| Abstract: | ![]()
Objective: To calculate ocular residual astigmatism (ORA) by vector analysis and to evaluate the impact of ocular residual astigmatism on refractive and visual outcomes after correction of myopic astigmatism by small incision lenticule extraction (SMILE). Methods: In this prospective case-series study, 115 eyes with myopic astigmatism were treated with SMILE from Jauary 2019 to August 2019 atRefractive Center of Ophthalmology Department, Shengjing Hospital, China Medical University. ORA was calculated by vector analysis and patients were divided into two groups according to the magnitude of ORA: high ORA group (ORA≥1.00 D) with 42 eyes and low ORA group (ORA<1.00 D) with 73 eyes. The follow-up period was 3 months after the operation. Uncorrected visual acuity (UCVA) and pythagorean length were measured and compared after the operation. The following measurements were compared: refractive outcomes, total higher order aberrations (tHOAs), vertical trefoil, vertical coma, horizontal coma, oblique trefoil, oblique quadrafoil, oblique secondary astigmatism, spherical aberration, vertical secondary astigmatism, and vertical quadrafoil. Contrast sensitivity was compared between the high and low ORA groups under either 85 cd/m2 or 3 cd/m2 illumination from 1.5 c/d to 18 c/d. The data were analyzed by an independent-samples t test and Mann-Whitney U test to compare the differences between the two groups. Results: Three months postoperatively, refractive outcomes showed that postoperative residual astigmatism in the high ORA group was significantly higher than in the low ORA group (t=3.293, P=0.001). Vector analysis showed that the error vector (EV), absolute error of angle (absolute EA) and index of success (SI) were higher in the high ORA group (t=-3.235, P=0.001; t=-2.326, P=0.020; t=-2.587, P=0.010). After SMILE，all cases had achieved a desirable visual acuity: high ORA group: -0.15±0.05, low ORA group: -0.15±0.05. There were no statistically significant differences in visual acuity, pythagorean length, tHOAs, vertical trefoil, vertical coma, horizontal coma, oblique trefoil, oblique quadrafoil, oblique secondary astigmatism, spherical aberration, vertical secondary astigmatism, or vertical quadrafoil between the two groups. An obvious difference was found in contrast sensitivity, which showed a higher contrast sensitivity at a spatial frequency of 18 c/d with 85 cd/m2 in the low ORA group than in the high ORA group (t=-2.877, P=0.005), but this tendency was not present at 3 cd/m2 . Conclusions: Ocular residual astigmatism impacts the precision of SMILE in correcting myopic astigmatism. This leads to a tendency of more residual astigmatism in refractive outcomes, and reduces contrast sensitivity at high spatial frequencies. However, it does not affect the outcome of obtaining good visual quality in both visual acuity and higher order aberrations. |
