What's the difference between the corridor lengths?

Corridor length (or progression length) is the vertical distance over which a progressive lens gradually shifts in power from distance vision to the intermediate and near zones. A shorter corridor (lower number) means a quicker transition to near vision. This length plays a key role in how comfortable and functional the lens feels when worn. If there’s no specific requirement for a different corridor length, we generally recommend a standard length of 13 or 14 mm.