AIM: To evaluate the differences between the estimated and measured corneal ablation thickness in myopic eyes with different refractive errors in small incision lenticule extraction(SMILE)and investigate the precision of corneal ablation thickness in SMILE.

METHODS: This prospective study included 234 eyes(143 myopic patients), who had undergone SMILE in our hospital from January 2017 to August 2019. The patients were divided into three groups according to a manifest refraction spherical equivalent(MRSE): low myopia(-0.50 to -3.00D, 78 eyes), moderate myopia(>-3.00 to -6.00D, 78 eyes), and high myopia(>-6.00D, 78 eyes). Observe the uncorrected distance visual acuity(UDVA)and MRSE before and after operation. The central corneal thickness(CCT)was measured by Pentacam preoperatively and postoperatively at 1mo. Compare the discrepancy between estimated corneal ablation thickness and measured corneal ablation thickness of three groups to discuss the precision of corneal ablation thickness in different refractive errors in SMILE.

RESULTS: The UDVA was 0.8 or better in all eyes and 1.0 or better in 98.3% eyes postoperatively. The average measured corneal ablation thickness was significantly lower than average estimated corneal ablation thickness(84.92±23.15μm vs 100.07±26.83μm, P<0.01). The average cutting error was 15.15±10.34μm. The measured corneal ablation thickness of low myopia, moderate myopia and high myopia was significantly lower than the estimated corneal ablation thickness, respectively(P<0.01). The cutting error of low myopia, moderate myopia and high myopia was 8.81±7.78, 15.59±9.27, 21.05±10.03μm respectively. The average MRSE of all patients was -4.85±2.15D preoperation, there was a linear regression relation between MRSE and cutting error(Y= -2.2495X+3.9287, R²=0.1589). The cutting error increased with MRSE(t=-6.620, P<0.001).

CONCLUSION: The measured corneal ablation thickness was lower than estimated corneal ablation thickness,the higher the refractive power was, the larger the cutting error would be in SMILE. Although there was significant discrepancy between measured corneal ablation thickness and estimated corneal ablation thickness, the effect of this surgery was ideal, the mismatch did not influence the precision of different refractive errors.