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 severe 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 index eye is often in a blurred visual state, which can easily cause amblyopia, and the higher refractive index eye of a hyperopic person becomes amblyopic. The difference in refractive status and degree between the two eyes, generally more than 250 degrees between the two eyes, is called refractive aberration. The main causes of alternating binocularity include: 1. Developmental factors During the development of the eye, the degree of hyperopia is decreasing, while the degree of myopia is constantly developing. Trauma and other diseases can also cause refractive aberrations The prevalence of refractive aberrations in patients with ptosis is about 55%, while others such as eyelid hemangioma, retinopathy (vitreous hemorrhage, etc.), nuclear cataract, etc.; 4. According to its etiology, it can be classified as follows: hereditary (hereditary), including congenital glaucoma, congenital cataract and some diseases that cause eyelid closure, such as congenital actinic nerve palsy, ptosis, etc.; acquired (acquired), including traumatic, intra- or perispheric occupying lesions and medical factors, such as lens-less eyes after monocular lens removal The following are some examples of acquired factors: refractive surgery, penetrating corneal transplantation, etc.