Risk factors for postoperative cylindrical prediction error after laser in situ keratomileusis for myopia and myopic astigmatism

Abstract

Purpose To study the risk factors for the occurrence of cylindrical prediction error (PE) after laser in situ keratomileusis (LASIK) for myopia and myopic astigmatism. Methods The study was a nested case-control study. Five hundred eyes of 252 consecutive patients who underwent LASIK for myopia and myopic astigmatism on the Chiron Technolas 217C laser and completed 6 months of followup. There were 435 controls and 65 cases based on the postoperative refractive cylindrical PE. The probable risk factors studied included preoperative sphere and cylinder, keratometry, pachymetry, suction ring used, flap thickness, hinge centeration, optic zone, ablation depth, and intraoperative complications. Results By univariate analysis, the cylindrical PE was found to be associated with preoperative spherical equivalent higher than À6 D (v 2 ¼ 10.83; P ¼ 0.001), preoperative sphere higher than À6 D (v 2 ¼ 6.15, P ¼ 0.013), preoperative cylinder more than À0.75 D (v 2 ¼ 6.61; P-value ¼ 0.010), and an optic zone less than 5.5 mm (v 2 ¼ 19.3; P ¼ 0.001). Risk factors for postoperative astigmatism by stepwise multivariate logistic regression analysis were an optic zone of less than 5.5 mm with an odds ratio (OR) of 2.81 (95% confidence interval (CI) ¼ 1.62-4.86) and preoperative cylinder more than À0.75 D with an OR of 1.60 (95% CI ¼ 0.92-2.77). Conclusion Postoperative astigmatism (as indicated by the cylindrical PE) is more likely to occur with an optic zone of less than 5.5 mm and a higher preoperative cylindrical error.

Topographic and surgical risk factors for high postoperative residual astigmatism after small incision lenticule extraction in patients with different degrees of myopia: a retrospective cohort study

“…The degree of steep corneal curvature was correlated with a high risk of postoperative residual astigmatism in both low myopia and high myopia populations, while the other topographic and surgical parameters were also related to a higher incidence of high postoperative residual astigmatism in the high myopia population. In a previous study, a smaller optic zone and higher degree of preoperative astigmatism were associated with the development of postoperative astigmatism after LASIK surgery [ 16 ], and a change in corneal curvature was also associated with the occurrence of postoperative astigmatism in patients who underwent photorefractive keratectomy [ 31 ]. However, few studies have evaluated the possible risk factors for high postoperative residual astigmatism after SMILE surgery [ 17 ].…”

“…This may be because fine attachment of the interface takes longer in patients with high myopia with deeper stromal pockets [ 34 ]; thus, preoperative corneal irregularities may persist more easily. In addition, the small optic zone contributes to lower refractive stability [ 16 ], and a longer corneal incision could prominently alter corneal structure 30 . These factors may cause corneal irregularity in the high myopia group.…”

“…The possible risk factors for post-LASIK astigmatism include small optic zone and high preoperative astigmatism [ 16 ]. Additionally, high preoperative astigmatism is correlated with high postoperative astigmatism in SMILE patients [ 17 ].…”

“…However, the topographic or surgical risk factors for high postoperative residual astigmatism after SMILE surgery have not been identified. Moreover, the risk factors for postoperative refractive error differ among patients who undergo LASIK surgery to correct different degrees of myopia [ 10 , 16 ], and the risk factors for high postoperative residual astigmatism after SMILE surgery for different degrees of myopia may also differ and need further investigation.…”