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LASIK and high myopia

High myopia is a pronounced form axile myopia can be defined by his power expressed in diopters (ex: myopia superior to-8 d), or by measurement of ocular axial length (the length of the eye: superior to 25 mm). The LASIK is the technique of choice for low and medium myopia, but it is rivaled by other surgical techniques in the field of high myopia. These techniques are to insert an implant in the anterior segment of the eye (keeping the lens in young patients, or after its withdrawal in beginner cataract case): they need to make an incision and inject a corrective lens (implant) in the eye.

General remarks

It is a frequent demand for surgical correction of high myopia. High myopia is very debilitating and is accompanied by a total dependence on the additive corrections means traditional (glasses, contact lenses). Corrective lenses of glasses for the high myopia are particularly unsightly (thick edges, concentric narrowing of the face from them through print, reflections) and sometimes uncomfortable because of their weight. Finally, they decrease the size of the retinal image and therefore the image perceived.

High myopia is often experienced by those who suffer as a genuine infirmity refractive surgery could "erase" permanently. The word 'disability' is often in the mouths of patients when they designate their Visual function.

Contact lenses is a seductive optical solution for correcting high myopia, as long as it is comfortable and the patient accepts the constraints (maintenance and manipulation). The appearance of intolerance to contact lenses is a very common reason for consultation for refractive surgery.

Benefits of LASIK for correction of high myopia

One of the major benefits of LASIK on implementation techniques is that this operation doesn't involve penetration surgical endoculaire, because no implant is placed.  She looks less invasive than techniques that require the installation of an intraocular implant (implant phakic), and less mutilating only when the placement of an implant is associated with excision of the lens (surgery of the clear lens with an pseudophake implant).

Back and observed long-term security enjoyed by LASIK (20 years for the first case) also represent a substantial profit. However, it is crucial for the surgeon to know the technical characteristics and the limits of LASIK for the correction of the strong myopiques ametropia. The preoperative assessment is particularly important, in order to determine the operability of the patient and provide a realistic prognosis on the expected result.

Moreover, certain situations can lead to indicate in the myopic LASIK technique particularly hard. In case of gap correction important between the two eyes (difference of degree between the eyes, called "Anisometropia" high myopia), the Equalization of refraction between right and left eye represents an interesting benefit to patients. Indeed, these can not tolerate a total correction in glasses because of the difference in size of image between the two eyes (aneisoconie) that causes the difference in power of corrective lenses.

High myopia and presbyopia

Become presbyopic, strong myopic patients are often surgery to midlife seeker, so they don't have to juggle different type of lens correction (lenses and glasses for presbyopia, progressive lenses, etc.).  For these patients, myopia is not really a help to see close without glasses: for example, the punctum point (the point where NET vision without effort) of a short-sighted patient-8 dioptres is located only 1/8 = 0.125 m = 12.5 cm from his face, which is not very convenient reading distance... In these patients, however, it discuss the possibility (or insufficiently thick cornea case, the need) a under correction, aiming for a close residual refraction-1.50 to-2D which will allow them to read at a comfortable distance after surgery, while greatly reducing the blur vision from afar.

A short-sighted including the ametropia goes-10 d to-1 d perceived a significant improvement in its capacity of Visual discrimination. Even if it remains insufficient for driving or shows, she allows him to walk comfortably in a familiar environment (home, office) without necessarily having to wear corrective lenses-1 d, it can however keep on hand in case of specific need.

In total correction (emmetropisation) case, the joy of finally being issued their myopia and the restoration of good uncorrected distance Visual acuity compensates largely correction close dependence in presbyopic patients motivated to see from a distance without glasses or lenses.

When the conditions for a functional outcome in line with the expectations of the patient are collected, LASIK is a technique well suited to surgical correction of high myopia.

High myopia and limits of LASIK

If low and medium myopia certainly represent the best indications of LASIK, the correction of high myopia is more discussed. It is difficult to set a specific upper limit for the correction of myopia by LASIK. The excimer laser can be programmed pourcorriger 15 diopters of myopia: but the number of operations in LASIK for high myopia to-12D remains very low.

For each case, the feasibility of surgery will be determined through the confrontation of the evidence gathered during the preoperative assessment and the expectations of the patient. In particular, the initial corneal thickness is a crucial point, since most nearsightedness is strong, more the laser must 'dig deeper' deep. The operability of a strong myopic is mainly conditioned by the thickness of the cornea. It shall also submit a good regularity and the lack of topographic signs of Keratoconus fruste (see the) page dedicated to the corneal thickness and LASIK).

The high myopia stabilizes later than low myopia or average; It is preferable to not operate on patients 'too young' (ex: before 25 years), unless the stability of myopia is well-documented, and warn them about the risk of renewed progressive myopia after correction.

 The pre-surgery LASIK for high myopia

As always in refractive surgery, it is important to eliminate the contraindications.

 At the strong myopic LASIK contraindications

High myopia is rarely isolated ocular abnormality. The preoperative assessment of a short-sighted patient strong applicant for refractive surgery is not limited to collecting information in optical sight, but must also eliminate a contraindication for LASIK:

-Keratoconus: strong myopia is common in case of advanced Keratoconus, because the increase of the Central corneal curvature causes an increase in the refractive power of the cornea. There is also a strong astigmatism myopic, often myopic or reverse direction. Corneal topography, as well as Tomography to detect Keratoconus in its more moderate, or infra clinical forms (cf screening of Keratoconus fruste). These forms of expression variables may not be that the translation of a corneal deformation induced then accentuated by the eye frottemens (caused by a related to a field of allergic pruritus).

-Beginner cataract (nuclear shape in particular): in this case, excision of the lens and the replacement with an implant is more appropriate (cataract surgery of the strong myopic:) example)

-glaucoma: critical eye pressure shall be readjusted based on the corneal thinning after LASIK. However, management and modern monitoring of glaucoma is based on factors other than the eye pressure. It is also possible to apply that reduction of the corneal "rigidity" would be beneficial to the stress exerted by hypertension on the emergence at the level of the ganglionic cells nerve fibers riddled blade. However, the simple section of the Bowman membrane by the realization of the flap changes the viscoelasticity of the cornea (9).

-the existence of a retinal disease of the macula must reconsider the surgical indication in myopes

Additional tests before LASIK for high myopia

The examinations are designed to assess the feasibility of the technique, i.e. ensure the adequacy between the degree of myopia to correct and (as well as some topographic features) thickness of the cornea.

Them topographers of elevation allow the measurement of corneal thickness, which can also be obtained by optical product or ultrasonic. Extended contact lens wear may be responsible for changes in corneal thickness. It is higher within hours of waking up. In case of extended wear rigid lenses, it is important to meet a deadline of at least one month of removal of lens, or more in case of deformation induced by these rigid lenses (corneal warpage).

Whatever the significance of the correction to be made, the diagnosis of infra clinical Keratoconus (Keratoconus frustrates) must be eliminated, and it will be raised through a review of corneal topography, revealing one or several signs following (nonexhaustive list): astigmatism irregular, low thickness in lower temporal eccentric position, low corneal thickness, and reduction of the enantiomorphism (the symmetry between the eyes). The occurrence of corneal ectasia after a LASIK done on eyes with a residual posterior wall thickness 250 microns is suspected the existence of forms not detected in subclinical (Keratoconus fruste) Keratoconus. We have recently demonstrated that these early forms of infra clinical Keratoconus screening, posterior topography and tomography (product optical point-by-point gained from the topographers of elevation as the Orbscan) offered a clear benefit in terms of sensitivity and specificity on the use of the previous specular topography of Placido. In some case,. the measurement of the corneal viscoelasticity by the Ocular Response Analyzer® (ORA) can be useful to support a suspicion of cornea 'at risk ectatique' (reduction of the hysteresis, aspect of the signal unfortunately).

It is accepted that the risk of luminous halos depends on the importance of output correction, as well as the dimensions of the zone of ablation: the influence of the diameter pupillary scotopic is controversial. In addition to the corneal topography, pupillary diameter can be measured at the average of conventional methods (scale, type pupillometer Colvard) or newer (measure then the) collection of topo aberrometrique review).  Pupillary diameter measures provided by the analysis module of the anterior segment of the topographers as the Orbscan or the Pentacam are difficult to interpret because of the lighting related to lighting of the targets projected in the review.

Constraints of thickness for LASIK in high myopes

In LASIK, you should always calculate the predicted the posterior residual wall thickness which is equal to the initial thickness of the cornea, less the thickness of the flap and the photoablation. Predicted the posterior residual wall thickness should in no case be less than 250 microns: this rule is enacted in an empirical manner, and represents a minimum threshold beyond which the risk of corneal ectasia is greatly increased.

Thus, in order to prevent a secondary corneal ectasia, the respect of a posterior stromal wall thickness greater than or equal to 250 microns is consensus adopted by the majority of refractive surgeons. The physiological minimum thickness of the cornea is located in the Central para-apicale region. A meta-analysis found an average central corneal thickness equal to 534 microns (standard deviation close to 30 microns). There is however a significant dispersion around this average, thicker corneas so offering the possibility of a larger photoablation.

The realization of a flap end to the femtosecond laser by technique LASIK helps preserve a larger posterior residual wall thickness. Greater predictability offered by the femtosecond laser with the mechanical microkeratome for cutting stromal thickness control makes an undeniable asset.  However, the thin flaps are more unstable and prone to neck folds, especially when they are repositioned on a deeply revamped geometry after residual wall. In our experience, it is best to not realize cutting stromal of less than 110 microns thickness if you want to escape the risk of micro pleats.

As to the depth of ablation of a conventional refractive treatment P, it is proportional to the treated correction (in diopters: D) and to the square of the diameter of the optical zone programmed (in mm, S):

P = 1/3 x D x S^2   This formula - called Munnerlyn formula simplified - is an approximate value

depth of optical zone ablation

Schematic representation of the corneal lens removed for correction of myopia by LASIK. Relationship between depth of ablation and diameter of the optical zone. The depth of albation (represented by the maximum thickness of the removed lens - myopia correction) varies with the square of the optical zone.

It is not possible for physico-mathematiques reasons to reduce the depth of ablation compared with this estimate. Some laser manufacturers sometimes advertise lower depths over large areas of ablation, but these also include the transition (to non optical sight) area, and the reduction in the depth of ablation is done so at the expense of the real optical zone diameter. Insist on the fact that the laws of physics are a must and we teach on an optical zone of 6 mm, it is not possible to correct a diopter of myopia without digging less than 12 microns year Center (in reality this revenue, the simplified formula of Munnerlyn, is rather under estimator: in practice, we can count 14 microns per diopter on this same diameter).

The depth of ablation increases with the square of the diameter of the optical zone. This diameter reduction "saves" thickness, but may expose to the greater risk of halos and myopic regression.

Using some programs of photoablation says 'tissue reduction' ('tissue saving") Although legitimate, represents an option that shouldn't have to be, and in fact points out that some platforms were originally designed to deliver the most expensive photoablation in corneal tissue than impose the laws of optics! At the time of the design of these lasers, tissue economy was not necessarily a priority.  These photoablation programs could be abandoned, because there is no interest to remove more corneal tissue that it is necessary. Some excimer lasers have been immediately with programs in line with the laws of optics, and in fact equivalent to the so-called modes of 'tissue reduction '. This has paradoxically deprived their manufacturers (or even the user surgeon) an asset of communication marketing...!

 

Thus, the correction of high myopia by LASIK meets anatomical boundaries and functional specific to each patient, and it is difficult to have a dogmatic attitude in this area. In practice, the maximum power of myopia treated are between-10 and-12 diopters, for an optical zone diameter between 5.5 and 6 mm. In a patient whose cornea is healthy but thin - ex: corneal thickness of 510 microns - the maximum depth of ablation shall not exceed 150 microns (based on flap of 110 Micron thick).

Reduction of the diameter of the optical zone helps reduce the depth of ablation Central (this effect is even more pronounced as the relationship between these two parameters is exponential).

relationship zone diameter optical depth ablation myopia

For a depth of ablation of 100 microns, this graph shows how many diopters can be treated on an optical zone diameter chosen (abscissa).

The realization of a zone of 5.5 mm Optics (diameter that we consider minimum if it does not induce excessive degradation of the quality of vision) will not treat over 12 dioptres; but that figure is in itself significant and the great majority of refractive surgery consultants present with a much lesser myopia.

Technical peculiarities of LASIK for correction of high myopia

The orbital and eye of the strong myopic conformation usually favors a good exposure of the eyeball for LASIK. Apart from a higher than normal axial length and depth of anterior Chamber, there is no strong myopia-specific biometric features. The size of the flap is determined by the dimensions of the zone of ablation; It will have to be slightly higher in case of astigmatism associated with myopia, because necessary enlargement of the transition next to the initially less arched Meridian area often induces an elliptical edge to the area where photoablation will be issued. The pupil is often slightly shifted in nasal at the strong myopic, and a slight refocusing of the flap on it allows to optimize the dimensions of the stromal bed available for the photoablation.

Obtaining an end flap may be a deliberate goal to reduce the risk of ectasia secondary: the creation of the flap using the femtosecond laser seems preferable to a mechanical cutting in the microkeratome, because there are significant variations in the thickness of the flap with mechanical systems no laser cutting. Because of the greater risk travel and folds of the flap; epithelial marking should be systematic.

The duration of treatment is proportional to the degree of correction and the use of an eye-tracker (tracking of the movements of the eye system) performance is required for the excimer laser.  The lasers beam full (Visx) or scanning by slot (Nidek) are well suited to the treatment of high myopia, as well as the lasers to scan by spots on condition that the firing frequency is high (Wavelight EC 500).
The following video concerns the correction of a 10-D myopia:

 

Conclusion

LASIK has a place in the arsenal of techniques able to correct high myopia, and can be indicated until - 12D about for the most favorable case. Respect for the contraindications and the patient information on the peculiarities of the achievement and the results of LASIK in this context to balancing safety and postoperative satisfaction for the patient and the surgeon.

 

 

25 responses to "LASIK and strong myopia"

  1. Mary Scott says:

    I have an eye-22 right and-16 left eye
    What solution I have I live near Clema Ferrante there's a clinic that could do something for me thank you

  2. Dr. Damien Gatinel says:

    This degree of correction is not available to LASIK; Depending on your age, and the presence of a cataract onset, interventions such as "phakes implants", or "clear crystalline" surgery, (or cataract if it started) are conceivable.

  3. Cyriel Antoni says:

    Hello, I would like to know if a myopia of-5.00 right and-5.75 diopters left is considered a sharp myopia... I know I have completely spherical eye so no worries level astigmatism, but when I was 16 I was told that my myopia was already too strong for Lasik, so I wonder...

  4. Dr. Damien Gatinel says:

    There is no absolute definition of strong myopia. Arbitrarily, the lower limit can be set to-6d. But strong myopia is better defined from my point of view as an evolutionary myopia (even after the Thirties). Your myopia is perfectly accessible to LASIK, a priori (subject to a corneal topography with no particularity).

  5. Jean says:

    Hello, you write in your article that "LASIK [...] Can be indicated up to-12D ".
    I have a myopia of-9/ -8, a slight astigmatism, eyes a little dry but not intolerant to lentils, a risk of keratoconus and my ophthalmologist had told me a few years ago that for this level of myopia an operation was not possible.

    What do you think? How can I get more information on the subject?

  6. Dr. Damien Gatinel says:

    The ability to make a LASIK correction depends on many parameters. It is certain that whatever the degree of myopia, an irregularity type "suspicion of keratoconus" represents a contraindication to the LASIK technique (this kind of corneal irregularity is observed in patients who rub a little too often and Vigorously eyes...). It is also necessary for strong myopias that the corneal thickness is sufficient. The realization of a good quality corneal topgoraphie is a prerequisite to be able to re-evaluate your operability.

  7. Chase says:

    Hello
    I have a very high myopia-11/-12 D and I am in addition astigmatism and longsighted. I'm 45 years old. is a LASIK operation or implant placement recommended? I have been wearing rigid lenses since the age of 15 years I support them very well. But I have my vision that is becoming less and less perfect between the evoluTino of my myopia and the presbyopia... what to do in this case?
    In advance thank you for your reply.

  8. Dr. Damien Gatinel says:

    There is no universal answer; Depending on the examination of your corneas, your crystalline lenses, and your "ambitions", a choice can be made. If you tolerate well the most sensible rigid lenses is to wait for the onset of a cataract that is often earlier in strong myopic (sometimes as early as fifties).

  9. Bel Cecile says:

    Hello, I came to see you about six years ago hoping to have an operation. I have a very high myopia (-11 lens correction with both eyes) and you advised me to wait for the occurrence of a cataract. I am now 34 years old, the occurrence of this cararacte seems to me remote. Do you think that six years later there have been advances that would allow me to have an operation? (You had found me a thickness of cornea in the middle)

  10. Dr. Damien Gatinel says:

    If your cornea thickness is average, and the corneas are regular, a LASIK intervention with completion of a flap and an adaptation of the diameter of the treated optic area is conceivable. It will be necessary to verify that your pupil diameter is not too large in low light conditions, as it may be exposed to a risk of night light halos.

  11. Syed says:

    Hello
    I have to have a myopia of-6.75 in both eyes. I have a pupil of 8.5 mm in low light condition. And a pachy of 548. No keratoconus. Do you think this is playable in flap of 110 wide cut? I do not fear the ectasia later?
    Thank you

  12. Dr. Damien Gatinel says:

    It is probably not possible to operate your myopia over a very large optical area, and the risk of night light halos remains higher in you. With respect to Ectasia, your surgeon will perform programming to guarantee a certain residual thickness to your cornea ("posterior residual wall"), and if you do not rub your eyes in postoperatively, you should be so The shelter of the ectasia.

  13. Kammi says:

    Hello doctor and thank you for what you do for patients. I am 33 years old and suffering from a high myopia as indicated in my last consultations below:
    OD:-7.00 (-2.5) 5 degree
    OG:-8.75. (-1.00) 160 degree.
    My questions are as follows:
    1. At this age am I still lucky to be corrected? If yes what option is possible? Because my ophtamo told me there is nothing more to do except pray.
    2. Could I be corrected to the point of driving in France or getting a driver's license?
    3. Could I be operated by implant?
    4. Could I become blind?
    I look forward to your answer. Thank you

  14. Dr. Damien Gatinel says:

    In your situation, a complete assessment must be carried out including, of course, a corneal topography. Depending on the thickness and regularity of your corneas, LASIK may be possible (thick and regular corneas). If LASIK is not possible, a surgery consisting of a implant a lens in the anterior segment of the eye can be proposed. In both case, a certificate for driving may be issued (certifying that eyeglasses or lenses are not required). There is no risk of becoming blind with refractive Chirurige practiced in proven centres, with respect for indications and the use of modern equipment.

  15. Emmanuella says:

    Hello, I am Belgian (Charleroi) and I would like to have an operation, because I can no longer put glasses or lenses. Moreover, I have the impression that my right eye no longer responds to corrections made by my lenses despite a readjustment of them. I am told that my right eye would be "lazy" due to a lack of maturity (I am a 7 month premature).

    After inquiring in a clinic specialized on l'alleud, I was advised to corrected my right eye (-4d) with the laser and my left eye (-10d) with an implant. According to the doctor, only this solution is possible, but I'm afraid to get an implant, if it was the laser, I would have already crossed the course.

    Do you think you can have a counter-notice and use the laser on my left eye (-10d)?
    Do you practice on Belgium or do you have a colleague to advise me?
    What choice do I have to make when I am only 28 years old?
    I'm thinking about being a mom again in three years. Do I have to wait for my last pregnancy or can I do my surgery before, without the risk of starting over?

    Feel free to be complete and sincere, I am ready to hear everything (or read)! Thank you

  16. Dr. Damien Gatinel says:

    It all depends on the thickness of your corneas, especially on the left side. If this is sufficient, a LASIK for-10d can give good results with modern lasers. A small under correction is not necessarily annoying, if the left eye is corrected in full. It is difficult to tell you more without test data. You can fully consider an intervention before being pregnant again.

  17. Arnaud says:

    Hello
    I was operated in 2006 at 24 years of my strong myopia, OG-12 and OD-9.
    Incredible results, perfect view! ... for 8 years. Then regression to the right eye first, then 2 years after the left eye.
    Continuous evolution: I am at OG-1.25 and OD-2.50 + 0.50 astigmatism. The analyses show no particular pathology.
    But how to explain it? Will this "new" myopia stabilize? Can I wear lenses?
    Thank you for your answers.

  18. Dr. Damien Gatinel says:

    Strong myopia is a pathology that is unfortunately never stable (that is why myopia is "strong" because it evolves faster and longer). That is why a slight myopia has reappeared. If the cornea has sufficient residual thickness, a retouching could be envisaged.

  19. Zengers says:

    Hello

    I'm at-10 of both eyes, I'm 54 years old, and now I'm longsighted. A pair of glasses to read, in addition to my lenses, I have the fine cornea, 6 years ago, I was advised not to have surgery, is there today new techniques for high myopia.
    Thank you for your response.

  20. Nicola says:

    Hello I have a myopia of-7 right-6gauche.. I want to know if I can do a lazer operation knowing I'm 27 years old

  21. Dr. Damien Gatinel says:

    LASIK is a technique perfectly adapted to the correction of this degree of myopia. A pre-operative checkup is necessary to verify that the thickness and regularity of your corneas allow the realization of this refractive surgery.

  22. Dr. Damien Gatinel says:

    I advise against the intervention by laser refractive surgery (LASIK, smile or PKR) If your corneas are fine. On the other hand, it might be interesting to consider Crystalline lens ; Exchange of Crystalline lens Clear by an implant, or cataract surgery When this occurs (the onset of cataracts is often earlier in patients with high myopia). With this technique (in both case We remove the Crystalline lens Replaced by a suitable power implant to correct myopia), it is possible to correct all or part of the high myopia (regardless of its degree)

  23. Michael Lewis says:

    Hello
    I am 60 years old with a strong but stable myopia for several years of:
    *-8.50 (-1.00 to 20 °) ADD 2.00 to right
    *-8.25 (-1.25 to 170 °) Add 2.00 Left
    I am also under annual macular surveillance (OCT) of the 2 eyes for reworking pigmented since 2007 (presence of small drusen serous left with macular profile conserved and 1 drusen serous large right without sign exsudatifs ( No DEP or DSR) and no modification of the external retina with a retained macular profile.
    Since 3 years detachment of the glazed to the right and left for two months with the ring of Weiss in the center of my vision.
    I am 60 years old and I would like to be operated at least for myopia. Is LASIK possible?
    What do you recommend?
    Thank you for your reply.

  24. Dr. Damien Gatinel says:

    If LASIK is theoretically feasible, it may be preferable to study the possibility of performing surgery in the Crystalline lens (or early cataract) in your case . Cataracts are usually earlier in the Sixties, and you may already have some degree of opalescence Crystalline lens That could lead to considering this option.

  25. Arnaud says:

    Hello
    Following the recurrence of a certain myopia 13 years after operation LASIK for strong myopia, is possible to replace my Crystalline lens clear at my age (37 years) to correct it, knowing that I have a detachment from the posterior side to both eyes?

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