LASIK or Lasik (laser-assisted in situ keratomileusis), commonly referred to simply as laser eye surgery, is a type of refractive surgery for correcting myopia, ...
- The incidence of flap complications has been estimated to be 0.244%. Flap complications (such as displaced flaps or folds in the flaps that necessitate repositioning, diffuse lamellar keratitis, and epithelial ingrowth) are common in lamellar corneal surgeries but rarely lead to permanent visual acuity loss; the incidence of these microkeratome-related complications decreases with increased physician experience. According to proponents of such techniques, this risk is further reduced by the use of IntraLasik and other non-microkeratome related approaches, although this is not proven and carries its own set of risks of complications from the IntraLasik procedure.
- A slipped flap (a corneal flap that detaches from the rest of the cornea) is one of the most common complications. The chances of this are greatest immediately after surgery, so patients typically are advised to go home and sleep to let the flap heal. Patients are usually given sleep goggles or eye shields to wear for several nights to prevent them from dislodging the flap in their sleep. A faster operation may decrease the chance of this complication, as there is less time for the flap to dry.
- Flap interface particles are another finding whose clinical significance is undetermined. A Finnish study found that particles of various sizes and reflectivity were clinically visible in 38.7% of eyes examined via slit lamp biomicroscopy, but apparent in 100% of eyes using confocal microscopy.
 Early postoperative complications
- The incidence of dry eye varies widely from research studies. A study by Hovanesian et al. reported that 48% of patients experienced dry eye symptoms at 6 months period post surgery.
- The incidence of diffuse lamellar keratitis (DLK), also known as the Sands of Sahara syndrome, has been estimated at 2.3%. DLK is an inflammatory process that involves an accumulation of white blood cells at the interface between the LASIK flap and the underlying corneal stroma. It is most commonly treated with steroid eye drops, and sometimes it is necessary for the eye surgeon to lift the flap and manually remove the accumulated cells.
- The incidence of infection responsive to treatment has been estimated at 0.4%. Infection under the corneal flap is possible. It is also possible that a patient has the genetic condition keratoconus that causes the cornea to thin after surgery. Although this condition is screened in the preoperative exam, it is possible in rare cases (about 1 in 5,000) for the condition to remain dormant until later in life (the mid-40s). If this occurs, the patient may need rigid gas permeable contact lenses, Intrastromal Corneal Ring Segments (Intacs), Corneal Collagen Crosslinking with Riboflavin or a corneal transplant.
- The incidence of persistent dry eye has been estimated to be as high as 28% in Asian eyes and 5% in Caucasian eyes. Nerve fibers in the cornea are important for stimulating tear production. A year after LASIK, subbasal nerve fiber bundles remain reduced by more than half. Some patients experience reactive tearing, in part to compensate for chronic decreased basal wetting tear production.
- The incidence of subconjunctival hemorrhage has been estimated at 10.5% (according to a study undertaken in China; thus results may not be generally applicable due to racial and geographic factors).
 Late postoperative complications
- The incidence of epithelial ingrowth has been estimated at 0.1%.
- Glare is another commonly reported complication of those who have had LASIK.
- Halos or starbursts around bright lights at night are caused by the irregularity between the lasered part and the untouched part. It is not practical to perform the surgery so that it covers the width of the pupil at full dilation at night, and the pupil may expand so that light passes through the edge of the flap into the pupil. In daytime, the pupil is smaller than the edge. Modern equipment is better suited to treat those with large pupils, and responsible physicians will check for them during examination.
- Late traumatic flap dislocations have been reported 1–7 years post-LASIK.
- Dry eye or in severe cases Chronic Dry eye. Due to nerves that are severed during the Lasik operation (around 70% of corneal nerves are severed), the lubrication system of the eye is affected and nerves may never recover to pre-operative condition. This may leave the patient with potential permanent dry eyes.
LASIK and other forms of laser refractive surgery (i.e. PRK, LASEK and Epi-LASEK) change the dynamics of the cornea. These changes make it difficult for your optometrist and ophthalmologist to accurately measure your intraocular pressure, essential in glaucoma screening and treatment. The changes also affect the calculations used to select the correct intraocular lens implant when you have cataract surgery. This is known to ophthalmologists as "refractive surprise." The correct intraocular pressure and intraocular lens power can be calculated if you can provide your eye care professional with your preoperative, operative and postoperative eye measurements.
Although there have been improvements in LASIK technology, a large body of conclusive evidence on the chances of long-term complications is not yet established. Also, there is a small chance of complications, such as haziness, halo, or glare, some of which may be irreversible because the LASIK eye surgery procedure is irreversible.
The incidence of macular hole has been estimated at 0.2 percent to 0.3 percent. The incidence of retinal detachment has been estimated at 0.36 percent. The incidence of choroidal neovascularization has been estimated at 0.33 percent. The incidence of uveitis has been estimated at 0.18 percent.
Although the cornea usually is thinner after LASIK, because of the removal of part of the stroma, refractive surgeons strive to maintain the maximum thickness to avoid structurally weakening the cornea. Decreased atmospheric pressure at higher altitudes has not been demonstrated as extremely dangerous to the eyes of LASIK patients. However, some mountain climbers have experienced a myopic shift at extreme altitudes.
Myopic (nearsighted) people who are close to the age (mid- to late-forties) when they will require either reading glasses or bifocal eyeglasses may find that they still require reading glasses despite having undergone refractive LASIK surgery. Myopic people generally require reading glasses or bifocal eyeglasses at a later age than people who are emmetropic (those who see without eyeglasses), but this benefit may be lost if they undergo LASIK. This is not a complication but an expected result of the physical laws of optics. Although there is currently no method to completely eradicate the need for reading glasses in this group, it may be minimized by performing a variation of the LASIK procedure called "slight monovision." In this procedure, which is performed exactly like distance-vision-correction LASIK, the dominant eye is set for distance vision, while the non-dominant eye is set to the prescription of the patient's reading glasses. This allows the patient to achieve a similar effect as wearing bifocals. The majority of patients tolerate this procedure very well and do not notice any shift between near and distance viewing, although a small portion of the population has trouble adjusting to the monovision effect. This can be tested for several days prior to surgery by wearing contact lenses that mimic the monovision effect. Recently, a variation of the laser ablation pattern called PresbyLASIK, has been developed to reduce or eliminate dependence on reading glasses while retaining distance vision