I. Refractive overview
The refractive state of the eye is divided into two categories: a class called orthoptic eye; a class called non-orthoptic eye, also known as refractive error.
Ortho-optic eye: an object 5m away from the eye, or reflected parallel light, through the refractive system of the eye without adjustment, the light is refracted into a focal point accurately on the retina, called ortho-optic eye.
Non orthoptic eye: After the parallel light enters the unadjusted eye, it does not form a focal point on the retina, which is called non orthoptic eye or refractive error. Li Hua, Ophthalmology Department, Yongchuan Hospital, Chongqing Medical University
Refractive error is usually divided into three types: farsightedness if the focal point is behind the retina; myopia if the focal point is in front of the retina; astigmatism if the refractive power is different in each diameter and cannot form a focal point.
Myopia
Myopia is also called short-sightedness, because this eye can only see near but not far. When this eye is at rest, parallel light from infinity, after refraction by the eye’s refractive system, collects into a focal point before the retina, and forms an unclear image on the retina. The distance vision is significantly reduced, but the near vision is still normal.
(A) Causes of myopia
The causes of myopia are not uniform in the past, but there are two types of causes: endogenous and exogenous.
1. Internal factors
Genetic factors: Myopia has a certain genetic tendency, which has been recognized. This is especially true for high myopia. However, for general myopia, this tendency is not so obvious. For those with genetic factors, the age of the disease is early, mostly above 6.00D. However, there are cases of high myopia with no family history. High myopia is an autosomal recessive disorder, while general myopia is a multifactorial disorder.
Developmental factors: Infants are farsighted because their eyes are small, but as they grow older, the eye axis gradually lengthens until puberty when it develops normally. If the development is excessive, myopia will be formed, which is called simple myopia and starts in the school age. Generally, it is below 6.0D and stops developing at the age of about 20.
If the progress is very fast in early childhood, the progress will be faster at the age of 15-20, and then it will slow down. This kind of myopia is often higher than 6.0D and can reach 20-25D or 30D, which is called high myopia or progressive myopia or pathological myopia, and the degenerative changes of the fundus occur in the late stage, and the vision decreases and cannot be corrected.
2, external factors: that is, environmental factors
People who work in writing or other close work have more myopia, and there are more myopic eyes among teenage students, and their prevalence rises significantly from the fifth or sixth grade of elementary school. This phenomenon shows that the occurrence and development of myopia is very closely related to close work. In particular, the eye of adolescents is in the growth and development stage, with strong adjustment ability and large extension of the spherical wall. The adjustment and collection during close work such as reading and writing make the extraocular muscles (mainly the internal rectus muscle) exert certain pressure on the eye, and the intraocular pressure rises accordingly. The ciliary muscle and extraocular muscles are often under high tension, resulting in ciliary muscle spasm, which causes a temporary loss of vision, but after rest or the use of ciliary muscle paralyzing agents, vision can be improved or completely recovered. Therefore, some people call this myopia functional myopia or pseudomyopia. If this state persists for a long time without effective relief, it will make myopia deeper and deeper as well. Lack of visual hygiene, especially during adolescence, is a direct cause of myopia. Lack of attention to general health can contribute to the development of myopia. In addition, in a broad sense, the pollution of trace elements in the atmosphere, changes in nutritional composition and ergonomically unsuitable teaching aids are also objective factors that have been reported to affect the occurrence of myopia in students. However, these factors are of secondary importance when compared with myopia caused by looking close.
(B) Classification
1. The degree of myopia.
(1) 3.00D or less – mild myopia.
(2) 3.00D-6.00D – moderate myopia.
(3) 6.00D or more – high myopia, also known as pathological myopia.
2. According to refractive component.
(1) Axial myopia: caused by excessive development of the anterior and posterior axes of the eye.
(2) Curvature myopia: caused by excessive curvature of the cornea or crystal surface.
(3) Refractive index myopia: caused by excessive refractive index of the refractive interstitium.
3.Pseudomyopia: also known as regulatory myopia
It is caused by the failure to relax the adjustment when looking at distance. It is fundamentally different from true myopia, where the refractive component is altered.
(C) Clinical manifestations of myopia
1. Visual acuity: The most prominent symptom of myopia is reduced distance vision, but near vision can be normal. Generally speaking, the distance visual acuity will not exceed 0.1 for 3.00 D or more, 0.2-0.3 for 2.00 D, and 0.5 for 1.00 D. It may be better.
2. Visual fatigue: common especially in those with low degrees. However, it is not as obvious as hyperopia. It is due to the incoordination of adjustment and assembly. Highly myopic people due to gaze at the target is too close to the eye, the role of the collection can not cooperate with it, so more monocular gaze, but will not cause visual fatigue.
3, eye position: because myopic eyes do not need to adjust when looking near, so the collection function is relatively weak, until the eye balance can not be maintained, the visual function of both eyes is destroyed, only rely on one eye to see things, the other to the outside, become a temporary alternating strabismus.
4, eye: high myopia is mostly axial myopia, the anterior and posterior axis of the eye is elongated, and its elongation is almost limited to the posterior pole, so it often shows protruding eyes, deeper anterior chamber, large pupils and dull reflexes.
5. Fundus: low degree is not obvious, but high degree can cause degenerative changes in the fundus due to excessive elongation of the eye axis, such as leopard-like fundus, myopic arcuate spot, macular atrophy spot, hemorrhage, post-scleral staphyloma, cystic degeneration at the serrated edge, etc.
6.Complications and sequelae
(1) Vitreous liquefaction, clouding, posterior detachment: high myopia is obvious. Self-perceived symptoms are more common is flying mosquitoes, feel a black dot floating in front of the eyes. Often accompanied by the light in front of the eyes, sparks and flashes of light and other sensations.
(2) Lens clouding
(3) retinal fissure, retinal detachment
(4) Glaucoma: open-angle glaucoma is 6-8 times higher than normal
(5) Prolonged dark adaptation time: the retinal pigment epithelium is inevitably affected by the photochemical reaction process of the optic cells after lesions.
(D) Prevention of myopia
The etiology of myopia is complex, with two main factors: genetic and environmental. In the case that genetic engineering cannot be used to change the genes, the focus of prevention and treatment should be on improving the visual environment.
1. Vigorously promote education and set up a specialized agency.
2.Improve the visual environment
(1) The lighting and illumination of classrooms should be standardized.
The ratio of the light-transmitting area of windows to the indoor floor area is not less than 1:6
The blackboard should not be reflective and kept black or dark green
The illumination on the desktop is not less than 100LX
Light should come from the left or left front, not to make the shadow of the hand blocking light when writing
(2) desks and chairs to meet the requirements of ergonomics, suitable for children’s growth and age characteristics.
So that the correct body position and posture can be maintained in class or when doing homework. When reading and writing, the distance between the eyes and the desktop
Distance should be kept at about 30CM, not less than 23CM
(3) Develop good reading and writing habits and posture.
The working time should not be too long, after 45 minutes of study should rest 10-15 minutes or look into the distance, so that the ciliary muscle can get a proper rest.
Make the ciliary muscle get proper rest. You can also use eye exercises.
Do not lie in bed to read, do not read in a walking or moving car, and do not read in bright light or under dark streetlights.
Don’t read and write under strong light or dark street lights, and don’t watch TV programs or play with computers for a long time at close range.
In order not to cause visual fatigue and regulation tension.
3, pay attention to physical exercise and balanced nutrition, reduce the burden of study, and enhance physical fitness.
4, reduce the influence of genetic factors: myopia and genetics have a close relationship, both parties are highly myopic
If both partners are highly myopic, the chance of heredity is very high after marriage, so attention should be paid to eugenics.
(E) Treatment of myopia (true myopia)
1.Frame lens correction
First of all, you should go to the hospital ophthalmology to do a specialist examination and medical optometry to find out the true degree of myopia and exclude eye diseases, for adolescents optometry should be carried out under ciliary muscle paralysis.
Some teenagers are afraid of the trouble of going to the optician directly, because the optician is not generally under the ciliary muscle paralysis, myopia inaccurate situation often occurs.
2. Corneal contact lenses
Such as refractive disparity, monocular myopia, special occupations and other cases can be equipped with corneal contact lenses. But must pay attention to cleanliness and hygiene, disinfection and maintenance and frequent replacement as required. Complications such as macropapillary conjunctivopathy often occur with long-term use. Long-term wear of poorly oxygen permeable corneal contact lenses can also cause corneal neovascularization.
3.Surgical treatment
From RK-PRK-lasik surgery, myopia surgery is becoming more and more mature. At present, lasik surgery is one of the safest and most mature excimer surgery methods recognized by the U.S. FDA.