Building a Successful Presbyopic GP Practice
BY EDWARD S. BENNETT, OD, MSED
Bifocal contact lenses are the most underused vision correction modality today. Studies have found that multifocal contact lenses (both soft and GP) perform better visually than monovision, that GP multifocals provide improved contrast sensitivity compared to soft multifocals and, when given the choice, 75 percent of patients who wore both GP multifocal contact lenses and monovision preferred GP multifocal lenses.
Presenting GP Multifocals
I usually present this option before a patient becomes presbyopic so that he'll expect this modality when he enters presbyopia. I present other options as well, but I usually discuss bifocals (typically GP because they provide better vision) first. I always mention that some compromise in vision may occur because these are dynamic pieces of plastic that move on the eye with the blink. I also tell patients that I'll strive to meet their visual goals with GP multifocals, but they may need over-spectacles for occasional use. In other words, it always pays to "under-promise and over-deliver."
I also tell patients that I may need to make a lens change or two to optimize fit and vision, but with patience and motivation we have about an 80 percent chance of success with GP multifocal contact lenses.
Fitting Aspheric GP Multifocals
GP presbyopic designs are relatively easy to fit, especially aspheric multifocal designs. Good candidates for aspherics include individuals who need an intermediate correction, who still participate in sports and who don't have quality distance vision demands.
Fit most aspheric designs 1.00 diopter to 1.50 diopters steeper than K. They should center well with minimum movement with the blink. If excessive movement occurs, then make the lens 0.50 diopter steeper. These lenses should translate during reading.
Several aspheric designs are available for patients who need a higher add (+1.50D to +2.00D), although the effective distance optical zone is reduced and the optical quality may be as well. But patients often perform well with a higher add in the non-dominant eye or -- in the case of >= +2.00D -- a "modified bifocal" approach in which you overplus the non-dominant eye 0.25D to 0.50D.
Fitting Translating Designs
Fit segmented or concentric translating designs for patients who have critical distance and/or near vision demands. These lenses are prism-ballasted, with a base curve slightly flatter than K to allow the lenses to position on or close to the lower lid with little movement with the blink.
Position the seg line at or slightly below the lower pupil margin in straight ahead gaze. Make sure the lower lid isn't positioned >1mm below the lower limbus. The lens translates properly when, on lifting the upper lid while the patient looks inferiorly, the lens shifts superiorly to place much of the near zone in front of the pupil. If a lens exhibits less than optimum translation, try selecting a flatter base curve and/or increase edge clearance. A flatter base curve radius also stabilizes a lens that rotates excessively on the blink. Increase prism ballast when the seg line lifts well into the pupil on the blink.
Confidence Breeds Success
If you're just starting out with GP contact lenses, then you can gain confidence by fitting a few patients who are most likely to succeed (motivated, single-vision spherical GP wearers who have early presbyopia). Start with aspheric multifocals, then progress to translating bifocals. Consultants from your GP lens lab and resources from The Gas Permeable Lens Institute (rgpli.org) can also help you build a successful GP multifocal practice.
Dr. Bennett is an associate professor of optometry at the University of Missouri-St. Louis and is executive director of the GP Lens Institute.