prescribing for presbyopia
Tips for Fitting GP Multifocal Lens Designs
BY JOHN MARK JACKSON, OD, MS, FAAO
In my last column, I discussed a GP-wearing friend who was wearing monovision. He was surprised to later learn that GP multifocals were available and was disappointed that his eyecare practitioner had not suggested them.
This is a fairly common story that I hear from GP patients new to our practice. When speaking to other clinicians about GP multifocals, they often seem reluctant for a variety of reasons to fit the wonderful designs that are now available. Is this reluctance a lack of comfort in fitting GPs in general, or is it specific to multifocal designs?
GP multifocals can be a little overwhelming. In some ways, the great number of choices available may make the process intimidating. Should I used a lined (translating) or a non-lined (simultaneous vision) design? Do I want one that lid attaches or one that centers? Should the lens be aspheric on the front, the back or both? The choices seem to go on and on. Here are a few suggestions to get you started down the right path.
A simultaneous vision design is usually the right choice. This kind of lens has a huge advantage over lined multifocals: intermediate vision. You'll be hard pressed these days to find someone who wants to wear multifocal contact lenses and doesn't use a computer. The power in simultaneous vision lenses fades gradually from the center outward in all directions, providing distance, intermediate and near vision.
Let lid position guide your choice. Lined (translating) multifocals are somewhat finicky in the way they fit. They are designed to more or less rest on the bottom lid, and they drop quickly to this position after a blink. To get this to work, the bottom lid needs to be at or close to the lower limbus and the upper lid needs to be at or above the upper limbus. It also helps if the upper lid is a little loose so it can let go of the lens.
Most patients (especially early to moderate presbyopes) don't have this lid configuration. Most patients will have lid anatomy that is better suited to a mildly lid-attached, simultaneous vision design.
If in doubt, try on a spherical GP first. This will allow you to get a rough idea of how the lid is going to interact with a multifocal lens. If the lens achieves mild lid attachment or centers well, the simultaneous vision lens should work well. If the lids won't hold onto the lens, then the translating design will probably work better.
Of course, if patients already wear GP lenses, then you can just evaluate where their old lenses position.
Use the lens fitting guides to help choose a design. There are many ways to make a simultaneous vision lens. It can be aspheric (to generate the add power) on the front, the back or both. Where these curves are placed will affect the way the lens fits and how it performs visually.
The fitting guide will usually tell you how the lens design is made and, more importantly, what type of cornea and lid configuration will work best for that particular lens. Going against the guide's suggestions will only lead to frustration.
Finally, be sure to develop a good relationship with the lens consultant at your GP lab. Lab consultants are invaluable in helping you find the right lens and the best performance for your patients. CLS
Dr. Jackson is an associate professor at Southern College of Optometry where he works in the Advanced Contact Lens Service, teaches courses in contact lenses and performs clinical research.