Translating Bifocals
Fitting
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- Follow recommended fitting guidelines; these lenses are typically fit slightly flatter than “K” and are intended to position on or close to the lower lid due to the prism incorporated in the lens
- Have, at minimum, one diagnostic fitting set of these lenses; for recommendations, call your CLMA member laboratory
- Good candidates:
- Critical vision demand
- Any add requirement
- Lower lid positioned near to or slightly above lower limbus
- Normal or tight lower lid tension
- Lens positions on or near the lower lid and moves no more than 1mm with the blink. Photo shows a Good Bifocal Fit.
- The seg line is, in most designs, positioned at or near the lower pupil margin in straight ahead gaze
- The lens should shift upward or translated with downward gaze such that, at minimum, one-half of the near zone is in front of the pupil. This can be observed with the slit lamp while pushing up the upper lid.
Problem-Solving
 Excessive rotation of the lens; manage by flattening the base curve (typically by 0.50D) and/or increasing the amount of prism. Photo shows Excessive Rotation |
 The lens is picked up too high with the blink; manage by increasing prism (typically by 0.50D) and/or flattening the base curve radius. Photo shows High Bifocal |
 The lens is not translating (or only intermittent translation); try a flatter base curve lens or flatten peripheral curve radius to increase edge lift. Prism and truncation can also be increased. Photo shows Non Translating Lens |
- Patient reports blur at distance; rule out:
- Lens is picked up too high
- Lens is too small (does not adequately cover pupil); therefore, increase diameter
- Seg height is too high
- Patient reports blur at near; rule out:
- Seg height is too low
- No or intermittent translation
- Excessive lens rotation
- Patient drops head (not eyes) to read
– OR –