Multifocals
Finding the Right Fit with Multifocal Lenses
Use these prescribing pearls to find the optimal prescription.
BY ROBERT L. DAVIS, O.D., F.A.A.O., Oak Lawn, Ill.

Chances are you've worked with more than one presbyopic patient who has had difficulty adapting to his new bifocal contact lens prescription. Before bifocals, these patients likely never had problems with their contacts and never experienced this much visual discomfort. "The doctor," your patient might think, "obviously doesn't know how to examine or fit these new bifocal lenses."

Although you probably can't provide consistent clear vision from distance to near point, you can take steps to help your patient. Successful bifocal lenses create a delicate balance of distant and near vision that overlaps the intermediate visual ranges.

As you know, multifocal lens designs incorporate more than two zones of clear vision without the need to hunt and search for clarity. Offering the patient a lens design that doesn't require him to make adjustments represents the objective of lens selection. In this article, I'll provide you with some practical techniques to help you reach this goal.

First things first

In deciding lens design options, first look at the following factors:

Patient birth date. This gives me an idea of the bifocal strength needed according to Donder's table. If the patient's age is between 38 and 48, my first lens selection is a progressive lens. If the patient is older than 48, the bifocal power required to provide adequate near vision will need to incorporate a spherical near component.

Occupational and hobby requirements. Obtained during the case history, this information directs the next phase of lens selection. Individual patients will place a greater importance on either distance or near activities. Ask about and discuss personal visual needs with patients. Make sure your testing conditions are in normal room illumination and outside the phoropter with loose lenses. Don't be surprised if the patient does wonderfully at the office and fails miserably at home. This experience will lead you to the appropriate lens modifications to help solve the problems of the first lens design.

For the patient, trial lens fittings provide firsthand experience of lens design. For the practitioner, they provide the ability to refine the prescription, fitting parameters, and the patient's subjective response. You can check lens fit and movement and gauge the patient's ability to see at all visual ranges. Keep in mind what you've no doubt heard many times with bifocal lens fittings: "One design won't fit every patient."

Patient as partner

Besides trial lens fittings, your job involves keeping the patient motivated to find a usable solution. Explain the presbyopic alternatives and how the various designs focus light on the retina. Patients can easily appreciate the visual adjustments that need to be made if they comprehend the limitations that each design incorporates.

Provide your patient with written materials and explain that the prescriptions of these different lens modalities are all the same. The only difference involves the image quality focused on the retina and their visual system's ability to interpret the information presented. In short, make your patient a partner in the bifocal fitting process.

Prescribing pearls

In prescribing the best lens for your patient, also keep these items in mind:

Monocular vs. binocular. The multi-prescription lens design integrates multiple spherical, progressive or combination components. The position and zone size of each component differentiates the various lens options. (see Table below).

The refraction represents only a starting point. Some designs require an addition or subtraction of a half diopter. Some patients will tolerate over plus, aiding in the near prescription; others will require over minus to arrive at acceptable distant vision.

Investigate acceptable visual ranges monocularly. This helps you understand the improvement or deterioration of adding or subtracting a half diopter.

Always inspect lens design quality under binocular conditions. Patients with 20/30 vision monocularly will frequently achieve 20/20 vision binocularly after summation.

Don't be discouraged if a patient has poor vision monocularly as well as binocularly. That doesn't mean that the patient is a poor bifocal candidate. Instead, indicate that while the particular lens design won't work, others have a good chance of success. Each lens design will focus light uniquely on the retina.

Pupil size. Pupil size can be an ally in these target zone lenses. A successful lens design in the daytime might be a crippling lens design at night. Flare and glare can destroy the image quality without any solution except selecting a different lens design.

Each lens design has a unique zone configuration that provides different options. Some designs have a near prescription in the center and distance in the periphery, which aids night vision during scotopic dilation. Some designs are aspheric, reducing the flare and glare consequence. Investigating light and dark pupil size will reduce your chair time and narrow lens selection.

Push and pull. The most important facet in the fitting procedure involves pushing and pulling the prescription by
+/- 0.25D to arrive at the optimal lens power for a patient. Your final prescription will always be the least minus to provide good distance and adequate near vision. Changing the bifocal power will always influence distance clarity. The dilemma consists of three different visual ranges but only two eyes. Mixing and matching the prescriptions and lens designs still requires the eyes to feel as if they're balanced by suppressing the holes in the patient's visual field.

B&L's distance-centered aspheric.

Multifocal lens design features

The Bausch & Lomb Disposable Seequence I in minus and Seequence II in plus is a distance-centered aspheric lens to fit your beginning presbyopes. It incorporates a +0.75D add that is plenty for these patients.

This aspheric lens design provides more add than the patient's previously worn distance-only lenses. You can also offset the distance prescription by a maximum of one-half diopter without degrading distance vision.

The CIBA Vision Focus Progressive is a near center aspheric lens design with a higher add prescription (+1.25) that can be used with patients who require more add. Usually, a +0.50 D must be added to the manifest sphero-equivalent prescription for the appropriate distance prescription. This prescription alteration will take advantage of the full bifocal power but won't degrade far vision. This lens design can also be fit by offsetting the distance prescription by another half diopter to integrate more add power.

The Lifestyle 4-VUE and XTRA incorporate a higher add than the aspheric lenses and represent excellent lens design for your moderate presbyopic patients. Routinely these lenses need to add an additional -0.50 to the distance prescription to provide good distance vision. The Lifestyle 4-VUE is a multiaspheric annular lens design with distance in the center and the outside ring. The Lifestyle XTRA lens is a multispheric lens design with distance also in the center and the outside ring. As the bifocal prescription increases, distance vision is adversely affected. These two lens designs can be fit binocularly as well as in combination.These pupil-dependent lenses can be a wonderful solution for the right patient although some will describe the consequence of simultaneous overlapping prescriptions.

	Here's the lens optic zone surface topograph for Focus Progressives.

The Cooper Vision Frequency Bifocal represents an excellent lens design for the moderate to late presbyopic patient. It incorporates a spherical center zone surrounded by an aspheric intermediate zone with another spherical zone in the periphery.

The real advantage to this lens design involves the integration of a distance-centered lens for the dominant eye and near-center lens for the non-dominant eye. The distance-centered lens integrates a 2.3 mm spherical distance prescription; the near-centered lens has a 1.7 mm spherical near prescription in the center. The distance center lens design usually needs a +0.25 added to the distance prescription while the near-centered lens requires -0.25 added to the distance prescription.

The manufacturer suggests an initial selection of a D lens for the dominant eye and an N lens for the non-dominant eye. Initially, I select two D lenses and check the quality of the near vision. If the patient requires improvement in the near vision, replacing the non-dominant lens with the N lens usually solves the inadequacy. If the patient still needs improvement in the near vision, I replace the D lens in the dominant eye with an additional N lens. The higher add prescriptions usually have a deteriorating effect on the quality of the distance vision. The real advantage of this lens design is the flexibility to fit most patients with one lens modality due to the many options.

Frequency Bifocal's patented Inverse Geometry lens system provides superior vision at all ranges.

The Vistakon Acuvue Bifocal is a flexible lens design that can be used with the entire spectrum of presbyopic prescriptions. The bifocal add powers can be configured with a +1.00, +1.50, +2.00 or +2.50. This two-power lens design can be fit in a bifocal arrangement or a multifocal lens design by offsetting add powers.

The alternating distance and near-concentric annular power strategy reduces the problems encountered at night or in dim illumination. In light when the pupil dilates, light falls upon an adjacent zone of distance power, aiding distance vision in conditions such as night driving. Typically, the distance prescription must be increased by -0.50D for optimal distance viewing.

This simultaneous lens design incorporates alternating distance and near powers inside the pupillary zone. Increasing the bifocal power reduces the quality of vision in the distance because the near prescription affects alternating power separation within the pupil. Offsetting the bifocal powers creates a multifocal approach, resulting in an improved distance, near and intermediate visual range as compared to the straight bifocal fitting strategy.

Increasing success

Recent lens designs have tweaked the annular and aspheric lens concept to create additional lens options. Future bifocal contact lenses will employ lens designs to reproduce the advantages of the focusing mechanism prior to the degrading accommodative system. They will increase permeability and develop more wettable surfaces.

The next step involves incorporating a two-lens design fitting approach, using an aspheric lens for distance and an annular lens for near vision. Instead of using a pure annular or aspheric design, the combination with varying zone sizes will increase success with multifocal lenses.

Dr. Davis is in practice and conducts clinical research in Oak Lawn, Ill. He is a diplomate in the Cornea and Contact Lens Section of the American Academy of Optometry.