Obtaining the correct knowledge of eyeglasses and lenses, which you do not know unexpectedly, will help you to care for your own eyes and eyesight. Please use it as a reference for living a healthy and comfortable visual life.
Vol.2 What is refractive error?
Symptomatisms such as "myopia," "hyperopia," and "astigmatism," which are seen in many people from children to adults, are collectively called "refractive error." I will explain the mechanism of each symptom and the type of lens to correct it.
Refractive error and the mechanism of each symptom
When the light that enters the eye is refracted by the cornea and the crystalline lens and then the image is properly formed on the retina, the object is clearly visible, and this is called emmetropia.
If the force that refracts light between the cornea and the crystalline lens does not match the distance to the retina, it will be out of focus, and this is called refractive error.
Refractive errors can be broadly divided into myopia, hyperopia, and astigmatism.
1. About myopia
Myopia is a condition in which the light that enters the eye forms an image in front of the retina, and occurs because the cornea or crystalline lens has a strong refractive power or the eyeball is long. You can focus on nearby objects, but it will be difficult to see in the distance.
In myopia, the focus in front of the retina is corrected with a concave lens.
2. About hyperopia
Hyperopia is a condition in which the light that enters the eye forms an image behind the retina, and occurs because the cornea and crystalline lens have weak refractive power or the eyeball is short.
Hyperopia always causes the ciliary body to be tense, the crystalline lens to be thickened and the refractive power to be strengthened (accommodation), which tends to cause eye strain. I can see it.
In hyperopia, the focus behind the retina is corrected with a convex lens.
3. About astigmatism
Astigmatism is a condition in which the light that enters the eye is formed in multiple places due to distortion of the cornea and crystalline lens. There are two types of astigmatism: regular astigmatism that can be corrected with glasses and irregular astigmatism that cannot be corrected with glasses.
Astigmatism is more likely to cause eye strain because the crystalline lens does not focus on the retina even if it adjusts its refractive power.
Astigmatism is corrected by a cylindrical lens.
About presbyopia
Presbyopia is a condition in which the muscles that regulate the thickness of the crystalline lens deteriorate due to aging, and the crystalline lens itself becomes less elastic and harder, making it impossible to focus on nearby objects.
In presbyopia, the focus behind the retina is corrected with a convex lens.
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