Combining refractive and topographic data in corneal refractive surgery for astigmatism: a new method based on polar value analysis and mathematical optimization.

PURPOSE: To provide a theoretical approach for combining refractive and topographic data in the planning of corneal laser refractive surgery for astigmatism.

METHODS

Refractive and topographic data for astigmatism were transformed to the corneal plane. Net astigmatisms were converted to polar values. An optimization process was performed with the use of differential calculus.

RESULTS

With this method, the magnitude of the corneal astigmatism is reduced or unaltered, while its orientation is maintained. The method identifies the reduction in corneal astigmatism, which will yield the largest reduction in refractive astigmatic magnitude.

CONCLUSIONS

The advantage of the optimization method described in this article is a consistent reduction in corneal astigmatism towards sphericity. No new corneal astigmatism is carved on the cornea, and probably less tissue is ablated. The optimization method may also be used to combine refractive and topographic data for higher order aberrations with sinusoidal components. However, compared to the traditional purely refractive driven treatment, more refractive astigmatism will remain in the eye in most cases. A controlled clinical trial is necessary for comparing these two treatment modalities.