The effects of programmed optical zones on achieved corneal refractive power with myopic astigmatism after small incision lenticule extraction (SMILE): a vector analysis

Purpose To evaluate the effects of different programmed optical zones (POZs) on achieved corneal refractive power (CRP) with myopic astigmatism after small incision lenticule extraction (SMILE). Methods In total, 113 patients (113 eyes) were included in this retrospective study. The eyes were divided into two groups according to POZ: group A (6.5, 6.6, and 6.7 mm, n = 59) and group B (6.8, 6.9, and 7.0 mm, n = 54). Fourier vector analysis was applied to evaluate the error values between the attempted and achieved corneal refractive power (CRP). Alpins vector analysis was used to calculate surgically induced astigmatism (SIA), difference vector (DV), magnitude of error (ME), and astigmatism correction index (ACI). Multivariate regression analysis was performed to assess potential factors associated with the error values. Results The error values in the group with large POZ were closer to zero, and significantly associated with the POZ at 2 and 4 mm of the cornea ( β = − 0.50, 95% confidence interval [CI] [− 0.80, − 0.20]; β = − 0.37, 95% CI [− 0.63, − 0.10], P < 0.05, respectively). For the correction of astigmatism, the values of SIA, ME, and ACI were lower in group B than in group A ( P < 0.05). The fitting curves between TIA and SIA were y = 0.83 x + 0.19 ( R 2 = 0.84) and y = 1.05 x + 0.04 ( R 2 = 0.90), respectively. Conclusions Smaller POZs resulted in higher error values between the achieved- and attempted-CRP in the SMILE procedure, which should be considered when performing surgery.