If you’re thinking about laser eye surgery and have done any kind of research either on the internet or through information picked up at your local opticians or eye surgery clinic, you may be familiar with different laser surgery terms such as LASIK, LASEK, PRK, Intralase and Wavefront. Each of these terms describes a slightly different variation of laser eye surgery and the one which is best suited to correcting your vision will depend upon the nature and complexity of your visual impairment and upon your personal preference. So how does laser eye surgery work?
Well, although there are now different technologies and techniques to choose from, the fundamental way in which laser eye surgery works remains the same for all of them. Laser eye surgery is concentrated on the eye’s cornea; the transparent, convex ‘window’ at the front of the eye which covers the iris and pupil and which is responsible for around two-thirds of the eye’s focussing capability. Visual impairments, whether related to long-sightedness, short-sightedness or astigmatism occur as a result of the light which enters the eye being incorrectly focused on the retina at the back of the eye. Laser eye surgery reshapes the cornea in whichever way is appropriate to ensure that light is correctly focused on the retina. To correct long-sightedness the laser will increase the curvature of the cornea and for short-sightedness the laser will flatten the cornea. In astigmatism, the natural curvature of the cornea resembles the elongated curvature of a rugby ball, whereas a normal cornea possesses the uniform curvature of a football. Laser eye surgery can be used to reprofile an astigmatic cornea to provide as uniform an overall curvature as possible.
LASEK / LASIK
In each of these cases, laser eye surgery works by removing corneal tissue beneath the surface layer to achieve the appropriately reshaped cornea. In LASEK laser eye surgery, the outer corneal layer (the epithelium) is softened and loosened by the application of an alcohol solution. It is then moved to one side exposing the lower layer of corneal tissue. LASEK surgery is normally used for the 10% of patients who have an unusually thin cornea and are therefore unsuitable candidates for the more commonplace LASIK laser eye surgery. LASIK involves the cutting of a hinged flap in the cornea using a fine surgical blade known as a microkeratome. The hinged flap is folded back to reveal the tissue beneath.
Once the tissue beneath the upper corneal layer has been exposed, a highly accurate laser is used to vapourise sections of it in order to reshape the cornea appropriately. Depending upon the type of laser eye surgery used, the epithelium or the hinged flap is then replaced and the cornea is allowed to heal. LASEK patients will require a slightly longer recovery period (three to four days) and may experience more discomfort than LASIK patients, who typically recover within 48 hours of surgery.
Intralase laser eye surgery works in the same way as LASIK with the exception that the incision to create a hinged corneal flap is made with another laser rather than with a surgical blade. Wavefront technology can be applied both to LASEK and LASIK laser eye surgery and provides a more accurate ‘map’ of the corneal surface of the eye using twenty-five independent measurements. This more detailed profile of the cornea provides an increased likelihood of 20/20 vision being restored following laser eye surgery but also increases the cost of the operation.
Once the eye has healed following laser eye surgery the reshaped cornea should once more accurately focus light onto the retina, correcting the former visual impairment and removing the need for visual aids such as spectacles and contact lenses.