LASIK is a technique of refractive surgery Corneal commonly practiced to correct the vision of myopic, farsighted, astigmatism and presbyopic through the laser. The definition of the word LASIK corresponds to an acronym of Laser in situ Keratomileusis (keratomileusis by laser in situ). "Kerato", "mileusis" and "in situ" are words of Greek origin which mean respectively " cornea ', 'train', 'in '. The keratomileusis is a sculpture of the cornea in his breast, that is to say in its thickness, which is called corneal stroma. LASIK is, with the PKR, the technique of refractive surgery The most common practice in the world. It provides excellent visual results and allows the surgery to no longer wear glasses or contact lenses. It is estimated that more than 30 million LASIK procedures have been conducted around the world since 1999.
Principle of LASIK
The LASIK surgery is a surgical procedure purely corneal, and which allows the correction of a wide range of myopia, hypermetropies and astigmatismes. LASIK is performed under local anesthesia (drops anaesthetic). There is no eye gesture, or implant placement.
In LASIK, must achieve a pane (or flap (superficial) of the cornea, then recline it before making the remodeling to the excimer laser (The laser correction, called "Photoablation", is delivered in the thickness of the cornea). The flap is then rested and covers the area that received the photoablation. The creation of flap is specific to the technique of LASIK. It is mainly done with the femtosecond laser.
aLASIK has three main steps: the cutting of the flap (or component) stromal, corrective photoablation, then the rests of the flap.
The technique of the LASIK operation therefore requires the use of the excimer laser. This laser is needed to reshape the cornea in its thickness, within the corneal stroma,. in order to compensate for an optical defect and correct the short-sighted vision, farsighted and astigmatic. The excimer laser is the thinnest laser for corneal surgery: an impact has an accuracy of the order of 0.25 microns (or 0.00025 mm).
Prior to the sculpture to the excimer laser, the trace of the flap through another type of laser is needed: the femtosecond laser. Some surgeons, lacking the femtosecond technology, still use a microkeratome to mechanical blade to create the flap slat; This use, however, tends to disappear.
The LASIK technique is the culmination of various surgical procedures that have been game to correct a refractive defect by a change of corneal, accompanied by a lamellar cutting geometry. His story is told here: history of LASIK
Cornea and LASIK
The cornea is the transparent tissue made up of two main layers: the stroma and the epithelium. The epithelium covers the surface of the cornea. The regularity of the epithelial layer allows the tear film to spread out on the surface of the cornea. The stroma constitutes about 90% of the corneal wall thickness. It consists of strips of collagens, produced by cells called keratocytes. These strips are organized to give to the corneal tissue its curved shape, strength and transparency (the latter depends on the regular spacing of the collagen fibrils). In LASIK, the corneal stroma which is exposed to the excimer laser is: the cutting and the soulevment of a superficial flap (consisting of the epithelium and a layer of superficial stroma underlying) allows you to sculpt and reshape the corneal stroma in its depth.
Main surgical time of LASIK
LASIK is done under local anesthesia by anaesthetic eye drops. one technique has three main parts:
(1) the cutting then the uprising of a superficial flap,
(2) the issuance of the beam under the flap excimer laser (this sculpture of the corneal tissue - called tissue stromal - by the excimer laser is called "photoablation").
(3) the rest of the component on the redesigned corneal tissue.
LASIK: cutting of the flap
The component (or flap) corneal is the specific time of LASIK. The flap is superficial and overall circular: it has a hinge which links it to the cornea. It includes the epithelial layer, and a part of the stromal layer. It allows the cornea remodeling 'in situ' (in its thickness), unlike the procedures to Refractive aiming (PKR) and more generally the techniques called "surface", where the remodeling is done on the surface of the corneal stroma (after epithelial coat).
The cutting of the stromal flap was initially done in mechanics (microkeratome), then way more modern way Optics (laser Femto Second). Laser femtosecond to the advantage of providing more repeatable cutting quality, better control of the set thickness, and a better balance.
Imaging high resolution offered by the latest generation of instruments OCT allows to better visualize the different corneal tunics involved in the realization of the LASIK:
The flap rested in the shape of the underlying stroma which was carved by the excimer laser: the following image shows the changing profile of the cornea, recorded with the camera Scheimplflug of the Pentacam topographer, consecutive to the realization of a LASIK for high myopia.
Unlike the mechanical microkeratome cutting, the path to the femtosecond laser allows to Preview the layout of the cutting of the flap, and refocus it on the pupil. A more focused and regular thickness flap is guarantee of better integration of the profile of ablation excimer within the corneal tissue, and a final optical quality. The edge of the flap in the femtosecond laser has a more "vertical" fitting angle, allowing you to increase the stability of the flap in post operative.
The laser platform latest integrates within a same therapeutic unit the best of excimer and femtosecond laser technology to deliver customized treatment (see:) Suite - Alcon Wavelight refractive laser). In the Paris region, it is available exclusively to the Rothschild Foundation.
Here is a video showing the creation of the flap step laser femtosecond, CG:
The following video is from a real 100% laser LASIK procedure:
The femtosecond laser cutting is better for safety and increased accuracy it provides to the patient. In addition, it is particularly interesting to some eyes with a particularly fine and included cornea in an orbital conformation, making more difficult mechanical cutting (narrow eyelid, eyes recessed, etc.). The correction of hyperopia in LASIK requires the achievement of flaps wide and well centered on the pupil.
case pronounced astigmatism, it is interesting to perform a circular perimeter flap (or elliptical), expanded next to less arched meridians of the cornea, because the impacts of the excimer laser will have a larger and wider distribution according to these meridians (see:) LASIK and astigmatism , profile of ablation excimer for correction of astigmatism).
Most centers of spikes and surgeons hyper-specialized in the technique of LASIK have abandoned the microkeratome for the laser femtosecond for the realization flap of LASIK. Some "low cost" centres continue to offer LASIK to mechanical microkeratome, due to the realized economy (the acquisition and use of a femtosecond laser represent an additional cost).
In case of particular corneal finesse to deliver the necessary correction (see:) thickness of cornea and LASIK), or associated with topographic anomalies such as curvature asymmetry, or evoking the possibility of a starting infra-clinical form of Keratoconus (Corneal deformation caused by eye rubbing repeated), the principle of prevention of ectasia directs towards the realization of a surface laser technique (eg: PKR).
LASIK: excimer laser correction licensing
The realization of the flap in LASIK does not change the curvature of the cornea, but allows to issue the correction by the excimer laser in the thickness of the corneal tissue (stroma). During laser treatment, the flap is recline but remains close to the cornea through its hinge (higher in the majority of the case).
This CGI video shows the time corresponding to the excimer laser photoablation, after the uprising of the flap:
Here is the procedure of photoablation excimer in real-time:
In LASIK in PKR, the the optical defect correction is in all case by laser excimer (photoablation of the corneal tissue). This process time determines the optical result (the accuracy of the correction of the patient depends on the balance and the amount of tissue photoablaté by the excimer laser). Photoablatif treatment may be conventional or custom (ex: guided by the Wavefront), optimized for wave-front (wavefront optimized: designed to not induce an excessive rate of optical aberrations of high degree), or guided by corneal topography. In case pronounced astigmatism of large pupillary diameter, a personalized treatment or "wavefront optimized" is preferred.
Certain modes oftissue economy (« tissue saving") were sometimes offered as an option to the patient, but they did not provide any real advantage other than to upgrade the laser ablation profile used (Laser Technolas Z100) with that of the latest laser platforms. With recent lasers, the choice of a tissue minimum removal is accomplished by defaultin a systematic manner and without additional cost.
Automated detection and compensation of eye movement (eye tracker) system to ensure a good balance of treatment, even if the eye "moves" (micro jerks) during the delivery of the laser)details on the interest of the eye tracker here). The best performing eye trackers allow you to neutralize the eye rotation movements (cyclotorsion) during fixation, using the patient's iris mapping to adjust the excimer laser shots on the cornea in real time! With these maps, the centering of the correction towards the supposed visual axis (located between the Pupillary center and the location of the corneal vertex) is also possible.
There is a page dedicated to representation concrete of the bright spot to fix for the excimer laser procedure (see the video at the end).
LASIK: rests of the pane
After excimer laser refractive sculpture, flap stromal is positioned. He adheres quickly Thanks to a gradient of osmotic pressure within the corneal tissue, and its stability is then ensured by epithelial scarring that covers the edges of the cutout. The preservation of the epithelium allows a quicker recovery and the absence of pain (some nervous nets are interrupted by the achievements of the flap, and this contributes also to post operative analgesia, but also to the induction of some degree of dry eye).
Thanks to the excimer laser sculpture, the cornea thus adopts a new curvature: this change alters the optical power, so as to correct the optical defect (refractive error) of the eye. This change is stable in time, once the initial healing phenomena of age (generally, this stability comes after 3 months).
Learn more about LASIK: Lasik 100% laser:
Video: LASIK 100% laser (France 5):
Technological and technical advances in LASIK
Technical advances offered by modern platforms allow to combine the best of technology as recognition irisne with compensation for cyclotorsion, the realization of LASIK, custom components, and optimization of the centering on the Visual axis, depending on the respective positions of the corneal vertex and the center of the pupil irisne. These opportunities are offered by the latest laser platforms (ex: suite Alcon refractive, Wavelight). They repel the indications towards strong corrections, astigmatism or hyperopia LASIK, as shown by the following videos.
The following video shows a procedure of bilateral LASIK custom (Wavefront optimized treatment) with realization of flaps of elliptical contour for better marry the characteristics of the profile of ablation issued for the correction of astigmatism:
This video shows the realization of an optimized proecedure of LASIK with a custom centering, customized components, for the correction of myopia associated with a presbyopia:
The following video includes custom correction (taking into account the pupillary diameter, of the Visual axis, realization of flaps 'tailor-made') a strong farsightedness in LASIK:
What do you see for LASIK?
This question is a source of anxiety on the part of candidates for LASIK: I see the instruments, laser? During the procedure, the vision can be very veiled during certain phases (ex: realization of the flap with the femtosecond LASER). There is nothing truly dreadful, and the laser light is not truly perceived because it does not penetrate into the eye (it is focused in or on the surface of the cornea). It is however a step where it should be to set a light spot, so that (the corrective photoablation) excimer laser treatment is perfectly centered in the Visual axis. The following video is designed to show in "subjective" view that the patient can perceive at this stage of fixing, when is lying under the excimer laser, after the creation of the flap by the femtosecond laser:
Can we move the eye for LASIK?
Modern lasers are equipped with very sophisticated systems that combine a camera high frequency to the licensing of the laser firing system. The eye is filmed continuously by a camera, which records the movements and eye saccades. These jerks are analyzed in real-time and accurate information about the movements of the eye and their management are used to compensate for the direction of the firing of the laser. This system called 'eye tracker "(eye prosecution enslavement) is all the more remarkable (and crucial for a good visual result) that recent lasers have a rate of fire that can reach 500 Hz (or 500 shots per second).
The following video allows you to get an idea of this technology: it shows that a recent laser can compensate for the movements of a target and deliver its impacts where they should be:
Vision and LASIK
How is the vision after LASIK surgery? Just after the LASIK surgery, it is possible to perceive the effect of the correction, but the vision is still "foggy" and a bit blurry. This "MIST" dissipates in the first hours. There is no pain, but a local discomfort is possible, with in some case some difficulties to open eyes, a persistent watery eyes, burning eye sensation. Once the postoperative early past, LASIK vision is comparable to that obtained with the lenses; There is no particular effect of "magnification" or "shrinking" of the Visual field. The color vision is not changed after LASIK. The color of the eyes is not changed by LASIK, or techniques of corneal refractive surgery in general. As with any surgery, LASIK exposes some side effects or complications. In our experience, the risk of severe complications is exceptional and is explained in the vast majority of the case by a bad operative indication (performing a LASIK patient who was in fact a bad candidate).
Safety of LASIK
LASIK is the most practiced surgery of comfort technology in the world. In the USA, LASIK procedures performed since the last two decades is estimated at 16 million (30 million worldwide). The findings of a lengthy study conducted by FDA and designed to assess the safety and effectiveness of LASIK are unequivocal: lLASIK is a safe technique, and results measured three months after surgery revealed that 95% of the operated patients benefit from a Visual acuity of at least 10/10 without correction. According This studythe nocturnal vision undesirable visual phenomena tend to be less pronounced after LASIK than before surgery (6% vs 33%), when the eyes are equipped with glasses or contact lenses. LASIK is the Queen of the refractive surgery technique because it combines recovery speed, accuracy, efficiency, and security, all with a decline of nearly 20 years.
Adhesion of the flap after LASIK
After LASIK,. the flap adheres quickly to the cornea. You should avoid touching and rubbing your eyes in the hours following the procedure. Protective shells are given for the first night, and UV-tinted eyeglasses can be worn outdoors during the first few days or even the first few weeks. There is no risk of spontaneous detachment from the flap and after 24h it is possible to remake quickly.
In all case, and whatever the technique of corneal surgery, it is formally advised not to rub your eyes in a repeated and vigorous manner. This recommendation is not related to the existence of the flap but to the reduction of the corneal thickness which makes it more susceptible to the important mechanical stresses exerted by the frictions. The makeup must be done gently, without "kneading" the cornea (this recommendation is valid even in the absence of LASIK surgery).
Touch-ups after LASIK
One of the great advantages of LASIK is to allow for comfortable and effective retouching, even late (several years), in case of evolution of vision. This may be useful in recorrecting a myopia whose evolution would not have been halted, refining the correction to case of myopia or residual astigmatism, or to give back the "vision of Close" In patients who have become presbyopic, and LASIK surgery in the past. If the re-uplift of the flap is not problematic (see recovery after LASIK), this is not to say that the LASIK component would never stick. Simply, it is possible, surgically, to re-raise it by using an adapted technique, even 20 years later. The retouching after PKR is rather made in PKR. Unlike LASIK, the smile technique does not allow retouching without changing techniques, and requires to perform a PKR. The possibility of retouching is a fundamental advantage of LASIK, especially vis-à-vis the smile.
The following video corresponds to one of the "oldest flaps" (17 years old) that I had to re-raise to correct a hyperopia induced by an implant power calculation error in cataract surgery. The patient had had LASIK 17 years earlier to correct an average myopia.
It may be noted that the history of LASIK surgery can simply correct a defect in biometric correction (calculation of the implant's potency) to a cataract surgery (see next section).
LASIK and cataract surgery
The realization of a LASIK is not a source of technical difficulty the cataract surgery. It is quite possible to operate cataracts an eye with history of LASIK, without having to change the operative technique. The calculation of the power of the implant to replace the clouded crystalline is however carried out in this type of situation with modern calculation formulas and which take into account the presence of a surgical modification of the curvature corneal. These details are detailed on the site (see:) Biometric calculation and calculation of implant after refractive surgery). LASIK comes into competition with clear crystalline surgery (technically identical to cataract surgery) for the correction of certain visual defects (high myopia, presbyopia, high hyperopia After quarantine).
What do you see on the side of the surgeon during the procedure?
The intervention in LASIK requires the use of two lasers (femtosecond and excimer). These sophisticated systems can deliver the exceedingly quick and accurate laser radiation. The hand and the eye of the surgeon, however, are essential to guide the licensing on the cornea femtosecond laser system, lift the cut stromal component, and then optimally align the eye surgery with the excimer laser centering systems, etc.
These surgical steps are conducted under Visual control, thanks to surgical microscopes integrated lasers, as well as viewing cameras. The following video shows simultaneous display screen seen by the surgeon, and the direct observation plan of the patient's eye, during the bilateral a high hyperopia associated with a pronounced astigmatism correction. The first part of the video concerns the programming of flaps of custom LASIK, with circular geometry and the position of the hinge are designed to allow excimer laser refractive aiming a sculpture in the best conditions. The second allows to visualize in real time the stages of creation of the flap (left eye and right eye), and refractive correction (uprising of the flap, issuance of the laser correction, rests of the flap).