GPs and presbyopia: why today's designs are easier to fit; The anatomical and optical considerations for fitting presbyopes with GP multifocals. (Contact Lenses)

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Just as presbyopes are the most underserved group of the contact lens-wearing population, so are gas permeable (GP) multifocal and bifocal designs the most underutilized types of contact lenses.

Yet, GP designs give you the opportunity to improve the presbyope's quality of life by providing crisp vision at all distances without spectacles, or without the loss of stereopsis and vision quality of monovision. A recent survey of diplomates of the Cornea and Contact Lens Section of the American Academy of Optometry shows a recent trend in these practitioners' preferences of bifocal contact lenses over monovision. (1)

Many O.D.s opt for what they think is an "easier" solution--monovision, single-vision contact lenses and reading glasses, or spectacles. They think that GP bifocal and multifocal designs are too complicated. It's not uncommon for a patient to say she has never heard of bifocal contact lenses when a doctor presents this option.

GP bifocals, however, are a good primary management option for most presbyopes interested in contact lenses. These designs are not complicated to fit and the learning curve may take as few as three fits of any specific lens design. The 50 members of the RGP Lens Institute Advisory Committee said as much when they were asked how many fits it took them to become comfortable with any particular GP bifocal lens design.

Also, newer lens designs provide better optical quality than older designs, and the availability of higher add powers in aspheric multifocal designs make GP multifocal or bifocal lenses viable options for many presbyopes. Here, we'll review the steps in fitting presbyopes in GP bifocal and multifocal designs, and which design best meets an individual's needs. To get started, you'll need at least one set each of simultaneous vision and translating bifocal trial lenses.

Anatomy of the Fit

Consider these anatomical features when evaluating an individual for GP bifocal or multifocal lens wear:

* Lid anatomy and position. GP translating designs can either be segmented (i.e., crescent or executive) or annular, both of which are prism-ballasted. Multifocal designs can either be aspheric (i.e., progressive) or annular in design--both of which are thin and not prism-ballasted. They're called "simultaneous vision designs" because all three viewing zones are often in front of the pupil at the same time.

The patient's lid anatomy and position are important factors. Measure and record the lid-to-limbus relationship, the lid tonicity, and the palpebral fissure size. Avoid a translating design if the lower lid is positioned [greater than or equal to]1mm below the lower limbus in straight-ahead gaze. The lens will not shift sufficiently with downward gaze, and the bifocal segment will position in front of the pupil. Likewise, a very small palpebral fissure may make it impossible for you to position the near segment line at or below the lower pupil margin as desired. It will, instead, position too high and interfere with distance vision.

Lid tonicity is important as well. As a person ages, the lids can become more flaccid. This makes lens translation more challenging.