ONE OF THE MOST effective presbyopia contact lens designs also happens to be one of the most intimidating to fit. But these translating (also known as alternating) GP bifocal/multifocal lenses offer many benefits.
Compared to the optics of aspheric and concentric multifocal lenses, those of translating lenses are less compromised by overlapping points of focus from simultaneous powers (Dinardo and Fosso, 2014). However, fitting translating lenses can be tricky; patient selection is critical and close consultation with the GP laboratory is necessary to understand specific design idiosyncrasies.
The best candidates for a translating design can adapt to lens wear (i.e., they are willing to “push past” the initial discomfort of a GP lens) and are not averse to a few additional in-office visits and lens remakes, if needed. The reward of having superior optics and vision should motivate them to put in some extra time adapting to these designs. Patients who have previously worn simultaneous GP, hybrid, or soft lens multifocals but are now aging into more advanced presbyopic status are great candidates for translating designs.
It can be difficult to reach higher adds in a simultaneous design without affecting the patient’s distance vision; a well-fitting translating GP lens keeps these optics separate. Options exist for both distance/near flat-top segmented designs and progressives that incorporate intermediate vision areas.
Physiologically, translating designs require the patient to have average or slightly more tight/taut lower eyelids. Any lower lid laxity or ectropion will allow the lens to slip under the lower lid and prevent translation upward on downgaze (Figure 1). This will result in poor near vision. Additionally, the lower lid should sit at the level of, or no more than 1mm above or below, the inferior limbus.
It helps to measure corneal diameter/horizontal visible iris diameter to choose the overall diameter of the initial lens. Measuring pupil size, centration, and the distance from the inferior limbus to the inferior pupillary margin will be helpful to determine the segment height.
Troubleshooting is highly dependent on design. Older designs were often fit very flat and heavy with significant prism to assist in dropping the lens down to hit the lower lid to assist with translation on downgaze.
Newer designs may be fit on-K or even steeper than K, often with aspheric back surfaces. There are variations in truncation and prism, and some have uniquely beveled inferior edges.
It is advisable to follow the fitting guide or discuss needed changes with laboratory consultants when issues arise. Making note of lens centration, rotation, fluorescein pattern, segment height in relation to inferior pupillary margin, and lens translation in downgaze will be helpful in troubleshooting discussions (Tuong and Jackson, 2015).
The visual demands of presbyopic patients are more critical than ever before. Many patients desire freedom from spectacles but aren’t willing to compromise their vision in contact lenses. Offering a solution that considers these needs can be a worthwhile effort for both practitioner and patient. CLS
- Dinardo A, Fosso T. Multifocal Contact Lens Success: Fact or Fiction? Contact Lens Spectrum. 2014 Nov;29:30-35,49.
- Tuong C, Jackson JM. Tips for Translating GP Bifocals. Contact Lens Spectrum. 2015 Apr;30:16.