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Myopia is a type of refractive error. When the eyes are in a relaxed state, parallel light rays enter the eye and are focused in front of the retina. This results in the inability to form a clear image on the retina, which is called myopia. At this time, the optometry test will prompt the degree of myopia. For example, it is usually called 50 degrees of myopia and is recorded as "-0.50D".
When the eyes are in a relaxed state, parallel light from the outside enters the eye, and its focus falls exactly on the retina, forming a clear image. This is called emmetropia; if the focus cannot fall on the retina, then It is called non-emmetropia, which is refractive error.
Axial myopia and refractive myopia
Axial myopia: The most common, the anteroposterior diameter of the eyeball is too long (that is, the axial length of the eyeball exceeds the normal range), and the refractive power (that is, the cornea and The refractive properties of the lens and other refractive components of the eye) are basically within the normal range.
Refractive myopia: Mainly due to excessive curvature of the cornea or lens, or abnormal combination of refractive components, causing the refractive power to exceed the normal range, while the axial length of the eye is basically within the normal range.
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