The technique of Lasik surgery is the eye . Its principle is to cut a thin strip in the thickness of the cornea (the transparent part is that the surface of the eye) to allow a thorough reshaping of the corneal curvature laser . Its purpose is mainly to correct myopia , but also other optical aberrations such as hyperopia , the astigmatism or presbyopia (referred to as "Presber-lasik by modifying the shape of the cornea ). This operation will continue without a system of correction ( glasses or contact lenses ).
The laser used is called " laser excimer "that would be better named" Laser exciplex . The beam generated by exciplex which emits in the ultraviolet .
In most cases, the exciplexes are composed of at least a halogen gas and sometimes a rare gas. The term "excimer" comes from English "excited dimer" which means an excited molecule composed of two identical atoms. Gold excimer lasers use exciplexes which are molecules composed of two different atoms (rare gases and halogen, for example, ArF) that remain together as the excited state. The electrical excitation of the mixture of halogen and rare gas molecules produced these exciplexes. So we should call them rather than exciplex lasers excimer lasers. After the photon emission, the exciplex disappears because its atoms separate, thus the photon can be reabsorbed by the excimer unexcited, allowing a good performance laser. His high-energy beam can break the bonds of gaseous molecules ( photolysis laser) to produce radicals. He finds particular utility in measurement experiments of kinetic constants of gas reactions to interest atmospheric .
The first advantage of this laser was initially the possibility of thinner slices, allowing operating corneas thick medium, in which conventional surgery was sometimes refused.
It soon became apparent that this tool was also huge benefits 1 in terms of security, accuracy in the reproducibility of the corneal cutting and quality results. Technically, the duration of the intervention is not changed and the postoperative courses are comparable.
The operation is performed under anesthesia local ( topical drops by). The first step of the procedure consists of cutting a corneal flap surface (90 to 180 microns) which is usually held by a hinge at 12am.
The laser can then work on an inner zone of the cornea (stroma) without altering the Bowman and change by photo-ablation. When the intervention laser (which takes about a minute) is complete, the flap is reattached by surgeons.
Until the early 2000s , the most common way of cutting the corneal flap is the use of a microkeratome , a mechanical device (plane miniaturized and sophisticated), and the surgeon applied to the eye. This first phase is very delicate now done by a laser, the femtosecond laser.
The femtosecond laser allows this transaction 100% laser. Cutting the corneal flap is then performed in a few tens of seconds, then the ablation is performed using an excimer laser. Risks related to the character "mechanics" of the cut here are reduced, and the characteristics of the cut (angle, thickness, homogeneity ,…) are better mastered.
The LASEK ( laser epithelial keratomileusis-assisted sub ) is a hybrid surgical technique applied to the eye that lies between the PRK (photo refractive keratectomy) and LASIK.
The epithelium , previously prepared with a solution of ethanoic acid, is off. After the action of the excimer laser, the epithelium is replaced on the cornea.
The technique of Epi-LASIK (epithelial-LASIK) uses the excimer laser. It is established from the technical Lasek, unlike the detachment of the epithelium is via a microkeratome and not a solution as ethanoic for it.
Lasik is nearly 15 years the gold standard for the operations of myopia and other vision abnormalities that are the farsightedness , the astigmatism and presbyopia .
If the principle of this surgery is not questioned, its methods have evolved to arrive today to the concept of Ultralasik , which is the "ultimate" technological Lasik, with:
- An all-laser Lasik, in which cutting the corneal flap is made femtosecond laser.
- Excimer laser treatment in custom mode, also called aberrometry as to the correction of optical aberrations pre-existing. This method of treatment has now shown a substantial benefit when astigmatism must be corrected, it is associated with myopia or hyperopia. It is also interesting when the pupil is large diameter.
The ultralasik generated the concept of Ultra Vision or supervision, that is to say obtaining a postoperative visual acuity 15/10 or 20/10 up to patients whose acuity reached "only" 10 / 10 with glasses before surgery, and thanks to the reduction of optical aberrations preoperatively .. Well-understood, such visual results are not systematic, but ultralasik has in any case the interest of limiting the optical aberrations, and thus act qualitatively on the vision of the operated eye. Optical aberrations measured at a high level before surgery is an argument for preferring an Ultralasik.
Finally, this type of treatment, giving rise to intervention before conducting a personal magnetic card just makes impossible any error or patient side during the procedure.
Side effects ( halos , photosensitivity , degeneration of the macula, etc..) occurred in some patients. They appear more or less transient, in the days following the operation. A U.S. study has estimated at 6% the number of patients with adverse events within six months after surgery 6 . In other patients, myopia itself has recovered. The Food and Drug Administration (FDA) received 140 cases of patients disappointed with the operation from 1998 to 2006.
Side effects "direct", occurring during the hours of operation are: the feeling of irritation, like having a grain of sand in the eye, the perception of a "veil" … A few hours later or the next day, the vision usually reaches 80% of the final result. However, for several weeks or several months, the patient may experience the following side effects, more or less transient: dry eye, loss of contrast, reduced acuity in dark halos visible around accompanied by light sources or areas of high contrast, etc..
Most important side effects may occur, as the image splitting, or a postoperative infection.
Many side effects, and their evolution over time, are conditioned by the operating tools. Thus, the most modern cutting the hood that is the femtosecond laser, theoretically reducing the likelihood and intensity of post-operative discomfort.
Similarly, individualized treatment programs, although more expensive, have an interest in reducing these side effects or duration, since the ablation is performed optimized according to the treated eye. One can, for example, choose an optimized treatment vis-à-vis the aberrations , or treatment "Tissue saving", optimizing the operation to minimize the thickness of the ablation.
Finally, the thinning of the central cornea caused by the myopia surgery alters the measurement of intraocular pressure which will then be underestimated in proportion to the importance of corneal thinning. This data should therefore be taken into account in the surveillance, however remote, of eyestrain.
- Arevalo JF, Mendoza AJ, W. Velez-Vazquez, FJ Rodriguez, A. Rodriguez, Rosales-Meneses JL, Yepez JB, E. Ramirez, A. Dessouki, Chan CK, Mittra RA, Ramsay RC, Garcia RA, Ruiz-Moreno JM, Full-thickness macular hole after LASIK for myopia of The Corrections. in Ophthalmology , 2005 Jul; 112 (7) :1207-12. PMID 15921746.
- Albietz JM, Lenton LM, McLennan SG. "Dry eye after LASIK: comparison of outcomes for Asian and Caucasian eyes." Clin Exp Optom. 2005 Mar; 88 (2) :89-96.
- Lasik Surgery: When the Fine Print Applies to You , New York Times , March 13, 2008.