الفهرس 
Physics of femto-second laserOnly 14 pages are availabe for public view
Abstract
Refractive surgery through laser vision correction (LVC) has evolved significantly within the past few decades. from the first generation techniques involving surface ablation to LASIK, refractive surgery has now become intrastromal with the advent of refractive lenticule extraction (ReLEx) technology.
This procedure when performed through a small incision (2–4 mm) was described as small incision lenticule extraction (SMILE), which is essentially a bladeless, flapless and minimally invasive technique compared to LASIK, where a corneal flap is created using either a blade or a femtosecond laser.
Currently, ReLEx SMILE corrects myopia up to −10.00 D, myopic astigmatism up to −5.00 D and a spherical equivalent (SE) of up to −12.5D. The correction of high myopia and high cylindrical errors are currently investigated as technique lacks automated centration and cyclotorsion control. Hyperopic SMILE treatments are not commercially available yet.
In SMILE, a single laser (FSL) is used to make two curved cuts inside the cornea (without breaching the outside) that separate a lenticule of tissue. This part of tissue is removed as once piece rather than evaporated as in LASIK.
Recent advancements in the laser frequency and energy delivery patterns, instrumentation, and surgical techniques have shown significant improvement in the visual recovery and outcomes after SMILE, compared to its initial results.
SMILE is a surgeon-based procedure involves a learning curve, which can be negotiated by ensuring good docking, optimizing energy levels, and gentle tissue handling. Outcomes may be further refined by developing surgeon-specific nomograms and manual cyclotorsion compensation for high astigmatic errors.
Although the outcomes of SMILE have been shown to be similar to LASIK in terms of safety and predictability, evidence is increasing that SMILE may be better than LASIK in terms of corneal biomechanics, postoperative dry eye and long-term stability of correction of high myopia.
There are also potential future application related to SMILE, as treatment of hyperopia by increasing transitional zone of lenticule showing promising results. Another procedure is SMILE XTRA, used in keratoconus, in which SMILE is followed by cross linking.
However, there is a possible drawback of the SMILE procedure in its inability for in situ enhancement. Currently, SMILE-treated eyes would either require an add-on surface ablation or a surgical opening (with FSL or manually) of the side cut incisions, thus creating a flap, for enhancement purposes.
SMILE also considered more expensive and costing procedure for the patient as it is double the conventional Lasik and 1.5 times the femto-Lasik.
Overall, SMILE procedure has proved to be promising, delivering equivalent, or better visual and refractive results to LASIK and providing clear advantage in terms of being a flapless, minimally invasive procedure with minimal pain and postoperative discomfort thus offering high patient satisfaction. SMILE potentially will overtake LASIK, it is only a matter of time.
Will SMILE Replace Conventional Refractive surgeries? SMILE will not immediately replace LASIK and PRK. It is not an anti-LASIK procedure, it is a next generation as a new option for patients who have questions about the existing ones. It enlarges the opportunity as a complementary invention, it will increase the number of people who will have refractive surgery, rather than steal patients away from other procedures.