Differences in Image Quality after Three Laser Keratorefractive Procedures for Myopia

Clinical outcomes of stromal lenticule rotation to correct mixed astigmatism

PURPOSE

To describe a stromal lenticule rotation surgical technique to correct mixed astigmatism and evaluate the initial clinical outcomes of this innovative approach.

METHODS

This retrospective case series included five eyes from five patients with mixed astigmatism that underwent intrastromal lenticule rotation surgery. The eyes were evaluated for uncorrected visual acuity, corrected distance visual acuity, manifest refraction, central corneal thickness, corneal volume, anterior and posterior K readings, and corneal higher order aberrations (HOAs) (including total HOAs, spherical aberrations, coma, and trefoil) using the Scheimpflug-Placido topographer before and 3 months after surgery. The corneal epithelium and stroma were imaged using anterior segment optical coherence tomography (AS-OCT) postoperatively. A paired-sample t-test was used to analyse the data.

RESULTS

Clinical improvement was found in the uncorrected distance visual acuity (0.64 ± 0.11 logMAR vs. 0.20 ± 0.17 logMAR) and spherical and cylindrical diopters (D) (+2.65 ± 1.32 D vs. -0.05 ± 0.51 D and -4.95 ± 0.94 D vs. -1.10 ± 0.78 D, respectively). Anterior flat keratometry readings showed a steep trend (40.65 ± 1.24 D vs. 42.73 ± 0.63 D). Anterior corneal astigmatism decreased from 4.50 ± 0.55 D to 2.05 ± 0.73 D. According to the AS-OCT images, no significant epithelial remodelling was observed postoperatively. Although no significant differences were found among the increased corneal HOAs, the coma and trefoil changed much more than spherical aberrations 3 months postoperatively.

CONCLUSIONS

The results for these five eyes suggest that the autologous stromal lenticule rotation technique is safe and effective; it may be an economical and feasible surgical option for correcting mixed astigmatism.

Temporal fluctuations in defocus may reverse the acuity loss encountered with induced refractive errors

A recent template-matching model hypothesized that simulated visual acuity loss with uncorrected refractive errors may be recovered by adding temporal defocus fluctuations up to the magnitude of the refractive error. Acuity recovery saturates or gets attenuated beyond this magnitude. These predictions were confirmed for monocular high-contrast visual acuity of 10 young, cyclopleged adults with 0.5-2.0D of induced myopia combined with the same range of temporal defocus fluctuations at 4.0 Hz frequency. The outcomes reinforce that spatial resolution may be optimized by averaging time-varying defocus over the entire stimulus presentation epoch or around the point of least defocus within this epoch.