Evaluate the effect of the size of optical zones (OZ) on myopia and astigmatism correction in small incision lenticular extraction.

To retrospectively study whether different surgical optical zone sizes affect the correction of diopter and astigmatism in myopia patients. Divided into 2 groups according to the diameter of the optical zone. The vector analysis method was used to analyze the changes and errors of astigmatism in TR and SIR after operation. Generalized Estimation Equation (GEE) model is used for multiple regression analysis to evaluate the potential factors related to the error value.

Inclusion Criteria:

• no ocular conditions
• normal topography
• central corneal thickness, >500µm
• residual stromal thickness, >280 µm
• pupil diameter, 2.78-4.9 mm (average, 3.76±0.43 mm);

Exclusion Criteria:

• history of intraocular surgery
• pupil diameter, >4.9 mm or <2.78mm
• keratoconus or corneal ectasia

age of patients between 18-45 years; spherical refraction of -3.00 to -6.00 diopters (D) with or without astigmatism (<-3.00 D); spherical equivalent, -3.00 to -6.00 D; corrected distant visual acuity (CDVA), >20/25