The intrastromal LASIK technique
This term is an abbreviation for Laser Assisted In situ Keratomileusis, and it is currently the reference technique in refractive laser surgery (nearly 80% of laser surgeries). It was introduced in France in the early 1990s, subsequent to the introduction of Excimer laser surface ablation de surface (PRK).
The technique essentially consists in two steps: cutting out a thin corneal lamella (between 100 and 130µ) followed by Excimer laser treatment of the vision defect, whether it be myopia, hypermetropia, astigmatism or presbyopia, by sculpting the cornea into a new shape.
While the advantages of Lasik in comparison to the other surface technique (PRK) are numerous, it is preoperative testing that will determine the possibilities and, more precisely, possible contraindications for a given technique (fine and/or asymmetrical corneas, keratoconus…). Middle and long-term (after 2 months) visual results are identical, but Lasik allows for more rapid visual recovery.
There exist two ways to cut out a corneal lamella (flap); one is mechanical, with an automated apparatus (microkeratome), and the other is femtosecond laser.
The first can be studied with the benefit of hindsight; tens of thousands of eyes have been quite satisfactorily treated throughout the world for more than fifteen years. The second, which has been chosen by the Poitiers CHU, more recently arrived in France (in summer 2004, when the first centers were equipped); it is more precise (diameter and thickness of the cap) and more reassuring for the patient (“100% laser treatment”) with an even lower risk of incidents when cutting the corneal lamella. The working routine of a given surgeon and preoperative testing (particularly as regards corneal thickness) will determine the most appropriate technique. That much said, numerous international studies have proven that there exists no difference between the two cutting methods in terms of quality of results (effectiveness, stability, absence of side effects…).
In both cases, the operation itself is quite rapid and painless: less than twenty minutes for the two eyes by Lasik using a mechanical cutting tool, and less than thirty minutes by Lasik with laser cutting. In both techniques, the two eyes are operated at the same time under local anesthesia with simple eye drops.
After surgery, during the wound-healing phase, the eye itches, stings and tears for several hours (4 to 5 maximum); the day after, vision is good. Total correction may take several days, especially in corrective treatments for hypermetropia and presbyopia. If at the end of the normal wound healing period (from 1 to 3 months), the visual result is not complete, particularly in cases of severe visual defects, it will be possible to proceed to a second operation to correct the residual visual defect (re-operation rate lower than 15%, all cases included).
Side effects are mainly characterized by a variable degree of ocular dryness (especially in women over 50 years of age), refractive regression (for less than three months) and possible nocturnal halos (especially for severe myopia in patients with large pupils, which are also associated with refractive regression (for one to four months).
Individualized, customized laser, guided by aberrometry or topography
Individualized laser is a means of delivering laser beams (through Lasik or surface treatments) facilitating treatment of patients with an atypical but non-pathological cornea (asymmetrical astigmatisms, for example) and presenting, independently of their refractive disorder, preoperative disorders pertaining to quality of vision (halos and glare). For the purposes of preoperative detection in patients liable to derive benefit from this treatment, it is indispensable to use the diagnostic tools known as wavefront sensors or aberrometers (Zywave or OPD-Scan). This treatment is also useful in cases of previous decentered treatment (re-treatment). “Customized” treatments are currently overvalued; studies have shown that only 5% of patients could achieve enhanced visual comfort using this tool.
Risks, side effects and recommendations common to laser surgeries
It is indispensable to indicate that as with any other surgery, risks exist.
The technological development of lasers and the experience of surgeons have nonetheless reduced their frequency to a considerable extent. As a result, the prevalence of significantly damaged vision (the risk of a lost eye is all but theoretical, only a few cases having been described in the literature, even though several million patients having been treated) is approximately 1/1000.
There exist three main categories of complications:
- The first is associated with a problem of (Lasik). In certain cases the flap may be incomplete or less than perfect, which means that surgery has to be postponed for one to three months to assure satisfactory flap healing. This complications is hardly bothersome; all it does is postpone surgery.
- The second is associated with the laser beam: decentering. However, this complication has become even more exceptional with the arrival of new machines characterized by highly effective eye pursuit: eye-trackers. More often than not, the patient achieves satisfactorily corrected visual acuity, but it is accompanied by some degree of discomfort (perception of halos, glare, double image). In these cases, it is necessary to re-treat the patient in view of rendering his cornea more symmetrical (specific “Topolink” software).
- The third complication is inflammation-infection. Its risk is reduced by systematic use of antibiotic and anti-inflammatory treatments.
In addition, there are some possible side effects:
- Ocular dryness: It can be observed over a transitory period ranging from fifteen days to three months. Visual acuity tends to fluctuate during the day. To diminish this side effect, artificial tears are systematically prescribed. It is particularly frequent in women over 50 years of age.
- Perception of halos, glare : At times there appears a perception of halos in poorly lit environments during the night, especially in patients with a sizable visual defect and young patients with large pupils. The halos diminish with wound healing and in time, totally disappearing over a period ranging from one to three months.
The recommendations are very simple
No recommendation is given prior to surgery, except to avoid wearing contact lenses on the day of the operation — and women should not be wearing make-up.
Some physicians prescribe local treatment during the three days preceding surgery (antiseptics, antibiotics). On the day of surgery, after the operation, the patient should stay home and do nothing. Over the following ten days, it is highly preferable to avoid all aquatic activity.