Laser in situ keratomileusis (LASIK) represents a safe and effective treatment for refractive errors (primarily myopia, hyperopia and astigmatism). Both a combination of technological advances and increasing surgeon experience has resulted in improved refractive outcomes and reduced complication rates.
But although LASIK is an effective and safe procedure for the right patient, the possibility of developing postoperative complications is always present. Still, a large number of intraoperative complications are potentially preventable with appropriate preoperative and intraoperative precautions and careful maintenance of surgical instruments.
Flap-related complications are most common intraoperative complications following LASIK surgery. An incomplete flap is reported in 3% of cases, and it can occur when the smooth passage of the microkeratome (precise instrument with an oscillating blade) is obstructed within the surgical field. Other significant causes are the intraoperative loss of suction, electrical failure, accidental release of the vacuum and damage to the microkeratome.
Thin flaps and buttonholes can result from application of inadequate suction, irregular corneas and poor blade quality. These flaps are cumbersome to manipulate as they are more likely to wrinkle, and a buttonhole flap is often detected after the reverse pass of the microkeratome. The complication can be reduced or avoided by proper preventive maintenance of the microkeratome.
Corneal perforation represents a devastating intraoperative complication during creation of the flap. A poorly secured blade of microkeratome can perforate the cornea (with subsequent damage to the underlying lens and iris), but it has also been seen during laser ablation. Today it represents a rare event, as modern instruments tend to use fixed depth plates.
Early postoperative complications
In the first 24 hours after LASIK surgery, flap dislocation can occur as a result of mechanical disruption. Significant pain and severely reduced vision are common signs of the condition. Such dislocated flap should be repositioned as soon as possible in order to prevent formation of fixed folds and epithelial ingrowth.
Flap striae after LASIK can occur in up to 3.5% of patients – more common than full flap dislocations. They are a result of misalignment of the flap, and can be classified into macrostriae and microstriae. Gentle flap manipulation is shown to decrease the incidence of striae, and additional treatments (such as suturing) are required for persistent striae.
Epithelial trauma at the time of surgery can lead to the proliferation of epithelial cells into the space between the stromal bed and the flap, which in turn may result in epithelial ingrowth. Important risk factors for this condition are peripheral epithelial defects, poor flap adhesion or its perforation and free cap.
Albeit rare, infections are potentially vision-threatening early postoperative complications of LASIK. Most of them are acquired intraoperatively, although some of them are caused by postoperative contamination. The incidence ranges from 0 to 1.5%, and they typically presents within 72 hours after surgery. The usual common symptoms are increased light sensitivity, redness, pain and loss of vision.
Late postoperative complications
The coordinated action of the cornea, conjunctiva and accessory lacrimal glands in normal tear function is vital to the healthy functioning of the eye. Post-LASIK dry eye syndrome represents one of the most common late postoperative complications of this procedure. The main risk factors implicated in this complication are preoperative eye dryness and chronic ocular surface inflammation.
Chronic tear dysfunction is a subset of the Post-LASIK dry eye syndrome and can be accompanied by neurotrophic keratopathy or neuropathic pain. This condition can range from asymptomatic or mild and to severe and debilitating. Injury of the epithelium during refractive surgery alters the tear film cytokine levels; LASIK has also been associated with the loss of goblet cell mucin (leading to the tear film instability).
Corneal ectasia is another rare, but serious complication of LASIK which manifests as a progressive corneal thinning in the area of ectasia with unstable topographical steepening. It can ensue even several years after the surgery, and is linked to a reduction of unaided or spectacle-aided visual acuity. Collagen cross-linking is studied as a potential treatment of ectatic disorders and thus far shows significant promise.
Starbursts (glare), ghosting, haloes and double vision are occasionally reported after LASIK. They are often referred to higher-order visual aberrations. Those symptoms usually resolve in time, but sometimes they may permanently affect the quality of vision.