Why are humans nearsighted?

The human eye is an organ that can perceive light. The pupil of the eye is like the aperture of a camera, which will automatically change its size when stimulated by light. When the light is dark, the pupil will be dilated, which will increase the hanging light entering the eyes. At this time, the peripheral retina plays a major role, but the sensitivity is far from that of the macula. Therefore, in order to see the object better, it is necessary to move closer, and the ciliary muscles of the eyes will contract hard to enhance the adjustment force. In the long run, when the ciliary muscle is tired, it will produce fatigue symptoms such as spasm, blurred vision, swollen eyes, eye pain and headache. If these symptoms are not corrected in time, the eyeball will gradually become longer and become true myopia.