Nowadays, our country is paying more and more attention to the monitoring of children’s growth and development, especially the screening and prevention of amblyopia and refractive error in children is included in the latest version of the National Standard for Children’s Health Care, therefore, eye examination has been listed as a mandatory item in the health check-up for preschool children. After the checkup, children often receive a notice of “refractive error” and are asked to take their children to a specialist hospital for a review. Parents are always confused when their children are diagnosed with “refractive error”. In fact, if we know how our eyes see and what “orthokeratology” is, we can understand what “refractive error” is. The eye does not need to use adjustment to see objects 5 meters away, that means the object can be focused on the retina imaging, this is the “ortho-optic eye”, is usually called “good eyes”. If you can’t focus on the retina, you can’t form a clear image, and this phenomenon is collectively called “refractive error. Refractive errors in children include: myopia, hyperopia, astigmatism, and refractive error. Nearsightedness: Objects beyond 5 meters are focused in front of the retina and cannot form a clear image on the retina, so they cannot see distant objects, but can see near objects clearly, so the initial stage is often manifested as watching TV and always coming forward. Farsightedness: Objects beyond 5 meters are focused on the retina and cannot form a clear image on the retina, so you cannot see objects. Mild farsightedness can use adjustment to strengthen the refractive power of the eye, so that the light entering the eye can be focused on the retina and form a clear image. However, too much accommodation can lead to visual fatigue and even to the development of accommodative internal strabismus. Hyperopia that exceeds the ability to adjust is not clear in both distance and near vision. Astigmatism: Myopic, hyperopic or normal eyes are like basketballs, the curvature of each direction is the same, so the refractive power is also the same, while astigmatic eyes are like rugby balls, some directions have a large curvature, the refractive power is large, some directions have a small curvature, the refractive power is small, so it can not be gathered into a focus, also can not form a clear image on the retina. No matter seeing far or near vision will be affected. Astigmatism can exist alone or in combination with myopia and hyperopia. Mild astigmatism can also maintain normal vision with the help of the eye’s adjustment function, so it is also easy to produce symptoms of visual fatigue. Refractive reference: The diopter and refractive properties of the two eyes are different, collectively known as “refractive reference”. Generally speaking, there is a mild difference in the refractive state of the two eyes, and complete agreement is rare. During the development of the eye, the degree of hyperopia is decreasing, while the degree of myopia is developing. If the two eyes differ in the degree of farsightedness reduction or myopia progression, this can cause refractive disparity. Since the activity of both eyes is simultaneous, the ability to turn what the two eyes see into one is called “fusion function”. There are many causes of refractive error in children, of which genetic factors are the most important. Of course, unreasonable eye use is also a cause that cannot be ignored, children are in the growth and development period, if you do not pay attention to eye hygiene, such as reading, writing incorrect posture, or poor lighting, resulting in eye and book distance is too close, or reading for too long, or walking, reading in the car, etc. can cause excessive eye fatigue, easily contribute to the occurrence of acquired myopia. In reality, there are very few true “orthokeratology” eyes, which can compensate for mild refractive errors and maintain normal vision within the range of the eye’s adjustment function. Farsightedness and astigmatism are usually natural, and if the prescription is high and there are no glasses at an early age, it is harder to detect than myopia because there is no good or bad comparison from childhood to adulthood. Refractive aberrations, in particular, are much less likely to be detected early because there is a good or better eye. In contrast, people are born with poor vision, and to get normal development, they need to rely on the refractive system of the eye to project a clear image onto the retina in order to stimulate the development of the visual center. People with farsightedness and astigmatism have blurred vision, and the visual center is not sufficiently stimulated and will be underdeveloped, so wearing glasses will not improve vision, which is “amblyopia”. If not detected during the period of visual development, the effect of amblyopia treatment will be greatly affected. Children do not tell their parents that their vision is not good, and in many cases they need to be examined by a doctor to find out the problem, so it is important to have regular eye examinations to detect and treat the problem as early as possible. Because the best age for amblyopia treatment is 3-5 years old, the treatment method is not complicated, which is to correct refractive errors as early as possible during the visual development period, plus some masking, fine visual training, etc. For most children, the treatment is very effective, but over 12 years old treatment is basically ineffective.