No surgical procedure is completely free of risk. It is not possible to list every complication that can occur. The risks outlined below apply to both PRK and LASIK except where specified otherwise.

Infection and delayed healing

There is about 0.1% 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 effect.

Undercorrection and 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 because of residual myopia, hyperopia, or astigmatism. In many cases, but not all, a second procedure can be done to improve the result.

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 which 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 retreatment is often feasible. Significant regression happens much less often after LASIK than after PRK.

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. However, new technology has greatly decreased or eliminated this problem.

Raised eye pressure

The fluid pressure inside the eye increases, in some patients, as a result of the steroid drops which are used for a few months after PRK. With regular postoperative checkups during the time when steroids are being taken, such a pressure increase can be monitored by a simple measurement and controlled by an adjustment to the patient’s medications. Steroids are generally not used after the first week after LASIK, thus eliminating this risk.

Post-operative shifting of the flap (LASIK only)

For the first year after surgery the corneal flap is somewhat vulnerable to poking or rubbing. Therefore, wearing protective eyewear is important when engaging in sports or other activities in which the possibility of a ball, elbow, fist, or other object striking the eye is high.

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 you 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 eyes. 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.