Complications

The incidence of refractive surgery patients having unresolved complications six months after surgery has been estimated from 3% to 6%. The following are some of the more frequently reported complications of LASIK:

Dry eyes

Overcorrection or undercorrection

Visual acuity fluctuation

Halos or starbursts around light sources at night

Light sensitivity

Ghosts or double vision

Wrinkles in flap (striae)

Decentered ablation

Debris or growth under flap

Thin or buttonhole flap

Induced astigmatism

Epithelium erosion

Posterior vitreous detachment

Macular hole

Complications due to LASIK have been classified as those that occur due to preoperative, intraoperative, early postoperative, or late postoperative sources

Preoperative sources of complications

Intraoperative complications

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. This risk is further reduced by the use of IntraLasik and other non-microkeratome related approaches.

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.

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 diffuse lamellar keratitis (DLK), also known as the Sands of Sahara syndrome, has been estimated at 2.3%. When diagnosed and appropriately treated, DLK resolves with no lasting vision limitation.

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%.

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.

Other

Although there have been a number of improvements in LASIK technology, a large body of conclusive evidence on the chances of long-term complications is not yet in place. Also, there is a small chance of complications, such as slipped flap, corneal infection, haziness, halo, or glare. The procedure is irreversible.

The incidence of macular hole has been estimated at 0.2% to 0.3%.

The incidence of retinal detachment has been estimated at 0.36%.

The incidence of choroidal neovascularization has been estimated at 0.33%.

The incidence of uveitis has been estimated at 0.18%

Although the cornea usually is thinner after LASIK because of the removal of part of the stroma, refractive surgeons strive to maintain a minimum thickness in order to not structurally weaken the cornea. Decreased atmospheric pressure at higher altitudes has not been shown to be extremely dangerous to the eyes of LASIK patients. However, some mountain climbers have experienced a myopic shift at extreme altitudes. There are no published reports documenting diving-related complications after LASIK.

Laser in situ keratomileusis increases higher order wavefront aberrations of the cornea. Glasses do not correct higher order aberrations.

Microfolding has been reported as "an almost unavoidable complication of LASIK" whose "clinical significance appears negligible".

Factors affecting surgery

The cornea typically is avascular because it must be transparent to function normally. Its cells absorb oxygen from the tear film. Low oxygen-permeable contact lenses reduce the cornea's absorption of oxygen, which sometimes results in the growth of blood vessels into the cornea, a process known as corneal neovascularization. This can cause a mild increase in inflammation and healing time and some discomfort during the surgery because of augmented bleeding. Although some contact lenses, notably modern RGP and soft silicone hydrogel lenses, are made of materials with higher oxygen permeability that help reduce the risk of corneal neovascularization, patients considering LASIK are cautioned to avoid overwearing their lenses. It is usually recommended that contact lens use be discontinued several days or weeks before the LASIK procedure.

A 2004 Wake Forest University study found that LASIK results are affected by heat and humidity, both during the procedure and in the two weeks before surgery.

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