According to a data from the World Health Organization, the proportion of myopia in China is as high as 47%; the rate of myopia among young people is more than 70%, ranking first in the world. Even elementary school students have a myopia rate of 40%. By this year, China’s population has reached 1.4 billion, which means that there are 600 million people with myopia.
Except for a small number of mild myopia, the vast majority of myopia need to correct their vision to meet the needs of normal life, study and work. Although the use of glasses to correct vision is still the mainstream, with the development of myopia correction surgery technology, the proportion of choosing surgery to correct vision has become higher and higher.
So, to what extent has modern myopia correction surgery developed? What choices do people have?
For people who use their eyes excessively at close range, the ciliary muscles are in a state of excessive tension for a long time-when looking at distant objects, the image can only fall in front of the retina, thus showing myopia. Long-term tension of the ciliary muscles will also affect the length of the eye axis, which may lead to the occurrence or aggravation of true myopia.
For adults whose axial length has been fixed, they only need to be equipped with a corresponding concave lens to allow the image to fall on the retina and restore vision. Since the length of the eye axis cannot be changed, all current myopia correction operations are essentially to create a concave lens directly on the eye.
The human cornea is completely transparent, and there are no blood vessels, which is the most suitable place to create a concave lens. There are three main types of myopia correction surgery on the cornea: excimer laser keratomileusis, excimer laser in situ keratomileusis, and full femtosecond.
Although myopia surgery is a modern technology that has only been developed in the last 30 years, in fact, as early as 100 years ago, medical scientists discovered that selective destruction of the superficial cornea can change the curvature of the cornea, thereby improving myopia.
How to make a concave lens
After 40 years of exploration, in 1933, a Japanese professor Sato took the lead in using “radial keratotomy (RK)” for myopia correction surgery, and published a related paper in 1939. This kind of operation will cut the cornea radioactively, the incision is as deep as 90% to 95% of the thickness of the cornea. Such an incision can deform the cornea through the pressure inside the eye, thereby correcting vision.
However, due to the uncontrollability of the operation and operational problems, most of Sato’s myopia surgery patients have serious sequelae.
In the next few decades, the development of myopia surgery was very slow. In the 1970s, after improvements in the Soviet Union, modern technology was used for radial keratotomy, which greatly improved the success rate and surgical results.
This technology has developed around the world, and China has done a lot in the 20 years since 1978. Although the incidence of sequelae of RK surgery has dropped to 0.04%, it is still much higher than that of later laser surgery—maybe within 1 to 3 years after surgery, the patient will develop keratitis, corneal incision dehiscence, and even some serious ones. Probability of total blindness.
Selective destruction of the superficial cornea can change the curvature of the cornea, thereby improving myopia.
Correction plan for myopia (from the left in the vertical bar in the figure): glasses, laser surgery intervention cornea, anterior chamber intraocular lens implantation, intraocular lens implantation instead of eye lens
In 1983, excimer laser keratectomy (PRK) came out, and myopia correction surgery opened a new page.
PRK surgery is to scrape the epithelial tissue of the cornea, and then use an excimer laser to cut the central area of the cornea to create an artificial concave lens, thereby reducing the refractive index of the cornea and achieving the effect of correcting myopia.
Excimer laser is a kind of ultraviolet light with a wavelength of only 193 nanometers, which is excited by a mixed gas of fluorine and argon. This kind of laser will not penetrate the eye, but it can break the biomolecular bonds in the cornea through photochemical effects, and precisely control the ablation of cells and tissues.
Therefore, the accuracy and effect of PRK surgery are far less than RK surgery. With the development and popularization of PRK technology, RK will naturally be gradually eliminated.
Although PRK surgery has unprecedented advantages, it still has its own shortcomings compared to subsequent corrective surgery. Because the corneal epithelium is scraped off during the operation and the anterior elastic layer of the cornea is damaged, patients need to wear contact lenses to promote corneal growth after surgery. Although most of them can recover in one week, they will still be affected in the next few weeks. Not adapted.
Clinically mainstream thousand-frequency Smart all-laser myopia surgery equipment
PRK surgery may also lead to corresponding complications, especially the high incidence of “refractive index” and “sub-corneal haze”. Therefore, PRK also has a higher rework rate compared to subsequent myopia correction surgery.
In order to reduce the incidence of complications, laser in situ keratomileusis (LASIK) was born in 1992.
When performing LASIK surgery, first use a corneal lamellar knife to make a corneal flap with a diameter of about 8.5 mm and a thickness of 160 microns. Then the corneal flap is opened, and then the corneal stroma is refractionally cut, and finally the corneal flap is reset.
Compared with PRK technology, LASIK technology directly retains the corneal epithelial layer and anterior elastic layer, avoiding the occurrence of “sub-corneal epithelial haze”.
However, due to the existence of mechanical incision, when the outer corneal cells heal, the inner corneal flap cannot heal. When the face encounters a violent impact, it may cause the corneal flap to fold, shift, or even detach.
Due to the complexity, difficulty, and low controllability of the operation, LASIK surgery places extremely high demands on physicians. Different doctors, or even the same doctor, may have very different surgical results under different conditions. And compared to subsequent surgery, it still has a high risk of complications.
However, with the development of modern technology, LASIK surgery was quickly improved. For example, with the emergence of iris recognition rotation positioning and wavefront aberration guidance technology, the TORION LASIK operation was born, which greatly improved the accuracy of the operation and the vision correction effect has been greatly improved.
In order to solve the problem that the corneal flap is easy to fall off, in 1996, on the basis of LASIK, the excimer laser subepithelial keratomileusis (LASEK) was developed. Although there is only one letter difference between the two operations, they have different postoperative effects.
LASEK surgery does not require a separate corneal flap. Instead, after soaking the cornea with low-concentration alcohol, the corneal epithelium is opened and the operation is performed directly on the anterior elastic layer. The cornea can be healed very well after the operation, and the operation effect is good. Compared with LASIK, it is more suitable for soldiers and athletes. But the disadvantage is that alcohol is chemically toxic to the corneal epithelium, and there are more painful irritation symptoms after surgery.
With the development of mechanical technology, the “technical microkeratome” excimer laser epithelial keratomileusis (EPI-LASIK) combining the advantages of LASIK and LASEK appeared. This technology uses precise mechanical control and uses a microkeratome to produce a flat corneal flap, so as to achieve a good postoperative healing effect and avoid corneal flap-related complications.
Femtosecond laser is perfect for myopia correction
After 2000, LASIK technology has undergone a revolutionary change-the application of femtosecond laser technology.
Femtosecond itself is a unit of time, one thousand billionth of a second. Since the first ruby laser came out in 1960, humans have gradually mastered femtosecond laser pulses by shortening the laser pulse. Femtosecond laser has the characteristics of fast and high resolution, and is inherently suitable for myopia correction surgery requiring high precision.
The femtosecond laser used for myopia surgery has a single duration of only 200 to 600 femtoseconds, with an accuracy of 3 microns, and even only a few tenths of the diameter of a hair. Compared with excimer lasers, femtosecond lasers can directly penetrate the corneal tissue, generate tiny cavitation bubbles inside the corneal stroma, and then form a cutting surface through expansion and fusion, light bursting, etc., without causing any damage to other tissues.
The result of the combination of femtosecond technology and LASIK is half femtosecond laser surgery. Although it is still LASIK surgery in essence, the precision and safety of the corneal flaps produced by femtosecond lasers instead of lamellar knives are essentially improved.
With the development of femtosecond technology, half-femtosecond laser surgery has become the mainstream of myopia surgery. Its main advantage is that compared with traditional LASIK surgery, there are less corneal cuts in half a femtosecond. It is suitable for most people within 1000 degrees and can recover after 24 hours. Although the recovery speed is not as fast as full femtoseconds, the cost is also cheaper.
Since femtoseconds can be used to make corneal flaps, why not perform refractive cutting? Medical workers quickly replaced other surgical procedures with femtosecond lasers—so after 2006, the full femtosecond technology was born.
Corneal thickness is an important indicator of whether laser correction surgery can be performed.
Full femtoseconds are divided into FLEX and SMILE technologies. The technical idea of FLEX is not much different from that of LASIK. The femtosecond laser is used to make the corneal flap and the stroma lens at the same time. Although the technology is much more accurate than LASIK, there is still a large 20 mm incision.
Compared to FLEX, SMILE is more like a minimally invasive surgery. It does not need to make a corneal flap, but by adjusting the parameters of the laser, the corneal stromal layer of different depths is precisely blasted, a stromal lens is cut directly inside the cornea, and then a tiny incision of 2 to 4 mm is made next to it. , Take out the lens, and complete the operation.
In addition, the almost eliminated PRK technology has once again shined with the application of femtosecond technology, giving birth to the thousand-frequency Smart all-laser technology. This technology uses the precision of the femtosecond laser to cut directly on the surface of the cornea, and the corneal epithelium can get excellent self-healing after the operation, thereby avoiding the “sub-corneal haze” and other complications that occur with the traditional PRK technology.
Although the recovery time of Thousand Frequency Smart all-laser surgery is much longer than that of full-femtosecond, it takes several days, but its visual effect is also the best of all laser correction surgery.
In general, with the development of technology, myopia correction surgery is becoming safer and less sequelae.
L ASIK procedure diagram
But not everyone is suitable for myopia correction surgery. For example, laser correction surgery is not suitable for eye inflammation, glaucoma, cataract, keratoconus, or systemic diseases such as diabetes or connective tissue disease.
ICL lens implantation technology has increasingly become a newer and safer technology than laser correction surgery.
Intraocular lens (ICL)
For normal people, the thickness of the cornea that can be cut directly determines the scope of laser correction surgery.
China has stricter requirements for the safety value of the remaining cornea, which is 410 microns, which is 20 microns thicker than the international standard of 390 microns—a sufficiently thick remaining cornea can ensure sufficient eye safety.
For people with high myopia, super high myopia, or the cornea itself is too thin, if the thickness of the remaining cornea is less than 410 microns after the theoretical correction of vision is achieved, it is not suitable for laser correction surgery. In general, corneal thickness is an important indicator of whether laser correction surgery can be performed.
Lens implantation is the optimal solution for high myopia?
For myopic people who cannot undergo laser correction surgery, there is actually another option, which is the implantation of intraocular lens (ICL).
ICL is a soft intraocular lens, a gel lens made of collagen polymer, essentially equivalent to a special contact lens. It’s just different from traditional contact lenses. It is implanted inside the eyeball to achieve refractive correction.
During ICL surgery, you only need to make a small 2mm incision on the edge of the cornea, and then use a special syringe to inject the gel lens into the ciliary sulcus. The ciliary sulcus is located between the iris and the lens, where the gel lens will automatically unfold.
The thickness of ICL is only about 50 microns, which is thinner than the diameter of a hair. The postoperative visual effect is almost better than any other refractive correction technique. The most important thing is that it will not have any cutting, nor will it change the structure and shape of the eyeball tissue. It can also be used for hyperopia and astigmatism other than myopia, as well as different degrees from low to high.
When there is a significant change in vision and it is no longer suitable for ICL, you can also remove the gel lens to replace it at any time, or choose another vision correction program.
Although the effect of ICL surgery is great, there is still a very low risk of complications; it is not suitable for conditions such as high intraocular pressure, sensitivity to collagen, insulin-dependent diabetes, and low corneal endothelial cell count. ICL surgery.
Generally speaking, with the emergence of more and more clinical experiment results, ICL lens implantation technology has increasingly become a newer and safer technology than laser correction surgery, especially for patients with high and ultra-high myopia, ICL implantation Almost the best choice.
Of course, no matter which vision correction program you choose, the one that suits you best is the best. Any medical plan must be based on the recommendations of professional physicians.
