[LASIK nomogram modifications for the treatment of myopic astigmatism]

The predictability of laser-assisted in situ keratomileusis (LASIK) can be improved by adjustments to treatment nomograms. The aim of this research was to clinically evaluate two different methods of nomogram optimization, to compare them with a reference and to analyze the effectiveness of individual cylinder modifications on the distribution of the postoperative spherical equivalent.

Patients with myopic astigmatism formed three patient collectives and were treated consecutively with LASIK. In total 146 Femto-LASIK procedures were performed with the VISX S 4 excimer laser and the Intralase FS 60 Femto laser. Patients in the first collective (group A) received identical spherical nomogram adjustments, independent of the preoperative refraction. Individual adjustments of the treatment sphere and treatment cylinder in relation to the preoperative manifest refraction, were used for the treatment of a second patient collective (group B). Patients in a third collective were treated with the internal standard nomograms of the excimer laser without further modifications (reference group). The 3 months results were used for the outcome analysis.

Both methods of nomogram adjustment significantly improved the predictability of the postoperative spherical equivalent. Of the attempted spherical adjustment 82% was achieved by group A and 70% by group B. The postoperative astigmatism and spherical equivalent did not show a significant improvement due to the individual adjustments of the treatment cylinder.

A spherical modification of the treatment sphere was effective in the optimization of refractive outcomes for myopic astigmatic patients undergoing Femto-LASIK. The more demanding individual treatment adjustments with cylinder optimizations were safe but not capable of further improvement of the postoperative spherical equivalent distribution.