Alternate binocular use means that the lens is designed to move in the direction of gaze across the cornea so that the distant and near areas can be almost completely covered by the pupil. The distance or near vision allows alternate selection of vision through different areas of the pupil. Alternating vision occurs in cases where both eyes have good visual acuity and both eyes can focus on the target, so both eyes can be used alternately. The patient may not have any symptoms. The patient only sees far away in one eye and near in the other eye. In the long term, the visual function will be greatly reduced, forming alternating vision, destroying the normal visual stereoscopic sense, and in serious cases, causing strabismus. It is a clinical symptom of refractive error. Refractive aberration refers to the unequal refractive power of both eyes. Those with a difference of more than 2.00D usually have symptoms due to difficulty in image integration. As the adjustment activity is simultaneous in both eyes, the higher refractive error eye is often in a state of visual blur, which can easily cause amblyopia, and the higher refractive error eye becomes amblyopic in hyperopic refractive error. The difference in refractive status and degree between the two eyes, generally more than 250 degrees, is called refractive aberration. Extraocular myopathy and amblyopia are also causes of alternate use of both eyes. There is no organic lesion inside or outside the eye, but the corrected visual acuity is not normal (less than 0.9) is called amblyopia. Amblyopia and strabismus are closely related, as monocular strabismus can lead to amblyopia in that eye, which in turn can lead to strabismus. Vision is a developmental perceptual function, at birth, does not function relatively amblyopic, through appropriate visual stimulation, gradually develop into normal vision, if in the process of visual development, due to strabismus, refractive error, congenital cataracts, etc., can not make the visual cells get sufficient stimulation, visual development is affected, will probably occur amblyopia (abblyopia), such as in infancy or early childhood, one eye receives This is due to the fact that when the brain associates visual stimuli from both eyes separately, if the images on both sides are different, the brain will select the clear image and suppress the blurred or contradictory new one, even if the eye with good vision in the month, the other eye “is not used” As a result, the visual development of the eye is abnormal, thus, the amblyopic eye is also called “lazy eye” (lazy eye), the definition of amblyopia is not fully agreed, it can be considered that amblyopia is during visual development, due to various reasons caused by the lack of effective stimulation of visual cells, resulting in corrected vision is lower than normal children of the same age, generally The prevalence of amblyopia is usually unilateral, but there are also bilateral cases, and the prevalence in the youth population is about 2%-4%.