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Geometric ray tracing for design of customized ablation in laser in situ keratomileusis.

PURPOSE
By means of an individualized optical model of the visual system, a customized surgical correction is proposed to achieve emmetropia and best visual acuity.


METHODS
The study included 64 eyes with myopia or myopic astigmatism that underwent LASIK with the Nidek EC-5000 excimer laser. The mean age was 33 years (19 to 54 yr). Mean myopia was -3.70 D (0 to -7.50 D) and mean astigmatism was -0.90 D (0 to -4.00 D). The model included a personalized Le Grand eye model, a geometric ray tracing process, and a statistical study of postoperative corneal flattening. As a final result, the model provided an interval of corneal radius to be sculpted in the stroma to maximize visual acuity attainable without correction. The mean radius of the interval was used to obtain the sphere-cylinder correction.


RESULTS
In 100% of eyes with 0 to +0.50 D of residual spherical equivalent refraction (n = 39), the sculpted radius was inside the surgical interval and in the 30% of the "non-satisfactory" surgeries (7/25 eyes) the sculpted radius was outside the interval.


CONCLUSIONS
An objective optical method has been developed to obtain a customized ablation for LASIK.