Possible risks of LASIK
Like any surgical procedure, LASIK, LASEK and PRK involve risks of unsuccessful results, complications, or serious injury, from unknown and unforeseen causes. Certain inflammatory conditions can cause corneal inflammation, progressing in rare cases to thinning of the corneal flap; this could result in permanent loss of clarity in the vision, or other visual disturbances as above. Although it is not possible to list every potential risk or complication that may result from the procedure, many of these are described below.
Although the vast majority of our patients experience a significant improvement in their vision, neither your surgeon, nor your optometrist, nor the Centre nor its staff, can promise or guarantee that the procedure will be 100% effective or make your vision better than it was before the procedure. During your pre-operative examination, the likely surgical efficacy outcome (e.g. the chances of you seeing well without glasses or contact lenses after one surgery) will be conveyed to you based on the level of your particular refractive error.
There is a small possibility that the procedure or a complication arising from the procedure could cause your vision to be blurred, doubled, distorted, or have halos or other disturbances, and that these would NOT be correctable with glasses or contact lenses. In the event this should occur, your surgeon will discuss and offer you advice on further treatment, which may involve medications or more surgery. If the outcome cannot be corrected by medications or more external surface corneal surgery, the only way of restoring the vision may be a corneal transplant. However, it is believed that with current techniques and technology, the combined risk of all causes of a corneal transplant being necessary is approximately one in 20,000 or less.
Although it is not possible to list every potential risk or complication that may result from the procedure, many of these are described below.
Halos, Starbursts (more likely after LASIK)
Some patients do not see as clearly at night or in dim light and may notice an optical effect called a "halo" or a "starburst" around lights and illuminated objects after the procedure. Patients who notice these effects may need to wear glasses to drive at night. These effects are for the most part temporary, typically lasting between two weeks and three months. Glare and halo could be permanent, and this would be more likely to occur in patients with high levels of shortsightedness or longsightedness and for patients with larger-than-average pupil size. Halos often result when a patient's night time pupil size is larger than the corneal area treated with the laser. Given the fact that the newest generation of lasers can treat a wider zone, halos now occur much less frequently than in the past.
Under-correction or Over-correction
The exact removal of tissue performed by the laser is overridden in some cases by the healing response of the eye. While the treatment of your refractive error is designed to completely neutralise your refractive error (unless otherwise discussed with your surgeon) this treatment is aimed at the "average" eye. If your eye tends to heal in a different way from the "average," your refraction may result in an over- or under-correction of the refractive error. A patient's tolerance for under-correction or over-correction varies. In the majority of instances, the over- or under-correction can be corrected with glasses, contact lenses or additional surgery. A minority of patients would not be able to safely have laser retreatment, most likely because of insufficient corneal tissue. Your surgeon would in most cases be able to advise you before your initial surgery of the likelihood that you would not have sufficient remaining corneal tissue for retreatments.
Light Sensitivity, Fluctuating Vision
Patients may be extremely sensitive to light and glare or find that their visual acuity fluctuates after the procedure. These conditions are generally temporary and usually go away within one (1) to three (3) months after the procedure, as the eye heals and stabilises. However, in less than approximately 1% of cases, they could be permanent.
If the surgeon performs the procedure on each eye on different days, the eyes may not be able to balance and focus properly until the procedure is performed on both eyes because there will be a power difference between the two eyes.
Equipment Malfunction (in LASIK)
The microkeratome and excimer laser are maintained according to manufacturer specifications. However, despite this regular maintenance, the microkeratome or the excimer laser could malfunction, requiring the procedure to be stopped before completion. In some instances, this could result in a rescheduling of the procedure, or damage to the vision.
Infection, Hemorrhage, Blockage and Other Complications
Other risks include severe infection that cannot be controlled by antibiotics, hemorrhage, corneal swelling, retinal detachment, venous or arterial blockage, cataracts, drug reaction, or other complications. These complications can be minor, temporary problems. There is also a remote risk, estimated to occur in less than 1 in 10,000 cases, of major, permanent conditions, including but not limited to perforation of the cornea, retinal damage, or loss of an eye, which can cause partial or total blindness.
The cornea is living tissue. Once tissue has been removed from the cornea during the procedure, the surface epithelium ("skin") can thicken to compensate for the change in shape that has occurred. This happens to a variable degree among treated patients, accounting for the reason why some patients have a stable immediate result (minimal epithelial thickening) and others regress (more significant epithelial thickening). Regression is more likely to occur in patients with high shortsightedness or Longsightedness. In the majority of cases, the patient can have another laser surgery to improve distance vision. The ability to perform further surgery will depend on safety parameters set by your surgeon. In some cases, it may not be possible to remove further tissue, and the residual refractive error will need to be corrected with glasses and/or contacts.
Increased Pressure in the Eye
The steroid drugs used during the first week after surgery may, in rare individuals, cause increased pressure in the eye. The increased pressure typically drops to normal levels upon cessation of steroid therapy. This raised pressure needs to be closely monitored and may require additional topical and/or oral medications if significantly elevated. It is important for you to attend scheduled follow-up visits to monitor your eye pressure in order to modify the medication schedule as needed.
Fragility on Impact (in LASIK)
For at least three (3) months after the procedure, the corneal flap should be considered fragile to direct trauma. When participating in sports or other activities involving possible contact with the eye during this period, you should wear protective eyewear. In any event, it is advisable to protect your eyes from direct trauma after the procedure as much as possible.
The eyelids have a natural tendency to droop with age. The eyelid speculum that is used in the procedure may hasten this process slightly.
Corneal Ectasia (in LASIK)
A certain amount of corneal tissue must remain under the flap after the laser has achieved tissue removal. This is believed to relate to the long-term stability of the cornea. In rare instances, less tissue is left under the flap than intended. This can have two effects: it can either result in bulging of the cornea thus reversing the intended flattening effect of the treatment, or it can lead to progressive deformity of the cornea with thinning and increasing curvature changes, and the cornea can develop an irregular shape. This progressive corneal deformation is called ectasia, sometimes requiring a corneal transplant in order to restore vision. The probability of ectasia and transplant occurring with currently employed modern technology is estimated to be 1 in 10,000.
Faulty or Improperly Created Flap (in LASIK)
The corneal flap may be too thin, too thick, uneven, and too short, may wrinkle, become displaced or may not heal properly. This condition could be temporary, requiring that LASIK be postponed until the surgeon can create a new flap, or could cause permanent damage to the cornea. The risk that such a flap complication might produce damage to the vision by two or more lines on the vision chart is in the range of 3 to 10 in 1,000. In addition, there is a risk, estimated at 1 in 5,000, that the "hinge" of the flap may be cut off from the cornea (also known as a "free flap"). Free flaps usually allow your surgeon to complete laser treatment, but this is sometimes postponed. Rare patients experiencing free corneal flaps might lose correctable vision, in some cases requiring corneal transplantation. The overall risk of corneal transplantation is less than 1 in 10,000.
Debris under the Flap or Infection under the Flap (in LASIK)
There can sometimes be a small amount of debris or tissue under the flap after the surgeon has completed the LASIK procedure. Debris can result from the instruments used or consist of tear-film oil or floating material. The surgeon may decide in the immediate post-operative period to irrigate beneath the flap to remove this debris. Small amounts of debris can generally be left in place and monitored without surgical intervention. In almost all cases, debris under the flap does not affect the patient's visual result. Infection, on the surface of, or beneath the flap is a rare event, estimated to occur at a rate of one in 10,000. Infection is managed by starting antibiotic eye drops and in most instances, taking cultures of the cornea. Your surgeon might even need to lift the corneal flap to culture and treat the infection. If the infection results in significant scarring of the cornea, a partial or complete corneal transplant may be necessary to restore vision.
Diffuse Lamellar Keratitis or "Sands of the Sahara" (in LASIK)
One in 500 patients experience a temporary inflammatory reaction beneath the flap. This condition has been called "Sands of the Sahara" or Diffuse Lamellar Keratitis (also known as "DLK"). The exact cause of this complication has not been proven, and is likely due to many different factors. Patients with DLK may not show any symptoms at all or may experience blurred vision and tearing, which can last from several days, up to several weeks, which can delay the healing process. DLK can generally be treated with topical and/or oral steroids, occasionally with possible need for surgical intervention (the surgeon irrigates beneath the corneal flap).
The epithelium is the surface layer of cells that protects the cornea as the "skin" over the stromal layer of the cornea. If the epithelium is cut or removed, it generally grows back. In LASIK, the surgeon creates a flap, consisting of epithelium and stroma, and holds the flap back while performing the laser treatment. The epithelium in some people is not as well attached to the underlying stroma; such eyes are at increased risk for epithelial scratches or epithelial sliding, especially as the flap-maker passes over the corneal surface to create the flap. In some cases, we can identify eyes at risk and advise about the increased risks associated with surgery. There are, however, rare patients where there are no pre-operative clues; the likelihood of having a scratch during LASIK with no preoperative warning signs is approximately 1 in 500. In addition, older patients are more likely to have areas of weakened surface epithelium during flap creation. In such instances, the surgeon places a bandage contact lens over the cornea after LASIK to assist in healing and to reduce discomfort. Patients who experience an epithelial slide, abrasion or erosion may experience a longer recovery period and may be at risk for complications including infection, inflammation, recurrent erosions, flap wrinkles or epithelial ingrowth. In the event of a severe epithelial scratch, your surgeon will still typically be able to lift the flap and perform laser treatment. However, he or she may recommend delaying the LASIK procedure on the second eye until the vision has improved in the first eye. This would be the case for the 1 in 500 patients at risk for significant scratches. Your surgeon may recommend against LASIK in the second eye if you are considered predisposed to epithelial scratches. In such cases, LASEK/PRK would be a viable alternative to glasses or contact lenses.
Epithelial Ingrowth (in LASIK)
Epithelial ingrowth is a condition in which epithelial cells from the surface of the cornea grow under the edge of the flap. The vast majority of these cells regress on their own. However, if the cells continue to grow, they can affect the underlying tissue causing astigmatism, flap edge thinning and reduction of vision. This condition is generally treated by medication and observation, although further surgery to remove the epithelial cells from the interface may be necessary. This occurs in less than 1% of cases.
Dry eye is a common, but generally temporary, complication arising from LASIK or LASEK/PRK. This condition can usually be treated with lubricating eye drops and occasionally with temporary inserts or "plugs" that prevent the normal drainage of tears into the nose. Dry eye generally improves within a few months after surgery, but in rare instances can continue for longer periods of time, and may require long-term use of lubricant drops and permanent plugs. Patients who have dry eyes prior to LASIK or LASEK/PRK are likely to experience dry eyes after the procedure.
Vascular Occlusion (in LASIK)
When the suction ring is applied to the eye during the flap-making process, the pressure in the eye increases significantly and many patients will notice that the light will dim or go out completely in the eye. When the suction ring is removed, the vision is restored to the eye within a few seconds. There is an extremely remote risk that when the suction ring interrupts the blood supply to the eye, permanent damage to the retina (the film of the eye camera) or blood vessels in the retina can take place, with loss of vision. This possible occurrence has a theoretical probability of less than one in 1,000,000.
Microscopic Corneal Surface Irregularities (in LASIK)
Microscopic irregularities on the surface of the cornea can cause slight vision loss. The probability of these irregularities increases with the level of prescription treated. In general, a fraction of 1% of patients may lose two lines of vision on the eye chart after the procedure. The chances of losing vision in an eye to a level worse than 20/40 is thought to be 1 in 10,000.
Excessive Corneal Haze (LASEK, PRK)
Corneal haze is part of the normal healing process, and gradually subsides with little or no permanent effect on vision. However, if the haze is excessive or does not go away, the patient may need additional treatment. Haze might be seen in the rare LASIK patient experiencing a significant corneal scratch or erosion. For LASEK/PRK patients, significant haze can occur in patients undergoing high levels of correction (e.g. above 5 dioptres of myopia or above 4 dioptres of hyperopia). To avoid haze formation, you can by advised to use Mitomycin C (MMC) during the surgery for additional fee.