The three main reasons are as follows.
Firstly,you know, before you take lasik surgery, you need to have your eyes examined to check whether it is apprpproate for you to have such an eye surgery. Wearing contact lens would make your cornea change irregularly, which will have a bad effect on getting the accurate statistic about your eye examination, as well as the result of the surgery.
Secondly,when you wear contact lens, your cornea in fact is under the state of lacking of oxygen, if you have lasik right away, your eyes probably get infected after the surgery.
Thirdly although often cleaned, there lies plenty of bacteria on the surface of the lens, it is quite possible to get your eyes infected by the bacteria during the operation.So from the above potential dangers, it is better not to wear contacts before your surrey.