Early visual quality outcomes after small-incision lenticule extraction surgery for correcting high myopic astigmatism.

BACKGROUND: To evaluate early optical quality outcomes after small-incision lenticule extraction (SMILE) surgery for correcting high myopic astigmatism. METHODS: This retrospective study enrolled 55 eyes from 37 patients who had preoperative myopic astigmatism of ≥2.00 diopters (D) who had been treated with SMILE surgery. Preoperatively, the mean cylinder was - 2.41 ± 0.54 D (range, - 2.00 D to - 4.50 D). The preoperative and postoperative visual outcomes, refraction, and higher-order aberration (HOA) at 1 and 3 months were compared. Refractive astigmatism changes were analyzed by the Alpins vector method. RESULTS: Three months after SMILE surgery, the average cylinder was - 0.14 ± 0.31 D, and the average astigmatism vector was - 0.09 D × 6.34°. The angle of error (AofE) was limited to within ±10°, and the magnitude of error was limited to within ±1.0 D in all patients. The correction index (CI) was 0.98 ± 0.07, the index of success (IOS) was 0.08 ± 0.13, and the flattening index (FI) was 0.97 ± 0.07. Significant positive correlations were found between IOS and |AofE| (P = 0.000); negative correlations were found between FI and |AofE| (P = 0.000). The postoperative total HOA, spherical aberration, vertical coma aberration, and trefoil 30° were increased significantly compared with preoperative measurements, and the increase in HOA was closely related to preoperative astigmatism (P < 0.05). CONCLUSIONS: SMILE has preferable outcomes for correcting high myopic astigmatism. Axis rotation during the surgery might influence the undercorrection of astigmatism. The increase of HOA after surgery is related to preoperative astigmatism.

[Analysis of the dynamic changes of cornea after myopic excimer laser in situ keratomileusis using an Orbscan II topography system].

OBJECTIVE: To study the changes and influence factors of an Orbscan II topography system in myopia after excimer laser in situ keratomileusis (LASIK). METHODS: Two hundred and sixteen myopia patients (230 eyes) were treated by LASIK, their corneal thickness and curve of corneal posterior surface was measured with an Orbscan II topography system before and after surgery. The results of measurement in different time points were compared. RESULTS: The thinnest point of cornea, the mean keratometry of the posterior best fit surface (BFS) and the distance from the apex to the BFS were significant difference before and after operation (P < 0.05). There were significant difference among those groups in different degree of myopia in the same time point (P < 0.05) after surgery, but there were no significant difference in the same group in difference time (P > 0.05). A significant difference in the area of the thinnest cornea before surgery and after surgery was detected among those groups (P < 0.01). The regression equation for preoperative Diff value was established as Y = 0.0941 - 0.000,53X(1) - 0.000,471X(2) - 0.0063X(3) + 0.001,22X(4) (P < 0.01), X(1) = corneal thickness of the thinnest point (microm), X(2) = central corneal thickness (microm), X(3) = corneal diameter (mm), X(4) = length of ocular axis (mm). The regression equation for postoperative decrease Diff value between the third month and the first month was produced as Y = - 0.027 - 0.000,78X(1) + 0.002,01X(2) - 0.0055X(3) (P < 0.01). X(1) = decrease in corneal thickness of the thinnest point (microm), X(2) = intraocular pressure pre-surgery (mmHg), X(3) = decrease in curvature of posterior corneal surface (D). CONCLUSIONS: The application of Orbscan II has an important clinical significance before and after LASIK. The Diff value measured before LASIK for myopia is influenced by the corneal thickness, corneal diameter and ocular axis. The postoperative decrease in Diff value between the third and first month is influenced by the postoperative decrease of corneal thinnest point and curvature of posterior corneal surface, and preoperative intraocular pressure.