One of the risks of LASIK is loss of vision or loss of best spectacle corrected vision, due to:

1. infection, scarring or other causes, which is not successfully controlled by antibiotics, steroids or other necessary treatment;
   
   
2. the cornea healing irregularly or decentration of the laser treatment zone, which could induce astigmatism and make wearing spectacles and/or contact lenses necessary.
   

It is also possible that the patient may not be able to successfully wear contact lenses after LASIK.

Other possible complications and side-effects of LASIK are:-

1. difference in power between the two eyes (anisometropia);
   
   
2. difference in image size between the two eyes (aniseikonia);
   
   
3. double vision;
   
   
4. hazy vision;
   
   
5. fluctuating vision during the day and from day to day;
   
   
6. increased sensitivity to light which may be incapacitating for some time and may not completely go away; and
   
   
7. glare, starbursts, multiple images and halos around lights which may not completely go away.

Some of these conditions may affect the patient’s ability to drive, judge distances and function in dim light conditions. It is advisable that the patient drives only when he/she is certain that his/her vision is adequate.

It is possible that LASIK may not give the patient the result he/she desires. It may result in:-

1. under-correction, in which case an enhancement surgery may be considered if appropriate;
   
   
2. over-correction, in which case an enhancement surgery may be considered if appropriate;
   
   
3. regression of the initial results over time.

The continued use of spectacles or contact lenses may be necessary. Enhancement procedures could be considered in some but not all cases.

It is possible that the corneal flap created may be irregular, too small, too thin or completely detached from the cornea (free flap), or a buttonhole may occur in the flap, in which event the surgeon may choose not to proceed with the laser treatment.

The flap that is created during LASIK may slip or dislodge, and if this occurs, it will need to be repositioned. Small folds may also occur in the flap causing a blurring of vision and a reduction in or loss of best spectacle-corrected vision. These folds can usually, but not always, be removed  by lifting and smoothing out the flap. 

Generally, flap problems do not have a permanent effect on vision, but they can sometimes cause a decrease in spectacle-corrected vision, haziness of vision or scarring of the cornea, leading to a decrease in quality of vision and/or glare.

A rare but severe complication of LASIK is corneal ectasia in which the cornea, following LASIK, progressively thins and becomes architecturally unstable. This can lead to loss of best corrected vision which may require wearing of rigid gas permeable or hard contact lenses or even further corrective surgical procedures including partial thickness or full thickness corneal transplants using donor corneas.

Epithelium is a thin layer of cells covering the surface of the cornea. These cells normally grow back over the flap after surgery. However, they sometimes grow under the flap instead (epithelial ingrowth) and this can cause blurring or distortion in vision, irritation, light sensitivity or glare. Epithelial ingrowth is usually treatable by lifting up the flap and removing the cells. However, this can recur after treatment.