Analysis Of The Difference Between Predicted And Achieved Ablation Amount In Trans-Prk Using The Amaris 1050Rs Excimer Laser And Accelerated Cross-Linking In Extreme High Myopia (>-8 Diopters)

Discrepancies between predicted and achieved ablation amounts in Trans-PRK using the Amaris 1050RS excimer laser for myopia and astigmatism correction have been reported, influenced by factors such as epithelial thickness, corneal curvature, and ablation zone size. Minimizing these discrepancies is particularly critical in extreme high myopia. This study aims to analyze these differences in Trans-PRK combined with accelerated cross-linking and identify the influencing factors.

A retrospective analysis was conducted on patients who underwent Trans-PRK combined with accelerated cross-linking for the correction of extreme high myopia.

A total of 108 eyes that underwent Trans-PRK with accelerated CXL were analyzed. The predicted ablation amount was compared with the achieved ablation amount at two months postoperatively. The achieved ablation depth was calculated by excluding epithelial thickness changes, considering the known epithelial remodeling process. Factors such as epithelial thickness, degree of myopia and astigmatism, planned ablation depth, corneal curvature, and asphericity were analyzed. Additionally, surgical parameters, including ablation depth, optical zone size, total laser treatment zone, and epithelial thickness changes, were evaluated to determine their impact on the difference between predicted and achieved ablation depths.

The achieved ablation depth in extreme high myopia cases was consistently lower than predicted, with greater discrepancies as the target refractive correction increased. Compared to moderate myopia cases (<-6.00 D), the ablation per diopter decreased as myopia severity increased. Eyes in which a thinner-than-actual epithelial thickness was used for ablation planning showed a significantly greater discrepancy. In cases with lower-than-predicted achieved ablation, the actual optical zone size was not reduced compared to the planned size. The degree of myopia, total ablation depth, and optical zone size were significant factors affecting the difference between predicted and achieved ablation depths.

Trans-PRK combined with accelerated CXL in extreme high myopia enhances procedural safety by minimizing achieved ablation depth. Alongside previously recognized benefits such as faster visual recovery, refractive stability, and effective optical zone expansion, this approach also reduces unnecessary corneal tissue removal. Therefore, it can be a viable alternative for myopia exceeding -8.00 D, where precise ablation control is crucial. Additionally, adjusting the epithelial thickness parameter during surgical planning can further optimize tissue preservation without compromising the optical zone, making it a valuable strategy for extreme high myopia correction.