Abstract: Objective: To evaluate the visual acuity changes and influencing factors under 4 mm and 7 mm pupil diameters after small incision lenticule extraction (SMILE). Methods: A prospective analysis was performed on 46 right eyes of 46 myopia or myopic astigmatism patients (age, 18-36 years) who underwent SMILE surgery in Eye Center of Xiangya Hospital, Central South University. Modulation transfer function (MTF), modulation transfer function cutoff ( MTF cutoff), and strehl ratio (SR) were measured under the 4 mm and 7 mm pupil diameters by an optical quality analysis system before surgery and 1 week and 1 and 3 months after surgery. A subjective visual quality questionnaire assessed the subjective visual quality of patients. Repeated measures analysis of variance was used for preoperative and postoperative comparison of visual acuity, diopter, MTF value, and so on. Multiple linear regression was used to explore the influencing factors of visual quality changes at 3 months after SMILE. Results: The differences in uncorrected visual acuity (UCVA) and spherical equivalent (SE) before and after SMILE surgery were statistically significant (F=210.976, P<0.001; F=144.129, P<0.001). At 3 months after surgery, the efficacy and safety indexes were 0.97±0.11 and 1.00±0.06, respectively. SE was limited within ±0.50 D in all patients. The differences of SR, MTF, and MTF cutoff values between 4 mm and 7 mm pupil diameters before and after surgery were statistically significant (all P<0.05). Under the photopic environment (4 mm pupil diameter), MTF, MTF cutoff and SR decreased initially after surgery, increased thereafter, and recovered to the preoperative levels at 1 month after surgery. Under the scotopic environment (7 mm pupil diameter), MTF and SR returned to preoperative levels at 3 month after surgery (P>0.05), while MTF cutoff returned to preoperative levels at 1 month after surgery. Under the scotopic environment, the MTF values of 20, 25 and 30 c/d spatial frequencies and SR were mainly negatively correlated with age and dark pupil diameter before surgery (Bage=-0.440, -0.409, -0.404, -0.389, all P<0.05; Bdark pupil diameter=-0.404, -0.333, -0.371, -0.368, all P<0.05). The MTF cutoff value and the MTF values of 5, 10 and 15 c/d mainly had a negative correlation with age (B=-0.522, P=0.003; B=-0.403, P=0.008; B=-0.409, P=0.008; B=-0.416, P=0.004). Night vision and glare halo scores had negative correlations with the preoperative dark pupil diameter (B=-0.370, P=0.020; B=-0.417, P=0.013). Conclusions: Visual quality decreased slightly under the photopic and scotopic environments in the early stage after SMILE. The visual quality under the scotopic environment was negatively correlated with preoperative dark diameter and age.
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