The selection of spectacle frames must meet the optical requirements:
1. The geometric center size of the spectacle frame should be close to the distance between the pupils of the eyes (less than 4 to 10 mm is better).
Taking into account that the lens blank must be centered and cut to fit the spectacle frame in front of the eyes, the position of the pupil is best to face the geometric center of the spectacle frame, preferably less than 4-10 mm. If the lens shift is very large, it may cause effects such as prisms and affect the comfort of wearing glasses.
2. Make sure that the distance between the lens and the eyeball is about 10mm after wearing the glasses.
If the lens is too far away from the eye, not only will the optical function change, but the wearer will also see the outer edge of the lens, causing difficulty in positioning; if the lens is too close to the eye, the eyelashes will touch the lens, which will not only cause the lens to blur, but also cause irritation. Therefore, it is best to ensure that the distance between the lens and the eyeball is about 10mm after wearing the glasses.
3. The angle between the front mirror of the glasses and the vertical line of the wearer’s face is about 4°～18°.The size of the angle is related to the field of view. Generally speaking, the upper part of the frame cannot touch the eyebrows, and the lower part cannot touch the face. If the frame cannot reach the required forward inclination angle, it is recommended to find a professional to adjust the nasal pads or change a pair of frames.
