LASIK is today the reference technique in refractive surgery, whether for myopia, hyperopia, or presbyopia surgery. LASIK stands for Laser In situ Keratomileusis, which means “laser internal corneal sculpting.”
Appeared in the mid-90s for the surgical correction of myopia, LASIK is, in fact, the culmination and, even more precisely, the “crossing” of two distinct techniques that preceded it:
Keratomileusis has existed for over 20 years in myopia surgery and has included several approaches, now abandoned, but already consisting of cutting a corneal lamella to modify its shape.
Excimer laser corneal remodeling arrived at the end of the 1980s and was initially a surface treatment, very effective in myopia surgery, but with limits to which we will return. It remains an effective method today.
The LASIK technique with discover vision for example has two distinct phases: the first phase consists of cutting a thin corneal lamella which will be raised to move on to the second phase, that is, that of the sculpture of the cornea with an excimer laser.
The cutting phase of LASIK is very delicate since it consists of cutting into the thickness of the cornea, which measures 530 microns on average, a strip of approximately 100 microns. Until 2003-2004, this lamellar cutting used mechanical systems corresponding to very sophisticated electric micro-planes, but subject to the limits and the vagaries of mechanical systems. Today, this cutting phase is carried out using a femtosecond laser, which has nothing to do with the excimer laser that drives the second phase.
The femtosecond laser is the first Laser used during a Lasik. The patient is lying down, and the laser procedure takes about 15 seconds.
In the smile lasik technique, the femtosecond laser has no corrective effect on the vision anomaly. It just creates this lamellar cutout. It has major advantages over the old mechanical techniques in terms of safety, precision, and reproducibility. The femtosecond laser is also capable of making finer covers than mechanical systems. It also has the enormous advantage of making cut diameters independent of the corneal curvature, which was not the case with microkeratomes, likely to cut flaps smaller than expected on corneas that are too flat.
The femtosecond laser begins its progression made of lines of impact, which will draw a corneal flap of determined diameter
The corneal flap is being made using a femtosecond laser.
The femtosecond laser has already made two-thirds of the corneal cut, drawing the corneal flap, which will then be lifted to give access to the excimer laser
The passage of the femtosecond laser is complete; the corneal flap is virtually cut.
The application of the femtosecond laser lasts about 20 seconds, with real-time control of the cut: a horizontal band sweeps the cornea vertically.
The treatment phase uses the excimer laser.
The excimer laser is the Laser that will perform the actual correction. The excimer laser achieves a real corneal sculpture since it volatilizes the corneal tissue without thermal effect, making it possible to modify the cornea’s curvature. Thus, the excimer laser will be applied to the center of the myopic cornea to flatten it or, on the contrary, to the periphery of a farsighted cornea to make it bulge. The greater myopia, the greater the central hollowing generated by the Laser, and the greater the initial thickness of the cornea desirable. On an astigmatic cornea, depending on the case, we can flatten the most curved meridian to arch the flattest meridian to obtain, in both cases, two meridians of identical curvature. These two mechanisms can even be associated with correcting the most important astigmatisms.
