When treating a patient with preexisting astigmatism, most wavefront-guided LASIK lasers are designed to treat regular astigmatism as determined externally by corneal topography.
2.
In patients who have an element of internally induced astigmatism, therefore, the wavefront-guided astigmatism correction may leave regular astigmatism behind ( a cross-cylinder effect ).
3.
Thus, vector planning offers a better alignment between corneal astigmatism and laser treatment, and leaves less regular astigmatism behind on the cornea, which is advantageous whether irregular astigmatism coexists or not.
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