Post-operative complications are complications associated with healing that occur after the patient leaves the operating room.

The CRS-USA LASIK Study noted that overall, 5.8% of LASIK patients experienced complications at the three-month follow up period that did not occur during the procedure itself. These complications included corneal edema (0.6%), corneal scarring (0.1%), persistent epithelial defect (0.5%), significant glare (0.2%), persistent discomfort or pain (0.5%), interface epithelium (0.6%), cap thinning (0.1%) and interface debris (3.2%). It is important to note that interface debris - retained metallic particles, lint, etc. under the flap - almost always causes no harm to the health or vision of the eye. None of these complications resulted in a loss of two or more lines of BCVA, and there were no infections amongst the study population.¹

A study of 598 eyes by Knorz et al noted post-operative complications in 0.9% of cases.²

Overcorrection, Undercorrection and Regression

Every eye heals differently. The surgical plan is based upon an average healing response. Patients who are either aggressive or slow healers may experience an under, or overcorrection.³

In addition, the stroma (the thickest part of the cornea and where the laser ablation takes place) may experience some slight remodeling and/or the epithelium (the thinnest and outermost layer of the cornea) may thicken after LASIK. Either of these conditions might result in a slight loss of refractive surgical effect (regression) post-operatively.4 In general, the higher the correction undertaken, the more likely regression is to occur, and this is especially true for treatment of hyperopia greater than +5D.³

In most cases, undercorrection (where the treatment is insufficient to yield the desired change in vision) and regression (where the surgical effect is lost during the healing process) can be treated with an enhancement procedure. An overcorrection of myopia may be corrected by performing a hyperopic LASIK enhancement, whereas a hyperopic overcorrection would in most cases be correctable via a myopic LASIK enhancement. However, eyes with very thin or steep corneas or high degrees of refractive errors may not be eligible for enhancements. Therefore, patients should be sure to speak with their physicians about their potential eligibility for an enhancement.

Diffuse Lamellar Keratitis (DLK)

Diffuse lamellar keratitis is a unique and relatively rare post-operative condition following LASIK. Non-severe forms have been estimated to occur in 1% of cases; severe cases comprise only about 1 in 5,000 surgeries.⁵ A number of names including Sands of the Sahara have been used to describe this condition, which is characterized by an accumulation of inflammatory cells under the flap. The condition usually appears at one to three days after LASIK. However, there have been recent reports of late onset DLK.^6-7 Multiple causes have been hypothesized, but no single explanation accounts for all cases.

Patients should understand that at the early stages of the condition, they most likely will not experience symptoms they would be able to discern, and only upon examination by a doctor could this condition be detected. When caught early, the inflammation associated with DLK is easy to treat. Patients should be aware, however, that while approximately 80% of the condition will clear up within the first 24 to 48 hours, it could take several weeks until the condition completely subsides.

We emphasize that this condition can be treated without significant visual loss when it is detected and treated early. Therefore it is imperative that all patients maintain their surgeon's recommended post-operative follow-up examination schedule.

Flap Folds, Wrinkles & Striae

Usually minor flap striae, or wrinkles in the flap after LASIK surgery, do not interfere with vision. In such cases of visually insignificant flap striae, surgical treatment is usually unnecessary. However, sometimes the striae are serious enough to decrease visual acuity. In such instances, intervention is necessary.

To remove the striae, a surgeon might ift the flap, irrigate beneath it and lay it back down in the proper position. In cases of persistent striae, sutures may be necessary.

According to a study conducted by Drs. Lin and Maloney that considered 1019 eyes, 11 eyes experienced folds in the flap that required repositioning because of poor vision. The mean postoperative time for repositioning was 6 days. In one eye, the folds persisted to the next day, so the flap was repositioned again and sutured.⁸

There are a number of causes of striae. Sometimes, rubbing the eyelids before the flap has had a chance to bond can cause subtle wrinkles. Patients can reduce this risk by avoiding rubbing their eyes for several weeks after surgery. Sometimes, malposition of the flap (laying it down in a different position from where it was lifted) can cause striae. Sometimes, striae form without an apparent cause, and they seem more common in very high myopes than in other patient populations.

Epithelial Ingrowth

Epithelial ingrowth is a condition in which epithelial cells, which normally cover the surface of the cornea, grow beneath the flap.

One study of 1013 eyes demonstrated a 14.7% incidence rate, with 1.7% of eyes requiring surgical removal because it interfered with vision.⁹ Another study of 783 eyes noted only 3 eyes experienced this complication.¹⁰ A study of 589 eyes by Knorz et. al. noted that peripheral epithelial ingrowth occurred in 4 cases (0.6%).²

Most epithelial ingrowth does not affect vision and does not require treatment. In such cases, many doctors will simply leave the ingrowth alone and monitor it at post-operative visits. However, in about 1-2% of cases, epithelial ingrowth occurs within the field of vision or affects an area wide enough to require surgical treatment or removal. Central visually significant epithelial ingrowth can appear as early as 1-2 days post-operatively. However, epithelial cells most often appear at 1-3 months post-operatively. Therefore, it is important that patients attend all follow-up visits with their doctors, especially for the first 6 months post-operatively.

According to a study published by Drs. Wang and Maloney, the incidence of clinically significant epithelial ingrowth after laser in situ keratomileusis (defined as epithelial ingrowth which required surgical removal) was 0.92% after primary treatment (35 in 3,786 eyes) and 1.7% after retreatment (8 in 480 eyes).¹⁰ Central visually significant epithelial ingrowth can appear as early as 1-2 days post-operatively. However, epithelial cells most often appear at 1-3 months post-operatively. Left unattended, the cells that characterize visually significant epithelial ingrowth can release enzymes that melt the flap, causing vision loss.

Sometimes, doctors will prescribe eye drops to minimize the effects, and this protocol will be sufficient. However, at other times a more aggressive approach will be necessary. Removing the epithelial cells is a relatively simple procedure. The ophthalmologist would lift the flap, wipe the underside of the flap with a swab-like sponge, then lay the flap back down. In rare cases where the epithelial ingrowth persists despite such removals, the surgeon may need to use sutures to secure the flap down and ensure that ingrowth cannot occur. According to the Wang and Maloney study, clinically significant ingrowth recurred in 10 of 43 affected eyes after the initial surgical removal.¹⁰