Article Date: 7/1/2005

MULTIFOCAL LENSES
Mastering Multifocals

With the presbyopic population steadily rising, fitting multifocal contact lenses is a skill worth learning.

If you're looking for more fun in day-to-day practice, look no further than multifocal contact lenses. Many soft and GP bifocal/multifocal contact lenses are available today. I'll explore some examples in each category, discussing the appropriate patient population for each and presenting a fitting approach that will breed success.

First, let's review some general considerations of bifocal and multifocal lens designs and some of the lens options that are currently available.

Simultaneous Image Designs

There are two basic design philosophies for bifocal contact lenses: Simultaneous image designs and alternating image designs. In the simultaneous image type, the retina receives images from multiple distances at all times. The brain must determine which image is primary and filter out the others. These designs allow for intermediate vision as well as for distance and near vision. Simultaneous image designs are available in both soft and GP materials and include aspheric (Figure 1), concentric (Figure 2) and diffractive lenses.

Aspheric Lenses incorporate an aspheric front or back surface to create a multifocal effect. As a rule, front-surface aspherics are center-near, while back-surface aspherics are center-distance. Each design has its advantages. Center-near designs tend to favor near and intermediate vision, whereas center-distance lenses usually provide better distance vision. Choosing which aspheric design to use depends on a patient's needs and ocular characteristics.

Concentric Designs feature a central zone of distance power or near power surrounded by one or more rings of the opposite power. Some designs, such as the Acuvue Bifocal (Vistakon), alternate distance and near powers in a repeating pattern (Figure 3). This seems to improve pupil coverage and visual input under various illumination settings and pupil sizes.

Diffractive Designs, as the name implies, diffract light entering the eye to produce the images the retina receives. CooperVision's Echelon diffractive design features a distance center and a series of diffractive phase-plate rings that surround it (Figure 4). As add power increases, the number of phase-plate rings increase, and they get closer together.

Alternating Image Designs

Also called translating designs, alternating image designs have dedicated areas for distance and near correction. Often the top of the lens is the distance portion and there's a "line" at which patients can access the near area. This design is what patients visualize when you mention bifocal contact lenses because it follows the same design as bifocal spectacles.

In theory, patients wearing alternating image designs see well at distance when looking straight ahead, and when the patient looks down, the lens moves up to position the near power area before the pupil (Figure 5). Unfortunately, patients tend to lose intermediate-distance focus with translating bifocal designs. As I'll demonstrate, many of the newer lenses combine features of both simultaneous and alternating designs to optimize visual performance.

Figure 1. Aspheric simultaneous design.
 
  Figure 2. Concentric simultaneous design.
 
  Figure 3. The Acuvue Bifocal incorporates a distance center and alternating distance and near rings.
 
  Figure 4. Diffractive simultaneous design of CooperVision's Echelon lens.
 
  Figure 5. For translating designs, the lens moves on downgaze to correct near vision.
 
  Figure 6. Fit newer aspheric GP designs with alignment or near alignment fit.
   

GP Lens Options

Translating Designs The Metro-Seg (Metro Optics) features a crescent-shaped segment so that slight rotations of the lens have less impact on vision compared to some other designs. This thin design is available in a wide range of powers for both the distance and near areas, and you can order it with or without truncation.

The Tangent Streak (Fused Kontacts) is available in a bifocal or a trifocal design with a straight "executive" style segment and add powers to +3.50D.

Another long-standing translating design is the concentric, or annular, configuration. An example is the Mandell Seamless Bifocal (Con-Cise Contact Lens). This center-distance lens has distance zones ranging from 2.8mm to 4.2mm in size. Add powers to +3.00D are available.

Aspheric Designs Moving to aspheric designs, many choices are available. The number-one lens in this category for the past few years has been the Essential Bifocal (Blanchard Contact Lens, Inc.), a back-aspheric, center-distance design that has three add "Series" available. Series 1 features add powers to +1.75D, Series 2 to +2.25D and Series 3 to +2.75D. Each successive Series fits a bit flatter than the previous one. A wide range of parameters is available, and you can order it in the original Essential design or in the slightly steeper Essential Xtra. You can also order both designs with the concentric S-form add enhancement (CSA), which places an annular segment on the front. CSA increases add power by up to an additional +2.00D, creating what Blanchard terms a segmented, translating, aspheric multifocal.

The Boston Multivision (Bausch & Lomb) employs a back-surface, multi-aspheric concept. It features a "Low" add of +1.50D and a "High" add of +2.00D. The idea is to fit the dominant eye with the "Low" add and the fellow eye with the "High" add to maximize acuity at each distance. This lens also has a range of parameters available.

You should fit most of these newer aspheric GP designs with an alignment or near alignment approach (Figure 6). Strive for lid attachment to enable the lens to position properly in primary gaze and to translate up on down gaze. Intermediate vision is almost automatic in these designs because they represent a blending of the two design philosophies.

A crossover lens is the Essential Solutions (X-Cel Contacts/Blanchard), which combines an aspheric posterior surface based on the Essential Series 1 lens with an anterior surface based on the segmented Solutions lens (X-Cel). This design offers add powers to +3.50D, as well as a wide range of other parameters. It's prism ballasted and truncated if necessary.

Soft Lens Options

Simultaneous image designs, either aspheric or concentric, are the most popular soft contact lens multifocal designs. As I noted earlier, the Acuvue Bifocal is a center-distance, concentric design that uses alternating distance and near zones. This multi-zone design provides better distance and near power coverage of the pupil as it dilates or constricts. It has four add powers available (+1.00D, +1.50D, +2.00D, +2.50D), plus a wide range of distance powers.

Bausch & Lomb's SofLens Multifocal is an aspheric, front-surface, center-near design. It features a "Low" add to +1.50D and a "High" add from +1.75D to +2.50D as well as a range of available distance powers.

Focus Progressives (CIBA Vision) is another center-near design with an aspheric front surface. It's available as a monthly or a daily replacement lens, although the latter is somewhat more limited in parameters.

The Frequency 55 Multifocal (CooperVision) is a combination aspheric and spherical design. It's a planned replacement version of the Ultravue 2000 Multifocal lens that Opti-Centre Labs, which CooperVision now owns, originally designed. Add powers, ranging from +1.00D to +2.50D (in 0.50D increments), come in D and N configurations. The D lens, which you typically fit on the dominant eye, features a central spherical distance power zone, surrounded by an aspheric annular portion of intermediate correction, surrounded by a near zone. The N lens, which you typically fit on the nondominant eye, is exactly the opposite. CooperVision calls this fitting approach Balanced Progressive Technology. Coopervision also now makes a Proclear (omafilcon A) version of this lens design. Both come with distance powers from +4.00D to –6.00D. The Ultravue 2000 is available in a wider range of distance and add powers, multiple base curves and even a toric version.

Several other laboratories also manufacture soft toric multifocal designs. Examples include the C-Vue 55 Toric Multifocal (Unilens), the Essential Soft Toric Multifocal (Blanchard) and the recently introduced Cibasoft Progressive Toric (CIBA Vision). Note that all of these designs are made to order and are available in spherical (non-cylinder) versions for patients who require astigmatism correction in only one eye.

The C-Vue 55 Toric Multifocal, like the C-Vue 55 Multifocal, uses patented aspheric power shifts to provide power for all activities. It features a wide range of powers in a center-near-aspheric front, toric-back-surface design.

The Essential Soft Toric Multifocal also features an aspheric front surface with a toric back surface and a center-near design. It too has a large parameter range including three base curves.

The Cibasoft Progressive Toric features a double slab-off, front-surface toric design combined with a center-near progressive add on the back surface. It's available in two base curves, sphere powers of –9.00D to +9.00D, cylinder powers from –0.75D to –2.75D in 0.25D steps with around-the-clock axes in five-degree increments.

The single soft translating design is the Triton Translating Bifocal (Gelflex Laboratories). It can incorporate a patient's full prescription, including toric powers.

Getting Started in Your Practice

With these various design choices in mind, let's take a look at incorporating bifocal and multifocal contact lenses into your practice. Many patients aren't aware that bifocal contact lenses exist, even though they have for more than 50 years. Word is spreading, however, and with more than 100 million presbyopes today, you need to prepare yourself to assist these active patients. Most presbyopes don't want to compromise their lifestyles just because they now need reading or multifocal correction. Many current single-vision contact lens wearers fear they must give up contact lenses to achieve good distance and near vision. This presents a perfect opportunity to educate patients and simultaneously grow your practice.

Selecting Candidates You need rational criteria for screening potential multifocal candidates. First, assess a patient's motivation to ascertain whether he'll comply with the visits and lens changes necessary for success. Next, discuss the patient's expectations. If perfect vision at every distance is his goal, then he's likely to become dissatisfied. Make sure the patient realizes that presbyopia requires visual compromise. There are times when neither contact lenses nor eyeglasses are perfect.

You also must consider the patient's ocular health and physiology. Multifocal patients need a healthy cornea and conjunctiva, good lid structure and function and a wet enough eye to sustain a contact lens. Check the lid position relative to the limbus, check pupil sizes in average and low light, and assess tear film quantity and quality. Age affects all of these areas, so it's important to be critical. If a patient isn't an appropriate candidate, then inform him directly.

If ocular health and physiology are satisfactory, then discuss the patient's vision requirements at work and at leisure. Most patients have some computer use in their day, which necessitates reasonable intermediate-distance vision. Patients who need sharp vision at any or all distances or who work in low light may be disappointed.

Lastly, consider the patient's refractive error. In the past, we believed that if the distance need was less than –1.00D or if the add power was too high, then the patient wouldn't do well. But with the newer available designs, you can often meet these challenges.

What about Monovision? In the past, monovision was the method of choice for early presbyopes. It can provide good vision at various distances, and it's less time-consuming and less expensive for both the patient and practitioner. However, monovision does disturb depth perception, especially as the add power increases. Bifocal or multifocal contact lenses can eliminate some of this difficulty, and they provide a more equal image size and quality between the two eyes. They also can cover a broader range of prescription needs. Monovision and bifocal/multifocal contact lenses aren't mutually exclusive, but rather are complementary approaches.

Choosing a Design

Once you determine that a presbyopic patient is a good contact lens candidate, you need to discuss the various options for that particular patient. The choice of which design and which material to use comes down to patient needs and motivation. Patients who have –0.75D or more of corneal astigmatism will generally do better with a GP lens, although some soft designs are challenging this rule. Patients who do a large amount of computer work typically enjoy the benefits of a simultaneous image design, while people who have fine visual discrimination needs often require a translating lens. For athletes and outdoor enthusiasts, using distance contact lenses with reading glasses is often a good compromise. Office workers may prefer near/intermediate range contact lenses combined with over-spectacles for distance viewing. The majority of patients, however, really desire a contact-lens-only approach.

Fitting Approaches

As I stated earlier, once a single-vision lens is no longer adequate for all of a patient's viewing tasks, then we must make adjustments to help him see comfortably throughout the day. We have many methods for achieving this goal. Ideally, a total bifocal fit, in which each eye gets the maximum vision for distance and for near, is the best approach. In reality, this approach can create visual stress because the visual system has a dominant eye and we need to respect this dominance. You can determine the dominant eye with a simple "hole in the hand" test or fogging technique, in which you add plus power over-correction to each eye in turn. The nondominant eye accepts the most plus.

Consider Modified Monovision Sometimes called enhanced monovision, modified monovision is a good way to solve the dominance issue. In this situation, you provide the dominant eye with better correction for distance and the nondominant eye with slightly greater add power. In this way, both eyes have nearly equal visual input and patients adapt easier. Many manufacturers have long recognized this and reflect it in their designs and fitting nomograms. It can simplify and enhance fitting success and reduce chair time. Even so-called "total" bifocal fits usually result in a form of modified monovision when fitting more advanced presbyopes.

Make a Commitment Practitioner motivation is as important as patient motivation. If you're excited and believe you can succeed, it shows in your motivation and in your approach to patients. Don't hesitate to fit bifocal or multifocal contact lenses for fear of failure because of complex designs or negative prior experiences. Today's design and parameter availability, in addition to the generous exchange or cancellation policies of most laboratories, allow you to fit multifocal contact lenses with almost no material outlay and risk.

Practice Makes Perfect Develop experience with a few of the many designs by following the manufacturers' fitting nomogram. Manufacturers have invested a great deal of time and money into making their lenses perform in a predictable fashion with minimal chair time. By fitting a few patients in these designs, you'll increase your comfort level and streamline your approach for any appropriate patient.

You don't need expertise with every bifocal/multifocal contact lens design, but you should master and have available fitting inventories of three or four different lenses, in both soft and GP materials, that you use regularly. Diagnostic fitting is very advantageous. It helps you learn the pros and cons of each lens and improves your ability to predict which patients will fare best in a particular design. It also allows you to evaluate the likelihood of changes after you dispense the initial lenses and to properly educate the patient on the need and rationale for follow-up visits.

Be Patient Both you and your patient will need patience during the follow-up period, as it's not uncommon to require modifications in the distance power, add power or both. Pay careful attention to the patient's complaints and comments at each progress evaluation. These can guide you in the quest to improve visual performance. It also helps to use loose lenses during over-refraction and to vary the lighting levels to allow the patient a more natural visual setting.

Professional Fees

All of these great advances in lens design and performance do come at a price. Multifocal lenses are more complex and thus more expensive than their single-vision counterparts. You need to charge appropriately for your professional services. These designs do take more time to fit successfully, at least when you first start out, and your fees should reflect this factor. Inform patients of your fees for this type of fitting at the beginning of the process. It�s best to separate your professional fees from the material charges in all cases so patients don�t perceive the charge as �just for two contact lenses.� Lastly, keep the professional fees higher and the material charges lower. This keeps replacement lens costs lower and encourages patients to return for appropriate follow-up care.

Easier than You Think

Nothing about multifocal or bifocal lens fitting is that difficult. It�s just a progression of standard contact lens practice. As the number of presbyopic patients increases, providing these services can bring more patients into your office and keep them there. Enjoy the challenge and satisfaction of being a specialty contact lens practitioner.

Dr. Benoit is in private practice with an emphasis on contact lens care and external disease treatment. He is a Diplomate in the American Academy of Optometry's section on Cornea and Contact Lenses and is currently the program chair for the section. He has published numerous articles, is a consultant to contact lens and pharmaceutical laboratories, and lectures frequently on contact lenses and external disease.

 



Contact Lens Spectrum, Issue: July 2005