PRK-excimer laser keratomileusis surgery is based on the principle of applying excimer laser to cut the central anterior surface of the cornea, i.e., removing the anterior elastic layer of the epithelium and the superficial stroma, so as to reduce the curvature of the anterior surface of the cornea, increase the radius of curvature, decrease the refractive power, and move the focus backward to the retina, so as to achieve the effect of correcting myopia, which is like grinding a pair of myopic lenses on one's own cornea. It has been gradually replaced by LASIK due to postoperative pain, the need for long-term medication and the tendency to regression.
Editorial LASIK - excimer laser corneal in situ grinding surgical principle is to first use the automatic micro corneal laminating system in the corneal surface to produce a tipped lamellar corneal flap, after flipping the flap, the application of excimer laser computer-controlled multistep zoning of the corneal stroma cutting, and finally the flap will be repositioned. This method preserves the integrity of the corneal epithelium and anterior elastic lamina, and cutting the corneal stroma with the 193-nm excimer laser avoids the occurrence of postoperative haze clouding. This kind of surgical equipment is sophisticated and expensive, requiring high surgical techniques and a sterile surgical environment, and can only be carried out in large hospitals with better conditions. LASIK has become the most commonly used refractive surgery method and is widely used worldwide, removing glasses for many myopic and hyperopic patients. This technique is suitable for patients with myopia up to 1400 degrees.
PRK has been gradually replaced by LASIK due to postoperative pain, the need for long-term medication and easy regression.
Torsion Lasik, or TK for short, which translates to iris recognition rotational positioning + wavefront aberration-guided excimer laser myopia surgery, is a leap forward from traditional laser myopia surgery. At present, there are only a handful of such surgeries in China.
Edit LASEK - excimer laser corneal epithelial resurfacing LASEK is a newer generation of excimer laser surgery. The difference between LASEK and LASIK is that instead of using a microkeratome to make a flap, a corneal epithelial ring drill is used to cut an epithelial flap with a thickness of 60-80 micrometers, a diameter of 8-10 millimeters, and a curvature of the tip of the flap of 30 degrees, which is then lifted off to carry out in-situ grinding by an excimer laser to change the refractive error of the cornea to achieve the purpose of correcting nearsightedness and astigmatism, and then the epithelial flap is reset. After the surgery, aberrations and glare can be solved for patients with high myopia. Since the epithelial flap thickness is 60-80 micrometers, it solves the thickness problem for patients with high counts and relatively thin corneas, and at the same time improves the safety for such patients.
Editing the biological properties of excimer lasersAny change in biological tissue caused by the interaction of laser light and biological tissue is called a biological effect of laser light.
What happens when an excimer laser interacts with biological tissue is not a thermal effect but a photochemical reaction. The so-called photochemical reaction means that when the tissue is subjected to far-ultraviolet light, it breaks the bond between the molecules and separates the tissue directly into volatile fragments that dissipate into thin air, leaving no effect on the surrounding tissue.
The light energy of the excimer laser is almost completely absorbed by the corneal epithelium, Bowman`s membrane and stroma. Marshall, UK, made photolytic excision of animal corneas with a hydrofluoroexcimer laser and carried out ultrastructural examination, and the experiment found that the photolytic incision had clear boundaries and there was no thermal damage phenomenon in the surrounding area.
The 193nm argon fluorine excimer laser has many features suitable for application in corneal refractive surgery. Each pulse has an energy of up to 6.4eV, which is far more than the binding energy of carbon and carbon bond of the binding molecule of 3.5eV, so the photon can break the bond between molecules and separate the tissue into volatile fragments, and the absorption range of the laser is extremely narrow at this wavelength, which is about 3.7-3.9μm, that is to say, tissues beyond this range will not absorb the laser, and each laser shot can cut 0.2-0.5μm of cornea. Each shot of laser can cut 0.2-0.25μm thickness of biological tissues, and each time the consistency is good, there will not be deep and shallow situation, so the depth of cut is proportional to the number of laser shots. Since the entire pulse of the laser is only 10-20 μs, the thermal diffusion effect is very small, and only 0.3-0.8 μm of the surrounding tissue can be harmed.
In addition, since the penetration of electromagnetic waves into the cornea decreases with shorter wavelengths. Below 400nm, the penetration power decreases to zero. Therefore, far-ultraviolet rays with a wavelength of 193nm lead to no corneal penetration. Therefore, there are no adverse side effects on the internal tissues of the eye.
The excimer laser's ability to cut the cornea is characterized by ultra-fine precision and ultra-fine degree of damage. 193nm wavelength far-ultraviolet light produces very little thermal effect, thus limiting the damage to the surrounding tissues to a very small extent. Moreover, an exceptionally smooth cutting plane is provided.
Edit Aftermath of Surgery and Precautions Intraoperative Precautions
[1]Myopia surgery is mainly performed on the cornea of the eye, and there are no blood vessels or nerves on top of the cornea, so you're in for a painless procedure. During myopia surgery, the good cooperation of the patient is an important prerequisite for the success of the surgery, therefore, myopia surgery, the patient should pay attention to the following points: 1, relax, do not be nervous.
2, do not squeeze your eyes hard, do not move your eyeballs at will, and hold them still according to the doctor's guidance.
3, the critical moment of surgery, to follow the doctor's instructions, do not speak, not to mention allowed to move around.
4. During the operation, you must keep your eyes on the flashing red or green eye light, even if you can't see the eye light, don't move, and gently move your eyeballs according to the doctor's guidance and don't move your head.
5. On the operating table, do not touch the sterilized area with your hands.
After surgery
1. Undercorrection or overcorrection: Myopia remaining after surgery or hyperopia exceeding the expected correction is the most common side effect, which can be corrected again after the correction is stabilized.
2. Photophobia: The sensitivity to light increases within 3 to 6 months after surgery, but most of the time it disappears gradually after 6 months, and in very few cases it persists.
3. Glare or diplopia: It is more common at the beginning of the surgery, especially at night when the pupil becomes bigger, but most of it will disappear gradually and only a few cases will continue.
4. Surgical complications: Most of them are due to poor cutting of the corneal flap, such as incomplete or uneven cutting; they can be recovered by repositioning the flap, and the surgery can be repeated after three months.
5. Poor healing of the epidermis: most commonly seen in PRK; therapeutic contact lenses and artificial tears can be used to help recovery.
6. Corneal clouding: It occurs only after PRK, and is positively correlated with the individual's physical condition and the higher the degree of correction. It is most obvious in the first 1-3 months after surgery, and is controlled by steroid eye drops, and then most of the corneal clouding will fade away slowly.
7. Corneal flap folding or displacement: only seen in LASIK, may be caused by trauma, will cause irregular astigmatism affecting vision, can then be paved with surgery.
8. Sub-flap impurities or epidermal invasion: mild cases do not affect vision, serious cases must be flipped to remove the flap.
9. Infection: Due to surgical or postoperative uncleanliness, the wound is infected by germs, the chance is very low, as long as the early detection, most of them can be controlled by drugs.
10. Dry eye: Tear secretion will be reduced after laser surgery, which may produce dry eye symptoms or worsen the symptoms of those who originally had dry eyes, and require supplemental artificial tears treatment, which can be improved in about 3-6 months.
11. Presbyopia: People who are close to or over 40 years old may already have presbyopia. Even if you don't need to wear glasses to look at the distance after myopia correction, you still need to wear glasses to look at the near distance or to read books, so please discuss with your doctor about the correction method that is suitable for you.
12. Surgery does not guarantee 1.0 visual acuity, and in some cases you may need to have another surgery or wear glasses to get the best possible vision.
Dangers of surgery on the cornea
Clouding of the center of the cornea: David Griffin School of Medicine at the University of California, Los Angeles, USA. Griffin School of Medicine's Barris . Barris Sommertz, of the David Griffin School of Medicine at the University of California, Los Angeles, and Robert K. Maloney, of the Maloney School of Vision, have published an article in Ophthalmology describing their experience in the management of "corneal center clouding" after myopic laser surgery.
Some ophthalmologists have noted that cases of corneal lesions from laser surgery have been occurring since 1998. Prof. Sommertz and Maloney studied 14 similar cases*** involving 23 eyes. In 19 of these eyes, vision improved after LASIK surgery. However, four eyes developed problems after undergoing the procedure. Clouding of the center of the cornea usually occurs 3 to 6 days after surgery. The lesions were located in the center of the cornea, the area of the eye where the laser power is the highest during myopic LASIK surgery. The patient also develops "hyperopia," or light-focusing disorder. However, the clouding gradually disappeared after 2 to 18 months.
Possible allergy to the laser: Drs. Sammertz and Maloney agree that the "central corneal lesion" was not inflammatory, and they warn against the use of "corticosteroid" medications because prolonged use could lead to cataracts, glaucoma, and other eye diseases. cataracts, glaucoma and even blindness.
Seven of their patients had LASIK surgery after the corneal clouding had disappeared, improved their vision, and never experienced corneal clouding again. The doctors speculated that the clouding after myopic LASIK could be a reaction of the patient's cornea to an allergic reaction to the laser, and that some external stimulation was "needed" to improve the symptoms.
Pre-operative precautions
1. Stop wearing contact lenses for at least 1-2 weeks for soft lenses and 2-3 weeks for hard lenses before the examination.
2. Practice staring at a point without moving for at least 2 minutes at a time.
3. Do not use any makeup or perfume for three days before surgery.
4. Arrange for a surgical escort for post-operative escort.
Possible Problems After Surgery
1. Glare and Night Vision Impairment: If the myopia is 700-1000 diopters or more, 80% of people will experience slight glare at night and 25% will have problems with night vision. This is mostly caused by the surgical area being closer to the center of vision during surgery.
2. Dissatisfaction with the corrected vision: It is possible to feel under-corrected after surgery, not as effective as expected, or over-corrected, and farsightedness, also known as presbyopia, may advance.
3. Dry eye: There is a possibility that the tear film nerves may be injured during the surgery, which may reduce tear secretion.
4. Pseudoconical cornea: extreme postoperative problem. This is caused by cutting too deep and can cause even more vision loss, fortunately the chance of occurrence is very low.
Post-operative precautions
For 24 hours: Sleeping in a supine position is preferred to avoid touching the cornea.
There may be a foreign body sensation or tearing, do not wipe with your hands, pay attention to hygiene.
Do not wash your hair, shower. Do not use eye cosmetics.
Within one week:
Protect your eyes by wearing an eye mask when you sleep, so as not to displace the corneal flap due to external force.
Ban smoking, alcohol, betel nut, and eat less stimulating food. Watch less TV, computer and books and newspapers to avoid eye fatigue.
In order to prevent sand and dust or foreign objects from entering the eyes, you can wear sunglasses, flat lenses or eye shields outside.
Do not swim or take a steam bath.
For one month: avoid strenuous exercise or activities that can injure the eyes. Do not drive or operate dangerous machinery.
Over a lifetime: pay attention to hygiene and avoid overusing your eyes.
Edit this section of modern myopia surgery each classification of the main surgical methods conventional lasik
The principle of the operation is to first use the automatic micro corneal lamellar system to produce a tipped lamellar corneal flap on the corneal surface, flip the flap, the application of excimer laser computer-controlled multistep zoning of corneal stroma intracorneal cutting, and finally the flap will be reset. This method preserves the integrity of the corneal epithelium and anterior elastic lamina, and cutting the corneal stroma with the 193-nm excimer laser avoids the occurrence of postoperative haze clouding. This kind of surgical equipment is sophisticated and expensive, requiring high surgical techniques and a sterile surgical environment, and can only be carried out in large hospitals with better conditions. At present, LASIK has become the most commonly used refractive surgery method and has been widely used worldwide, removing eyeglasses for many myopic and hyperopic patients. This technique is suitable for myopic patients up to 1200 degrees.
Ultra-thin lasik
Ultra-thin LASIK is a LASIK procedure in which the corneal flap is made thinner. Using the French ultra-thin corneal flap production technology, the thickness of the flap is controlled at about 100 microns. For patients with the same corneal thickness, ultra-thin LASIK makes the corneal flap thinner, retains more corneal stroma than ordinary LASIK, reduces the risk, and further improves the safety of the operation, combining the advantages of LASIK and EPI-LASIK to make the operation adaptable to a wider range of people, so that many patients with high counts, thin corneas, and patients who are not able to be operated by ordinary LASIK can have the opportunity to realize the goal of surgical lens removal. For patients who are suitable for LASIK, if they choose ultra-thin LASIK, more corneal stroma will be preserved, and the safety and postoperative stability of the surgery will be higher. Currently, ultra-thin LASIK has become the main refractive surgery method to replace conventional LASIK surgery.
Epi-lasik
Using a special corneal epithelial knife (which cuts into the epithelial layer of the cornea and intelligently stops going deeper, then automatically separates the epithelial layer of the cornea from the underlying tissues in a smooth manner) to create a corneal epithelial flap of a thickness of only 50-60 micrometers, which is completely computerized and controlled by a fully automated machine to make an epithelial flap of exceptionally smooth thickness. The thickness of the epithelial flap is only 50-60 micrometers. After laser cutting, the epithelial flap is repositioned and the surgery is completed. It combines the advantages of LASIK and LASEK, and the quality of vision after surgery is greatly improved. Its advantages of better long-term results, more savings in corneal thickness, providing a greater range of correction, and greater safety have a very attractive clinical value.
Q-value-guided LASIK
Q-value-guided LASIK surgery individualizes corneal cutting according to the aspheric characteristics of the individual cornea and maintains the aspheric characteristics of the cornea, which results in a quantum leap in treatment precision and effectiveness. Together with finer adjustments to the optical zone, transition zone and treatment parameters, more satisfactory surgical results can be obtained. The quality of post-operative vision is better than conventional surgery, and it also reduces glare and improves night vision. This has very positive implications for patients who need to drive at night, for example.
Lens surgery
The principle of the surgery is to make a tiny incision in the corneal rim of the patient, and implant a special artificial lens into the anterior or posterior chamber of the patient's eye, which does not damage the cornea and does not require the removal of the original crystalline lens, thus preserving the integrity of the physiological structure of the patient's eyeball and the function of adjustment. This kind of surgery, in fact, is to move the lens from the outside of the eye to the inside of the eye. Moreover, the surgery is reversible, in case the IOL is not needed, it can be removed with a minor surgery. The surgery is effective and corrects a wide range of refractive error. This technique is suitable for patients with 1300-3000 degrees of ultra-high myopia, astigmatism of 300 degrees or more, and a thin cornea that cannot be operated with laser surgery.
The main types of crystalline lens surgery are:
Anterior chamber iris clamping type (referred to as ACL)
Posterior chamber type (referred to as ICL)
[2]
Edit this section of the process of excimer myopic surgery preoperative counseling - to unveil the mystery of the excimer surgery
Patients can be through various ways to Professional consultation, for example: call the hotline consultation of professional hospitals, professional consultants will patiently and carefully answer your various questions. In addition, you can also through the professional website for online consultation. Or come to the hospital directly to consult with a professional physician. By establishing a basic understanding of LASIK surgery, the unnecessary mystery and fear of this surgery will be eliminated.
Pre-operative consultation - safe checkup, assured diagnosis and treatment
Choose a suitable date to come to the hospital for the initial consultation, and the whole process of the initial consultation will be carried out in an orderly manner under the guidance of the doctor.
The initial consultation is mainly to examine the patient's basic condition, and to do a detailed examination and analysis of your eyes through various professional instruments to determine whether you are suitable for excimer laser surgery. Professional doctors can make a surgical plan according to the analyzed data of each person and make a general prediction of the surgical effect. Therefore, this session is very important. In this session, the doctor will screen out patients who are not suitable for surgery, such as some lesions on the bottom of the eye, diabetic patients, cone cornea, scarred body, etc. If you pass this examination, it means that you are not suitable for laser surgery, and you are not a candidate for laser surgery. If you pass this screening, you are a candidate for the surgery. The safety of the surgery must start from the preoperative examination and continue until the end of the surgery.
The surgeon who specializes in excimer surgery must have a rigorously approved qualification and many years of surgical experience, and the patient can decide whether or not to proceed with the surgery based on the surgeon's recommendation.
Pre-operative review - the second firewall of surgical safety
The main purpose of the review is to verify the accuracy of the data from the initial examination, and through a series of professional equipment testing, another firewall for the safety of the surgery. The finalization of the surgical program will be finalized. The surgeon will explain the entire surgical arrangement, the precautions to be taken on the day of the surgery and the protective measures to be taken after the surgery. You can determine the time of surgery according to your own situation and the doctor's advice, and sign the informed consent for surgery. Experts especially remind that the preoperative examination must be very strict and serious. If you fail one of the tests, you cannot undergo excimer surgery.
To undergo the surgery - experience the process of excimer removal
On the day of the surgery, you will need to make arrangements for the surgeon's recommendations, such as wearing comfortable clothing, avoiding contact with stimulants such as alcohol, tobacco and related medications in advance, and refraining from the use of cosmetics, etc. The procedure takes about 15 minutes. The procedure takes about 15 minutes, and the actual time spent with the excimer laser is less than 30 seconds. After the surgery, you need to take a short break, and the doctors and nurses will do some professional protective measures to protect your eyes from being affected by the surgery.
Post-operative health care - clear world, gradually revealed
After the surgery, you must come to the hospital regularly for review according to the physician's advice, in order to keep track of the operation. The surgeon will have a set of detailed instructions on what to do and what to protect yourself against after the surgery. The patient needs to follow these instructions one by one. In addition, the hospital will provide a complete post-operative service system, so that patients can enjoy the warmth of medical services at any time. [3]
Edit paragraph myopia laser surgery to adapt to what symptoms ① patients have the requirement of removing glasses.
② Age above 18 years old (preferably 20 years old).
③ The refractive error has been stabilized in the past two years.
④ Corrected refractive range: myopia preferably not more than 1500 degrees, astigmatism not more than 600 degrees, hyperopia not more than 600 degrees.
5 Refractive error.
6 Current wearers of corneal contact lenses: soft lenses should be stopped for more than 2 weeks, hard lenses should be stopped for more than 3 weeks, OK lenses should be stopped for more than 1-3 months.
⑦ Corneal thickness greater than 450 um (depending on the refractive state).
⑧ No active disease in the eye, etc.