We have "repaired" the laser Boomburum , and in post , where he talked about his new eyes, a discussion arose on the comparison of PRK methods, LASIK methods and SMILE methods. We (I mean the German holding company <{short}> <{full}>

 
We have "repaired" the laser Boomburum , and in post , where he talked about his new eyes, a discussion arose on the comparison of PRK methods, LASIK methods and SMILE methods. We (I mean the German holding company <{short}> ? SMILE EYES
, Which includes our Russian clinic) do all three types of operations, but absolute supporters of the method that will give more with less loss. Thus, any kind of LASIK or PRK is recommended only when SMILE is impossible: first, with farsightedness (this is another story), and secondly, in cases of a diseased or damaged cornea (for example, with scars). But, of course, the economic side is taken into account.
 
 
It would seem that I explained in the first posts why this is so. But in the comments to the post it is clear that this was not enough. So let's do everything according to the rules of scientific discussion. We will analyze the theses and give relevant research to them.
 
 
This is what the scientific and medical world does. If there is an opinion - it needs to be justified. It is desirable, on a sample of 20 or more patients with the same distribution in a double study. It is desirable - that the studies are confirmed by different clinics in different countries where such operations are conducted.
 
 
Let's start.
 
principle of the operation , and here the operation itself. Inside the holding company SMILE EYES - ?5% on enchancment (pre-correction), around the world - up to 2%.
 
 

 
This is how ReLEx SMILE
is executed.  

 
FLEX 2005 is the precursor of the SMILE method, also 100% femtosecond technology. Now it is fashionable to sell it as "pseudo SMILE". The difference is that like SMILE, an individual lens is cut in the cornea, but to remove it around the circumference, a cover-flap is cut out. That is, there is no heating and evaporation - this is a plus, but otherwise - the same opening of the "cover". It is done under one laser, the excimer is not needed. Do not give the patient a significant advantage over femtoLASIK. The manufacturer of the equipment offers it as part of the surgeon's preparation for the SMILE method.
 
 
femtoLASIK (FS-LASIK, femtosecond LASIK) born in 2000 is a method using two lasers: a femtolaser and an excimer laser.
 
To form a "lid" in the cornea, a femtolaser is used, then the lid is manually folded. To evaporate the lens in the middle layers of the cornea, an excimer laser is needed. There is a thermal effect. The operation depends on the quality of each of the two lasers (old models of both, in the aggregate, can spoil the overall result). Then the lid fits into its original place. It never grows up, you can always raise it. The purpose of the operation is not to burn over the upper layers of the cornea, which are the most durable and contain the greatest number of nerve endings. Now this is one of the most common operations in Russia and in the world. Inside the holding is only about 5-10% of the entire correction of myopia. Statistics on pre-correction in the world - 8-12%.
 
 
The term SUPER-LASIK - not a separate method - used as a characteristic of the evaporation profile by an excimer laser - means an individual profile of evaporation in the cornea. That is, it can be either "SUPER-femtoLASIK" or "SUPER-just-LASIK". In scientific medical publications, the term "Super Lasik" (with the prefix "Super") is not used and is not official medical terms. It has received some distribution in the advertising of some medical clinics, apparently wishing to attract additional attention due to "bright terminology."
 
 
LASIK (Laser-Assisted in Situ Keratomileusis) - born in 1989 - the surgical department of the cap-flap with a microkeratome device, a special machine with a "shaving" blade and subsequent excimer laser evaporation of the lens on the cornea. For evaporation of the lens in the middle layers of the cornea, one laser is needed - an excimer and a mechanical device with a microkeratome. LASIK is a combination of mechanical and laser action. The result depends on the quality of the laser and on the quality of the microkeratome. There is a thermal effect.
 
 
Also morally obsolete all of its varieties: the technique Epi-LASIK - an attempt to reduce the thickness of the corneal cut indicates that the cut is made on the very surface of the cornea and the procedure REIK (REIK) - "horseradish radish is not sweeter" - this is the same LASIK. By the way, the thin flap "frowns" more strongly and "flies" with trauma more easily.
 
Also, the flap becomes the "culprit" of additional optical aberrations affecting the postoperative quality of vision.
 
 
In our clinic today microkeratome is "shrouded" as an exhibition exhibit, for modern surgical practice - this is barbarism. It is extremely rare, for example, to cut through the scars.
 
 

 
Scheme LASIK /femtoLASIK
 
 
FRK (Photorefractive keratectomy, PRK) - born in 1985 - method of evaporation of the lens in the upper layers of the stroma of the cornea without the creation of a phlebit with the preliminary removal of the surface layer of the epithelium. The oldest method of all laser correction methods.
 
 
Complications are well studied, the largest statistics on them - up to 15%. Within the range of 1-1.5 diopters correction appears to be quite good, with higher myopia - all the flaws creep out. Due to complex healing, a large wound surface and risks, it can be recommended only for economic reasons.
 
 
From the minuses - the huge (πR2 - area of ​​the circle!) Surface of the cornea is evaporated, it is important that the most durable surface layers are destroyed, the boundary Bowman membrane is evaporated, the tissue is evaporated exactly as much as with LASIK, possibly scarring with the appearance of persistent opacities - haze.
 
 
The cornea of ​​the eye has a layered structure: epithelium, Bowman's membrane, stroma, descemet's membrane, posterior epithelium (endothelium). Stable refractive effect is achieved only by changing the stroma geometry (the main layer of the cornea). Achieving the stroma is a serious problem, therefore all types of PRK differ in the way they "pass" the first two layers: the epithelium and the Bowman shell. The old "classical" method mechanically removed the epithelium - scraped off the surface. There is a variant of chemical action of 20% alcohol solution - and then scrape. Then it will be LASEK or epi-LASEK .
 
 
The epithelium can be "burned" with the same excimer laser - this will be transepithelial PRK or Trans-KRK . In foreign publications, it occurs under the designations "ASA", "ASLA", "C-Ten" and "TransPRK". In the early years, trans-PRK was a two-stage procedure, in modern lasers - one-stage.
 
 
Therefore, it is correct to say that Trans-KRK is an improved technique, but only within the framework of this method - it allows reducing a number of inevitable drawbacks of the PRC method itself and errors in the results.
 
 
And the method itself, alas, can not be called a new one. Although even today there are clinics that sell Trans-FRC as "the most modern method", and sometimes "the most sparing". And KFR - he and in Africa FRC, even if he is "Trans". Marketing geniuses often manage it perfectly! For example, the Estonian procedure eLASIC Despite the similar name to another method - it's PRK.
 
 

 
This is what FRK looks like.
 
 
The only plus - all so there is no "lid" and related problems. Well and one more - the surgeon does not need to bother by pressing the pedal twice and controlling the transitions from one software to another.
 
 
The appearance of the method. ReLEx SMILE almost completely eliminated the need to perform PRK in any version.
 
 
We use PRK method exclusively for medical reasons in cases where correction is not possible in other ways or it is necessary to remove just the upper layers of the stroma (for example, if there are opacities).
 
 
Here is here comparison of the entire line of methods.
 
 

 
 

SMILE AGAINST FRK ON SCALE SCREENING

 
Study Nethradhama Superspeciality Eye Hospital, doi: ??? /2017/5646390.
 
 
A sample of 120 eyes from 60 patients (34 women, 26 men) who underwent bilateral correction of low degree myopia (up to 4 diopters) either with ReLEx SMILE or with PRK. Visual acuity, contrast sensitivity and higher order aberrations were recorded before surgery and compared after surgery. Three months after the operation, a comparison was made.
 
 
Results: 3 months later, the SMILE group showed significantly better visual acuity compared to the PRK group. The postoperative spherical equivalent was comparable in both groups (SMILE = -??? ± ??? D, PRK = -??? ± ??? D, p = ???). However, the predictability of SE (spherical equivalent) was better in the SMILE group - 97% of the eyes within ± ??? D compared to 93% of the eyes in the KGF group.
 
 
General aberrations of higher order were significantly higher in the PRK group than in the SMILE group. The SMILE group showed slightly better contrast sensitivity. Four eyes from the PRK group lost one line of visual acuity due to blurring in the eyes.
 
 
Both SMILE and PRK are effective for the correction of low degree myopia. Nevertheless, the SMILE procedure offered a better quality of vision and better patient satisfaction because of greater postoperative comfort and lower induction of aberrations after 3 months.
 
 
My comment: when the sample is expanded to 6 diopters, the PRK method would lose numerically stronger, since it gives a much higher probability of haze (haze, haze) and subsequent blurring with increasing depth of cut. The structure of the cornea is restored after a serious burn of KGF with scars almost always, often they lie outside the visual area, at the boundaries of evaporation of the lens and have little effect on visual acuity. However, this risk is decisive in the medical choice of the method for a healthy patient without special indications. Plus, in this study, patients noted the subjective quality of life higher in SMILE-methods, since the postoperative period was painless for them (except for the first day).
 
 
By the way, the German refractive community Kommission Refraktive Chirurgie (KRC), as well as the union of ophthalmologists in Germany (DOG), prohibits the use of PRK methods for correction of myopia by spheroequivalent more than -6 diopters. That is, if you have 4.5 and astigmatism more than 1.5 - PRK can not be done! In general, choosing SMILE and cornea save and time for recovery is minimized.
 
 
But let's look at another study. It is more modern, so it was no longer the PRK-methods with SMILE, and the more modern LASIK (transmitting much less energy to the eye, and in the middle parts of the stroma, not to the skeleton) and SMILE. Here it is:
 
 

ESTIMATION OF CORNER TRANSPARENCY

 
Department of Ophthalmology, Philipps University of Marburg, Marburg, Germany, doi: ??? /???
 
 
58 eyes with myopia from 33 patients who underwent SMILE were compared to 58 eyes of 33 patients who had passed FS-LASIK. All procedures were performed using a femtosecond laser. VisuMax and the excimer laser MEL 80. The result was evaluated for 3 optically significant concentric radial zones (0-2 mm, 2-6 mm and 0-6 mm) around the tip of the cornea and on 3 different anatomical corneal layers (anterior, central and posterior).
 
 
After SMILE, the total corneal layers in the 0-6 mm radial ring showed no significant changes compared to the preoperative values. After FS-LASIK, the overall result was significantly reduced. After 3 months after the operation, the results were leveled-there were no statistically significant differences between the two groups from all the investigated annular spaces.
 
 
I translate the result: turbidity with SMILE does not remain immediately, and opacities with femtoLASIK-methods almost completely disappear within 3 months.
 
 
My comment: By the way, chases after PRK are visible after decades - as well as traces from scars after keratotomy. They look like this:
 
 

 
Hayes after PRK
 
 

 
Corneal scars after radial keratotomy
 
 
Predictability of the cornea to the haysee is not yet possible: the effect arises from the fact that the outer epithelium of the eye separates the Bowman membrane from the cells of the embryos of the ectoderm (cornea). When it is burned out by the PRK, then on the histology, a pseudo-membrane membrane is seen - this epithelium is directly in contact with the cells of the ectoderm and the skeleton begins to form in order to replace the lost membrane. Not always this framework is transparent.
 
 

BOUMENOVA MEMBRANE AND HAESE - THAN DANGER OF FRK (TRANSFRK)

 
PRK (transFRK, etc.) is a cheap, practical and well-studied method. But from him went to femtoLASIK-methods, and then to SMILE. Why? Now I'll try to explain it in simple words, and then I'll show the research.
 
 
In its morphology, the cornea as a pie consists of 5 layers: the epithelium, the front boundary (Bowenova) membrane, its own substance (stroma), the posterior border (Descemetova),bogs and endothelium.
 
 
At the stage of embryonic development, three different types of tissue are formed: from the superficial ectoderm the epithelium develops later, from the mesoderm - the middle layer of the stroma, and from the neuroectoderm - the inner layer of the endothelium. As development and differentiation, each of these tissues needs isolation in order to preserve its structure and specificity, which is achieved by the parallel development of the boundary shells - the endothelium forms the Descemet's shell, and the stroma forms the Bowman shell.
 
 

 
This is the structure of the cornea
 
 
Normally, the cornea has physiological defects of the Bowman shell, through which nerve fibers enter the epithelium from the stroma. In a healthy cornea, there are few such holes, and there are certain protective mechanisms. When we evaporate the Bowman shell in PRK, we break the protective barriers and cause inflammation, the body reacts to this by the formation of fibrous connective tissue. Just subepithelial and intraepithelial fibrosis is chase (haze (fleur) - from English haze - fog). It is the reason for the rather slow achievement of the final results when performing photorefractive keratectomy (PRK), this remains one of the main problems of the method. Stabilization of refraction, as a rule, lasts several months and can be accompanied by regression or the emergence of haze.
 
 
Weakly treatable, pronounced opacities, occur infrequently. But even the transient mild haze during its existence can reduce uncorrected sharpness and contrast of vision, which becomes a partial return to preoperative refraction and worsens the quality of life of patients.
 
 
Thus, the possible opacity of the cornea, the slow achievement of the optical effect and pain syndrome, make PRK (transFRK) one of the most unpopular methods of laser vision correction.
 
 
Traditional treatment after PRK presupposes long-term use of corticosteroids, which allows to reduce the frequency and intensity of the appearance of heza, and also to a certain extent influence the postoperative dynamics of refraction. True, in some cases, corneal opacities in the photolytic zone are quite persistent and intense, which requires a different approach to treatment. In this case, to medical therapy, laser and even surgical methods can be added.
 
 
It should be noted that when using PRK as a method for correcting the risks, the risks are minimal, since the refractive component to be corrected is small. Especially in combination with surface treatment with antimetabolites. But with a primary correction of more than 1-2 diopters, all the shortcomings of PRK manifest themselves with might and main.
 
 
Here it is there are details about the complications.
 
 
Nerves are restored, but it takes time. Therefore, after FRG methods, supportive therapy (up to six months) is needed so that nothing bad happens with the eye during this time. Full regeneration until enough to control the trophic level takes about a year. With SMILE-method, only about 10-15% of nerve endings are stopped, which generates significant differences.
 
 
The second feature is the cornea skeleton. By there is a description of keratoconus - protrusion of the cornea forward due to intraocular pressure. This is the most frequent complication, and it is extremely unpleasant. The only way to avoid it is to go deeper into the cornea. The cornea is not uniform. On the surface the most durable layers. At a depth of 120 to 150 microns, already loose layers begin. It is there that work is being done on all methods since LASIK. With FRK, we remove the most solid upper part of the stroma - see the picture above.
 
 
About the features of what is better to keep the epithelium and stroma divided, I already said. With PRK this is not possible, with other methods - it is performed.
 
 

ABERRATIONS

 
"Comparison of the visual results after SMILE and femtosecond laser-assisted LASIK for myopia. Lin F, Xu Y, Yang Y. "
 
 
Sixty eyes from 31 patients with an average spherical equivalent of -??? ± ??? diopters were subjected to myopia correction by the SMILE procedure. Fifty-one eyes of 27 patients with an average spherical equivalent of -??? ± ??? diopters were treated with the FS-LASIK procedure. Results: neither in 1 nor in 3 months there were statistically significant differences in the parameters of visual acuity. High-order aberrations and spherical aberration were significantly lower in the SMILE group than the FS-LASIK group.
 
 
Conclusion: SMILE has a lower level of induction of higher-order aberrations and a lower spherical aberration than FS-LASIK procedure.
 
 
My comment: Visual acuity after femtosecond LASIK and after SMILE in quantitative measurement was the same in the two groups, but the quality of vision in the group after SMILE was higher due to smaller induced aberrations.
 
 
This is due, firstly, to the fact that the SMILE profile itself is aspheric, and the creation of such a profile by an excimer is possible only on modern machines and requires 5-10% more evaporation of the cornea.
 
 
Secondly, the optical zone after SMILE is always slightly larger than or equal to the planned one, and with femtosecond LASIK - slightly less than planned.
 
 
The damage factor, which is significant in femto- and mechanical LASIKe +, is completely absent from the excimer laser at SMILE.
 
 

 
The test of Schirmer (on tear production) and its result
 
 

 
Norn test (stability of tear film)
 
 
Now the next study.
 
 

BIOMECHANICAL PROPERTIES OF HUMAN CROPS

 
doi: ??? /s10792-017-0575-6
 
 
In this experimental study, 11 pairs of human corneas unsuitable for transplantation were divided into two groups. The corneas of the right eye were treated with femtosecond laser LASIK (FSLASIK), the cornea of ​​the left eye - using a small-cut extraction of the lenticle (SMILE). Pachymetry was measured in each eye immediately before laser refractive surgery. All corneas were subjected to refractive correction of the sphere -??? D and -??? D cylinder at 0 ° with a 7 mm area, or with a 110 μm flap (FS-LASIK), or with a cap of 130 μm (SMILE). For two-dimensional biomechanical measurements, the corneoscleral discs were subjected to two cycles of testing (a preliminary strain-strain curve from ??? to 9.0 N and stress relaxation at 9.0 N for 120 seconds) to analyze the properties of elastic and viscoelastic material. An effective modulus of elasticity was calculated. Statistical analysis was performed with a confidence interval of 95%.
 
 
In deformation-strain measurements, the effective modulus of elasticity was ??? times higher. The size of the effect is significant. There were no significant differences among relaxation-stress measurements with an average remaining voltage of 181 ± 31 kPa after SMILE and 177 ± 26 kPa and after FS-LASIK after relaxation.
 
 
Conclusions: Compared to a flap-based procedure, such as FS-LASIK, the SMILE technique can be considered superior in terms of biomechanical stability, with experimental measurement on ex vivo human paired eyes.
 
 
My comment is : before that, the same results were calculated by the mathematical modeling method of Professor Ranstein (Great Britain), and Professor Secundo confirmed the theoretical conclusions by measuring on paired human eyes (his corneal strength after SMILE is even higher than in theory) in a special Swiss laboratory. These are truly revolutionary results!
 
 
So,
 
 

So what is better with myopia?

 
Let's take another look at the theses:
 
 
1. The operations of PRK, femtoLASIK and SMILE are neither better nor worse than each other, each has its own scope. PRK is logical to use as a method of pre-correction and for special medical purposes. For a primary correction, it is not worth considering. FemtoLASIK can be done if there is no technological or financial opportunity to make SMILE, and the thickness and shape of the cornea allow cutting off the lid. ReLEx SMILE - the most gentle operation, the operation of choice in myopia and /or myopic astigmatism. It combines the advantages of two predecessor technologies - FemtoLASIK and PRK, but lacks their disadvantages.
 
 
2. The PRK method (trans-PRK) destroys the outer epithelium of the eye, the Bowman membrane and the upper (most durable) layers of the cornea. In cons - violation of innervation (and dry eyes), turbidity in the formation psevdobumenovoy membrane, the average risk of keratoectasis (protrusion of the cornea). In pluses - the ability to conduct this operation several times. FRK is certified in many countries for active sports.
 
In short, cool for those who love the old stile technology - I'm ready to change a new Mercedes to the old Volga GAZ-21.
 
 
3. FemtoLASIK suppresses about 75-90% of the superficial nerve endings in the cornea, the remaining barely enough to control the trophic, but this is better than burning out the entire surface. The work is in loose corneal layers, the skeleton suffers from the cutoff of the lid. Because of the risk of displacement or detachment, the phlepe is not allowed for correction in a number of dangerous occupations and for athletes. If everything went smoothly - it gives a good optical effect and an accurate correction.
 
 
4. SMILE - the most modern method, clinical use for more than 10 years: the first patients (except for test pigs) are walking after surgery since 2007. The cornea skeleton is retained, about 80% of the nerves are retained. For use, you need a unique VisuMax laser and a well-trained surgeon to extract the cut material through a narrow tunnel. The most painless operation that allows you to use your eyes from the next day without restrictions is the cost of it. Gives the smallest amount of distortion of vision due to aberrations. Now about two million operations are carried out around the world, but the number of devices, clinics and operated patients is growing exponentially.
 
 
5. Laser methods of vision correction are not the only possible methods of surgical correction of vision: it is possible to incorporate lenses into the eye, into the eye cornea-segments or to replace the own lens with an artificial lens with new optical properties (more here ).
 
 
6. Correction of vision - in most cases is done because of the desire to improve the quality of life, rarely for medical reasons. Insurance medicine in most countries (including Russia) does not cover the costs of its implementation. Doing a vision correction or wearing glasses /contact lenses - you decide, but in any case to choose the right option you need to be information-savvy.
 
 
I suggest that you decide by using the facts.