Over the past 20 years, a wide variety of surgical techniques and technologies have evolved to reduce dependence on contact lenses or glasses for use in routine daily activities. As a new frontier, the field of refractive surgery is expected to see continued innovation and progress. To give the reader a glimpse of the possible future, this chapter highlights some refractive surgical procedures that are not currently approved by the US Food and Drug Administation (FDA). These procedures include all-femtosecond laser keratorefractive surgery as well as corneal crosslinking (CCL) for ectatic disorders combined with additional refractive intervention to achieve visual rehabilitation with greater spectacle and contact lens independence.
Refractive Lenticule Extraction
In 1996, investigators first described the use of a picosecond laser to generate an intrastromal lenticule that was removed manually after the flap was lifted. The main drawbacks of this procedure, which was a precursor to modern refractive lenticule extraction (commonly referred to as ReLEx) were the relatively low precision and accuracy of the laser. In 1998, the first studies involving this technology were performed in rabbit eyes and in partially sighted eyes.
Following the debut of the VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany) in 2007, the intrastromal lenticule method was reintroduced in a procedure named femtosecond lenticule extraction (commonly referred to as FLEx) This procedure involved intrastromal dissection of a refractive lenticule as well as creation of a corneal flap and was performed exclusively by femtosecond laser. The refractive results were similar to those observed in laser in situ keratomileusis (LASIK), but the visual recovery time was longer.
More recently, a method called small-incision lenticule extraction (SMILE), has been developed. It is also a form of lenticule extraction but has the advantage of being performed entirely within a pocket, thereby avoiding the need for a flap. Conformité Européenne (CE) marking was achieved in 2009. SMILE received FDA approval in September 2016 after US pivotal studies.
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Krueger RR, Juhasz T, Gualano A, Marchi V. The picosecond laser for nonmechanical laser in situ keratomileusis. J Refract Surg. 1998;14(4):467–469.
Sekundo W, Kunert KS, Blum M. Small incision corneal refractive surgery using the small incision lenticule extraction (SMILE) procedure for the correction of myopia and myopic astigmatism: results of a 6-month prospective study. Br J Ophthalmol. 2011;95(3): 335–339.
Shah R, Shah S. Effect of scanning patterns on the results of femtosecond laser lenticule extraction refractive surgery. J Cataract Refract Surg. 2011;37(9):1636–1647.
Vestergaard A, Ivarsen A, Asp S, Hjortdal JØ. Femtosecond (FS) laser vision correction procedure for moderate to high myopia: a prospective study of ReLEx® FLEx and comparison with a retrospective study of FS-laser in situ keratomileusis. Acta Ophthalmol. 2013;91(4): 355–362.
Indications and Preoperative Evaluation
The SMILE procedure (as of the printing of this book) is approved for the treatment of myopia with or without astigmatism from –1.00 D to –10.00 D sphere, and –0.75 D to –3 D cylinder with MRSE >–10 D in the eye to be treated in patients aged 22 years or older with documentation of stable manifest refraction over the past year. Preoperative evaluation is similar to that for patients undergoing photoablative procedures, such as LASIK or photorefractive keratectomy (PRK); as in all refractive procedures involving tissue removal, a primary goal is to exclude patients with corneal ectatic diseases and susceptibility to postoperative ectasia.
Ambrósio R Jr, Ramos I, Lopes B, et al. Ectasia susceptibility before laser vision correction. J Cataract Refract Surg. 2015;41(6):1335–1336.
Moshirfar M, McCaughey MV, Reinstein DZ, Shah R, Santiago-Caban L, Fenzl CR. Small-incision lenticule extraction. J Cataract Refract Surg. 2015;41(3):652–665.
Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.