Mixed astigmatism means in which one meridian is hyperopic and the other meridian is myopic, which are caused by the unequal curvature of the cornea. Usually the LASIK can treat mixed astigmatism. However, the effect may not be as good as you expect for the surgery of the simple nearsighted astigmatism. You'd better talk to your doctor about the detail of the LASIK.
Mixed astigmatism means two focal lines will not projected in the same part. One of them is projected in front of the retina while the other focal line is projected behind the retina. There are some kind of surgical techniques can treat mixed astigmatism. You can consult your eye doctor for detailed information.