Clipped Topography-Guided Treatments: A Different Approach to Custom Corrections.

PURPOSE

To present a new approach to customized treatments that inherently saves tissue by design, especially for pathological corneas.

METHODS

From the elevation of the anterior cornea and the refractive error of the eye, the target cornea can be calculated and the difference between actual and target cornea corresponds to the tissue to be removed. In this approach, it is further possible to preset the ablation depth at one (Model 1) or two (Models 2 and 3) particular locations. In all three models, the target cornea floats in z-direction, until the depth is reached at one of these defined locations. In Model 2, the depth at the second location is reached by modulating the asphericity, whereas in Model 3, asphericity is maintained but average curvature is modulated to achieve the desired depth at the second location. After floating in z-direction, and modulation, locations with a negative ablation value are set to zero (primary clipping). Additionally, locations exceeding a preset maximum ablation depth are set to a predefined depth (secondary clipping).

RESULTS

Simulated cases based on patient diagnosis were used to better explain and illustrate the technique.

CONCLUSIONS

With this approach, free-form ablation zones are generated, providing for a tissue-saving correction of refractive error and partial correction of higher order aberrations, the overall corneal shape will be recentered, and the corneal curvature gradient is reduced. .