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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.

PKR: definition

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 flapunlike LASIK. It is performed under local anesthesia (drops). Both eyes are operated on the same day. There are two variants depending on how the epithelium is removed:

  • in "manual" technique, the epithelium is removed (peeled) with a sponge after application of a diluted solution
  • in "all-laser" or "transepithelial" technique: the epithelium is photo-ablated by the excimer laser.

The choice between "manual" or "all-laser" technique depends on the preferences of the surgeon and the patient. The initial clinical results do not allow to attribute to one or the other of these variants a particular benefit in terms of visual result. The "transepithelial" procedure is faster in its execution, and could be particularly suitable for the correction of small myopias. In cases caseof higher myopia (e.g. -5 or -6D), it may be preferable to perform manual debridement of the epithelium, to limit the total laser dose delivered to the corneal tissue.

PKR: principles and technique


It should be remembered that the cornea consists of two main tunics: the stroma (tissue made up of intertwined collagen fibrils and representing 90% of the corneal thickness), and the epithelium, located on the surface, which is a tissue made up of several layers of cells called "epithelials". This arrangement is similar to that of the dermis and epidermis at the cutaneous level. In PKR, the epithelium is separated from the underlying stroma and then removed. The correction is delivered to the superficial stroma, immediately below the corneal epithelium. The epithelium then grows back in a few days to cover the corneal surface.

The principle of refractive correction (corrective effect) in PKR is similar to LASIK, both processes using an excimer laser to reshape the profile of the cornea to change its optical power (LASIK and PKR have in common the so-called "photoablation" operation time of stromal corneal tissue).


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.

Anatomy of the cornea and laser surface pkr

In surface laser technique, epithelium is removed gently of the surface of the cornea at the level of the central area. The area then exposed to the excimer laser is the most superficial part of the corneal stroma, called layer of Bowman. Once the procedure is over, a contact lens is placed on the cornea and epithelium begins the healing process.


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.

PKR laser

This image represents schematically the beam of the excimer laser sculpts the superficial stromal tissue. We see the residual epithelial flange on the edge of the zone of ablation.

The classic 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).

The transepithelial PKR in video (close-up):

This video, made by filming the eye operated on as closely as possible (with a slow motion x4), concerns a transepithelial PKR procedure (Streamlight mode, EX500 laser, Alcon Wavelight). The first phase (epithelial removal) is performed using laser impacts that are delivered to photoablate the epithelial layer over a surface at least equal to the programmed optical zone. The thickness of the central layer of the epithelium is about 50 microns (this thickness can be measured using high-resolution corneal OCT technology).


PKR: postoperative

If the PKR procedure is painless during its performance, a feeling of discomfort, burning occurs in the hours that follow and usually lasts less than 24 hours. Most surgeons cover the surface of the eye with a Contact lensspecial at the end of the operation, which makes it possible, in addition to taking painkillers, to make the postoperative pain completely bearable. It Contact lensis kept a few days before 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 surface of the corneal stroma (the stroma is the main corneal tissue, which represents 90% of the corneal thickness, and which is largely composed of collagen fibrils). If the photo-ablative laser treatment was performed directly on the corneal surface without removing the epithelium, this epithelial layer would certainly be "planed", but the shape printed by the laser on the epithelial layer would only be temporary. The epithelium is indeed a stratified multi-cellular layer (the cells are "stacked one above the other"), whose shape can be modulated by the multiplication of superficial epithelial cells (epithelial hyperplasia is used to describe this proliferation). In other words, if the laser treatment were applied directly to the epithelial surface of the cornea, the epithelial regrowth would erase the effect in a few weeks. The correction printed in the stroma is more durable: the epithelium sometimes tends to thicken compared to the thinned stroma, which can induce a regression of the refractive effect. This occurs especially after correction of hyperopia, for which LASIK is more suitable. On the other hand, low and medium myopias are perfectly eligible for surface laser correction.


Is the PKR less modern than LASIK?

This common misconception is widespread, as LASIK was introduced after the first corrections were made by PKR (early 1990s). PKR and LASIK are based on a similar principle: the remodelling of the cornea, and both benefit from the extraordinary precision of the excimer laser. The "transepithelial" version of PKR has been introduced more recently.

LASIK is not a "revolution" with respect to PKR, it simply consists in delivering laser correction (identical whatever the technique) within the stromal tissue of the cornea, i.e. in depth. This allows a faster recovery, with a reduction in post-operative sensations. However, the use of the LASIK technique is not possible in all patients. Those with thin or irregular corneas, or with certain abnormalities (scars, etc.) are better candidates for PKR. It is up to the surgeon to determine the best technique(s) to correct the patient's optical defect. When both techniques are possible, the choice may be that of the patient, and linked to personal preference or the practice of certain activities.


See : the PKR by steps (video)

Consult : the postoperative after PKR

48 responses to "The PKR (surface laser technique)"

  1. Dr. Damien Gatinel says:

    Astigmatism of the eye could be the subject of a correction in LASIK or PKR.

  2. wadad says:

    Good evening.
    I'm getting ready to do a PKR to correct a myopia of-1, 75. Many people talk about unreliable results and regression of sight one or two months after the intervention. Is it true that the risk of wearing glasses even after the operation is great? My apprehension is to have to choose between a daily discomfort and blurred vision or to go back to the starting point and wear glasses or even to initiate a progression of my myopia which has been stable for more than 10 years. Thank you, Doctor.

  3. Dr. Damien Gatinel says:

    You present a myopia whose magnitude is quite accessible by PKR (surface laser) surgery. The risk of needing to wear a residual correction are quite low for this type of correction, with this technique. If the record does not reveal of contraindications for the PKR, you should be able to benefit fully from this technique.

  4. Angelique fan says:

    Hello I'm about to do the PKR (surface laser) but my correction is of-6 diopters is - that I have a chance that this does not work? Thank you

  5. Sylviane says:

    Hello, my daughter is suffering from Keratoconus and his ophthalmologist suggests they make a PKR (she already had a cxl whom she had trouble recovering and rings intraconeeen) what do you? (it seems that the laser is however indicated in case of Keratoconus and it worries me a lot)
    Thanks in advance for your answer

  6. Dr. Damien Gatinel says:

    The CXL sequence / rings / then PKR is a 'classic' support of Keratoconus. From my point of view, the interest of the CXL is questionable (lack of scientific evidence of effectiveness despite the hype and popularity of this method from most ophthalmologists). The placement of rings is of interest in certain specific indications. The PKR is not necessarily contraindicated, this is certainly a less pronounced stress for the corneal tissue than the simple CXL! He must enjoy each case as a special situation. In all case, stop strict and definitive of the eye rubbing, as well as the adaptation of lenses remain the most appropriate measures for support of a KC. The stop of the friction is sufficient to stabilize the disease: these friction being the main element of my point of view of what we called Keratoconus, but is probably a disease whose origin is before all mechanical, a process of deformation reactive of the cornea related to friction trigger and necessary repeated.

  7. Sébastien says:

    Hello, I have a appointment for a PKR to correct my nearsightedness. My contact lenses are-3.50 right and-3.25 left. The exams operating pre for the PKR, an ophthalmologist told me to 'program' the PKR with-3.25 right and-3.00 left. He visibly removes 0.25 on each side of my lenses which, according to him, sur-corrigeraient. I'm afraid to see less well after the PKR excimer with my lenses. Should I really worry? Thanks in advance.

  8. Castel says:

    I would like to be operated on for a presbyopia, I have a very good vision and no other problem in the eyes except this one.
    is PRK possible for this problem? What would make another technique better for my problem?
    Thank you in advance.

  9. Dr. Damien Gatinel says:

    LASIK is a priori better, because it allows the realization of more stable corrections at the time, and easier retouching. The PKR may be considered in some case however, when LASIK is not feasible.

  10. Dr. Damien Gatinel says:

    It is difficult to answer your question without knowing the reason for this change. If the laser tends to be slightly 'surcorrecteur', can be a way to get the correction of your lenses (the laser will process a little more that he entered the processing software). In general, it must be the correction that is comfortable for the patient.

  11. Sarra says:

    Good evening
    J have a strong myopia (— 20d right eye) (— 18 D left eye)
    I also have a lightness of astigmatism:(

    Is PRK possible for my case? This would prefer another technical?
    Thanks in advance.

  12. amazit says:

    Hello jaimerai do a pkr my edt a-1 myopia is t he util to do or better to wait? Deplus frightens me and I can't stand the lunettes.merci.

  13. Piotrowski says:

    Hello, I was operated in 2003 by lasik. I have again a myopia-1 of the 2 eyes. In order to avoid invasion epithelial I wish to turn to the pkr. Is it risky and is what it is likely to work this time. Kind regards

  14. Dr. Damien Gatinel says:

    After a dozen years, the PKR seems to me not represent a particular risk. The risk of epithelial invasion is low if the lifting technique is well conducted, the uprising of the initial flap seems also possible (provided that the residual thickness of the rear wall is sufficient).

  15. Dr. Damien Gatinel says:

    The PKR for the correction of nearsightedness light to medium is a very on and effective. Talk to with an ophthalmologist who practices refractive surgery near you.

  16. Dr. Damien Gatinel says:

    The PKR and LASIK are unfortunately ineffective to fix such a degree of myopia. In some case, the phakes implants may be proposed. Rigid lenses are a priori the best way to fix for such a degree of myopia.

  17. Greg says:

    Hello, I was operated in 2009 to lasik for myopia of-4.50 only for my right eye.
    The result is still perfect today.
    My ophthalmologist cannot operate my left eye because the latter's myopia is more important-6.75 and the thickness of my cornea does not allow it.
    I have seen that PKR allows for myopia if the cornea is too fine for the use of Lasik.
    My question is this:
    What minimum cornea thickness is needed to correct a myopia of-6.75?
    Thank you in advance for your answer.

  18. Dr. Damien Gatinel says:

    It is difficult to answer with a precise figure, because we can reduce the depth of ablation laser by reducing the diameter of the optical zone on which the laser is issued. Even if the correction was not total, there is an interest to decrease the myopia of the left eye in your case, in order to reduce the Anisometropia (the gap correction between the eyes, which prevents a good binocular vision). Apart from the thickness of the cornea, the regularity of it is important to judge the possibility of refractive surgery (see: review of corneal topography).

  19. Philippe says:

    Hello doctor
    I was operated by PKR only from the dominant eye (monovision) for a small myopia. My other eye is at-1.25. Apparently I'm a little slow to heal and after 10 days I always see very blurry especially closely. I can't work on a PC.
    I'm pretty worried about the sequel because I don't see any improvement. Is that normal?
    Thank you for your return. Well cordially

  20. Dr. Damien Gatinel says:

    It is too early to make a first assessment of the intervention. He must wait until the end of the first month post surgery in order to judge the functional result in your case, and adaptation to monovision is sometimes a little more long. It is interesting to test (with a lens) in preoperative to check that this strategy works and not occaseionne not too much discomfort.

  21. Roxane says:

    I am myopic (OG-8 and OD-9.50), I met two surgeons, one offered me a Lasik operation and the other an operation by PKR. Both have confirmed that the thickness of my cornea is sufficient for both method of intervention.
    I wonder what technique is safest to recover a good vision and keep it as long as possible thereafter?
    Note that I am quite athletic and I have been wearing rigid lenses for 15 years.

  22. Dr. Damien Gatinel says:

    It is a priori preferable to opt for LASIK if both corrections are possible, since the risk of under correction in PKR is relatively high in this range of myopia correction.

  23. Emmanuel says:

    I am myopic: OD-1.25 (-0.75 to 50 °), OG-2 (-0.5 to 95 °) and I like Atcd: a thyroiditis of Hashimoto under no treatment because it is asymptomatic and no disturbance of TSH..., a areata treated by dermocorticoides, and a chalazion of the left eye treated By surgical ablation. I met a surgeon who told me that refractive surgery is contraindicated in my case because I have a dry eye (5 seconds), immunoallergiques deposits and a épithélite séquellaire in the form of a band Level of the right oiel. and TT This despite the thickness of the cornea exceeds 500 microns.
    I wonder is that I can despite this benefit from a PKR...?
    Note that I am 30 years old, and my profession requires bcp of precision and concentration.
    Very cordially.

  24. Dr. Damien Gatinel says:

    It is difficult to answer your question without a detailed examination. In some case, PKR can be carried out, on séquellaires lesions and which are not likely to reactivate. The exact cause of the corneal scar should be known.

  25. Florian says:

    keratoconus + PKR (for interested)

    I am afflicted with a kératocone present on both my eyes. I made a CXL with the right eye at the Lille CHR in 2013. Since discovering this disease, I have stopped rubbing my eyes which probably stopped the evolution of this one. Lenses were proposed to me but my character preventing me from wearing lenses (too embarrassing), I currently wear glasses. My vision is OD:-0.75 (-2.50) to 90 ° and OG:-2 (-2.50) to? °. I often move without a bezel to walk around, wearing glasses is not always necessary. My kératocone having stabilized for a few years after stopping friction, I am very interested in the evolution of technology to discharge my glasses. With LASIK being banned, I would like to get some information about PKR + CXL in the visual processing of Kératocone. is PKR allowed in France in the treatment of this disease? Does the 50 micron limit correct all problems of a affected eye (myopia, astigmatism)? is the ectasîe possible in PKR even without the friction factor?
    Kind regards.

  26. Dr. Damien Gatinel says:

    PKR can be considered in some case of keratoconus, depending on the thickness of the cornea, the degree of correction... and also the friction stop. In your case, a PKR could be considered because your correction is not very high, the keratoconus is stabilized (friction stop)... but it is necessary to carry out suitable complementary examinations (topography, Aberrometry ) to confirm the indication.

  27. Salima Aissa says:

    I am myopic with left eye – 8 and right eye – 8.5. I have a not very thick 6 in diameter. One ophthalmologist advised me LASIK and another the PKR. I don't know about her operation opting.

  28. Dr. Damien Gatinel says:

    The diameter of your corneas certainly measures more than 6 mm (generally: 11 mm). However, if your corneas measure around 600 microns in thickness (0.6 mm), LASIK is certainly the technique to be promoted, because the scar regression is quite important in PKR for this degree of correction (risk of under correction of the Correction of strong myopia in PKR).

  29. Claire says:

    I have a unilateral strong myopia (healthy left eye and right eye with-8.5 myopia and-3.5 astigmatism!). I've been wearing glasses since I was a kid.
    My cornea being very fine, I was directed to a PKR and I was told that the treatment will be only partial.
    Is there a real interest in doing the surgery?

  30. Dr. Damien Gatinel says:

    The interest lies in reducing the degree and simplification (less astigmatism) of the residual correction – which will still be necessary in glasses. It is also possible that you can read text comfortably at a distance of 40 cm without glasses (e.g. residual myopia of 3 or 4 diopters).

  31. Rezwana says:

    I am about to make a PKR (end of January). Already having a relatively severe dry eye I fear that the discomfort will worsen in the aftermath of the intervention. What do you think?

  32. Dr. Damien Gatinel says:

    PKR is a technique whose realization is likely to temporarily amplify the effects of dry eye. Nevertheless, it does not imply, unlike LASIK or smile, the section of nervous trunks within the cornea (only nerve endings are concerned). A regression and a return to the previous state is usually observed within a few months after PKR.

  33. Yoyo says:

    I have a ectasia post LASIK (operated in 2003 for myopia-6.5 of both eyes). The right eye has a strong astigmatism (3.5) with a distorted cornea. How to know if it evolves again, I am told that the measurement of the thickness (350 mic in my case ) is not the only element to take into account but it is necessary to look at the evolution of the Kmax (from 45.3 to 46.4 for 6 months until Auj).
    According to you there is an interest to make Auj a CXL (strongly advised by a ophthalmologist to avoid a graft later while another tells me that it is better not touch the eye)....,?

  34. Dr. Damien Gatinel says:

    There is no real (medical) interest in the realization of a CXL, contrary to what is proposed, despite the absence of robust studies, control group, and non-significant variations of the classical parameters measured. Ectasia Corneal post LASIK is not the direct consequence of too soft, but of a biomechanical imbalance caused by corneal thinning, and eye rubbing Past or present. The sleeping position (pressing one or both eyes of the head when sleeping on the belly or side) is another favouring factor. It is therefore necessary to stop any eye rubbing, even if the eyes are dry and itchy, and change its position of sleep, the case Appropriate. Your evolution of the Kmax is not necessarily significant in this context. CXL does not avoid grafting in patients who rub their eyes continuously. On the other hand, the physico-chemical trauma caused by CXL often leads patients to no longer rub, at least for a time... This explains the "stabilization" or slight regression after CXL (which we observe in patients who stop rubbing without CXL).

  35. Charlotte says:

    I have a myopia at-6 diopters left (eye director) and-4.50 right with moderate astigmatism, stable for ten years. My pachymetry is less than 500. I'm 28 years old, no special antécedent. Normal topography.
    So I am advised a PKR with mitomycin.
    However I fear to develop a haze and therefore hesitate to do this operation.
    What do you think?
    Thanks in advance.

  36. Dr. Damien Gatinel says:

    The risk of haze seems low in your case (Maximum correction: 6 D). It depends on various parameters, such as UV exposure (avoid skiing, beach, etc for 3 months in your case And if this is not possible always wear filter glasses 3 or even 4 in the mountains). The newer lasers also have less haze levels. Haze is a complication that is mainly punitive by the degree of myopia regression that accompanies it (severe haze with reduced vision even corrected are today very rare for the usual fixes in PKR).

  37. Linaa says:

    I just got out of an exam to get an operation.
    I have-1.5 OD and -2, 5OG in myopia and Astigmatie.
    I was told that even after operation my left eye would always have a slight astigmatie, is it possible?
    I'm afraid I have to postpone glasses after the surgery.

  38. Dr. Damien Gatinel says:

    In principle, PKR can correct myopia and astigmatism if it is not too pronounced (less than 4d). Ask your surgeon the reasons for this expected sub-correction.

  39. Nass says:

    Jai-4 AA each eye mn ophthalmologist Precone The PKR I am elogible also lasik but it tells me that the PKR should do lalas.
    With PKR y a ti a risk of regression of the view? I'm also afraid to do LASIK because the cut scares me

  40. Dr. Damien Gatinel says:

    LASIK is an extremely safe technique with modern laser platforms (especially the latest generation femtoseconds lasers such as Wavelight FS200). Several million eyes are operated around the world (almost one million a year in the USA), and the good candidates do the right things.

  41. Vasseur says:

    Hello I was able to read the information about PKR and LASIK do you think I'm potentially eligible for PKR? This one interesting me more because no cutting.

    Knowing that my correction is OD-4.75 (-1.25) 20 º and OG-5.25 (-0.75) 170 º
    Thank you very much in advance for your attention.

  42. Dr. Damien Gatinel says:

    This degree of myopia is a priori compatible with the realization of a PKR (surface laser).

  43. Quentin says:


    I'm considering having PKR surgery with the ex500 wavelight laser. (I can't stand the idea of the Lasik flap)
    My myopia and my astigmatism are standard, and apparently without suspicion of Keratoconus.
    OD:-1.75 (-1.25 to 165 degrees)
    OG:-2.5 (-1.0 to 5 degrees)

    I was surprised during the pre-operative examination not to pass an aberometry test, only a topography by Oculus pentacam.
    The surgeon explains to me that they do not do anaemetry treatment because they have not seen any real interest.

    Is this a so-called "Topo-guided" operation?
    Can you confirm that a method using the wave front, WF-Optimized or WF-guided, is not necessarily justified?

    In advance I thank you for that

  44. Byla says:

    I have a correction of -6 for the OG and -5.5 in OD what is between the two techniques PKR, Lasik best suited?
    Thank you

  45. Dr. Damien Gatinel says:

    Both techniques are possible, but the indication to one or the other depends on the preoperative balance (thickness and regularity of the corneas, etc.). LASIk is often preferred by patients because it allows a quick return to professional life, and there is less discomfort and postoperative pain.

  46. Dr. Damien Gatinel says:

    The aberrometric balance is not necessary but recommended to assess the optical quality of the eye, and collect an objective and original appreciation of regular eye astigmatism vs. the irregular component of the wave front. The corrections guided by the Aberrometry may have some direct benefits (correction of the wave front not limited to bezel correction), and indirect (centered correction and adapted to pupil diameter, etc.). Some studies have shown the value of custom correcting wavefront aberrations, but it is possible that this interest stems from ancillary measures and methods (pupil diameter, centering, cyclotorsion prevention, etc.). If these measures are also put in place for the WF-Optimized correction (which is not guided by the wave front but aims not to increase high-degree aberrations), or topoguided, then the results of the corrections are generally equivalent for standard eyes.

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