Comparison of asymmetric and symmetric offset ablation in myopic astigmatism patients

To compare differences in clinical outcomes of symmetric offset (SO) and asymmetric offset (AO) centration strategies in photorefractive keratectomy (PRK) in patients with myopia and/or astigmatism,  forty refractive surgery candidates who visited Farabi Eye Hospital's refractive surgery clinic from May to August 2022 were enrolled in the study. We randomly assigned one of each patient's eyes to the AO and the other one to the SO group using random blocks. Patients were followed for four months (median of 114 days). Ablation profile, Visual acuity (VA), and higher order aberrations (HOAs) were evaluated. Effective optical zone (EOZ) and its circularity index were calculated automatically by a MATLAB-based algorithm. There was no significant difference between the two groups' total ablation volume and maximum and central ablation depth (all P > 0.05). The two groups showed significant differences in minimum ablation depth, with a higher value for SO than AO (0.03 ± 0.03 and 0.01 ± 0.01, respectively, P-value < 0.001). 95% and 93% of the eyes in the AO and SO groups achieved UDVA of 20/20 or better at four months postoperatively (P-value = 0.78, Chi-square). There were no significant differences between postoperative mean RMS of higher order aberrations (HOAs) among AO and SO groups (all P > 0.05). The EOZ was 6.05 ± 0.64 in the SO group and 6.05 ± 0.68 in the AO group (P value = 0.99, paired t-test). 95% and 93% of the eyes in the AO and SO groups achieved UDVA of 20/20 or better at four months postoperatively (P-value = 0.78, Chi-square). Symmetric and asymmetric offset centration strategies result in safe and effective refractive correction. The refractive and visual outcomes of both methods were similar in low and moderate myopic astigmatism patients.