The PKR (surface laser technique)
The PKR is an eye operation using laser excimer (photoablation) and intended to improve vision, by changing the shape (optical power) of the cornea to correct nearsightedness or astigmatism.
The PKR or procedures to Refractive sight is based on the issuance of a refractive correction on the surface of the corneal stroma, after removal of superficial corneal epithelium. It requires no cut of flap, unlike LASIK. It is performed under local anesthesia (drops). Both eyes are made the same day.
PKR: principles and technique
The principle of the refractive correction is similar to LASIK, 2 processes using an excimer laser to reshape the cornea (LASIK and the PKR have in common operating time said 'photoablation"of the fabric corneal stromal). Remember that the cornea is haters of two main tunics: the stroma (fabric made of collagen fibrils interlaced and 90% of the corneal thickness), and the epithelium, which is a fabric made up of several layers of cells 'epithelial '. This provision is reminiscent of the DermIS and the epidermis at the skin level. In PKR, the epithelium is separated from the stroma under underlying then removed. The correction is issued on the superficial, immediately located stroma under the epithelium of the cornea. The epithelium pushes back then in a few days to cover the surface of the cornea.
The main difference of the PKR with LASIK is based on the removal of the epithelium and the absence of flap cutting. In LASIK we preserve the superficial epithelial layer, which is not exposed to the beam of the laser: the cut is recline: this component includes the epithelial layer and part of the stromal layer). During the PKR, theepithelium is gently peeled After administration of drops anesthetics to numb the cornea: the superficial part of the stroma, called layer of Bowman, is then exposed to the excimer laser.
The beam of the excimer laser, which is controlled by a computer coupled with the licensing system, is then projected onto the corneal surface stripped to sculpt the fabric superficial corneal stromal.
The PKR in video:
The following video shows the entire of a procedure of PKR (surface laser) bilateral, started by the left eye. The treatment is optimized for wave-front (wavefront optimized) and use iris recognition for alignment and optimal balance of treatment. The technique used for the removal of the epithelium is thrifty and not traumatic (unlike the classic PKR and the EpiLASIK, who uses a machine to separate the epithelium of uncontrolled way). Done this way, the technique of PKR is without risk intraoperative. Anesthesia is purely topical (drops).
If PKR is painless, a feeling of discomfort, burning occurs in the hours that follow and generally lasts less than 24 hours. Most surgeons cover the surface of the eye with a special contact lens at the end of the intervention which allows, in addition to the painkillers, make the post operative pain quite bearable. The contact lens is kept a few days prior to withdrawal.
The PKR induces a slightly longer than LASIK healing phase, because we expect that the epithelium grows back on the surface of the reshaped cornea, which takes a few days. The pose of a non corrective soft contact lens on the right cornea after laser correction helps speed up the re-growth of the epithelium. Taking Painkiller to alleviate pain (whose duration does not exceed 24 hours, usually).
Why remove the epithelium of the cornea in PKR?
It is necessary to remove the epithelial layer to access the superficial part of the corneal stroma (stroma is the main corneal tissue, which represents 90% of the corneal thickness, and which is made up for much of collagen fibrils). If you realized the photoablatif treatment laser excimer directly on the surface of the cornea without removing the epithelium, this epithelial layer would certainly "planed", but the form printed by the laser on the epithelial cou_che would be only temporary. The epithelium is indeed a pluri-cellulaire stratified layer (cells are "stacked one above the other), whose shape can be modulated by the multiplication of the superficial epithelial cells (known as hyperplasia of epithelial to describe this proliferation). In other words, if the laser treatment was applied directly to the epithelial surface of the cornea, epithelial regrowth to erase the effect in a few weeks. The correction printed in the stroma is more sustainable: epithelium sometimes tends to thicken up next to the thin stroma, which can induce a regression of refractive effect. This occurs especially after correction of hyperopia, LASIK is most suitable. The low and medium myopia, however, are quite eligible for the correction in laser surface.
Is the PKR less modern than LASIK?
This belief is commonly widespread, LASIK was introduced after the completion of the first correction by PKR (early 90s). The PKR and LASIK are based on a similar principle: remodeling of the cornea, and benefit both the extraordinary precision of the excimer laser. LASIK is not a 'revolution' with respect to the PKR, it is simply to deliver (identical regardless of the technique) laser correction within the corneal stromal tissue, that is to say in depth. This allows a quicker recovery, with a reduction in postoperative sensations. However, the use of the LASIK technique is not possible in all patients. Those whose corneas are thin, or irregular, or present anomalies (SCAR, etc) are better candidates to the PKR. It's the surgeon to determine the best techniques to correct the optical defect of the patient. When the two techniques are possible, the choice may be patient, and linked to a personal preference or the practice of certain activities.
See : the PKR by steps (video)
Consult : the postoperative after PKR