Abstract
Worldwide, femtosecond Laser Assisted In-situ Keratomileusis (LASIK) is a well known and commonly used refractive technique, although Small Incision Lenticule Extraction (SMILE) has become increasingly popular since it was introduced in 2011. In LASIK, a corneal flap is cut with a microkeratome or femtosecond laser, followed by thinning of the stromal bed with excimer laser ablation. In SMILE, a minor intrastromal lenticule is cut with a femtosecond laser and subsequently removed through a small incision, leaving the anterior and strongest part of the cornea almost intact. Both LASIK and SMILE require cutting of corneal lamellae that may reduce the biomechanical stability of the cornea, with the potential risk of corneal iatrogenic ectasia as a severe complication. However, SMILE preserves the anterior corneal integrity and may, in theory, better preserve the corneal biomechanical strength than LASIK after surgery.A review aimed to examine the current literature that describes and compares the corneal biomechanical properties after Laser Assisted In-situ Keratomileusis (LASIK) and Small Incision Lenticule Extraction (SMILE). A comprehensive search was performed in Pubmed.gov using the following search queries: Corneal biomechanical properties, corneal biomechanics, ocular response analyser, ocular response analyzer, ORA, ex vivo, in vitro, Corvis, Corvis ST, LASIK, and SMILE.
Highlights
During the last few decades, laser refractive surgery has gained extensive interest for correction of refractive errors such as myopia, hyperopia, astigmatism, and presbyopia
Corneal biomechanical properties are of major importance in laser refractive surgery and must be taken into consideration to reduce the risk for iatrogenic ectasia
Development and refinement are needed if Ocular Response Analyser (ORA) and Corvis ST should be implemented in a screening procedure of the biomechanical strength before refractive surgery
Summary
During the last few decades, laser refractive surgery has gained extensive interest for correction of refractive errors such as myopia, hyperopia, astigmatism, and presbyopia. In SMILE, an intrastromal lenticule is cut with a femtosecond laser, and subsequently removed through a minor incision. Both SMILE and LASIK have shown high efficacy, predictability, and safety [4 - 9], but SMILE may have an advantage of being a flap-free procedure preserving the corneal biomechanical strength better than LASIK [10, 11]. The Open Ophthalmology Journal, 2018, Volume 12 165 complications caused by a biomechanical weakening after laser refractive surgery, seen by corneal thinning, protrusion, increased myopia, irregular astigmatism, and decreased visual acuity [16]. LASIK may cause a greater reduction of the biomehcanical strength due to the almost circumferential cut during flap creation, compared with only a 2-3 mm incision length in SMILE. Comparisons with other laser refractive techniques such as photorefractive keratectomy (PRK), FLEX, and LASEK as well as the dependency of IOP, CCT, refractive status, cap/flap thickness, and age were outside the topic of this review
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