The current evaluation of corneal optical quality after small incision lenticule extraction (SMILE) is based on the single factor, such as scattering, diffraction or aberration, and all of them are not comprehensive and

methods.Modulation transfer function (MTF) and Strehl ratio (ST) are novel parameters of corneal optical quality, which can be used to assess the optical quality comprehensively. Objective This study was to evaluate the change of MTF and SR under the photopic and scotopic environment (3 mm and 6 mm pupil size, respectively) after SMILE procedure.

The study protocol was approved by Ethic Committee of Tianjin Eye Hospital, and written informed consent was obtained from each patient before any medical procedure.A series cases-observational study with self-control design was carried out.Sixty-three eyes of 32 myopia or myopic astigmatism patients who underwent SMILE surgery in Tianjin Eye Hospital were included from December 2013 to March 2014.The uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA) (LogMAR), the effective index (postoperative UCVA/preoperative BCVA) and refractive diopter were examined, and the MTF, SR and root mean square (RMS) on the anterior corneal surface were measured under the 3 mm and 6 mm pupil size at different spatial frequencies (10, 20, 30, 40, 50 and 60 c/d) by Sirius anterior analyzer before surgery and 1 week, 1 month and 3 months after surgery, respectively.

UCVA was ≥0.8 in 59, 62 and 63 eyes in 1 week, 1 month and 3 months after SMILE, with the percentage of 93.65%, 98.41% and 100%, and the effective index was 1.104±0.128, 1.126±0.145 and 1.158±0.208, respectively.The refractive diopter was normal in the eyes at postoperative 3 months.The MTFs of various spatial frequencies on the vertical and horizontal meridian under the 3 mm pupil size after SMILE were significantly higher than those before SMILE, while under the 6 mm pupil size, the MTFs were higher only on vertical meridian and 10, 20, 30 and 40 c/d, and there were not significant differences on the horizontal meridian (all at P<0.05). The SRs under the 3 mm and 6 mm pupil size showed increasing softly after surgery in comparison with before surgery, and the SRs were higher under the 3 mm pupil size than those under the 6 mm pupil size at various time points (all at P<0.05). There were not significant differences in RMS among different time points under both 3 mm pupil size and 6 mm pupil size (3 mm pupil size: F=1.348, P=0.184; 6 mm pupil size: F=1.990, P=0.137).

SMILE provides a great improvement in corneal optical quality for myopia or myopic astigmatism patients, which is more distinct in photopic condition than that in scotopic condition.

Optical quality, corneal; Cornea surgery, laser; Lasers, excimer/therapeutic use; Myopia; Modulation transfer function; Strehl ratio; Small incision lenticule extraction