Quantitative analysis of the effect of ocular rotation on postoperative residual astigmatism in small incision lenticule extraction for myopia correction.

OBJECTIVE

The aim of this study was to conduct a systematic investigation into the effects of ocular rotation on postoperative residual astigmatism in patients undergoing small incision lenticule extraction (SMILE).

METHODS

A prospective observational cohort study involved 79 patients (153 eyes) with myopia and astigmatism who underwent SMILE surgery. Ocular rotational magnitude was measured using manual corneal and scleral marking with a slit-lamp microscopy assessment. Preoperative and postoperative (1- and 3-month) assessments included uncorrected distance visual acuity (UDVA), best-corrected visual acuity (BCVA), refractive error, and other relevant ocular parameters.

RESULTS

Residual astigmatism showed significant correlations with ocular rotation magnitude (r = 0.429, p < 0.001), preoperative intraocular pressure (r = -0.178, p = 0.032), and preoperative cylindrical lens power (r = 0.175, p = 0.035). A multiple linear regression analysis indicated that rotation magnitude significantly impacted postoperative residual astigmatism (p < 0.001). However, preoperative intraocular pressure (p = 0.349) and spherical equivalent (p = 0.105) were not significantly related to residual astigmatism. Linear regression analysis further demonstrated significant positive correlations between rotation amplitude and various astigmatism parameters at both 1- and 3-month postoperative follow-ups (all p < 0.05). In particular, the relationships were quantified as follows: cylindrical lens (CYL [D]) (1 month: y = 7.058x + 17.480, p < 0.001; 3 months: y = 7.464x + 13.610, p < 0.001), target-induced astigmatism (TIA [D]) (1 month: y = 0.112x + 1.275, p = 0.012; 3 months: y = 0.097x + 1.217, p = 0.026), surgically induced astigmatism (SIA [D]) (1 month: y = 0.094x + 0.936, p < 0.001; 3 months: y = 0.059x + 0.911, p = 0.022), and difference vector (DV [D]) (1 month: y = 0.041x + 0.289, p = 0.005; 3 months: y = 0.037x + 0.866, p = 0.011). Notably, rotation amplitude exhibited the strongest association with postoperative CYL. Receiver operating characteristic (ROC) analysis determined the optimal thresholds for rotation magnitude in predicting residual astigmatism to be 1.5° at 1 month (AUC = 0.753; sensitivity 79.7%; specificity 58.2%) and 2.5° at 3 months (AUC = 0.929; sensitivity 92.9%; specificity 83.5%).

CONCLUSION

The magnitude of rotation shows a notably positive correlation with residual astigmatism during both the 1- and 3-month postoperative follow-ups. Thresholds of 1.5° (1 month) or 2.5° (3 months) prove predictive of residual astigmatism, with enhanced diagnostic precision at the later follow-up.