Laser in-Situ Keratomileusis
The technique of LASIK (Laser in-Situ Keratomileusis) is a surgery of the eye. Its principle is to cut a thin strip in the thickness of the cornea (the transparent part of the surface of the eye) to allow an in-depth remodeling of the laser corneal curvature. Its purpose is mainly to correct myopia, but also other optical aberrations as hyperopia, astigmatism or presbyopia (known as "Presb-lasik" by changing the shape of the cornea). This will happen a system of correction (eyeglasses or contact lenses).
Excimer laser
The laser used is "excimer laser." The beam generated by an excimer is located in the ultra-violet. Through this very energy beam, it allows to break the bonds of gaseous molecules (laser photolysis) to make radical. It finds its usefulness in experiments measures kinetic constants of reactions interest atmospheric gas.
Femtosecond laser
If this continues, the advent of the femtosecond laser, which can now make an all-laser surgery, has revolutionized production. The first advantage of this laser was initially able to make finer slices, to make corneal thickness averages, which conventional surgery was sometimes refused.
It soon became apparent that this tool was also huge benefits in terms of security, accuracy in the reproducibility of the corneal cutting and quality of results. Technically, the duration of the intervention is not changed and the operating suites are comparable.
Basic Principles
The operation is done under local anesthesia (by topical drops). The first stage of intervention is cutting a strand corneal surface (90 to 180 m) which is held by a hinge usually 12h.
The laser can then work on an internal area of the cornea (stromal) without altering the membrane Bowman and adjusted by photo-ablation. When the laser intervention (which takes about a minute) is completed, the component is replaced by the surgeon.
Until the early 2000s, the most common way of cutting corneal component is the use of a microkeratome, a mechanical device (miniature plane and very sophisticated), the surgeon applied to the eye. This first phase is very delicate now carried out by a laser, femtosecond laser.
The femtosecond laser now allows a 100% laser. Cutting the strip cornea is then carried out in a few tens of seconds, then removal is performed using excimer laser. The risks connected with the mechanics of the cut are therefore reduced and the characteristics of cutting (angle, thickness, homogeneity ,...) are better controlled.
The Lasek
The Lasek (laser assisted sub-epithelial Keratomileusis) is a hybrid surgical technique applied to the eye that lies between the PKR (photo-refractive keratectomy) and Lasik.
The epithelium, previously prepared with a solution ethanoïque, is off. After action of excimer laser, the epithelium is placed on the cornea.
The Epi-LASIK
The technique of Epi-LASIK (Epithelial-Lasik) is the excimer laser. It is based on the technical Lasek, unlike the posting of the epithelium is via a microkeratome and not ethanoïque as a solution for it.
The ultralasik
LASIK has been almost 15 years the reference to the operations of myopia and other abnormalities of vision as hyperopia, astigmatism and presbyopia.
If the principle of this surgery is not in question, how many have evolved to arrive today to the concept of Ultralasik, which corresponds to the "nec plus ultra" of Lasik technology, which combines:
* An all-laser Lasik in which the cutting of the cornea piece is performed femtosecond laser
* A excimer laser treatment in mode, also called aberrometrique because for the correction of optical aberrations pre-existing. This method of treatment has now demonstrated its interest when astigmatism must be corrected, whether associated with myopia or a hyperopia. It is also interesting when the pupil diameter is large.
The ultralasik generated the concept of Ultravision or supervision, ie obtaining a postoperative visual acuity of up to 15/10 or 20/10 in patients whose acuity was "only" 10 / 10 with glasses before surgery, and thanks to the decrease in optical aberrations preoperative .. Well-understood, such visual results are not systematic, but ultralasik has in any case limit the interest of optical aberrations, and therefore qualitatively act on the vision of the eye surgery. Optical aberrations measured at a high level before surgery to form an argument prefer a Ultralasik.
Finally, this type of treatment, which gives rise before the intervention to achieve a personalized card simply makes it impossible for any error or patient later during the intervention.
Side effects
Side effects (halos, photosensitivity, degeneration of the macula, etc.) Were observed in some patients. They appear in more or less transient, in the days following the operation. A U.S. study has estimated at 6% the number of patients with side effects within six months after the operation. In other patients, myopia itself restored. The Food and Drug Administration (FDA) has received 140 cases of patients disappointed operation from 1998 to 2006.
Side effects "direct" appearing during the hours of operation are: the feeling of irritation, feel a grain of sand in the eye, the perception of a "veil" ... A few hours later or the next day, vision in general reached 80% of the final result. However, for several weeks or months, the patient may experience the following side effects, more or less transitional dry eye, loss of contrast, sharpness reduced in dark environments with visible halos around light sources or areas of high contrasting so.
Side effects may be more important as the splitting image, or a post-operative infection.
Many side effects, and their development over time, are packaged by surgical tools. Thus, the most modern cutting the hood that the femtosecond laser, theoretically reducing the likelihood and intensity of post-operative discomfort.
Similarly, personalized treatment programs, though more expensive, have their interest in reducing these side effects or duration, since removal is best carried out according to the eye Treaty. For example, select an optimized towards aberrations, or a "saving tissue, optimizing the operation to minimize the thickness of the ablation.
Finally, we must mention, for the record, the fact that the thinning of the central cornea caused by the myopia surgery alters the extent of the tension that eye will be undervalued, in proportion to the importance of corneal thinning. This data should be taken into account in the surveillance, even distant, tension eye.(W3C)
Read also Ophthalmology
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