Myopia Overview: Myopia is a type of refractive error. Under the premise of refractive rest, distant objects do not converge on the retina and form a focal point before the retina, thus causing visual distortion and resulting in blurring of distant objects.
Myopia classification.
1. According to the degree of myopia
(1) 3.00D (300 degrees) or less is called mild myopia.
(2) 3.00D ~ 6.00D (300 degrees ~ 600 degrees) is moderate myopia.
(3) 6.00D (600 degrees) or more is high myopia, also known as pathological myopia.
2.According to the refractive component
(1) Axial myopia is caused by excessive development of the anterior and posterior axes of the eye.
(2) Curvature myopia, which is 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
It is also known as regulatory myopia. It is caused by the failure to relax when looking at distance. It is fundamentally different from true myopia in which the refractive component is altered.
Disease description.
Myopia is a refractive state in which the eye is not using accommodation and the focus falls in front of the retina after the refraction of parallel light rays through the refractive system of the eye. Therefore, myopic eyes cannot see distant targets clearly. If the target is gradually moved closer to the eye, the light emitted is spread out to a certain extent to the eye, forming a focal point that moves backward, when the target moves closer to a point in front of the eye. The closer this point is to the eye, the deeper the degree of myopia.
Myopia occurs mostly because the anterior and posterior axes of the eye are too long (known as axial myopia), followed by a strong refractive power of the eye (known as refractive myopia). Myopia occurs mostly in adolescence, and genetic factors have some influence, but its occurrence and development are closely related to insufficient lighting, improper reading posture, and working at close range for a longer period of time.
Most myopia occurs in adolescents, and it deepens year by year during the development and growth stages, but does not develop or develops slowly after maturity.
Myopia rarely exceeds 6D, no degenerative changes occur in the fundus of the eye, and vision can be corrected with glasses, which is called simple myopia. The other type of myopia occurs earlier (between the ages of 5 and 10) and progresses rapidly, continuing to develop after the age of 25, with myopia reaching more than 15D, often accompanied by changes in the fundus, and vision not easily corrected, called degenerative myopia. In addition, it is customary to refer to myopia below 3D as mild myopia, 3-6D as moderate myopia, and above 6D as high myopia.
Disease etiology.
The causes of myopia are still not well understood, and the accepted view is that myopia is caused by a variety of factors. Recent evidence suggests that a combination of environmental and genetic factors are involved in the development of myopia. I add: exogenous factors – prolonged close viewing of things, so that the ciliary muscle in the eye presses on the lens for a long time and causes the lens to fail to recover (thicker than it was born), so myopia occurs.
Genetic factors: Studies have concluded that families with two parents with high myopia have a higher incidence of myopia in the next generation, and it is well established that myopia has a certain genetic predisposition, especially for high myopia. However, the genetic predisposition for general myopia is not so obvious.
Environmental factors.
The occurrence and development of myopia is very closely related to the use of eyes at close range. The eyeballs of adolescents are in the growth and development stage, the adjustment ability is very strong, the stretching of the eyeball wall is also relatively large, reading, writing and other close-up work, not only need to play the role of eye regulation, both eyeballs also need to converge, so that the extraocular muscles exert a certain pressure on the eyeballs, over time, the front and back axis of the eye may become longer. The majority of this myopia is simple myopia, which is generally low, below 6 diopters, and progresses more slowly before and after puberty, which is called true myopia to distinguish it from pseudomyopia.
The formation of myopia.
1. Using the eyes too close to each other.
According to the data, myopia in adolescents is most often caused by long-term eye distance too close to the eye. The distance between the book and the eye is 7-10 cm, but if you often read and write at this distance, you will have abnormal tension in your eyes, which can lead to refractive (regulatory) myopia, the so-called pseudomyopia. If you over-regulate for a long time, the ciliary muscle cannot stretch flexibly, and the convergence is strengthened due to over-regulation, so that the extraocular muscle exerts pressure on the eye, the intraocular pressure increases, the intraocular tissue is congested, and the adolescent eye tissue is delicate, the wall of the eye is gradually extended by pressure, and the anterior and posterior axis of the eye becomes longer than the normal value, forming axial myopia, the so-called true myopia. The normal reading distance should be 30-35 cm.
2, too much time with the eyes.
Some teenagers read and write to do homework, watch TV and so on for 3-4 hours without rest, or even to sleep and rest late at night, which not only affects physical health, but also overloads the eyes, the muscles inside and outside the eyes for a long time in a state of tension and do not get rest, over time, when looking at the distance, the eye muscles can not relax and spasm state, so look at the distance to feel blurred and the formation of myopia. Some students’ eyesight declines significantly after a summer vacation for this reason. It is generally advocated that continuous reading and writing or watching TV for 40-50 minutes should be rested for a moment or look into the distance for a while.
3, lighting is too strong or too weak.
If the light is too strong, such as sunlight shining written, will cause strong reflection, stimulate the eyes, eye discomfort, it is difficult to see the font, on the contrary, the light is too weak, written lighting is not enough, the eyes can not clearly see the font, the head will be forward, close to the book, the above two cases can be easy eye fatigue, eye regulation is excessive or spasm and the formation of myopia.
4, in the car or walking when reading books.
Some adolescents make full use of the time to read books while walking or reading books in the walking car, which is very bad for the eyes. Because the carriage is vibrating, the body is shaking, the eyes and the book distance can not be fixed, coupled with poor lighting conditions, increasing the burden on the eyes, often so it may cause myopia.
5, lying down to read a book.
Many teenagers like to lie in bed to read, which is a bad habit. Because the human eye should maintain the horizontal state of reading, so that the regulation and collection (convergence) to achieve consistent, reduce eye fatigue. If lying down to read, both eyes are not in the horizontal state, eye and book distance is not consistent, both eyes are not consistent with the line of sight up and down, uneven illumination on the book, will make the eye regulation tension and easy to move the book close to the eye, which can increase the burden on the eye 2-3 times, the formation of myopia over time.
6, sleep deprivation.
When sleep deprivation, the next day, the spirit is not invigorated, dizzy, the brain is not fully rested, fatigue is not eliminated, increasing the burden on the eyes, prompting myopia to occur. Sleep deprivation is a very important cause of myopia.
7, desks do not meet the requirements, writing posture is not correct.
If the desk and chair is too low, so that the head tilted forward, the crest bent, the chest is pressed, the eyes adjust relatively tense. Or desks and chairs too high, feet hanging, the lower limbs are easy to swing, can not maintain the correct posture, can make eye fatigue, over time, it is easy to myopia.
8, the impact of the current space of the rays.
Often watch TV, especially the signal is insufficient, reception rate is not high in rural areas, no shared antenna, the screen is not clear, the snow point is also more, it is easy to make eye muscle fatigue, often play video games students are more likely to damage vision, the mall sold Ze Wang learning machine, can directly cause students myopia, today’s computer calculator is an indispensable course, too long operation caused by eye dryness and fatigue prone to myopia. All need to properly control the use of time.
9, the curvature of the cornea or the curvature of the lens in front of the back becomes large.
This is mostly a congenital change and is less common in clinical practice.
Current status and characteristics of myopia.
Myopia is very prominent in developing countries, the incidence of myopia in Asian countries is around 70%-90%; the incidence of myopia in the United States and Europe is 30%-40%, and myopia exists in almost all populations worldwide . Myopia is more common in Asians than in Europeans, and more common in women than in men (twice as common in women as in men), and less common in blacks.
In addition to genetics, physical factors are mainly related to malnutrition. The lack of one or more important nutrients during the growth and development of the eye makes the eye tissue more fragile and, under the influence of environmental factors, the sclera of the eye wall tends to dilate, thus making the anterior and posterior axes of the eye elongated and myopia occurs. Most myopic children have the habit of snacking, picky eating and partial eating. They eat mostly refined food and fast food, which lack nutrients or have more nutrients destroyed. At the same time, their diet lacks high-quality protein foods such as milk, eggs, milk, fish, meat, chicken and coarse food. The more types of foods lacking and the greater the total amount, the higher the incidence of myopia and the higher the degree of myopia.
Lesion characteristics
The formation of myopia is related to diet. Most myopic patients have low blood calcium and vitamin A deficiency; most adolescent myopic patients have low serum protein and low blood calcium and hematocrit. After getting myopia, it is important to take more vitamin A, B, group and trace elements such as calcium, chromium and zinc, and eat less candy and high-sugar foods. If you eat too much sugar, the increase in blood sugar content will cause changes in atrial fluid and crystal osmolarity. When the osmotic pressure of atrial water is lower than the osmotic pressure of the lens, atrial water will enter the lens, prompting the lens to become convex and causing the onset of myopia. Eating too much sugar and high carbohydrates will make the tissues in the eye less elastic and reduce the storage of the trace element chromium, making the eye axis easier to become longer. In addition, eating too much sugar can cause a large amount of acid to be produced in the blood. Acid is neutralized with salts in the body, especially with calcium salts, and is reduced in the blood, causing a decrease in blood calcium, which affects the toughness of the eye wall and makes the eye axis elongate, also causing the occurrence and development of myopia.
1. Visual acuity
The most prominent symptom of myopia is reduced distance vision, but near vision can be normal. Although, the higher the degree of myopia, the worse the distance vision, but there is no strict ratio. Generally speaking, myopic eyes with more than 3.00D will not have more than 0.1 distance vision; those with 2.00D will have between 0.2 and 0.3; those with 1.00D will have up to 0.5, and sometimes it may be better.
2.Vision fatigue
It is especially common in low vision, but not as obvious as in farsightedness. It is due to the incoordination of adjustment and assembly. High myopia because the target is too close to the eye, the role of the collection can not cooperate with it, so more use of monocular gaze, but will not cause visual fatigue.
3, eye position
Because myopic eyes do not need to adjust when looking at the near, so the collection function is relatively weakened, and when the muscle balance cannot be maintained, the visual function of both eyes is destroyed, and only one eye sees things, and the other eye is deviated to the outside, becoming a temporary alternating strabismus. If the visual function of the deviated eye is extremely poor and the deviation occurs early, the deviated eye may lose the ability to fix the vision and become monocular exotropia.
4.Eye
Highly myopic eyes are mostly axially myopic, with the anterior and posterior axes of the eye elongated, and their elongation is almost limited to the posterior pole. Therefore, the eye is often more prominent, the anterior chamber is deeper, the pupil is larger and the reflex is more retarded. The ciliary muscle, especially the annular portion, becomes atrophied due to the absence of regulatory stimulation, and in very high myopia, the crystal may not support the iris at all, resulting in mild iris tremor.
5. Fundus
In low myopic eyes, the changes in the fundus are not obvious, but in high myopic eyes, the excessive elongation of the eye axis can cause degenerative changes in the fundus.
(1) Leopard-like fundus: The blood vessels of the retina become thinner and straighter after leaving the optic disc, while the elongation of the choroidal capillaries can affect the nutrition of the retinal pigment epithelium, resulting in the disappearance of the superficial pigment and the exposure of the choroidal vessels, forming a leopard-like fundus.
(2) The choroid around the myopic arcuate spot is pulled by the scleral elongation force, and it is detached from the temporal side of the papilla, so that the sclera behind it is exposed, forming a white arcuate spot. If the posterior pole of the eye continues to extend, the choroidal detachment gradually extends from the temporal side of the papilla to the periphery of the optic disc, finally forming an annular spot. Irregular pigment and sclerotic choroidal vessels can be seen in this spot.
(3) Macula: irregular, solitary or fused white atrophic spots can be formed, and sometimes hemorrhage can be seen. In addition, degenerative lesions are occasionally seen near the macula, manifesting as a black ring-shaped area, slightly smaller than the optic disc, with clear borders, and small round hemorrhages can be seen at the edges, called Foster-Fuchs spots.
(4) Posterior scleral staphyloma: The elongation of the posterior part of the eye, when confined to a small portion, can be seen as a sharp protrusion from the section, called posterior scleral staphyloma. This atrophic lesion may be combined with a loss of central vision if it occurs at the macula.