What are the chances of failure of LASIK?
This question is a good one and is asked by many. Everybody considering LASIK should carefully consider the answer because the results are going to largely permanent.
I am not sure what you mean, though, by “failure rate.” Blindness? Still having to wear glasses full-time? Part-time? 20/20 visual acuity but still not happy with the results? With respect to that first, most dreaded outcome, “blindness” -not telling night from day-is as far as I know completely unknown. That does not mean everybody is happy and satisfied, though. It is possible to have even better than 20/20 distance visual acuity and not be happy.
It is important to realize that LASIK does not cure presbyopia, the near vision problem that comes with middle age. The cause of presbyopia is the aging degeneration of the natural lens inside the eye and LASIK by definition is a treatment to the cornea, the front surface. You need to understand the difference, especially if you are over 40. The aging lens problem only gets worse with time, so if you are over 50, LASIK is probably not the right thing to do to improve vision.
The most common problem with LASIK is dry eye. Everybody gets this, if only mildly and temporarily. It is caused by the damage to the sensory nerves of the cornea by the procedure. The lacrimal glands, while fully functional, will be getting a muted signal from these nerves and so will not be producing the full volume of tears the eye actually needs. While this typically gets better after 3–6 months as the nerves regenerate, your tearing will never return completely to normal. While this is rarely an issue long-term, people with any sort of chronic dry-eye issue (e.g. arthritis) should exercise caution.
The most unsettling issue, while still extremely rare, is the creation of optical aberrations that were not present with contact lenses or glasses, e.g. circles around lights at night, “ghost” images of overlapping images, and others. Fortunately, the technology of most up-to-date lasers have solved these problems, but they can still occur on rare occasions.
Overall, LASIK is one of the most successful and satisfyingly elective things you can do surgically to improve your quality of life. But it is important to realize it IS surgery and should be approached with a full understanding of what it can and cannot do.