Fitting the Presbyope With Gas Permeable Contact Lenses

By Keith Ames, OD
October 2001

Fitting RGP multifocals takes little time to master but brings benefits to both patient and practitioner.

The presbyopic patient is a perfect candidate for rigid gas permeable contact lenses as RGP multifocal lenses offer the best opportunity for obtaining functional distance and near vision without the visual compromises associated with soft multifocal and monovision contact lenses or the use of auxiliary spectacles. This is not to say that RGP lenses can provide perfect vision for all tasks or acuity equal to spectacle acuity for all patients, but the limitations of the alternative corrections make offering this option a professional responsibility you should not ignore.

Lens Designs

RGP multifocal lenses are available in two general categories: alternating and simultaneous. Alternating lenses work by presenting distance optics in straight-ahead gaze and near optics in downgaze when the lens translates or moves upward. Simultaneous lenses present distance and near optics at the same time but the proportion of distance/near optics can be controlled by the lens designer through zone width and positioning. In my experience, these lenses also translate to some extent in downgaze which accounts for their significantly better performance compared to soft multifocal lenses of similar design. Lens movement is critical in the ultimate success of RGP multifocal lenses because it allows different optical zones to be presented at different times, and conversely, the absence of lens movement is a fundamentally limiting factor for soft multifocal lenses.

Alternating RGP multifocal designs are available that can be fit lid-attached and rest in a superior position on the eye. Lid-attached fitting is my preferred technique and represents the majority of my current RGP patients.Therefore, I am inclined to begin with this type of bifocal as it is easy to convert current wearers and is consistent with my general fitting philosophy for new wearers. For patients who are currently fit intrapalpebrally due to wide apertures/high upper lid positions or non-lens wearers with similar lid anatomy, I will fit a prism-ballasted alternating bifocal design if lower lid support is sufficient. If the lower lid is too low to support a ballasted lens or too high so that the lens rests too high, then I will fit a simultaneous RGP bifocal that generally requires a centered fitting approach.

Fitting Approach

A simplified fitting approach is essential in today's competitive, managed-care environment. Downward trends with contact lens fees make re-engineering your fitting technique a top priority. You must bring your costs in line with the price the marketplace will support by improving efficiency without sacrificing patient outcomes. In my practice, I achieve this by designing the initial trial lens empirically and dispensing this lens. Assessing the fitting and visual performance of RGP lenses immediately after dispensing is usually misleading and can lead to unnecessary or counterproductive changes. Documenting the fit at dispensing is important, but I do not make changes until the one-week assessment as RGP lens performance can change significantly after adaptation.

This approach is successful for standard single vision rigid gas permeable fitting but can also be effective for multifocal RGP fitting. The advantages afforded by dispensing the trial lens and allowing adaptation to occur before considering changes to lens design or power are even more important in multifocal fitting. Lens positioning and movement are critical in the visual result obtained in multifocal fitting, and lens dynamics can vary considerably during the adaptation process. Remember, any lens can be fit empirically as long as you know what your average reorder rate will be. Simply factor this into your fees and/or order the lens warranted to allow for lens exchanges.

Patient expectations are also very important when fitting the presbyope. Do not over-promise. I tell my presbyopic patients that a multifocal contact lens will not usually provide the same precise level of vision obtained with spectacles. We may find a lens that satisfies 75 percent of their visual needs but a supplementary correction might be required for certain tasks like prolonged computer usage or detailed reading. It is far better to have this discussion prior to dispensing rather than after to maintain patient confidence in your abilities.

Empirically fitting multifocals can be successful only if you approach lens selection in a logical manner and limit your lens choices to a few fitter-friendly designs that you have worked with previously. When selecting the initial type of lens to attempt, I feel it is more important to fit the lens Mother Nature intended rather than focus solely on the patient's vision requirements. If a patient has a good upper lid position to support lid attachment, then attempt a lid attachment fit. If a patient has a high upper lid but has a lower lid at or near the limbus, then a ballasted lens should be fit. My bias is to fit alternating lenses whenever possible since they provide the least compromised vision. Fortunately, alternating designs are available that work through upper lid attachment as well as lower lid support. If the upper and lower lids are positioned poorly resulting in a wide palpebral aperture, then I will default to a simultaneous centered design. This fitting approach is outlined below.

Tables 1 to 3 list commonly available RGP multifocal designs in the three general categories previously discussed. It is critical to gain experience in fitting each category of lens since you will need to use each design type to satisfy the range of patients you will encounter in practice. But my experience shows that the vast majority of patients will be able to be satisfied by concentrating on a single design within each category. The designs you choose will be based on individual clinical experience and patient results as well as input and support from your local laboratories.

I can understand the hesitancy of practitioners to utilize empirical fitting methods in multifocal fitting. However, my experience in using this approach has been very positive. Reorder rates are not excessive although they are significantly higher than single vision RGP fitting. My typical reorder rate for routine single vision fitting is 10 percent. For lid-attached and centered multifocal fitting, the reorder rate is 50 percent and for ballasted bifocals 75 percent. Generally a maximum of two lenses per eye is required to either achieve success or recognize failure. The time savings realized by this approach more than compensate for any inconvenience incurred by reordering. Chairtime is the practitioner's greatest expense. This fitting approach significantly reduces chairtime while maintaining normal patient flow. Expenses are controlled by judicious use of warranties and appropriate professional fees.

I believe that significant reorders will occur even if non-dispensing trial fitting is employed. Often, trial fitting is accomplished with contact lenses very different from the patient's prescription. This can be especially problematic for the prism-ballasted multifocal wearer where lens dynamics play a pivotal role. A minus ballasted lens will fit very differently than a plus ballasted lens. Even moderate differences in power could, and often do, impact fitting. It is unlikely that the average fitter will possess the large fitting sets necessary to optimize trial fitting. I suggest the empirical approach would open up multifocal lens utilization for contact lens fitters in "the trenches" and enable their patients to benefit from this modality.

Summary

Multifocal RGP correction is an exciting and rewarding area of practice. My approach is win-win for patient and practitioner. Lenses are delivered quickly, which patients appreciate. The practitioner can assess fitting with precision and avoid unnecessary or counterproductive changes. Practice efficiency is maximized. I enjoy recommending RGP multifocals for my patients because I know their performance can be very impressive. This positive outlook when conveyed to patients is important in gaining initial acceptance of your recommendation and assisting in the adaptation process. If you're not experiencing much enjoyment dispensing contact lenses these days, try fitting RGP multifocals. They put the "fit" back in contact lens fitter and can enhance the professional image of your practice.

Dr. Ames thanks Ursula Lotzkat of the RGPLI for her assistance with the graphics for this article.