The principle of eye imaging is basically similar to that of a camera. The structure of the eye, including the cornea, lens, vitreous humor and retina. The cornea and lens are equivalent to the lens of a camera, while the retina is equivalent to the negative of a camera. Under normal circumstances, after the external light passes through the cornea and lens, which are refractive media, an image will be formed on the surface of the retina, and there are photoreceptor cells on the surface of the retina, which will transmit these signals to the visual center through the visual conduction pathway, and after feedback to the surface of the retina, a clear image will be formed, so that the human eye can see things. If the refractive state of the eye changes, such as the growth of the eye axis, resulting in an increase in refractive power, in this case, the eye will become blurred, this condition is called refractive error, including myopia, farsightedness or astigmatism.