Contralateral Eye Comparison Between Femtosecond Small Incision Intrastromal Lenticule Extraction at Depths of 100 and 160 μm

Abstract

Creating the refractive lenticule at a depth of 160 μm in SMILE had less effect on the corneal biomechanics than did creating a lenticule at a depth of 100 μm with no statistically significant differences in the refractive outcome and THOA between both groups.

Refractive Correction and Biomechanical Strength Following SMILE With a 110- or 160-μm Cap Thickness, Evaluated Ex Vivo by Inflation Test

“…35 A contralateral eye study of myopic SMILE using a 100-or 160-lm cap thickness reported significantly lower values of CH and CRF in the 100-lm cap group; this may suggest a more pronounced decrease in the postoperative viscoelasticity. 23 However, the average cylindrical and spherical correction was slightly higher in the group with a 100-lm cap thickness, although no significant differences were reported between groups. The positive correlation between lenticule thickness and the average decrease in CH and CRF 36 may explain the difference reported between the 100-and 160-lm cap groups.…”

“…23,32,33 One study evaluated the refractive outcome using cap thicknesses of 130, 140, 150, or 160 lm in patients with a mean preoperative spherical equivalent of À4.89 6 1.48 D. 32 The authors reported a 12-month postoperative undercorrection of À0.10 6 0.60 D (2%) and À0.17 6 0.25 D (3.5%) at a cap thickness of 130 or 160 lm, respectively. However, an intended overcorrection of 10% was performed in patients with a 160-lm cap thickness, because of possible energy loss due to a thicker cap.…”

“…Surprisingly, we observed an undercorrection of 43% in the À8 D group, with a 160-lm cap thickness, more than 4 times higher than in the À4 D group. Previous in vivo studies 23,32,33 have evaluated the refractive error in SMILE by using a 160-lm cap thickness in patients with low to moderate myopia, but the refractive error after high myopic correction remains unknown. It may be questioned if the amount of undercorrection is positively correlated with the intended correction when the stromal lenticule is removed in the deeper corneal layers.…”

“…However, an intended overcorrection of 10% was performed in patients with a 160-lm cap thickness, because of possible energy loss due to a thicker cap. 32 Another prospective contralateral eye study of SMILE 23 evaluated the refractive error when using a cap thickness of 100 or 160 lm (preoperative sphere of À4.05 6 1.50 D and À3.84 6 1.31 D, respectively). The average spherical error one month after SMILE was comparable between 100-and 160-lm cap thickness (100 lm, À0.03 6 0.35 D versus 160 lm, 0.02 6 0.35 D), but no intended over-orrection was performed in the 160-lm group.…”

“…4,22,23 The anterior one-third of the corneal stroma consists of an interwoven arrangement of collagen fibers, while the collagen fibers in the posterior twothirds of the corneal stroma are arranged in distinct lamellae with a predominant vertical and horizontal arrangement. 24 The collagen arrangement seems to be responsible for the depthdependent exponential decrease in the corneal tensile strength, with the 40% anterior stroma being the strongest region, and the 60% posterior stroma being at least 50% weaker.…”