Pantoscopic tilt refers to the frame alignment in the up and down position of the frame.
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 7 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 freeform 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.
Do we need to consider Pantoscopic tilt during Pre-fit frame Techniques?
Surely Yes! See how to How to adjust eyeglasses and fit frames with considering pantoscopic tilt?
Generally some pantoscopic tilt and Wrap Angel is desired but when these adjustments are made too drastically, they can affect the optical quality of the lens. Unlike vertex distance, these two adjustments create something called marginal astigmatism. This monochromatic aberration is the result of light passing obliquely through the lens, creating two focal points much like a toric lens designed for those with astigmatism. Flat base curves and excessive tilt are the major causes of this. Let's look at what happens to the above prescription when the pantoscopic tilt is changed from 14° to 22°.
• Many modern progressive lenses are optically optimized for a minimum amount of lens tilt
• Additionally, the line of sight must pass through an angle of 20° or more to reach the near zone
• This results in an effective tilt—and an apparent vertical narrowing—of the viewing zone aperture
• Pantoscopic tilt brings the near zone closer to the eye and increases the field of view through the near zone of the lens
This change may not seem like much to us, but for the discerning patient such a difference may be noticeable. Plus if we compound errors, such a 0.12 diopter lab processing error can make the situation even worse. During our troubleshooting process we often overlook the effects of how the lenses are fitting and how this will ultimately effect the prescription. We need not go through a series of complicated equations and measurements as the patient waits, but instead keep these suggestions in mind while helping the patient during frame selection and during the dispensing process.
Tags: Optician Knowledge
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