With LASIK and PRK, the curvature of the cornea is adjusted by means of laser beams. Near or farsighted corneas are flattened and hypermetropic or farsighted corneas are sharpened. This ensures that the light falls sharply onto the retina without the aid of glasses or contact lenses.
Laser treatment of the cornea can correct most of the refractive error:
The state-of-the-art Femtosecond laser first creates a corneal flap in a very controlled manner.
By means of infrared light pulses at a speed of 1 quadrillionth of a second, the cornea is split at a desired depth with an accuracy of 5 microns.
Until recently, all flaps were made with a mechanical microkeratome. This is a small scraper in which a metal blade oscillates back and forth.
The device with the blade is placed on a ring that is firmly attached to the eye by means of a vacuum pump. In this way, a flap can be cut mechanically. The disadvantage of this method is that occasionally a vacuum is lost during the making of the flap, resulting in an incomplete cut or an irregular flap.
Of course, the cutting edge is also less precise than when it is made with a laser that is accurate to 5 microns. However, the results with a mechanical microkeratome are very good and we have worked with this for many years with a high success rate.
The Femtosecond laser technology works much more controlled and safer.
Flap thicknesses are much more predictable and the homogeneity of the cut surface is much greater. Thinner flaps can also be made so that higher refractive errors can be safely treated.
However, treatment with the Femtosecond laser is significantly more expensive, as this high-tech device requires a lot of maintenance and expensive disposable materials per procedure.
After the flap has been lifted, the cornea is sharpened with the Excimer laser. This procedure is virtually painless and allows for rapid recovery of vision.
With this technique, only a superficial layer (the epithelium) of the cornea is detached and opened. The laser treatment is then performed as in LASIK. After the treatment, a contact lens protects the epithelium flap until everything has healed. This technique gives equally good visual results but requires a longer healing time. It is mainly used for thinner corneas. This technique is only rarely used.
This involves loosening and removing the superficial layer of the cornea. This layer heals itself after a few days. It gives the same results as the other treatments, but is slightly more difficult in the initial period.