient’s needs. Corneal LASER refractive procedures are always the first choice, either for patients or surgeons. However, corneal refractive surgeries have their limitations, including Small incision lenticule extraction (SMILE) has been reported since 2011, for treatment of myopia and astigmatism.
SMILE is a less invasive technique because only a small incision is required and without a flap. Therefore, avoiding the creation of a flap and preserving more corneal nerve fibers, SMILE is expected to remedy the shortcomings of laser-assisted in situ keratomileusis (LASIK) and femtosecond laser-assisted LASIK (FS-LASIK). Studies have reported that SMILE minimizes dry eye, and maintains higher corneal sensitivity. In addition, the postoperative corneal biomechanical strength is theoretically greater in comparison to LASIK and FS-LASIK.
Recent studies suggested that the SMILE procedure provided excellent clinical outcomes, considering its safety, efficacy, predictability, and postoperative ocular surface health. Therefore, SMILE is considered to be a good selection mode for refractive surgery. There have been studies on SMILE techniques, but most reported results on visual acuity and refractive outcomes. It is known that high-order aberrations (HOAs) are always responsible for postoperative symptoms, including halos, glare, monocular diplopia, and decreased contrast sensitivity after successful refractive surgery corneal parameters or a high refractive error.
The SMILE surgery was performed using a 500-kHz Visu Max femtosecond laser (Carl Zeiss, Meditec AG, Jena, Germany) with a laser energy of approximately 170 NJ. Following the application of topical anesthesia, the patient was required to fixate on an internal target light before corneal suction was initiated. The posterior surface of the lenticule was cut first from the periphery to the center, followed by cutting of the anterior surface from the center to the periphery. The diameter of the refractive lenticule measured from 6 to 6.5 mm with a transition zone of 0.1 mm. The incision for lenticule retrieval was made at the 12 o’clock position on the cornea and had a length of 2 to 5 mm with an average of 3.73 mm. The target cap thickness was 110μm. The energy offset was 25 for the lenticule, lenticule side, cap and cap side. Spot distance and track distance for the lenticule was 3.60 um, 1.5 for the lenticule side, 3.90 for the cap and 1.5 for the cap side. Scan direction was spiral in for the lenticule and spiral out for the cap. Scan mode is single for the lenticule and the cap A manual spatula was inserted through the small incision to dissect the surface plane, and a pair of forceps was used to extract the intra-stromal lenticule.
The aim of our study was to detect the effect of SMILE on quality of vision and the incidence of higher order aberrations following SMILE.
This study included 30 eyes of 18 patients, 10 females and 8 males were included, with an age ranging from 19 to 43 years.
In our study, we observed through the OPD III scan that there is post-operative increase in ocular higher order aberrations more in mesopic than photopic pupil. Moreover we detected decrease in modulation transfer function of no significance with mesopic or photopic pupils which means that the quality of vision is not affected with the pupil size.
On studying the post-operative corneal third order aberrations through pentacam we detected increase in post-operative vertical and horizontal coma, and spherical aberrations with non-significant change in vertical and horizontal trefoil.
According to our study results, SMILE is an effective refractive surgery that improves visual acuity. But causes decrease in quality of vision through modulation transfer function that is not related to the pupil size and increase in ocular higher order aberrations.