Refractive lenticule extraction small incision lenticule extraction: A new refractive surgery paradigm

Abstract

Small incision lenticule extraction (SMILE), a variant of refractive lenticule extraction technology is becoming increasingly popular, as a flapless and minimally invasive form of laser vision correction (LVC) for the treatment of myopia and myopic astigmatism. This review aims at summarizing the principles, surgical technique, and clinical outcomes in terms of visual and refractive results, safety, efficacy, postoperative dry eye, aberrations, and biomechanics of SMILE and its comparison with other conventional techniques of LVC, such as laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). 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 the initial results published by Sekundo and Shah et al. Most of the recently published literature on long-term outcomes of SMILE shows excellent stability of the procedure, especially for higher myopia. In terms of the postoperative dry eye, SMILE shows a clear advantage over LASIK as numerous studies have shown significant differences about the Schirmer's, Tear film break up time, corneal sensitivity, and corneal nerve regeneration to be better following SMILE compared to LASIK. There is some evidence that since the Bowman's membrane (BM) and the anterior lamellae remain intact after SMILE, this may be a potential advantage for corneal biomechanics over LASIK and PRK where the BM is either severed or ablated, respectively, however, the data on biomechanics are inconclusive at present. Overall, this 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.

Figure 1

The lenticule cut (1) is performed (the underside of the lenticule), followed by the lenticule sidecuts (2). Next, the cap interface (3) is created (the upper side of the lenticule), and finally a 2–3 mm small incision (4) is created superotemporally. The lenticule interfaces are dissected using a flap separator and the lenticule is extracted manually, all via the small incision (Reproduced after permission from Prof Dan Reinstein)

Figure 2

Clinical pictures of corneal interface in retroillumination after dilatation, on 1^st day postoperation in a patient who underwent small incision lenticule extraction with conventional dissection technique in the right eye (a) and lenticuloschisis (b) in the contralateral eye by the same surgeon in the same sitting for similar degree of myopia (−4.00 D both eyes). The corneal interface showed more roughness in the eye with dissection and showed prominence of the cap edge (white arrow) (a), whereas it was smoother in the lenticuloschisis eye (b). Patient also reported better clarity with the eye with lenticuloschisis. (Reproduced after permission from Journal of Refractive Surgery)

Figure 3

Anterior segment Optical Coherence Tomography of an eye showing retained lenticular fragment following a failed primary small incision lenticule extraction procedure

Figure 4

(a) Preoperative limbal marking with the Ganesh bubble marker (Epsilon Surgical, Chino, CA, USA). This instrument uses three marks on the limbus at 0°, 90°, and 180°, extending 2 mm toward the center of the cornea, which are easy to visualize while the eye is being docked. (b) Method of manual cyclotorsion compensation by a gentle rotation of the cone while holding the same at the attachment of the tube to the cone. (c) Position of the limbal marks (red arrows) under suction “ON” condition without cyclotorsion compensation before starting the laser, showing approximately 12° of cyclotorsion. (d) Final position of the limbal marks after manual compensation of the cyclotorsion error (alignment with the horizontal axis of the eyepiece reticule). Delivery of the laser follows this (reproduced after permission from Journal of Refractive Surgery)

Figure 5

Clinical Photographs of an eye at 15 days (a) and 1 year (b) following FILI for + 4.5 D of hyperopia showing well centered and clear lenticule at the last follow-up