Five Tips For Prescribing
RGP Multifocals

BY DAVID W. HANSEN, O.D.
DEC. 1996

Where do you start when considering fitting an RGP multifocal lens? Simplifying the bifocal fitting process will maximize your success. The following are my five best tips for organizing your thoughts and collecting measurements prior to the bifocal diagnostic examination.

INVESTIGATE THE VISUAL ENVIRONMENT

For patients who use a computer 30 percent of the time or more, I recommend simultaneous or aspheric RGP lenses. These designs allow patients to see adequately in the intermediate distance and with a smooth transition from far to near without a 'jump.'

CALCULATE AND PREDICT REFRACTIVE SUCCESS

If refractive and corneal toricity match, or if they're close, choose a simultaneous design. If you expect residual astigmatism, use a translating design. Translating lenses can usually incorporate a front or back toric design, providing optimum visual acuity and a better lens-to-cornea relationship.

ASSESS OCULAR CHARACTERISTICS

• Measure the visible iris diameter and the palpebral fissure size. Observe the position of the lower lid with respect to the lower limbus. If the inferior lid is below the lower limbus, don't use a translating design. If it's at or above the lower limbus, you may prefer a translating design (Fig. 1).
• Assess lid tonicity and meibomian gland integrity. Observe the convection currents of the tear meniscus, which are driven by the eyelids and which distribute meibomian and accessory gland secretions over the cornea and conjunctiva. Without a uniform tear consistency, lenses may not translate.
• Measure the position of the superior and inferior lids in relation to the cornea. Lid capture of the contact lens is one of the major problems in positioning a bifocal contact lens (Fig. 2).
• Use corneal topography to predict contact lens centering. It gives a more accurate understanding of the entire surface of the cornea and will aid in position and translation of most RGP multifocal designs.

PUPILS ARE IMPORTANT

Choose a simultaneous or an aspheric design for pupils smaller than 5mm with mesopic conditions. For pupils larger than 5mm, a translating lens is best (Fig. 3).

REMEMBER -- ALL BIFOCAL CONTACT LENSES TRANSLATE

Make sure the lens you choose, whether bifocal or multifocal, moves fluidly over the cornea.

Fit aspheric contact lenses with precise centration and minimal movement to allow translation into the near add lens power. Fit translating designs with a lens-to-cornea alignment fit and with minimal central fluorescein pooling. Keep translating design segments below the lower pupillary margin (Fig. 4). CLS

Dr. Hansen, a cornea and contact lens diplomate and fellow of the American Academy of Optometry, is in private practice in Des Moines, Iowa.