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L. M. Gonzalez, J. L. Hernandez-Matamoros, R. Navarro; Multizone Model for Postsurgical Corneas. Analysis of Standard and Custom LASIK Outcomes. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5638. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a model of post-surgical corneas and its application to analyze the outcomes of standard and custom myopic LASIK treatments.
The optical zone (OZ), transition zone (TZ) and periphery are segmented automatically by a clustering algorithm. For each point, we compute three physical magnitudes: Gauss curvature, root-mean-square (RMS) fit error, and distance to the vertex, which are then used as local descriptors in the segmentation. Both pre-surgical and post-LASIK corneal topographies were compared using monozone and multizone models. Three groups of patients (31 eyes) were studied according to the treatments applied: Allegretto (custom), Zyoptix (custom) and PlanoScan (standard).
The multizone model improved the goodness of fit from 2.4 ± 0.7 to 1.2 ± 0.4 µm (post-LASIK). The segmentation permitted us to estimate the diameter, shape and decentration of the different zones. The estimated central ablation (OZ) area was always lower than nominal value (average diameter 6.6 ± 0.3 mm versus 5.5 ± 0.4 mm) and showed elliptical shape (average e = 0.27). In the OZ, curvature radii increased after surgery, and conic constants (-0.41) became positive (+0.29). No significant differences were found between Zyoptix and PlanoScan: Corneal HOA increased by a factor of 2; for Allegretto HOA increased by 3.
The analysis of the three different LASIK treatments showed no improvement of custom over standard treatments. The mutizone model shows a higher fidelity representation of the corneal topography and permits a deeper understanding of the post-surgical cornea.
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