Study On The Effective Optical Zone After SMILE In Patients With Different Degrees Of Myopia

Objective: To explore the changes of effective optical zone(EOZ)and its influencing factors in patients with different degrees of myopia after SMILE.Methods: Retrospective study.From October 2019 to October 2020,68 myopia patients(133 eyes)who underwent SMILE surgery in Nanchang University Affiliated Eye Hospital with preoperative optical zone design of 6.5mm were selected,including 34 males(66 eyes)and 34 females(67 eyes),aged from 18 to 35 years.The patients were divided into three groups according to manifest refraction spherical equivalent before operation: 41 eyes in low myopia group(-0.50D≤manifest refraction spherical equivalent≤-3.00D),52 eyes in moderate myopia group(-3.00D< manifest refraction spherical equivalent≤-6.00D),and 40 eyes in high myopia group(manifest refraction spherical equivalent >-6.00D).The diameter of effective optical zone was measured by corneal topography tangent curvature difference map.The visual acuity,manifest refraction spherical equivalent,diameter of effective optical zone,Q value of cornea and high-order aberrations were collected before and3 months after operation.Results: Three months after operation,the effective optical zones of the three groups were(5.14 ±0.70)mm,(5.14 ±0.49)mm and(4.74 ±0.62)mm,respectively,and there were significant differences among the three groups(F=6.234,P=0.003).The diameter of effective optical zone after operation in all three groups was lower than that predicted by 6.5mm before operation.The corneal Q values of the three groups of myopic patients were 0.18 ±0.20,0.57 ±0.35,0.68 ±0.66 respectively,and there was significant difference among the three groups(F=15.020,P< 0.001).Three months after operation,the corneal Q values of the three groups were significantly higher than those before operation,and the difference was statistically significant(t=-14.567,-20.101,-9.389,all P< 0.001).There were significant differences in total high-order aberrations,spherical aberration and vertical coma among the three groups(F= 9.207,8.028,7.905 P< 0.05).The diameter of postoperative effective optical zone was positively correlated with preoperative manifest refraction spherical equivalent(r = 0.305,P< 0.001),negatively correlated with central corneal ablation depth(r =-0.253,P = 0.003),and negatively correlated with postoperative corneal Q value(r =-0.374,P < 0.001).There was a positive correlation between Δ Z40 and ΔEOZ after operation(r = 0.324,P < 0.001).Conclusion: The effective optical zone after SMILE was lower than that expected before operation,and the higher the myopia was,the smaller the effective optical zone was and the more the postoperative corneal spherical aberration increased.In addition,the depth of corneal ablation and aspheric changes of cornea can affect the size of effective optical zone after operation.