History of LASIK
"LASIK: l ' history
The LASIK East, with the PKR, the most common technique to correct refractive defects of the human eye (correction of nearsightedness, farsightedness, of the)astigmatismetc.). Like all techniques of surgery, she has not appeared "de novo", but is the result of a make of multiple 'trial and error' previous history which the main.
Remember first of all that the LASIK is a technique that is based on the sthe corneal tissue culpture (from the Greek... "keratomileusis") and aims to change the curvature of the anterior face of the cornea. Myopia in benefited first, then hyperopia and astigmatism.
José I. Barraquer (1916-1998) asked as early as 1963 the theoretical bases of the technique of the Keratomileusis (for myopia and hyperopia) which evolved into the technique of LASIK. The sculpture of the corneal stroma (keratomileusis) is common techniques that preceded the LASIK.
Ancestors of LASIK technology
The following Figure shows schematically the techniques 'foremothers' of LASIK.
Two times successive main common for this group of techniques are:
-the primary cutting flat lamellar cornea. It allows to create a stromal flap (the stroma is the deep tissue of the cornea: the made up flap consists of a superficial solidarity stromal of corneal epithelium layer.)
-refractive sculpture of the corneal tissue
Note that with the technique of Refractive procedures (or PKR), there is no cutting lamelllaire flat, and sculpture the stroma excimer laser is performed directly after epithelial coat (as the epithelium is a dynamic structure that repels, it wouldn't have to carve it, the effect would be erased in a few days by a re epithelial proliferation)
The development of the microkeratome
The experimental work of José I. Barraquer first concerned the development of the microkeratome, surgical instrument based on the principle of the dermatome, capable of achieving a cutting regular superficial corneal lamellardiameter and depth controlled. Most of the principles that led to the development of the first clinical models in 1975, are the basis of the functioning of the current mechanical microkeratomes (who are going to be superseded by the use of the) femtosecond laser for the cutting of the corneal flap). Cut a flap is not in itself the cause of the correction: there are a second refractive cutting. The cutting of the flap is an important time, but it's so cutting a refractive corneal stroma under this flap (to change the optical power of the cornea through a change in its geometry) which is the most important process time and most delicate of this surgery. Its profile, its diameter, its regularity and its centering are decisive for the quality of the Visual functional results, as well as for the stability of the correction. Searching for best settings is at the origin of all the technological evolutions of the keratomileusis.
Here are the main techniques which can be considered as the ancestors of LASIK, which occupy the places of choice within the family tree of this technique.
Keratomileusis with freezing and machining on cryotour:
José I. Barraquer first attempted to achieve the refractive sculpture in the microkeratome under the flap, in the posterior stromal, raising the principles of in situ keratomileusis. The initial results were disappointing (mechanical sculpture was not the precision offered by the excimer laser). He then turned to a refractive cut on the back of the issue the primary cutting lamella (the deep surface of the flap). To make it possible, he imagined flap machining stiffened by freezing. This flap was detached from the cornea, and machined on a lathe to modified contact lenses: the cryotour. The cryotour is similar to its basic principles in a "round of Potter. To be manipulated and sculpted, the diameter of the free flap had to be about 300 microns for the correction of myopia. The sculpture of this piece of corneal parameters were determined by a function of the desired correction algorithm. Once carved on the cryotour, the Board was thawed, then placed back to original position and maintained by a suture to the surgical monofilament. This technique has been practiced between 1975 and 1985 before falling into disuse; little predictable business results, and issues related to the freezing of the corneal flap were added to the difficulty of its realization. One of the main difficulties was to properly focus the lenticule carved on the Visual axis. However, this work showed that the lamellar corneal surgery was a promising technique: myopia could be reduced by a previous corneal sculpture, and above all, the cornea remained transparent after healing.
Keratomileusis without freezing with resection to the microkeratome on the stromal side:
To promote increased speed of Visual recovery postoperative and simplify the technique of Barraquer, Krumeich and Swinger have developed in 1984 keratomileusis without freezing technique. The cryotour was replaced by an "established" (called BKS 1000, initials of its inventors). After cutting a superficial cornea slat which diameter should be at least 9 mm, miniature Workbench allowed to perform refractive cutting the microkeratome on the back of the primary lamella. The corneal slat was maintained on a mold with a suction system. The shape of the mould allowed to determine degree of correction. Despite a significant improvement in functional outcomes this technology suffered the same through the keratomileusis with freezing; insufficient refractive precision, and irregular astigmatism associated with the problem of the often rough centering of the lenticule carved on the cornea.
Keratomileusis in situ with resection to the microkeratome in the posterior corneal stroma:
To simplify the technique of the keratomileusis and avoid freezing of the lenticule cut, Luis Antonio Ruiz proposed a technique of keratomileusis in situ for myopia with specific instrumentation in 1986. After cutting of the flap, a refractive cutting (it also parallel-faced) was performed at the microkeratome in the posterior stromal bed. An abacus (also called nomogram) allowed to choose are diameter and depth depending on the desired correction. This diameter was the function of the thickness of the ring, and the depth of the thickness of the plate picked and switched into the head of the microkeratome. This technique has produced functional results were disappointing due to an optical area too small and often biased. It is interesting to note that today ' today, the principle of the keratomileusis in situ could again become a technique used for the correction of myopia using laser femtosecond) technology flex - relex)
Ruiz did evolve his technique by offering automated in situ keratomileusis in 1991 ("") ALK ("for"Automated Lamellar Keratoplasty"). The movement of the microkeratome in the rail of the ring became mechanized through a system of gears, the progress of the speed constant and regular head being driven by an electric motor (called ACS, acronym for Automated Corneal Shaper). This evolution has allowed for a refractive cut perfectly centered on primary cutting. To further simplify the technique, Ruiz offered to let a hinged device on the part of the primary cutting, to facilitate its good positioning and avoid sutures. The centering of the optical zone could still prove to be imperfect because conditioned by the centering of the primary cutting, and influenced results in unpredictable ways by the biomechanical response of the cornea.
This technique has prefigured modern LASIK, because it has a flap cut and maintained by a hinge. It lacked the precision offered by the photoablation to the excimer laserwhich made LASIK and the PKR two more specific chirugicales techniques in the world. The excimer laser was invented in the early 1970s, and its first ophthalmological medical indications were at the end of the 1980s.
The primary lamellar cut today made by the femtosecond laser (abandonment of mechanical cutting as the microkeratomes systems) in modern centers of refractive surgery has further increased security and the quality of functional outcomes. Laser femtosecond and last generation excimer gathered today in a same platform)more Alcon refractive, Wavelight), which allows to adjust the precise dimensions of the corneal ablation profile issued flap.
CONSULT the main page dedicated to LASIK
Reference: Chapter 1: "History of LASIK", extracted from the book: "The LASIK, from theory to practice" (D Gatinel))here)