Some definitions first:
- Pantoscopic: The lens bottom is rotated towards the cheeks.
- Retroscopic: The lens bottom is rotated away from the cheeks. Rotation of the lens, around the horizontal axis occurs in frames at the hinge so temples mounted at the top of a frame are rotated like the above illustration.
Lens tilt improves the way a lens works and contributes to how good a pair of glasses looks on the patient. Tilt is dependent on the interaction of the heights of the ears and bridge of the nose. So, even though a new frame has about seven degrees of tilt when manufactured once lenses are added the frame may not appear to have any tilt at all unless it is well adjusted to the wearer before any measurements are taken.
So, when taking measurements for free-form or digitally enhanced lenses, place the frame on the patient, make sure the frame front is straight and lenses have about 8 degrees of tilt. The amount of tilt should look good i.e., correct for the way that this patient wears this frame.