Differences Between Low, Medium, And Large Cyclorotation Angles In Myopic Prk - Visual And Refractive Results

Cyclorotation of the eye upon reclining can potentially influence refractive outcomes during photorefractive keratectomy (PRK) by misaligning the laser treatment with intended axis. The acknowledged challenge is addressed through angle detection and correction mechanisms integrated into modern excimer lasers, yet the degree of cyclorotation and its impact on refractive and visual results remains an area of active investigation. Moreover, some surgeons tend to manually reduce the angle before surgery to refrain from large angels, which is time-consuming and risks stromal dehydration. The aim of this study was to evaluate the differences in myopic PRK results between small, medium, and large cyclorotational angle degrees.

Care Vision Laser Center, Tel Aviv, Israel

This restrospective study included 17214 eyes of 10859 consecutive patients who underwent myopic PRK between 2012 and 2023. Patients were divided into three groups according to their cyclorotation angle magnitude. A comparison of baseline and intraoperative parameters was performed. Refractive and visual outcomes were assessed, including Efficacy and safety indexes, and an Alpins vector analysis was performed. Multiple linear regression was performed to identify the effect of potential confounders.

The small angle group (26.1±7.58) was significantly older than the medium (25.69±7.35), and had a lower keratometry readings (K) than the other groups to different extents. The large angle group showed to have significantly lower best corrected visual acuity (BCVA) than the two other groups (small: 0.92±0.1, medium: 0.92±0.1, large: 0.91±0.11). At final follow-up, mean BCVA and uncorrected VA (UCVA) were found to be significantly lower in the large angle group (0.92±0.13; 0.9±0.15) compared with the medium (0.93±0.12; 0.92±0.14) and small (0.93±0.12; 0.92±0.15) angle groups, which was mainly due to similar baseline differences. Other outcomes, including safety and efficacy indexes, and Alpins’ vectors, showed no significant differences.

Cyclorotational angle magnitudes have limited impact on myopic PRK outcomes given autocorrection and thus have limited clinical relevance of in PRK, with other factors potentially playing a more significant role in surgical planning. These findings lend confidence to clinicians in iris registration and autocorrection to achieve favorable results without manual maneuvers.