Does LASIK have long term side effects after a few years?
I imagine you mean can there be problems with one's vision or eyes from having LASIK that do not show up until years later. For the most part, if there was good patient selection and an initial good visual result, the answer is "No." Most people with good distance vision from LASIK will stay that way until the natural lens of the eye starts to age enough you develop symptoms of Presbyopia (decreased near vision in middle age). [LASIK alters the focusing power of the cornea, not the lens.] Many people mistakenly attribute a change in their post-LASIK vision to it "wearing off" but this is rarely the case -most changes are due to aging of the lens.
The most common undesirable side-effect is decreased tear production due to the laser's unavoidable damage to sensory nerves while re-shaping the cornea. Within 3-6 months most nerves have regenerated, but there will always be a somewhat decreased level of tear coverage compared to what would be the case with no LASIK.
The most serious long-term problem is corneal ectasia, i.e. instability of the cornea caused by over-thinning it. This is rarely seen nowadays fortunately but can still happen if the doctor does not adequately evaluate corneal structure and/or tries to correct too high a prescription.