Clipped Topography Guided Treatments: A Different Approach To Custom Corrections

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

Preclinical science, simulated  ablation model derived from anterior cornea elevation data, the refraction of the eye and the target cornea (modulating asphericity and curvature) floating in the z-axis

In this procedure it is possible to pre-set the ablation depth at one (Model 1) or two (Models 2 and 3) particular locations.  the target cornea floats in z-direction, until at one of these defined locations the depth is reached. 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. After floating in z direction, and modulation, locations with a negative ablation value are set to zero (primary clipping). Additionally, locations exceeding a pre-set maximum ablation depth are set to a pre-defined depth (secondary clipping).

With this approach free-form ablation zones are generated providing correction of refractive error and HO Aberrations with a ~50%reduction of ablation volume.

Moreover compromised tissue is preserved. With the proposed approach it is possible to treat patients, also with pathological corneas and extremely irregular corneas, since the ablation depth at the critical location(s) is preset in the input parameters. In all cases the simulated post-ablation corneas suggest strong improvements in regularizing the cornea and adequate curvature changes following the intended plan.  Despite the large amounts of tissue saved in all examples, the simulated post-ablation corneas are very comparable to the simulated conventional topo-guided treatment.

With this approach free-form ablation zones are generated providing for a tissue-saving correction of refractive error and partial correction of high order aberrations, the overall corneal shape will be recentred and the corneal curvature gradient is reduced. We have shown cases of pathologic corneas, but the clipped topography could be used for normal corneas and retreatments too (without “any” compromise, but presumably without any “gains” either). The treatment could be planned by setting the maximal depth at one or two locations “beforehand” and get the (free-form) optical zone as a result. With this information it is possible to decide, if the treatment is possible or the optical zone is too small related to the pupil diameter.