Abstract
Purpose To evaluate the effect of corneal cap thickness on visual acuity and corneal biomechanics in small incision lenticule extraction (SMILE) for the treatment of myopia. Methods Forty eyes of 20 patients undergoing SMILE for the treatment of myopia were enrolled in this prospective controlled study. The patients with 510 μm–560 μm central corneal thickness (CCT) and a refractive spherical equivalent of −3.00 D to −8.00 D were included. It was designed randomly to undergo SMILE with a 110 μm cap thickness in one eye and 150 μm cap thickness in the other. Ophthalmic examinations included best-corrected and uncorrected visual acuity (UCVA); refractive status, contrast sensitivity, and objective visual quality were evaluated at 2 h, 4 h, and 24 h postoperatively; while at 3 months after the procedure, corrected intraocular pressure (IOP), higher order aberrations (HOAs), and morphologic modifications of corneal architecture of both eyes were assessed. Results Compared with the 150 μm group, the incidence of OBL was significantly higher in the 110 μm cap thickness group (P=0.004), and UCVA, Strehl ratio (SR), objective scatter index (OSI), modulation transfer function (MTF) cutoff frequency, and photopic and scotopic contrast sensitivity at medium spatial frequency were all significantly better in 110 μm group at 2 h and 24 h postoperatively (P < 0.05). Corneal spherical aberration and corrected IOP by Corvis ST were significantly higher in the 110 μm group at 3 months postoperatively (P < 0.05). No statistically significant differences were found in manifest refraction, UCVA, SR, OSI, MTF cutoff, and mesopic and photopic contrast sensitivity at low frequency, photopic contrast sensitivity at high frequency, endothelial density, corneal coma, and total HOAs at 3 months after the procedure. No visual decline was found in the patients in this study. Conclusions Both 110 μm and 150 μm cap thickness in SMILE were safe and effective for treatment of myopia. A 110 μm cap thickness demonstrated better visual outcomes during early and late postoperative periods with higher corneal spherical aberration and corrected IOP at 3 months postoperatively. This trial is registered with ChiCTR-IOR-17013369.
Highlights
Small incision lenticule extraction (SMILE) is a flapless, allfemtosecond laser refractive procedure, whereby the refractive lenticule is removed through a 2-3 mm keyhole incision. e safety, effectiveness, stability, and predictability of the procedure have made it a popular method for the treatment of myopia [1,2,3,4]. e SMILE procedure does not create a flap, thereby preserving more of the corneal nerve fibers, which has been shown to minimize dry eye and maintain higher corneal sensitivity [5]
uncorrected visual acuity (UCVA), Strehl ratio (SR), objective scatter index (OSI), and modulation transfer function (MTF) cutoff frequency results were better in the 110 μm group than in the 150 μm group at 2, 4, and 24 hours postoperatively (Table 2), no statistically significant difference was found in OSI at 4 hours between the two groups (P 0.06)
We performed SMILE on randomized eyes with a 110 μm cap thickness and the other eye 150 μm cap thickness to assess the influence of different cap thicknesses on visual function and corneal biomechanics at the very early stage (2 hours to 24 hours postoperatively) and the stable stage (3 months)
Summary
Small incision lenticule extraction (SMILE) is a flapless, allfemtosecond laser refractive procedure, whereby the refractive lenticule is removed through a 2-3 mm keyhole incision. e safety, effectiveness, stability, and predictability of the procedure have made it a popular method for the treatment of myopia [1,2,3,4]. e SMILE procedure does not create a flap, thereby preserving more of the corneal nerve fibers, which has been shown to minimize dry eye and maintain higher corneal sensitivity [5]. E safety, effectiveness, stability, and predictability of the procedure have made it a popular method for the treatment of myopia [1,2,3,4]. E SMILE procedure does not create a flap, thereby preserving more of the corneal nerve fibers, which has been shown to minimize dry eye and maintain higher corneal sensitivity [5]. Eoretically, it would be expected that deeper cap thickness would maintain more anterior peripheral stroma and corneal nerve fibers with stronger corneal rigidity and faster recovery of ocular surface function. The effect of cap thickness on visual function outcomes and biomechanical characteristics of cornea after SMILE has not been fully assessed. Journal of Ophthalmology observation to assess the effect of two different cap thicknesses in SMILE for myopia treatment, especially in the first 24 h postoperative period The effect of cap thickness on visual function outcomes and biomechanical characteristics of cornea after SMILE has not been fully assessed. erefore, we did a randomized, prospective
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