Laser vision correction is subject to complications. The complication rate is very low and problems can usually be readily treated. Complications will be more common in patients with high amounts of nearsightedness, farsightedness, or astigmatism, because these patients require larger amounts of treatment.
By far the most common complication of laser vision correction is under-correction or over-correction. This occurs because the patient absorbs slightly less or more of the laser energy than anticipated, or because the patient experiences an abnormal healing response. Further laser treatment, known as an "enhancement" or a "touch-up", can then be used, usually resulting in excellent vision without glasses or contact lenses.
Under-corrections and over-corrections are the main reason that all patients do not have perfect uncorrected vision after the initial laser treatment.
About 2% of laser vision correction patients will experience increased optical aberrations, including glare or halos at night. Every person, even if you have never had laser vision correction, to some degree has glare or halos when viewing a bright object against a dark background. Most people are not aware that they have glare or halos. You can demonstrate this to yourself by going outside, away from other lights, and viewing the moon; every person will notice a small glow or unevenness around the edge of this bright object. After laser vision correction, increased glare or halos is common during the first three months of healing. After the initial healing period, only a very small percentage of people will have more glare or halos than prior to the treatment, and a greater number of people will experience a decrease in the glare or halos. Large pupil size in low light in combination with a high amount of correction is more likely to result in increased glare or halos. Use of the newer lasers, with eye trackers and substantially larger treatment areas, has dramatically improved this problem.
Many patients will experience dryness during the first weeks or months following treatment. Dryness is most common in people who have a lot of dryness prior to laser vision correction. Eyedrops or pills are used to control the dryness, which usually resolves by three months after treatment.
Complications affecting the health of the eye are extremely rare, but are possible. During the early healing phase, the eye is susceptible to infection. You will be asked to follow certain instructions, including using antibiotic eye drops. Carefully following these instructions will decrease the infection rate to far below 1%. Even if an infection does occur, use of antibiotic eye drops will almost always control the infection.
Steroid eye drops are very important after laser vision treatment, because they are used to control the healing response. However, if used improperly for too long, these drops can damage the eye by causing cataracts or glaucoma. It is very important to go to all scheduled follow-up appointments, especially if you are still taking steroid eye drops