Of all the possible complications that may arise in LASIK surgery, the most unpredictable one is infection. Studies conducted worldwide have found that on average, the rate of infection is 1 in 5,000 cases. To minimise such an occurrence, aseptic procedures must be adhered to and the procedure must be carried out in a sterile environment. Strong antibiotic eyedrops are also prescribed after the operation to prevent infection. The first post-operative visit one day after surgery is for the ophthalmologist to check if any infection has occurred.
Creating the corneal flap is one of the most important parts of LASIK surgery. Flaps made with poor technique and old instrumentation (such as blunt or re-used microkeratome blades) can lead to the flap being torn or shredded. No microkeratome blade should be used more than once. However, some LASIK centres use a single blade for a patient’s left and right eye to save costs.
A rare complication that may occur during surgery is a free cap. In this instance, the patient’s corneal flap may be accidentally cut off. Some of the reasons for this happening could include the loss of suction and fixation of the eye, unnecessary pulling on the eye by the surgeon or a
sudden movement by the patient. Experienced surgeons are able to deal with this complication. No stitches are usually required to rectify this complication. The cap is placed back in position, and allowed to dry and adhere back onto the corneal bed surface. After 24 hours, the chance of a cap being lost are negligible. Should a cap be lost, severe scarring and poor visual acuity will result. This can only be rectified by complicated corneal transplant surgery with the aid of a donor eye. It is nearly impossible to create a free cap using the femtosecond laser because with this method of flap creation, the size of the flap and hinge are extremely precise and consistent.
In rare cases, epithelial cells (the most superficial layer on the surface of the cornea) may deposit under the corneal flap. These cells can sometimes multiply and obscure vision. The deposit of such cells has no detrimental effect to the patient, both vision-wise and to the eye itself if they are removed quickly. Fortunately, they can be easily removed by lifting the flap and flushing the cells out.
Corneal ectasia is a complication of LASIK surgery which usually occurs when excimer laser ablation removes too much corneal tissue. A minimum of 250 microns should be left in the bed of the cornea under the LASIK flap. Unfortunately, mechanical microkeratomes are less predictable and occassionally inadvertently make a thick corneal flap. This results in a thin corneal bed. If not measured and adjustments are not made to the excimer laser ablation, the corneal stromal bed is thinned below the 250 micron limit.
This weakened cornea may initially give good results, however the cornea continues to weaken and bulge forward. This results in a condition called corneal ectasia which resembles a pathological condition called keratoconus (see Keratoconus, page 41). Fortunately there is now a new procedure available called Corneal Collagen Crosslinking which can help strengthen these weakened corneas.