Myopes who are interested in a surgical solution to their refractive error rather than spectacles or contact lenses can choose from traditional procedures like PRK and LASIK or the newer technique of small-incision lenticule extraction (SMILE). As it’s still a relative newcomer, SMILE has been less well-studied, especially the finer points of its postoperative visual quality. In a cross-sectional study, researchers assessed the influence of SMILE for high myopia on visual outcomes using a method called the Strehl ratio (denoted “VSX” and measured logarithmically), which takes into account surgically induced higher-order aberrations (HOAs) and the patient’s ability to neuro-adapt. Results were compared with values seen among similarly myopic controls corrected with spectacles or contact lenses.
The researchers measures both the habitual VSX (i.e., the VSX as it was measured directly for each condition) and the optimal VSX (the theoretically best-achievable VSX, calculated to see how much the VSX could theoretically improve).
A total of 117 eyes of 61 patients and 64 eyes of 34 myopic controls were included. The study shows SMILE does not affect the habitual logVSX but decreases the optimal logVSX slightly. Among SMILE patients, the postoperative habitual logVSX was worse than for contact lenses but not spectacles, and the postoperative optimal logVSX was worse than for both contact lenses and spectacles. They found no statistically significant difference in either habitual or optimal logVSX between spectacles and contact lenses.
“Furthermore, this study showed that the optimal VSX is dependent on the amount of HOAs, and that even small amounts of spherical defocus had a detrimental effect on the calculated VSX, which likely explains the different results concerning the habitual and optimal levels of VSX,” the authors concluded in their study. “The observed differences in logVSX were smaller than what would be expected from the test-retest variation in defocus from a subjective refraction. Thus, SMILE effectively treats myopia with reassuringly clinically insignificant effects on the visual image quality compared with correction with spectacles or contact lenses; the visual image quality resulting from correction with either spectacles or contact lenses is equivalent.”
Gyldenkerne A, Ivarsen A, Nisted I, et al. Visual image quality after small-incision lenticule extraction compared with that of spectacles and contact lenses. J Cataract Refract Surg. 2021; 47:731-40.