For a long time, spectacles were the only solution for correcting visual deficiency. One alternative has been contact lenses, a method developed over many years.
Nowadays however, apart from the optical solutions, there are other possibilities to correct refractive defects such as innovative refractive surgery (LASIK, PRK, artificial lens implants, etc.).
With the LASIK, PRK, LASEK or EpiLASIK methods, thanks to laser energy, the curvature of the cornea is modified to achieve correct refraction, as in the case of a healthy eye. This is known as “surface” eye surgery because it only affects the cornea.
The implantation of artificial lenses is another surgical option performed at intraocular level, known as non-corneal refractive surgery.
LASIK (Laser-Assisted In Situ Keratomileusis) is the most commonly used method in refractive surgery. The results are predictable and the postoperative phase is quick and painless. Hospitalisation is not required, because the anaesthetic used is topical (drops) and the operation is very short.
A fine layer or flap is cut in the cornea using an instrument called a microkeratome to enable application of the treatment to the desired corneal layer, called the stroma. The flap is moved to one side and an excimer laser is applied to modify the curvature of the cornea, thereby correcting the myopia, hypermetropia or astigmatism. Finally, the flap is replaced to its original position, sticking to the cornea without the need for stitches.
The accuracy of laser treatments has been constantly improved on over the years. Today, instead of cutting the flap with a microkeratome, an instrument called a femtosecond laser is used, which offers major advantages and makes this initial step of the surgery considerably easier.
Additionally, through the use of precise diagnostic instruments it is possible to perform wavefront or optimised treatments, which can correct minor individual abnormalities and do not have an impact on sensitivity to contrast after the operation.
In some cases, such as when the number of dioptres is very high or the corneal thickness is too fine, it is not recommended to use this technique and another such as PRK, LASEK or even intraocular lens implant is used.
The arrival of Intralase or “femtosecond laser” to refractive surgery has resulted in a considerable improvement in operations of this type, as it offers greater precision when cutting the flap. This not only used in refractive surgery, but also in cataract surgery (
). The role of this laser is to cut the corneal epithelium without the need to use a microkeratome or any other manual tool, as is the case with LASIK, PRK, LASEK, etc. This makes it possible to exactly program the desired thickness, depth and diameter to obtain an optimum result that is personalised for each patient. Post-surgical risks are also minimised in this procedure.
In this surgery, two lasers are used. The first is a femtosecond laser, used in the first phase of the operation to lift a fine superficial corneal layer, in other words, the flap. This is where the improvement lies because it is much more precise, the cut is made with fewer irregularities than with the microkeratome and it is also possible to program the desired thickness of the flap. From this point on, the surgery is performed with the same method used in LASIK, with the laser applied and the rest of the procedure remaining the same.
PRK surgery consists of manually removing a fine epithelial layer which is then regenerated during the postoperative phase. The recovery time is longer than with other procedures but it is a very good option even today for patients with very fine corneas. The excimer laser acts on the corneal tissue in the same way as it does in other techniques, to modify its curvature. The only difference can be found in the first step. This procedure is also called “surface treatment”. After this type of surgery, the patient must wear a therapeutic contact lens for a period of time to aid healing and regeneration of the epithelial tissue. The side effects after PRK, such as dry eye, are much more infrequent than after LASIK.
In the LASEK (Laser-Assisted Sub-Epithelial Keratectomy) technique the form of excision of the epithelial layer is different to that used in PRK. In this case, the superficial epithelial layer is removed with an alcohol solution and moved to one side. The same steps as in the LASIK procedure are then performed, as the epithelial tissue is put back in place. Visual recovery is quicker than with PRK.
Epi LASIK is a variation of the LASIK procedure in its first step. Instead of using a microkeratome, an “epi-keratome” (semi-automatic blade) is used to be able to detach only the first layer of the cornea, the epithelium. Once separated, the surgeon uses the traditional laser method to mould the cornea. After this surgery, a therapeutic contact lens is inserted to aid recovery and healing. Like PRK and LASEK, this technique is ideal for fine corneas.
Other options in refractive surgery are intraocular lenses in the anterior or posterior chamber or refractive lens surgery.