You can deduct it if it is to correct "defective vision". LASIK is mentioned by name at http://www.irs.gov/pub/irs-drop/rr-03-57.pdf
as being for the correction of bodily disfunction and therefore a legitimate medical expense that may be deducted. For tax purposes, "cosmetic" surgery is surgery that is to make you look better to others (facelifts, breast implants, etc.), not surgery to help you see normally.
a. "You can include in medical expenses the amount you pay for eye surgery to treat defective vision, such as laser eye surgery or radial keratotomy. "
b. "...laser eye surgery is allowed under § 213(d)(9) because the surgery is a procedure that meaningfully promotes the proper function of the body. Vision correction with eyeglasses or contact lenses qualifies as medical care. See Rev. Rul. 74-429, 1974-2 C.B. 83. Eye surgery to correct defective vision, including laser procedures such as LASIK and radial keratotomy, corrects a dysfunction of the body. Accordingly, the cost of the laser eye surgery is an expense for medical care within the meaning of § 213(d) that B may deduct under § 213 (subject to the limitations of that section)."
c. You can deduct "Surgery to improve defective vision, such as laser eye surgery".
d. "The cost of items such as false teeth, prescription eyeglasses or contact lenses, laser eye surgery, hearing aids, crutches, wheelchairs, and guide dogs for the blind or deaf are deductible medical expenses."