Abstract
To examine the refractive correction and corneal biomechanical strength after small incision lenticule extraction (SMILE) by using a 110- or 160-μm cap thickness. Thirty-two human donor corneas were allocated into 4 groups, combining one of two cap thicknesses (110 and 160 μm) with one of two spherical corrections (-4 D and -8 D). Each cornea was mounted on an artificial anterior chamber. The chamber pressure was adjusted by an attached 8% dextran media column. The anterior and posterior sagittal 3-mm-diameter curvature (rsag3mm) and the total corneal refractive power (TCRP4mm,apex,zone) were obtained before and after SMILE at a chamber pressure of 15 or 40 mm Hg. The average changes after surgery (Δ = postoperative - preoperative) and at increased chamber pressure (δ = 40 mm Hg - 15 mm Hg) were compared. A 110-μm cap thickness caused more anterior flattening (Δr15,-8D, 1.02 ± 0.08 mm versus 0.60 ± 0.17 mm), less posterior steepening (Δr15,-8D, -0.19 ± 0.11 mm versus -0.45 ± 0.20 mm), and more myopic correction (ΔTCRP15,-8D, -6.30 ± 0.96 D versus -4.55 ± 1.66 D) than a 160-μm cap thickness for -8 D SMILE (P < 0.034), but not for -4 D SMILE (ΔTCRP15,-4D,110μm, -3.86 ± 1.31 D versus ΔTCRP15,-4D,160μm, -3.57 ± 1.27 D, P = 0.718). After SMILE, increased chamber pressure caused anterior steepening (P < 0.014), which was similar at cap thicknesses of 110 and 160 μm (δr-4D, -0.13 ± 0.14 mm versus -0.09 ± 0.05mm, P = 0.431). For high myopic corrections, a 160-μm cap caused less anterior curvature flattening and more posterior steepening than a 110-μm cap, and consequently less myopic correction. The inflation test revealed a reduction in the biomechanical strength after SMILE; this was similar when using a 110- or 160-μm cap thickness.
Highlights
To examine the refractive correction and corneal biomechanical strength after small incision lenticule extraction (SMILE) by using a 110- or 160-lm cap thickness
The inflation test revealed a reduction in the biomechanical strength after SMILE; this was similar when using a 110- or 160-lm cap thickness
S ince its introduction in 2011, small incision lenticule extraction (SMILE) for myopia or myopic astigmatism has been commonly performed by refractive surgeons worldwide.[1,2]
Summary
Thirty-two human donor corneas were allocated into 4 groups, combining one of two cap thicknesses (110 and 160 lm) with one of two spherical corrections (À4 D and À8 D). After SMILE, increased chamber pressure caused anterior steepening (P < 0.014), which was similar at cap thicknesses of 110 and 160 lm (drÀ4D, À0.13 6 0.14 mm versus À0.09 6 0.05mm, P 1⁄4 0.431). A total of 32 human donor corneas were allocated into 4 groups by combining one of two cap thicknesses (110 lm and 160 lm) with one of two myopic spherical corrections (À4 D and À8 D). Each donor cornea was mounted on an artificial anterior chamber (AAC; Barron; Katena Products, Inc., Denville, NJ, USA) containing transport medium. The humidity and room temperature were kept stable at 45% and 218C during pre- and postoperative measurements
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