rumor: myopia and presbyopia can offset each other. If you have a little myopia when you are young, you won’t get presbyopia when you are old.
truth: if you get myopia, you won’t grow old when you get old? Of course not. To make this clear, we must first explain the working principle of the eyes and what is myopia, hyperopia and presbyopia. Let’s follow and learn about it!
The eye is a camera
in fact, comparing the eye to the camera is really an injustice to the eye. The eye is more precise than the camera, but comparing the two can make it easier for us to understand the myopia, hyperopia The problem of old flowers. Like the camera, the eye can also be divided into two parts according to its function. The front cornea, aqueous humor, lens and vitreous are equivalent to the lens group of the camera and belong to the refractive system; The back retina is equivalent to the film or CCD of the camera and belongs to the photosensitive system. The refractive system is actually like a lens, which focuses the images of the wide world on the small retina. The important characteristic of
refractive system is refractive power. The greater the refractive power, the stronger the ability to focus the line. The cornea has the largest refractive power in the refractive system, about more than 4000 degrees. But the cornea is a & ldquo; Fixed focus lens;, Refractive power cannot be changed. The refractive power of the lens is slightly inferior to that of the cornea, about less than 2000 degrees. However, by changing the shape of the lens, the refractive power can be adjusted by more than 1000 degrees, just like the optical zoom function of a digital camera. The combination of cornea and lens constitutes almost all the refractive power of the eye. Their eyes, which are several tens of centimeters high, can be projected onto the building.
the way the lens regulates refractive power is very subtle. There is a circle of ciliary muscle around the lens, which is connected with the lens through small ligaments. The ciliary muscle and lens compete with each other at ordinary times. When the ciliary muscle is relaxed, it will pull around and flatten and thin the lens. In this way, the degree of the lens will be reduced by hundreds of degrees, and you can have a panoramic view of things in the distance; When the ciliary muscle is tense, the lens will return to its natural state, become round, thicker and have greater refractive power. In this way, you can improve the resolution by looking at things near you. In other words, the tighter the ciliary muscle, the looser the lens and the greater the refractive power. The more suitable it is to see small objects and see more clearly; The more relaxed the ciliary muscle is, the more tense the lens is, and the smaller the refractive power is. The more suitable it is to see a large scene and the larger the range it can see. The eyes can zoom, and the refractive ability can be adjusted according to the distance of the object, which is realized by the competition between the two brothers of ciliary muscle and lens.
Why can you get myopia?
if you read books and computers for a long time, your ciliary muscles will often be in a state of tension and gradually adapt to this state. If you look at the distance at this time, the ciliary muscles will not relax when they are used to tension, and the lens can’t become flat and tense. The excess positive degree of this part will make normal people feel like wearing a pair of reading glasses and can’t see things far away. You need to look closer. It is equivalent to that the camera is temporarily locked in & ldquo; Close range mode & rdquo;, We call it & ldquo; Myopia & rdquo;.
in this case, the eyedrops of atropine can paralyze the ciliary muscle, force it to relax, make the lens tense and thin, which is equivalent to removing the excess positive degree, and you can see the things in the distance. This kind of myopia that can return to normal is called & ldquo; Pseudomyopia & rdquo;. When you go to the hospital to get glasses, the doctor will give you & ldquo; Mydriatic Optometry & rdquo;, The purpose is to eliminate the reversible degree of pseudomyopia& ldquo; Mydriasis & rdquo; It is because the medicine that paralyzes the ciliary muscle can also paralyze the pupil muscle and dilate the pupil.
“ Pseudomyopia & rdquo; It’s reversible and can be eliminated, that’s & ldquo; True myopia & rdquo; And& ldquo; True myopia & rdquo; It is caused by abnormal eye structure. When the eyes are working closely, the eyeballs will converge inward under the action of extraocular muscles and become mild & ldquo; Eye to eye & rdquo;, Otherwise, ghosting will appear when looking at nearby objects. In this state for a long time, the extraocular muscles will compress around the eyeball, lengthen the anterior and posterior diameter of the eyeball, and the ball becomes an ellipsoid. This change cannot be reversed. When the anterior posterior diameter of the eyeball becomes longer, less refractive power is required for imaging. When looking at the distance, no matter how relaxed the ciliary muscle is, it can not thin the lens and remove the excess reading glasses. Therefore, the image that should have been projected to the retina is projected to the front of the retina and cannot be focused on the retina. This myopia that can no longer be reversed by self-regulation is called & ldquo; True myopia & rdquo;. If the degree of myopia is too high, the eyeball is too & ldquo; Ellipse & rdquo;, If the front and back are sharp, the retina is not firmly attached to it. If it is forced too hard or hit, it is easy to have retinal detachment, resulting in blindness.
pseudomyopia does not need to be corrected with glasses, but we should pay more attention to eye hygiene at ordinary times. True myopia should be corrected with concave lens of corresponding degree. Concave lens has the function of divergent light, so the degree is negative, which can remove the excess refractive power of the eye.
What about hyperopia?
hyperopia is usually caused by abnormal eye structure. Because the eyeball of young children is not fully developed, the anterior and posterior diameter of the eyeball is short, and the object reaches the retina before imaging, it can not become a clear image. Therefore, under 7 years old is the high incidence age of hyperopia. In order to see close objects, the ciliary muscle needs to be in a state of tension frequently to make the lens relax and achieve sufficient refractive power. Therefore, hyperopia eyes are prone to eye fatigue. When the degree of hyperopia is large, due to the excessive tension of ciliary muscle and the convergence of binocular reflex, it is easy to develop into esotropia for a long time, that is & ldquo; Cockfighting Eye & rdquo;. Mild hyperopia below
300 degrees generally does not need correction, but those with visual fatigue symptoms or esotropia should be corrected with convex lens as soon as possible. Convex lens has the function of converging light, so the degree is positive, which can make up for the diopter lacking in hyperopia. Preschoolers with high degree of hyperopia should also have optometry and glasses as soon as possible. However, with the growth of age and the development of eyeballs, the light should be re examined once a year to reduce the power of lenses in time to meet the needs.
presbyopia looks like hyperopia, but it’s far from that.
myopia and hyperopia are mostly caused by abnormal anterior posterior diameter of eyeball, while presbyopia is completely caused by decreased refractive ability of lens. Presbyopia, the scientific name of presbyopia, means that the elasticity of the lens becomes worse with age, and no matter how tense the ciliary muscle is, it can’t relax; Or the ciliary muscle itself is aging, and it’s not very nervous. Therefore, the adjustment ability of the lens with more than 1000 degrees will lose 50 ~ 100 degrees every five years, resulting in insufficient adjustment ability when looking close, and insufficient refractive power. The object reaches the retina before imaging. It also needs to wear convex lens to supplement refractive power for correction.
hyperopia and presbyopia seem to have the same correction methods, but they are not the same thing. Hyperopia is mostly due to the short anterior posterior diameter of the eyeball, while presbyopia is caused by the aging of the lens and ciliary muscle and the decrease of refractive power. Hyperopia often occurs in children. Usually, the correction degree decreases year by year. When the degree is not high, you can get a clear image through self-regulation regardless of looking close and far; Presbyopia generally occurs in the middle-aged and elderly. The correction degree increases year by year with age, and due to the decline of adjustment ability, even if the degree is not high, objects close to a certain distance cannot be seen through their own adjustment, and must be moved away.
Got myopia, won’t old flowers grow old?
from the above words, you must understand that people can not be short-sighted or hyperopia, but they can’t escape presbyopia. That got myopia, old don’t need to wear presbyopic glasses? It depends. If the degree of myopia is low when you are young, for example, you have a myopia of 50 ~ 100 degrees, and you are used to not wearing glasses at ordinary times, congratulations. When peers start wearing reading glasses, you need to wear reading glasses 5-10 years later than them. Because of you & ldquo; Reserve & rdquo; The refractive power of myopia can offset some of the refractive power lost by presbyopia, but presbyopic glasses may still be needed with age.
is relatively miserable for people with high myopia. Because the pathogenesis of myopia and presbyopia cannot offset each other, at the age when presbyopia symptoms occur and presbyopia glasses are needed, you still need to wear myopia glasses when looking at a distance, but the degree of myopia may be reduced. When looking close, due to the weakening of the adjustment ability of the lens, different situations will occur: some people need to take off their myopia glasses to watch, some people need to change into a pair of glasses with low myopia to correct, and some people even need to wear a pair of presbyopia glasses. In other words, after the occurrence of presbyopia, due to the narrowing of the eye adjustment range, people with high myopia are likely to be unable to see far and near clearly. They need two pairs of glasses with different degrees of myopia to correct refractive problems, even a pair of myopia glasses and a pair of reading glasses. Moreover, the degree of myopia seems to be lighter, but the risk of rhegmatogenous retinal detachment is not reduced.
conclusion: rumor cracking. People can not be short-sighted and farsighted, but they can’t escape presbyopia. The pathogenesis of myopia and presbyopia can not offset each other, so at the age of presbyopia symptoms, you may even need a pair of myopia and presbyopic glasses.