Medisave is claimable for LASIK or its alternatives (such as advanced surface ablation like LASEK/epiLASIK/ SMILE) if:
1) There is anisometropia, defined as a difference of more than 3 diopters (300 degrees) of the "spherical equivalent" power between the two eyes.
Spherical equivalent is the sum of the sphere (which means short or long sightedness) and half of the astigmatism.
2) It is performed to remedy the refractive error following a previous eye surgery such as cataract surgery.
The amount claimable is usually substantial, but not fully coverable, from my understanding.