A novel fitting algorithm for alignment curve radius estimation using corneal elevation data in orthokeratology lens trial.

PURPOSE

To evaluate a novel fitting algorithm for estimation of alignment curve (AC) radius during orthokeratology lens trial.

METHODS

Fifty myopic children were recruited in this study. AC radii were estimated by both traditional method using flat K readings and eccentricity values and by a novel fitting algorithm, which was composed of 256 circle fittings using corneal elevation data from the corresponding AC region and a succedent toric fitting based on these calculated AC curvatures. Parameters of the final ordered lenses were determined by fluorescein analysis and corneal topography. The number of lens trials was recorded for each patient, and the consistencies of AC radius and astigmatism between the first trial lenses and the final ordered lenses were tested by Pearson correlations and Bland-Altman plots.

RESULTS

The numbers of trials for the novel algorithm and traditional method were 1.2±0.4 times vs. 1.8±0.7 times, respectively, and Mann-Whitney test showed significant difference (z=-3.27, p=0.001). AC radii of the first trial lenses estimated by the novel fitting algorithm were more close to that of the final ordered lenses, showing a R square value of 0.994 for the fitting algorithm and 0.927 for the traditional method, respectively. Similar results could also be noticed for astigmatism estimation.

CONCLUSION

AC radius and astigmatism of ortho-k lens could be better estimated by two steps of fitting algorithm using corneal elevation data, which may shorten the time needed for ortho-k lens trial and achieve better lens fitting status.