What Are the Risks of Laser Surgery?
The risks outlined below apply to both PRK and LASIK procedures. The chances of having a serious vision-threatening complication are minimal, and there have been no reported cases of blindness following either PRK or LASIK, says James Salz, M.D., clinical professor of ophthalmology. However, FDA is aware of a few instances of severe eye injury requiring corneal transplant.

Infection and delayed healing:
There is about a 0.1 percent chance of the cornea becoming infected after PRK, and a somewhat smaller chance after LASIK. Generally, this means added discomfort and a delay in healing, with no long-term effects within a period of four years.

Undercorrection/Overcorrection:
It is not possible to predict perfectly how your eye will respond to laser surgery. As a result, you may still need corrective lenses after the procedure to obtain good vision. In some cases, a second procedure can be done to improve the result.

Decrease in Best-Corrected Vision:
After refractive surgery, some patients find that their best obtainable vision with corrective lenses is worse than it was before the surgery. This can occur as a result of irregular tissue removal or the development of corneal haze.

Excessive Corneal Haze:
Corneal haze occurs as part of the normal healing process after PRK. In most cases, it has little or no effect on the final vision and can only be seen by an eye doctor with a microscope. However, there are some cases of excessive haze that interferes with vision. As with undercorrections, this can often be dealt with by means of an additional laser treatment. The risk of significant haze is much less with LASIK than with PRK.

Regression:
In some patients the effect of refractive surgery is gradually lost over several months. This is like an undercorrection, and a re-treatment is often feasible.
Halo Effect: The halo effect is an optical effect that is noticed in dim light. As the pupil enlarges, a second faded image is produced by the untreated peripheral cornea. For some patients who have undergone PRK or LASIK, this effect can interfere with night driving.

Flap Damage or Loss (LASIK only):
Instead of creating a hinged flap of tissue on the central cornea, the entire flap could come off. If this were to occur it could be replaced after the laser treatment. However, there is a risk that the flap could be damaged or lost.

Distorted Flap (LASIK only):
Irregular healing of the corneal flap could create a distorted corneal shape, resulting in a decrease of best-corrected vision.
Incomplete Procedure: Equipment malfunction may require the procedure to be stopped before completion. This is a more significant factor in LASIK, with its higher degree of complexity, than in PRK.

Problems with a Perfect Procedure:
Even when everything goes perfectly, there are effects that might cause some dissatisfaction. Older patients should be aware that they can't have both good distance vision and good near vision in the same eye without corrective lenses. Some myopic patients rely on their myopia (by taking off their glasses, or by wearing a weaker prescription) to allow them to read.

Such a patient may need reading glasses after the myopia is surgically corrected. Another consideration is the delay between eye treatments. If one eye is being done at a time, then the eyes may not work well together during the time between treatments. If a contact lens is not tolerated on the unoperated eye, work and driving may be awkward or impossible until the second eye has been treated.