Opthalmic Frames
Final Fitting

In most cases frames are fit so that the pupil is positioned several millimeters above the optical center of the lens. When this occurs some pantoscopic tilt is desirable as shown in figure A on the previous page. Less commonly, when the pupil is positioned directly behind the optical center, an orthoscopic frame tilt is recommended. In the very unusual situation where the pupil is positioned below the optical center of the lens, a retroscopic angle is called for as in figure C.

For every millimeter the pupil is positioned above the optical center of the lens approximately two degrees of pantoscopic angle should be applied to the front.

Ideally, for good cosmetics, there should be approximately 8 - 10 degrees of pantoscopic angle for most frames. With some unusual shapes, it may be necessary to specify the vertical decentration of the distance optical center.

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Positive face form should be used when the patient's PD is narrower than the GCD of the frame. Since this is usually the case, most frames will have some positive face form. In instances where the GCD and the PD are the same, no face form is best. In the very unusual instance where the patient's PD is actually wider than the frame PD, negative face form should be employed. However, the need to apply negative face form can usually be avoided with a more appropriate frame selection.

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As mentioned earlier in this session, care should be taken during frame selection to insure a good fit for the bridge. When using non-adjustable bridges, little can be done to alter the fit at the time of delivery. When fitting frames with adjustable nose pads, the key issue is to be sure the entire area of the pad is resting on the nose. If the pad is angled in such a way that only a portion of it is resting on the nose, the tendency will be to �dig in� and cause soreness.