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 eye may not have any symptoms. Simultaneous vision means that light can pass through both the distant and near optical areas. If the patient looks at a distant object, the light passes through the distant optical area to form a clear image on the retina, and through the near optical area to form a non-retinal focus. Conversely, if the patient looks at a near object, the light passes through the proximal optical area to form a clear image on the retina, while the light passing through the distal optical area forms a focus outside the retina, resulting in some blurring always due to defocus. The difference between myopic and hyperopic refractive error: 1. The same visual correction in both eyes is more common in myopic refractive error than in hyperopic refractive error, and unequal visual correction is more common in hyperopic refractive error, and the difference in visual acuity between the two eyes is greater. 2. The visual acuity correction in the better eye decreases as the refractive error increases, and in hyperopic refractive parallax, the decrease is even greater. 3. In myopic refractive error, the corrected visual acuity of the eye decreases with the increase of refractive error, and the gradient of decrease is larger than that of the good eye on the opposite side; in hyperopic refractive error, the visual acuity of the eye decreases rapidly with the increase of refractive error, and is more rapid than that of the eye in myopic refractive error, 4. The average corrected visual acuity of hyperopic refractive error is worse than that of myopic refractive error. Refractive aberrations are not equal to the image of the two eyes, and they can exist simultaneously or separately. If the glasses for correcting refractive aberrations are placed in the front focal plane of the eye with axial refractive error, the retinal image size will be the same as that obtained from orthoptics (Knapp’s law). Image inequality is often seen in the following cases of refractive error, such as eye distention, dizziness, visual acuity and even diplopia.