Myopia is a common problem faced by modern humans. So far, we have clarified the optical principle of myopia, i.e., the eye is in a state of relaxed accommodation, and parallel light passes through the refractive medium of the eye to focus on the front of the retina. However, the mechanism of myopia development is still unclear.
The methods of analysis also vary, and so do the methods of preventing myopia and stopping its development. Some people believe that myopia is caused by over-regulation of the ciliary muscle, so myopia can be prevented or reduced by relaxation of the regulation; others believe that the anterior and posterior diameters of the eye axis are too long, so the lengthening of the eye axis can be stopped by surgical methods such as posterior scleral reinforcement to control the development of myopia; others believe that myopia is mainly due to over-curvature of the cornea, so myopia can be changed by PRK, LASIK or Othor-K. -Others believe that myopia is mainly due to corneal curvature, and therefore the corneal curvature can be changed by PRK, LASIK or Othor. In this article, we review the different methods that have been used in recent years to try to control the growth of myopia in order to understand the current dynamics of research on the occurrence and development of myopia and the future outlook.
I. Low correction
Half a century ago in Europe and the Americas, and currently in some parts of China, ophthalmologists and optometrists recommended the use of low correction to control the increase in myopia, typically in the amount of O.5O-O.75 D. This method was clinically tested in a school in the United States, and the teachers in this school strongly opposed the use of low correction for the reason that these low correction The reason was that the students were unable to read the teacher’s board, and it did not take long for the myopia to get worse. Soon after, many researchers also did comparative studies and found that low correction did not prevent the increase in myopia.
Second, vision exercises
A teacher once hung a Snellon vision chart in the classroom and asked the students to read at least one gray a day in their respective positions, and to read separately with both eyes until they could recognize the smallest view mark. It was found that the prevalence of myopia among the students in the school dropped from 6% to 1%, but there were no scientific statistics throughout the experiment to confirm that the visual acuity exercises had a stopping effect on the development of myopia.
Third, bifocal glasses
Many researchers believe that over-regulation is the main cause of myopia, so many people engaged in the study of bifocal lenses, but the results were also inconsistent. In 1959, an optometrist named Mandell did clinical tests in which he fitted 50 myopes with bifocal lenses and 116 myopes with monofocal lenses, and the results were that bifocal glasses had no inhibitory effect on the development of myopia. However, because his experimental and control groups could not be matched in terms of age, sex, and myopia, his conclusions were not endorsed by later generations. in 1967, Roberts et al. conducted a similar experiment and concluded that wearing bifocal glasses could stop myopia by about 0.09 D/year. although this result was statistically significant, however, the amount of myopia stopped by this method was too small, and even with continuous wear of In 1967, Grosvenor et al. of the University of Houston conducted a clinical study in which children of comparable age, sex, and myopia were randomly divided into three groups to wear single-focus lenses, plus +1.OOD bifocal lenses, and plus +2.OOD bifocal lenses, respectively. All three groups were found to have myopia growth of about O.33D/year. However, bifocal lenses had a significant corrective effect on patients with internal strabismus.
IV. Role of ciliary muscle paralyzing drugs
Because some optometrists believe that accommodation is the main cause of myopia, ciliary muscle paralytics are used in many normal people to reduce accommodation. Due to the loss of regulation in the eye after the medication, the patient is unable to do close work and has to use bifocal lenses as a solution. Some patients with low myopia also take off their glasses for close reading. Although bifocal glasses can take into account both near and far vision markers, they are unable to see mid-distance vision markers, and thus produce disadvantages such as the phenomenon of shadow jumping. In addition, many patients experience photophobia and are unable to participate in outdoor activities, and atropine drugs can cause toxic reactions in some patients.
Although a lot of literature points out that ciliary muscle paralyzing agents have a certain inhibitory effect on the development of myopia, due to the many disadvantages mentioned above, this method has not been promoted in clinical practice.
V. Application of IOP-lowering drugs
It is believed that the intraocular pressure increases when the human eye is adjusted and near vision, so some people began to try to use the hypotensive agent pilocarpine to inhibit the development of myopia. One of the more notable trials is that of Goldschmidt et al. and Jensen et al. The former concluded that twice-daily drops of IOP-lowering medication reduced myopia along with IOP. However, the latter concluded that there was no significant association between IOP reduction and myopia development.
Sixth, rigid contact lenses
The first person to discover that contact lenses could stop the growth of myopia was Frank Dickinson, who had given his daughter rigid contact lenses and, to his surprise, found that her refraction did not change after a few years. Soon after, similar reports were made by Robert Morrison, Jack Neill and John Nolan. Of course, these single case reports do not tell the story, but they have given many practitioners the insight as to whether rigid lenses have a role in controlling myopia growth. This necessitates the establishment of a better research protocol and scientific methodology whenever possible. In the 1950s, Robert Morrison fitted 1,021 myopic patients with these hard lenses and found no increase in myopia in all cases. He believed that the main reason why rigid lenses prevented myopia growth was because they flattened the curvature of the cornea, and possibly because they affected the physiological metabolism of the cornea.
In the 1970s, Janet stone and her colleagues conducted a similar clinical study in the United Kingdom using these rigid lenses. They followed 84 myopic children with rigid lenses and 40 children with frames for five years and concluded that rigid lenses may modify the anterior curvature of the cornea, flattening it, and that part of the effect may be that the rigid lenses prevent the lengthening of the eye axis, but she did not indicate why rigid lenses would prevent the lengthening of the eye axis. In the late 1980s, gas permeable rigid contact lenses (RGPs) began to be used in studies to stop myopic growth. Grosvenor clearly stated the belief that RGPs did more to stop the lengthening of the eye axis than flattening the cornea. Current research has evolved to analyze why RGP stops myopia growth, with researchers looking at the optical quality of the lens, the contrast sensitivity of the eye and the quality of vision, respectively.
Othor-K lenses are another type of contact lens that stops the progression of myopia. Unlike RGP, Othor-K lenses have a flatter base arc than the central corneal curvature, and the center of the inner surface of the lens contacts the cornea and continuously compresses and massages the cornea, thus changing its shape. -K technology requires a high level of doctor, if the fitting is improper, it can cause cone cornea, oblique astigmatism, and even complications such as corneal edema. The current blind promotion of this technique in China is bound to bring adverse consequences to many myopic patients.
VII. Surgical methods
Myopia surgeries include RK, PRK and LASIK. These methods effectively reduce myopia, but children with persistent myopia cannot undergo such surgeries; in addition, these surgeries cannot stop the lengthening of the eye axis, but only change the curvature of the central part of the cornea.
VIII. Current Research
Currently, there are studies on myopia starting from oculomotor parameters. It is believed that regulation, convergence, AC/A and dark focus are related to the development of myopia, and this study is gradually progressing, and in the near future, some connection may be found between oculomotor parameters and myopia. There are also studies on the quality of eye imaging, mostly from the point of view of defocus, and there are now many meaningful animal models supporting this research. The study of neural mechanisms is also a current favorite, and many neurophysiologists look forward to exploring the mechanisms of myopia onset and development from the anatomical and physiological perspectives of the brain nerves.