The most commonly performed refractive surgery procedure is LASIK. During LASIK the laser reshapes the cornea, but since the surface of the cornea is covered by a layer called the epithelium which regenerates rapidly if damaged, this layer must be bypassed to obtain an accurate result.
During LASIK a precise flap is created by a femtosecond laser. This laser creates thousands of microscopic bubbles in a precise manner resulting in the formation of a flap 130 microns thick and does not use a blade as is the case for classic microkeratome LASIK. This flap retains the epithelium intact so that it can be repositioned after the excimer laser corrects the refractive error of the eye. As a result of this, the surface recovers rapidly leading to functional vision after 4 hours and most visual tasks can be performed well the next day.
The femtosecond laser creates the flap when a calibrated cone docks with a suction ring that sits on the eye for 10-20 seconds. This suction ring feels firm against the eye but should not be uncomfortable since the eye is anaesthetised with drops. Whilst the laser creates the flap you will not see anything happening but the vision will be blurred until the procedure is completed. You can expect to be in the theatre for 15-20 minutes and in the building for 90 minutes on the day. Many people are concerned that they will do something wrong during the procedure such as blink or move the eye and that this will affect the outcome. Because of the tracking ability of the laser and the fact that the eye is held open for you, you should not be at all worried about this possibility.
The indications for LASIK are very broad. Mild to moderate myopia, hyperopia and astigmatism can be safely and precisely corrected. To be suitable for LASIK you must have a normal cornea and have sufficient cornea to ensure lifelong stability of the result. A detailed pre-operative assessment can determine suitability. Remember, the laser creates a fixed amount of change in the focus of the eye designed to provide normal distance vision without correction. Once over the age of 40 years, patients should make allowance for the gradual onset of presbyopia and its impact on near vision. This is an important consideration. In LASIK, presbyopia can be compensated for surgically by monovision. Most commonly however, reading glasses are used as the effects of presbyopia impact near visual tasks.
Complications from LASIK are rarely significant but you need to weigh up the potential for adverse events. The most common adverse effects are dry eye and residual refractive error. It is important to be very diligent with the use of lubricant eye drops before and after the procedure. You should expect to be on regular eye drops for a minimum of 3 weeks after the procedure and in a small number of cases for 3 months or more. Patients with pre-existing dry eye will still have this after LASIK. It may be that LASIK is contraindicated if the risk of bothersome dry eye is deemed to be too high.
The eye has individual biomechanical and wound healing properties. Because of this it is possible to have a small residual refractive error after LASIK. Once the eye has finished healing any residual refractive error can be treated with a second procedure to correct this error. This enhancement surgery is complimentary but it is important to consider benefits against any potential risk. The incidence of enhancement surgery increases with higher corrections and also in younger patients with myopia and patients with hyperopia. LASIK should be avoided in patients under the age of 21 years as structural strength of the cornea and stability of the refractive error cannot be safely predicted until this age. Further, before any refractive surgery procedure, stability of the refractive error should be demonstrated for 2 years.
Complications are rare and fall into 2 groups. There are those related to the flap healing and then there are the very rare potentially serious problems of corneal infection and corneal instability. Flap complications consist of:
- Misalignment or shift of the flap;
- Presence of epithelial cells under the flap;
- Inflammation in the flap interface.
The incidence of these flap complications is under 1:1000. With prompt treatment serious consequences are very rare. It is for this reason it is important for you to attend your postoperative consultation the day after surgery.
Corneal instability (ectasia) is now a rare complication seen predominantly in young myopic patients. With the introduction of devices such as the Pentacam (Oculyzer) in the mid 2000s, virtually all patients that have corneal abnormalities known to predispose to the development of ectasia can be detected prior to LASIK. Whilst prevention is the goal, corneal cross linking can successfully arrest the development of ectasia. The consequences of ectasia are recurrence of myopia together with astigmatism to an extent that cannot be corrected with spectacles necessitating the use of contact lens wear.
Corneal infection after LASIK is extremely rare but nevertheless an important complication. Performing the procedure in an accredited theatre environment combined with the use of targeted antibiotic drops minimises the risk greatly.