Most modern soft and GP multifocal contact lens designs incorporate simultaneous optics. However, there is another category of GP lens designs for presbyopes that work by a different principle, namely that of translation (Figure 1). The visual upside to translating optics is that, as patients look in primary gaze, the distance portion of the lens is centered over their visual axis and pupil. However, when they look down to read, the inferior portion of the lens interacts with their lower lid and translates up so that they are now receiving purely near optics over their visual axis in both eyes. In other words, the patients’ visual system is not simultaneously sifting through images that are vying for attention as it would be in the more common aspheric lens designs.
Of currently available GP lens options for patients who have presbyopia, translating lenses provide the purest optics for both distance and near; however, they also present a unique clinical scenario for prescribing practitioners.
First, evaluate the position of a patient’s lower lid margin as it relates to the inferior limbus. This is of paramount importance to the potential translation of the lens upon downgaze. The ideal location is with the lower lid just at, or potentially slightly above, the inferior limbus border. If the patient’s lower lid is too far below the lower limbus as the patient gazes downward, the lens will not be able to translate superiorly for the patient to appreciate the inferior add portion of the lens (Figure 2).
Next, determine the ideal lens-to-cornea fitting relationship by altering the base curve and/or diameter to ensure that the GP lens centers on the eye horizontally; the ideal position is centered along the vertical or just slightly below center. This is important because the lens is intended to interact with a patient’s lower lid upon downgaze.
Once centration is achieved, evaluate the segment line position as it relates to the patient’s lower pupil border in normal room illumination. Ideally, the segment height should be just at the lower pupil border or just into the lower one-quarter of the pupil (Figure 3). Some manufacturers choose to specify the segment from below the geometric center of the lens or, conversely, from the inferior lens border up to the segment line in millimeters.
When Vision Is Critical
When critical distance and near vision is desired, translating GP multifocals can be rewarding for patients and practitioners alike. CLS