How far apart are the progressive marks in multifocal lenses?

In multifocal lenses, specifically progressive lenses, the distance between the progressive marks, which indicate the appropriate alignment for the optical zones, is typically around 34 mm. This distance is significant as it reflects the average interpupillary distance (IPD) for adults, ensuring that the various focal points in the lens align properly with the wearer's line of sight.

Having the progressive marks at this distance allows for optimal progression from distance vision through to intermediate and near vision zones. Accurate placement is crucial to provide seamless vision correction across multiple distances, without causing visual distortion or discomfort. The 34 mm spacing helps accommodate the average anatomical position of the eyes, which is essential for the effectiveness of the lens design.

The other distances listed do not correspond to standard practices in multifocal lens design, as they would either place the optical centers too close together or too far apart, potentially leading to misalignment and ineffective vision correction for the wearer. Thus, the spacing of 34 mm supports functionality and comfort in the use of progressive lenses.