We got to the side effects of laser vision correction - and even before the diagnosis



    Let's start with the diagnosis, then move on to the tin, and then I will show a lot of photos of the equipment.

    In the 90s, the cornea was examined with an ultrasound pencil. Instead of a full-fledged map of the cornea, there were 10–15 measurements per eye, according to which the surgeon made a mental picture of what the patient had. In 1992, topographers based on the Placido system spread. The idea is that if you make a projection of the light rings on the cornea, then on the ideal they will be round, and any distortion will give distortion from the circle. That is, such a target was obtained in the eye in the ideal case, and an egg with astigmatism. And so they looked - they shone with a beam through the Placido disk. Now these disks have many surgeons in your pocket just in case.

    The method was, of course, very exemplary. Then the automatics came: the same discs became 32-36 rings instead of 8 or 10, and the device took photographs of them, and then recognized and counted distortions, and produced a "depth map" of the eye.


    This is the “target”


    “Depth map” of the eye.

    At the same time, for the diagnosis of keratoconus, it was important to measure the cornea not from above, but from the side, and the technology of the topographer Orbsken developed in parallel. Instead of a reflection profile, a beam went there in a slit lamp (as in a scanner for papers), and it allowed us to obtain optical media of the cornea, in particular, its back side.

    Accordingly, it was automated and did something like measuring with dozens of slices, and then assembling into a single map. As a computer x-ray tomograph, only easier and in the light.

    The next stage of evolution was the principle of the Shimpflug, that is, the rotating beam. As you can guess from the name, they invented it in Germany, and in the same city where Lake and Oculus are sitting. To date, the embodiment of this principle, the device "Pentakam" - the most popular diagnostic apparatus for refractive surgery. There is a lot of information - 4 or 5 other devices were collected into one: here is the thickness, the front surface, the back, the depth of the front camera. And this device is still evolving and becoming more accurate.

    But the system Placido is not dead. In the case of complex patients (and these are regularly sent to us when they do not know how to treat the problem), it complements information about the state of the cornea. In this case, the Placido system is good, because the topography of the surface after complications makes it possible to assemble a surface removal map to a perfect “target”, that is, to quickly calculate the difference between what is visible and what needs to be done, and then remove the excess fabric with a laser. This is the so-called topoguided-operation. Uneven corneas can be brought in a more or less decent condition. Approximately the same principle applies superLASIK, which is configured for each individual patient each time. Its analogue - femtoLASIK Custom Vue - is a wavefront-guided laser. Here the idea is that the wavefront of the eye is measured, and then the excimer laser blows off the necessary parts of the cornea. The method has pros and cons. The disadvantages are due to the fact that part of the distortion comes from the lens, and nothing can be done on the laser correction with the lens. The lens during life varies greatly, and the cornea almost does not change. He grows all his life. Accordingly, in this case, the supercorrections are enough for a couple of decades of young active life ... As a result, the “ideal” profile for the cornea, which is not associated with the current lens profile, is now much more often used.

    And there is also classical OCT (tomography) - it shows the thickness of the tissue better, and it is used additionally for corneal opacities, excluding other methods.

    So, according to the results of the diagnosis, a profile is selected. In the case of modern operations - the surgeon builds a profile in the likeness of a master, entering the necessary data. Mathematics for an aspheric lens is done by flashing the laser, then the surgeon selects from several possible results or simply confirms the scheme of the operation.

    Here is the ultrasonic "pencil":



    The rest is modern - at the end of the post. In the meantime, important practical things for the operation.

    We are not looking through the center of the pupil.


    The next thing that interests us is the cornea centering under the laser. The surgeon selects a cone for pneumatic auto-gripping - there are three sizes for different tasks. For myopia, the smallest is often taken, it lies on the periphery of the cornea.

    The minimum number of people looking through the center of the pupil. Usually our optical axis is slightly shifted towards the nose - this is the kapp angle. In hypermetropes (people with serious hyperopia, for example) this angle is greater. It comes to the fact that sometimes they look at the very edge of the pupil.

    In order not to cut the lens where it is not necessary, it is important to perform centering along the optical axis. Therefore, the patient himself looks at the flashing LED. But in fact, of course, we do not fully trust the patient here, and we definitely control the capture of the Purkinje reflex. In a sense, a glare, not a conditioned reaction. This is a highlight that you are familiar with from the “red eyes” in the flash photo, only it can be shrunk to near point. This is not the axis itself, but it is very close to the reflex, so much so that you can take this point as the center of the lens. In difficult cases, sometimes a point is chosen between the center of the pupil and this reflex - it all depends on the preliminary diagnosis.

    The reference beam is placed on this place, the center of ablation is marked. Then the laser turns on. In excimer lasers there is a high-speed camera that monitors the micromovements of the eye and moves the laser in concert with them. On older models of lasers during operations, if the patient looked away, the laser did not hit there. Since 2005, some systems of following the eye have moved along with the beam. In the case of FLEX or SMILE, when a femtosecond laser is used, the eye is simply captured in a pneumatic capturing device. The tracker is not there, but there is a vacuum loss sensor - before the eye is removed, the laser will turn off.

    Proper capture does not always happen. If this is the case, the surgeon performs the additional correction by turning or re-capturing. The capture control is done by overlaying two pictures - from the camera in real time and from calibration to capture. Someday we will have auto systems that will overlay two pictures and capture correctly automatically. Today it depends on the experience of the surgeon.

    Professor Sekundo did a study - he compared 36 patients with femptoLASIK and 36 with SMILE - the location of the tissue evacuation zone in the second case was better. Even on the old MEL-80 (the most modern at the time). Excimer laser in general is very much forgiving an inexperienced surgeon. But an experienced surgeon can create centration on VisuMAX better than a regular excimer automatically. Probably in the future there will be a firmware and a manipulator that will reduce this factor of experience and skill of the surgeon.

    In Istanbul, there was somehow a very difficult patient with two decenters close to a squint. It was rather difficult with him, because it was necessary to go through the language barrier, but in the end everything was possible. However, if there is a possibility, we always recommend that you choose a surgeon who speaks the same language as you for difficult cases.

    What is most important in the correction of astigmatism


    This is how a person with astigmatism sees the world:



    Simplifying what a healthy person would give a point on the retina becomes an ellipse or "eight" at a certain angle with astigmatism. By determining this angle and the relative dimensions of this distortion, you can make lenses for glasses, in which the curvature will vary non-linearly in comparison with conventional lenses for myopia or farsightedness. Some time later, they learned to make the same contact lenses (it is important to insert them into the eye without rotation), and then to calculate the profiles in order to cut such a “contact lens” directly on the cornea or inside it. That is, to solve the general problem of laser vision correction.

    Astigmatism is corrected by laser methods very effectively. However, the most difficult part is comparing the future profile of the lens and, in fact, the eyes. The fact is that if you miss with a turn of 10% - the effect will be lost by a third. If you miss by 30%, the effect will completely disappear. As a result, an important part when working with astigmatism is capturing the eye on the vacuum “sucker” of the laser. This is a question of the doctor's experience (fortunately, not necessarily manual, so they do it almost everywhere well). On modern lasers, it is possible to expand the grip “within oneself”, slightly rotating the patient's eye — it was proved at the Indian Research Center that it is safe to do so.

    How is the focusing of the laser through the lens of the fluid on the surface of the cornea and the micro droplet of fat?


    When premedication with anesthetic is done (usually with alkaine), quite a few drops fall onto the surface of the eye. Then the eye is wiped at least once with a wet swab just before contact with the laser pneumatic gripping device. If the eye is dry, lacunae will form between the cone of the laser and the cornea, which distort the focus. If the eye is wet, the liquid fills them, and there are almost no parasitic refractions. Mirkokapli fat driven by the seizure due to pressure. As a result, of course, the environment is still not ideal, and this is partly one of the reasons why the lenticle must be “circumvented” with a spatula on both sides, separating it from the upper and lower layers of the cornea. A significant mistake can be this: eyelashes emit fat, which begins to quickly and uncontrollably spread over the surface. This fat breaks the focus, and large bridges remain, which need to be separated with a sharp spatula (as was done on the previous generation of lasers) - or you need to stop the operation at the sight of such a problem. In our clinic, we do not leave anything to chance, using a number of necessary manipulations: aspirators to remove excess fluid and fat drops, special hygroscopic sponges, we can even deprive you of a pair of eyelashes near the central part of the eye - we will cut them in case they suddenly not arched as not necessary.

    How is the surgeon during the operation?


    Not worth it, but sitting. All eye operations are done strictly sitting, so the hand moves much more stable. Right-handers work to the right of the patient, left-handers - to the left. Accordingly, the incision for extracting lenticles is made where the surgeon is most comfortable to get access - closest to his arm with the instrument. Why it is so important, I will show a little later, when we talk about what is in the operating room.

    What are the worst complications?


    Complications with LASIK up to 6%, with femtoLASIK and FLEX - up to 2%, with SMILE - 0.5-1% (depending on the generation of lasers, 0.5% is the sixth). The last numbers are not confirmed by ten years of clinical trials - the data will be officially published only in summer 2017, but you can walk around Wikipedia - articles about various methods give fairly rich links to research.

    One of the worst complications of any correction other than PRK is keratoectasia.(when the cornea bulges, as with keratoconus). As a result of the operation, this may happen due to a significant violation of eye biomechanics - as a rule, either due to incomplete diagnosis, or because of a surprise, which the doctor’s diagnostic tools could not reveal. That is why it is important to make the diagnosis very carefully and using different methods. It must be admitted that the most expensive “reinsurance” equipment in clinics is often saved. On the other hand, if the patient already comes with keratoectasia, then he will most likely have direct indications for good old PRK. In general, any thin cornea, and even not quite straight - it is well leveled PRK. In the early stages of keratotonus, PRK levels the surface and immediately from above we still do cross-linking (treatment with a high content of B12, then the release of oxygen due to laser heating and fixation of collagen in the ultraviolet - everything to make it tough, but about that later separately). This niche will ensure the life of the PRK for another 10 years minimum.

    Keratoconus is a complex complication in the medium term. Immediately cross-linking is done, that is, koroektasiya treated as usual. Intra corneal half rings can be inserted.

    Historically, part of keratoectasia after SMILE is when the surgeon found the diseased cornea and decided not to do an invasive LASIK procedure or its derivative, but for some reason decided that with ReLEx it could “roll” because of its low invasiveness. Not. The diseased cornea does not need to be corrected without strengthening. You can do cross-linking, rings, transplantation.

    The next most popular flap is LASIK, femtoLASIK or FLEX.Most often, of course, LASIK gets - they have a total risk of various side effects under 6%, and at the same time they are doing a lot in the country even to this day. Any patchwork correction method is a contraindication to contact sports. You can give birth, but getting “in the face” is undesirable. There were cases when the flap was torn from the fact that the child simply inadvertently poked his mother's finger in the face, from the fact that the woman caught the tomato stick with his eye - in general, the most different. Let me remind you, the essence of the problem is that with these methods a “lid” is cut, which “leans back” to create a lens inside the cornea, and then this “lid” is closed back. It is connected with the eye by a thin jumper- “loop” and a thin layer of epithelium that has grown on top. The flap does not grow, and keeps, without opening, only with the help of superficial epithelium from above. The LASIK flop itself can be removed even after 8-10 years (there have been cases) - and it will disperse exactly where it is on the day of the operation. In the case of femtoLASIK and FLEX, the flap is stronger, there is often scarring along the edges (a thin white striped) - after 2-3 years you can already try to tear it off with your teeth, and it will not give in. In the case of SMILE, there is no flap at all, but there is a “tunnel” (2.5 mm incision) through which the lenticular from the cornea gets - it is also covered with epithelium, but before it grows, it is impossible to wash in order not to cause an infection. Our colleague from Yekaterinburg talked about a patient with SMILE, who was badly beaten - the injuries went over the eye very extensively, but the weakest point was not at the correction site. The eye managed to be saved, the patient sees well. More precisely, I began to see in a couple of weeks. A similar case was in practice with Bloom (the second inventor of the correction technology). In Germany, now to work in the police, you can only do PRK in 13 of the 16 federal states. Another three allowed femtoLASIK.

    Contrary to the common myth, the Bowman's membrane, which is located on top of the cornea (which is destroyed during PRK and is severely injured by the femtoLASIK methods), does not provide protection against mechanical damage of the impact type. It provides stability of the “slow” type, in particular, it compensates pressure from the inside of the eye.

    Now it's worth talking about the halo effect.- It is a halo around lights at night. It can give any laser correction. It depends on the size of the correction zone in relation to the pupil. The usual correction zone is 7 millimeters. The pupil of some people opens up to 8 millimeters in total darkness. Previously, they generally made correction zones of 4-5 millimeters. The second reason for the halo (more relevant for modern operations) is how flat you have the cornea in the center. The center should rise (the healthy cornea has more diopters in the center than at the edges - for example, 38 D in the center, 42 D at the edges). A good pro calculates a profile for a laser cut so that the cornea flattens over a large area. Excimer lasers have different aspherical profiles for this. ReLEx SMILE itself is aspherical in its intervention architecture itself. Yes,

    Next we have photophobia and tissue overgrowth. The problem is medication. In the PRK in Russia, the “usual” metamitsin is not used for this operation (it is not allowed at the state level). Analogs are a bit more risky. Now ophthalmologists are trying to lobby for permission of this drug for operations.

    The next case is incomplete extraction of lenticules during SMILE operation.. There were extremely rare cases where a part remained that could not be picked up with tweezers. In this case, cortisone is injected, which stains the small fragment and then you can go inside and remove it. In London, one of the very expensive surgeons makes a second cut for the opposite case of the first — he does not use it, but keeps it in case of problems during the operation. Usually, if the laser did not cut something in the lenticle, this is the problem of the surgeon, who for some reason reached out and tried to separate the place where there was no cut. That's right - give heal and make PRK with topography. Alternatively, switch to FLEX instead of SMILE.

    Then the incision edge tears- a very unlikely thing in experienced hands, when the surgeon with a tool tears through the entrance to the "tunnel" leading to the lenticule. In order for this to happen in practice, it is necessary to push it into the shoulder during the operation. However, there is usually no problem: there was a 3 mm cut, it will become 3.5 mm - in fact, it’s okay. In the overwhelming majority of cases, the incision is tearing radially, but there was one example at the very beginning of the history of corrections, when there was a strain of 1.5 mm in the direction of the center. From a zone of 7.8 mm, a zone of 6.8 mm was obtained, the patient received a halo effect in deep darkness. The solution is simple - you need to keep an eye with tweezers with your second hand, since it is in the obligatory SMILE protocol.

    Of the serious (but, fortunately, already reversible) it is worth noting keratitis. This inflammation of the cornea, most often - as a result of the infection. Its three stages - in the second, usually cortisone and treatment at the discretion of the physician, and in the third - rinsing of the pocket is necessary (there is a risk of irreversible scarring). Therefore, after surgery, you are observed the next day and several more times.

    All the rest, as a rule, takes place within a week or two after the operation, and is associated with the body's response to mechanical damage to tissues, or features of medicines. Yes, you can cry for a couple of hours, yes, it can pinch, yes, someone with painkillers causes a wild desire to honor the eyes (which cannot be done). And yes, the first couple of days you better not to appear at a beauty contest and shoot portraits for a dating site. Then everything will be fine.

    Diagnostic equipment


    Spectral optical coherent tomography - a high-frequency contactless method for diagnosing morphology of the cornea, retina and optic nerve. During the procedure, only a laser beam or infrared light is used. The result of OCT is a two-dimensional or three-dimensional image:



    Pentakam is the “gold standard” in the diagnosis of corneal diseases.



    Rotational Shimpflug camera for corneal computer topography and a comprehensive study of the anterior segment of the eyeball. Such important parameters as the curvature of the anterior and posterior corneal surfaces, the total optical power of the cornea, pachymetry, anterior chamber depth, anterior chamber angle of 360 ° and densitometry of the cornea and lens are automatically calculated. Non-contact measurement takes 1-2 seconds and includes 25 or 50 timesflug images (depending on the scan mode). In total, to build a 3D model of the anterior segment of the eye, up to 25,000 real elevation points are detected and analyzed. Automatic guidance control system provides ease of measurement and high repeatability of results.

    View from the doctor:



    On the left, an automatic auto refratoratometer is based on the use of a special wave-front sensor Hartmann-Shack, which allows analyzing the wave front reflected from the retina of light retransmitted point by point. With the help of wavefront analysis, we can analyze the aberrations of the optical system of the eye and select the optimal correction. On the right is an automatic contactless pneumotonometer that allows you to measure intraocular pressure and corneally-compensated intraocular pressure.

    Patient's view:



    Left - automatic contactless pneumotonometer.
    On the right is an automatic auto refrake meter.

    Automatic projector signs can be mounted on the wall or on the table. Works at a distance of 2.5 to 8.0 meters. Equipped with a remote control. Contains more than 40 of the most necessary tests, including for children. High speed slide change (0.15 seconds). High resolution (50 lines per mm) allows you to accurately assess the patient's visual acuity:



    Diagnostic room for complex diagnostics of pathology of the anterior and posterior segment of the eye, the projector shows:



    Automatic perimeter - analyzer of visual fields:



    Used to determine the threshold sensitivity of the retinal organ of vision, identifying pathological changes in the earliest stages.

    Optical coherence tomography (OST):



    OST - This is a method of displaying the structure of biological tissues of the body in a cross section with a high level of resolution.

    Diagnostic Cabinet for Primary Diagnostic Examination:



    The IOL Master 700 optical biometer is a new generation of the “gold standard” of optical biometrics:



    An optical instrument for contactless measurement of eye structures using the method of optical coherent tomography. Optical biometrics of a new generation using Swept Source OCT technology provides scanning of the anterior and posterior segment of the eye. This not only allows a better understanding of the surgical anatomy of the eye, but more accurately calculate the refractive result of the operation.

    The automatic lens meter is the optimal device for selecting points, assessing the quality of lenses, and taking prismatic readings: the



    IOL-Master 500 is simple and perfect. With it, accurate measurements of the biometric parameters of the eye, necessary for the calculation of IOL (intraocular lenses), are made in seconds.



    It is especially valuable that measurements are made in a non-contact manner. With one click of a button, you can quickly obtain accurate data on the length of the anteroposterior axis of the eye, the radius of curvature of the cornea, its diameter and the depth of the anterior chamber.

    A slit lamp with a video camera is a device that allows an inspection of the visible parts of the eye - eyelids, sclera, conjunctiva, iris, lens and cornea under magnification:



    With the help of special lenses in the slit lamp, the central and peripheral parts of the fundus are visible. The slit lamp consists of a binocular microscope and a source of narrow light. Inspection with a slit lamp is eye biomicroscopy. The possibility of photo and video fixing is very important.

    Aberrometer is a wavefront analyzer using Fourier algorithms, it reflects the unique flaws of the patient's eye using 100% of the available Hartmann-Shark points for more accurate detection of wavefront errors:



    The system provides the highest resolution available for any pupil size, allowing accurate, individual approach for a wide range of optical errors.

    An endothelial microscope is necessary for observing and analyzing the endothelial layer of the cornea, measuring the thickness of the cornea, and automating photographing:



    A digital photo slit lamp is used to produce a high-resolution digital image, a video image. The software allows you to optimally organize computer processing and storage of digital images:



    The primary diagnosis



    room : The TONO-PEN contact tonometer is a lightweight and ergonomic device:



    Despite its small size and weight, the accuracy of the readings is comparable to the Goldman tonometer. At the heart of the TONO-PEN strain gauge with a contact surface diameter of 1.5 mm, it touches the cornea almost imperceptibly and gives the arithmetic average of the results of four independent measurements and a statistical coefficient.

    Manual ophthalmoscope for examining the fundus of the eye:



    A set of test eyeglass lenses is designed for examining visual impairments: myopia, hyperopia, astigmatism and presbyopia, for the examination of strabismus and color blindness. Also, the kit is used for the selection of glasses and lenses:



    That's it for today. Next time I will talk about why a 3.5-inch drive is for some lasers, and show you how a femtosecond laser is controlled during an operation. After this, the cycle of posts about laser vision correction will almost end: there will be a comparison with lenses.

    Also popular now: