Definition: Refractive error between two eyes is called refractive error. Whether it is myopia, hyperopia, or myopia in one eye and hyperopia in the other, as long as the difference between the two eyes is more than 250 degrees, it belongs to refractive error. Clinical manifestations: 1. One eye has good vision and the other has poor vision. If the refractive error is high myopia or hyperopia, it can lead to low vision in both eyes.2. Refractive error of more than 2.5D, due to the unequal size of binocular image, it will cause fusion difficulty and destroy binocular monovision, and in order to make the image clear, it will cause contradiction between binocular adjustments, and so there are symptoms of visual fatigue.3. Binocular monovision dysfunction: simultaneous vision, fusion vision, and stereoscopic dysfunction can be appeared;4. The eye with high refractive error can develop strabismus (mostly exotropia).5. Alternate vision. It occurs in cases where both eyes have good visual acuity, both eyes can focus on the target, and the two eyes can be used alternately; another situation is that the child is myopic in one eye, and orthoptic or mildly hyperopic in the other, and will involuntarily use the myopic eye to look near, and use the orthoptic or hyperopic eye to look far away, forming the pattern of using both eyes alternately. Although only one eye is used each time, there may be no symptom as no adjustment and collection are used to look far away and near. Symptoms. Treatment points 1. Covering treatment. By covering the healthy eye or the better eye to slow down or eliminate the inhibitory effect on the amblyopic eye, increase the chance of using the amblyopic eye, so as to improve the visual acuity of the amblyopic eye.2 For those who can’t adapt to the lenses, the lower eye should be corrected sufficiently so as to achieve the best visual acuity, and the corrective lens should be lowered appropriately for the other eye.3 For those who can adapt to the lenses, the corrective lens should be corrected sufficiently and the lenses should be worn frequently so as to maintain the function of binocular monocularity and to eliminate the symptom.4 For those who have large refractive error and cannot be corrected by lenses, the treatment of amblyopia in the poor eye should be the main focus. After adults have normal vision in both eyes, surgery can be performed on the higher eye to treat the refractive error. 5. Select and use the compound amblyopia instrument according to the principle of refractory amblyopia treatment. 6. For refractory or difficult to cure amblyopia, it is better to treat it as early as possible with personalized plan. 7.