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| Vector Analysis of the Effect of Different Incision Sizes of SMILE on MyopicAstigmatism Correction |
| Caixia Tian1, Yan Wang2, Jiamei Zhang2 |
| 1Clinical College of Ophthalmology, Tianjin Medical University, Tianjin 300020, China 2Refractive Surgery Center, Tianjin Eye Hospital, Tianjin Eye Institute, Tianjin Key Laboratory of Ophthalmology and Visual Science, Tianjin 300020, China |
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Abstract Objective: To analyze the effect of different incision sizes of small incision lenticule extraction (SMILE) on the correction of myopic astigmatism. Methods: This was a retrospective series case study. Three hundred and forty-nine patients (349 eyes) with myopic astigmatism who underwent SMILE surgery in the Refractive Surgery Center of Tianjin Eye Hospital from February to December 2021 were consecutively included in this study. Data from the right eyes of each patient were analyzed. The patients were divided into two groups: 129 patients (129 eyes) who received SMILE with 2 mm incision as the 2 mm incision group, and 220 patients (220 eyes) with 3 mm incision as the 3 mm incision group. The patients were grouped according to their cylinder diopter, with those less than 1.50 D being assigned to the low astigmatism group and those with 1.50 D or greater assigned to the high astigmatism group. Subsequently, the degree of cylinder was further sub-grouped according to the incision. Additionally, patients were grouped according to the degree of spherical diopter: the patients with spherical of -3.00-0 D were in the low sphere group, those with a spherical diopter between -6.00 and -3.25 D were assigned to the moderate sphere group, and the patients with spherical diopter less than -6.00 D were defined as the high sphere group, after which the degree of spherical was sub-grouped according to the incision. The visual acuity, diopter, and corneal topography were performed on the operated eyes before and 3 months after surgery. The vector analysis method was used to analyze the correction effect of astigmatism. The observation indicators included target induced astigmatism (TIA), surgically induced astigmatism (SIA), difference vector (DV), correction index (CI), index of success (IOS), angle of error (AOE), absolute value of error angle (|AOE|), magnitude of error (ME), flatten effect (FE), and flattening index (FI). Independent sample t-test was used to analyse the differences in baseline parameters between different incision groups, and Mann-Whitney test was used to compare the differences for postoperative diopter, TIA, SIA, CI, IOS, AOE, | AOE |, FI, FE, ME after surgery. Results: There was no signifcant difference in spherical, cylindrical and SE values between the different incision groups at 3 months after operation (all P>0.05). The percentage of eyes with the uncorrected visual acuity≥20/20 at 3 months after surgery was 96% in the 2 mm incision group, and 95% in the 3 mm incision group. The vector analysis showed that the IOS of the 3 mm incision group was lower than that of the 2 mm group, with a statistically significant difference (Z=-2.27, P=0.023). In the low astigmatism group, the IOS and CI of the 3 mm incision group were less than that of the 2 mm incision group, with statistical difference (Z=-2.17, P=0.030; Z=-2.84, P=0.005). The FI and ME of the 3 mm incision group were greater than that of the 2mm incision group, with statistical differences (Z=-2.42, P=0.016; Z=-2.02, P=0.043). In the moderate sphere group, the IOS and FI of the 3 mm incision group was less than that of the 2 mm incision group, with statistical differences (Z=-3.33, P=0.001; Z=-2.39, P=0.017). The CI of the 3 mm incision group in the high sphere group was less than that of the 2 mm incision group, showing a statistical difference between the two groups (Z=-2.24, P=0.025). There was no significant difference for other indexes between the two groups. Conclusions: The SMILE procedure with different sizes of incisions achieves excellent correction of astigmatism. Although the 2 mm incision is minimally invasive, the 3 mm incision also shows several advantages in the correction of low-grade astigmatism from vector analysis.
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Received: 08 October 2022
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| Fund:National Natural Science Foundation of China (81873684) |
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Corresponding Authors:
Yan Wang, Refractive Surgery Center, Tianjin Eye Hospital, Tianjin Eye Institute, Tianjin Key Laboratory of Ophthalmology and Visual Science, Tianjin 300020, China (Email:
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| [1] |
. [J]. Chinese Journal of Optometry Ophthalmology and Visual science, 2023, 25(8): 0-. |
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