Steep corneal curvature tied high risk of residual astigmatism after SMILE surgery

The study published in BMC Ophthalmology further found that those with high myopia faced increased risks associated with higher cycloplegic cylinder power, greater topographic cylinder power, steeper corneal curvature, longer incision length, and smaller optic zone.

For more than 20 years, refractive surgeries have been performed to correct astigmatism and myopia. SMILE, laser in situ keratomileusis (LASIK), and photorefractive keratectomy are refractive surgeries commonly performed worldwide. Recently, there has been an increase in the number of individuals scheduled for SMILE surgery, which may be due to the reduced risk of dryness or other ocular symptoms.

Concerning the SMILE and LASIK procedures, the efficiency and predictability of both surgery methods are analogous and SMILE surgery results in better postoperative corneal sensitivity than LASIK surgery. Against this background, Chao-Kai Chang, Department of Optometry, Da-Yeh University, Changhua, Taiwan, and colleagues aimed to evaluate the possible topographic and surgical risk factors for high postoperative residual astigmatism in patients who undergo small-incision lenticule extraction surgery and have different myopia degrees.

For this purpose, the researchers conducted a retrospective cohort study enrolling patients who underwent SMILE surgery. 80 and 150 eyes from 40 to 75 individuals, respectively, were selected as the low myopia and high myopia groups.

The demographic data, refraction, visual acuity, surgical settings, and topographic parameters were recorded. Multiple linear regressions were performed with interaction tests to survey risk factors for high postoperative residual astigmatism in each group.

The study revealed the following findings:

· 6.25% and 6.00% of eyes presented with high postoperative residual astigmatism in the low myopia and high myopia groups, respectively, but these differences were not significant.

· A steep corneal curvature correlated with a greater risk of high postoperative residual astigmatism in the low myopia group, while a higher degree of cycloplegic cylinder power, steeper corneal curvature, greater topographic cylinder power, smaller optic zone and longer incision length were associated with a high rate of postoperative residual astigmatism in the high myopia group.

· The interaction effects of cycloplegic and topographic cylinder power and longer incision length on the incidence of high postoperative residual astigmatism development were more evident in the high myopia group than in the low myopia group.

"A steep corneal curvature correlates with a high postoperative residual astigmatism risk after SMILE surgery, and a higher degree of cycloplegic and topographic cylinder and longer incision are associated with high postoperative residual astigmatism in people with high myopia," the researchers wrote.

"There is a need for additional large-scale prospective studies evaluating the association between corneal biomechanics and high postoperative residual astigmatism after SMILE surgery," they concluded.

Reference:

Lee, CY., Shen, JH., Chao, CC. et al. 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. BMC Ophthalmol 24, 45 (2024). https://doi.org/10.1186/s12886-024-03296-x