Tools for Bifocal Lens
prescribing for presbyopia
Tools for Bifocal Lens
BY DAVID W. HANSEN, OD, FAAO
Fitting presbyopic conditions requires the proper tools for success, just like Vince Lombardi chose the appropriate plays for certain situations. Repetition, confidence and passion were the trinity of of Vince Lombardi's football success. He believed in finding the best football
players who collectively would execute his plans for winning. Most of his plays were well known to the opposing teams, but his teams' hallmarks were precision and adaptation. Practice is an integral component to successful football and similar to the diagnostic examination in contact lenses. Precise physical measurements and careful refraction prior to the application of the diagnostic contact lenses will assist the bifocal design process. Bifocal contact lens success is helped with a diagnostic appointment.
The following is a minimal investment for fitting bifocal contact lenses: bifocal trial lenses, biomicroscope with in-eyepiece reticle, keratometer, Burton lamp, sodium fluorescein strips, patience and a passion to succeed. To me, a corneal topographer is a necessary instrument for the practice of total vision care. It measures the entire corneal surface, which helps select the appropriate multifocal design before the diagnostic exam.
Before the introduction of disposable bifocal contact lenses, the cost of diagnostic lenses was an important factor in fitting the patient with this modality. RGP multifocal diagnostic lenses can still be costly, but you need only a few of the different lenses to start. Once you have gained confidence, other design options may fit a wider range of visual demands, including residual astigmatism, keratoconus and post- refractive surgical needs.
You will need a distance-center and a near-center soft bifocal design for different sized pupils with different visual demands. Select a disposable lens in each category, and at least one conven- tional soft bifocal with high add aspheric design capabilities. Practitioners usually have favorite materials, so this may be the factor when choosing the design. Custom soft bifocals with special needs, including astigmatism, can be ordered directly from a manufacturer consultant, our best friend for success.
RGP diagnostic bifocals can be obtained through laboratories as loaner lenses, but if you systematically select different designs to purchase, you will save chair time with the patient and be more efficient. You will need at least one translating option and a simultaneous and/or aspheric design.
Establish your fitting philosophy before the purchase because aspheric multifocals can be fit with either a lower or higher eccentricity posterior curve. To clarify, many aspheric multifocals are fit 1.75D to 6.00D steeper than K to obtain a higher near reading power. Other designs are fit on K, while some utilize anterior surface prescriptions made aspherically to accommodate higher adds.
You may need to obtain variations of the traditional aspheric design by adding front and back aspheric curves.
Translating RGP diagnostic lenses should be carefully selected to provide a thin and comfortable lens. Avoid lenses requiring a prism and ballasting system to align and assist movement. Also, obtain a translating design which can be manufactured with front toric, back toric and bitoric options. This will give you a full complement of bifocal lenses.
Make a small financial investment in the tools to fit all types of bifocal and multifocal modalities. You and your patients will reap the benefits. "Now go through that door and bring back a victory!" Vince Lombardi
Dr. Hansen, a diplomate and fellow of the American Academy of Optometry, is in private practice in Des Moines,
Contact Lens Spectrum, Issue: September 2000