FITTING PRESBYOPIC DESIGNS
8 Ways to Maximize Presbyopic Contact Lens Fitting Success
Your presbyopic patients want contact lenses. These tips can help you successfully fit them.
By Craig W. Norman, FCLSA
We all know that patients have a great deal of interest in wearing bifocal/multifocal contact lenses. Our aging presbyopes routinely inquire about them. Manufacturers successfully promote their brands to potential wearers in print, electronic and television media. We discuss them as a matter of course during lens exams and evaluations.
So why aren't more patients wearing them? More than 100 million Americans are now 40 years of age or older -- each of whom now or soon will need presbyopic correction. Unfortunately, the most recent estimates tell us that only one percent to two percent of these presbyopes are wearing bifocal/multifocal designs.
You can employ methods and strategies in your practice to fit more presbyopes successfully. I'll describe some tips that can benefit you and your potential presbyopic wearers.
TIP #1 -- Know What's Available
Colleagues often ask me what bifocal contact lens is my favorite. While I understand that we all want a panacea that will work every time, I usually respond, "I have a number of favorites." Today, scores of soft and GP lens offerings are available in the bifocal/multifocal contact lens category (See sidebar on p. 36 and CLASS online at www.clspectrum.com/class).
Should you fit every one of these products? No. But having trial sets for two to three soft lens designs and a like number of GP designs in your office will probably suffice. Choose designs with which you feel most comfortable and learn every nuance about how they work and when. Embrace new products as they become available -- or at least try a pair or two to evaluate their performance.
|TABLE 1 Presbyopic CL Patient Selection: Key Considerations|
TIP #2 -- Choose Patients Wisely
How do you increase your success rate in presbyopic lens fitting? The short answer is: Choose better patients. First and foremost, ensure that a patient is a suitable candidate for contact lenses. While this seems obvious, concerns specific to the presbyopic population exist that you must consider (Table 1).
Is this the patient's first attempt at contact lens wear? Emmetropic or latent hyperopes who are entering presbyopia have never had to consider an optical correction for visual improvement. They abhor the thought of wearing glasses, and they may think that contact lenses are the answer. Beware in these situations! Such patients will soon discover that wearing contact lenses requires an adjustment to their lifestyle, so they must be highly motivated to succeed. Most of these patients become part-time wearers -- which isn't a problem, but you should advise them that they probably won't be able to achieve full-time wear. On the other hand, presbyopic contact lenses work quite well for patients who have previously succeeded with either soft or GP lenses.
Next, look at a patient's present spectacle prescription. Besides distance and near correction, your next concern is the astigmatic component. We currently have only limited toric bifocal/multifocal soft lens options. Thus, GP products best suit most patients who have more than 0.75D of refractive cylinder, or you must consider monovision. Make sure that you determine whether patients can wear soft multifocal options before you discuss them.
Dry eye occurs more commonly in this age bracket, so carefully evaluate the patient's tear quality. If a patient doesn't have sufficient tears to support the lens type you choose, then that patient will fail regardless of how well he sees with presbyopic lenses. Also, identify and treat conditions such as chronic blepharitis, meibomian gland dysfunction or allergic conjunctivitis before considering patients for lens wear.
If patients have flaccid lids, then incomplete lid closure may result in lens intolerance from dehydration and deposition. The lid positions are also critical, particularly in GP designs. (I'll discuss lid position later.)
Contact lenses for presbyopia generally perform best when worn full-time, so ask patients how often they'll wear their lenses. I don't mean to rule out part-time wearers, but when patients wear presbyopic contact lenses at least five days per week, they seem to remain better adapted to their physical presence as well as the variability of vision that lens systems with various optical components may provide.
Ask presbyopic patients how much time they spend on a computer each day. Asking detailed questions about lighting, desk setup and the position of their computer monitor will also provide useful information. I choose multifocal rather than bifocal lenses first for patients who use computers daily.
TIP #3 -- Assess Motivation
We know that motivation is the key to success in presbyopic contact lens fitting, but whose motivation is more important -- the patient's or the practitioner's? Contact lens wearers (presbyopes included) don't differ much regarding motivation -- freedom from spectacles is the goal. Patients must adhere to your instructions and be willing to invest the time and money necessary to achieve success. So, evaluating patient motivation mostly entails discussing expectations, commitment and fees.
Practitioner motivation is another story. To successfully fit presbyopic lenses, you must first be sure that you're committed to this portion of the practice. Ask yourself, "Am I ready to commit the time, effort and financial obligation necessary to make fitting these contact lenses successful?"
Will you and your staff develop presentations to accurately describe all of the options available to potential wearers? Will you gamble with more expensive lens designs to achieve success? Most importantly, are you willing to update your skills to better understand the technical fitting aspects of complex specialty lens designs? If you're willing to pay the price to become an expert presbyopic contact lens fitter, then patient motivation may play a much smaller role than you previously thought.
TIP #4 -- Presenting Lens Options
Many categories of soft and rigid multifocal lenses are available today. To set the stage for the fitting process, first present the alternatives in a fair and balanced manner to prospective candidates. We compile all pertinent information about presbyopic lenses into a three-ring binder, which we use to make our standard presentation to every patient. Our presentation binder includes a picture of the eye (for discussing the pupil and lids), soft lens design photos and drawings, GP simultaneous and alternating design photos and a description of expected fees and office policies relating to refunds.
Information in the binder also describes expected compromises in vision, possible limitations in the range of sharp acuity and the potential for additional spectacles that patients may need to wear over their contact lenses to achieve optimal vision. This discussion lays the groundwork for setting realistic patient expectations about multifocal contact lens wear.
Figure 1. Note whether pupil size is excessively large (left) or small
TIP #5 -- Measuring Pupil Size and Dynamics
Many ocular measurements increase patient success with presbyopic designs, but pupil size (Figure 1) is key. First, assess the pupils in normal room lighting with a millimeter ruler or another type of measuring device. Use a white light source at the slit lamp to simulate the smaller pupil size common in bright light conditions. Then use low illumination and a cobalt blue filter to approximate pupil size at night.
These tests reveal whether the patient has a relatively small, normal or large pupil and how reactive it is to changes in lighting conditions. This can help you choose among presbyopic lens types, but it's not as definitive as placing a lens on the patient's eye and evaluating his visual response to changes in lighting.
Today's soft presbyopic designs primarily employ simultaneous vision concepts, with the reading portion usually located in the center of the lens. Thus, a patient who has small pupils will view through an inordinate amount of the reading zone for distance tasks. Conversely, for patients who have large pupils, the distance portion interferes with near vision. In general, designs with center-near adds work better with pupils >5mm, and center-distance adds are advantageous for smaller pupils.
Figure 2. Note how the power changes from the center to the periphery in these two lens
TIP #6 -- Understand How Simultaneous Vision Works
Most soft and some GP bi-focal/multifocal designs employ simultaneous vision, in which distance, near and sometimes intermediate optical portions of the lens position over the pupil at the same time. These designs may use either spherical or aspheric components. Because soft lenses don't move much during blinking, most manufacturers, as I previously stated, have placed the reading zone in the center of the lens. Some GP designs use simultaneous vision concepts, but because they move during blinking, translation actually occurs for reading.
In soft lenses, this central reading zone is quite small -- usually 1.7mm to 3.0mm in size (Figure 2). If this reading zone is spherical, then the lens functions as a bifocal; if the central zone is aspheric, then it'll provide more of a multifocal effect.
GP simultaneous designs usually employ posterior and/or anterior optics to correct presbyopia. These designs must also position centrally or slightly superior for distance vision, then move upward slightly during reading gaze. When the lens decenters in this way, the greater plus midperipheral lens portion aligns near the patient's visual axis.
If these designs decenter during distance vision, then distance acuity decreases and necessitates increased minus power to improve vision. The net result is a decrease in reading vision.
Figure 3. Translating vision GP design (crescent segment
TIP #7 -- Take Proper Ocular Measurements for Translating Designs
GP bifocals generally feature two distinct zones or segments in which one positions above the other (Figure 3), and the lenses must move or translate to function properly. These lenses position slightly inferior, often resting on the lower lid, then move superiorly during downgaze to place the reading zone in front of the pupil when viewing close objects.
Properly obtaining key measurements in addition to kerotometry readings and spectacle prescription will increase success when fitting this design.
Lid position is most important. The upper lid helps control rotation of prism ballasted bifocal designs, but the lower lid plays a greater role. For GP bifocals, the ideal lower lid position is at the lower limbus. This stabilizes translating bifocals in primary gaze, holding the lens when the eye alternates from distance to reading gaze. A lower lid that positions above the inferior limbus may cause the reading segment to ride high in front of the pupil. Lowering the segment position or decreasing the overall diameter will properly position the seg height in these cases.
A lower lid that comes to rest below the inferior limbus is a warning signal that ballasted GP bifocals may position too low in primary gaze. In these cases, limited interaction occurs between the lens edge and the lower lid in primary gaze, potentially limiting upward translation. Use a simultaneous soft or GP lens design when the lower lid can't help in positioning alternating vision lenses.
TIP #8 -- Consider Modified Monovision
While monovision has long served as a presbyopic contact lens option, it does suffer from some optical disadvantages. Likewise, some patients can't achieve maximum reading and intermediate vision in some bifocal contact lenses, especially those that have limited parameters. Modified monovision may overcome these inadequacies.
Here's the best approach: After determining full distance correction with bifocal lenses, overcorrect one eye by +0.50D to +0.75D. This increases reading and intermediate vision without substantially affecting the patient's ability to drive. Some practitioners recommend that you overcorrect the nondominant eye, but I test both eyes before making this determination. I hold a +0.50D or +0.75D ophthalmic lens over first one and then the other of the patient's eyes at both distance and near while he's wearing his full bifocal correction. If the patient consistently prefers one eye for distance and one eye for near, then his chance for success is high. If not, then only time will tell if he can adapt to modified monovision.
In a Nutshell
You can maximize your success with presbyopic lens fitting simply by selecting the right patients, knowing what designs are available and understanding simultaneous and alternating vision concepts.
Craig Norman is Director of the Contact Lens Section at the South Bend Clinic in South Bend, Indiana. He is a fellow of the Contact Lens Society of America and an advisor to the GP Lens Institute.
Presbyopic Lens Designs
Following are some of the many bifocal/multifocal lenses available from each design category.
The SemiCircle Bifocal and Trifocal (Progressive Vision Technologies), Solutions Bifocal (X-Cel Contacts) and Metro-Seg (Metro Optics) are crescent-shaped bifocal designs, which offer numerous add powers and stable rotation.
The Presbylite GP multifocal (Lens Dynamics, Inc.) features a sectored, wedge-shaped segment with an aspheric intermediate zone at the top. This prism ballasted design is available with adds of up to +3.00D.
Tangent Streak (Fused Kontacts) is an executive style bifocal: The reading segment is flat on top and runs from edge to edge. Segment height, add power, prism ballast amount and location and truncation are completely customizable.
The Essential Solutions Segmented Aspheric Multifocal combines the Essential (Blanchard) aspheric back surface with the Solutions Bifocal front surface to provide crisp acuity at all distances.
Mandell Seamless Bifocal (Con-Cise Contact Lens Co.) is a front-surface, concentric, center-distance lens with near optics in the lens periphery. The spherical optics at both distance and near connect through a seamless transition zone.
MagniClear (Art Optical) combines spherical distance optics, multifocal intermediate visual performance and bifocal near power. It's available in a wide range of posterior surface design options and fits like a single vision lens.
The Triton Translating Bifocal Soft Contact Lens (Gelflex Laboratories) incorporates a proprietary base curve and peripheral curve configuration, prism ballasting and a truncated inferior lens edge to facilitate lens translation.
ASPHERIC GP DESIGNS
The VFL3 (Conforma Contact Lenses) uses a small, steep curve-to-cornea fitting relationship and high eccentricity values to generate reading power. You can apply more near power to the anterior lens surface for a higher total add effect.
LifeStyle Gp Multifocal (The LifeStyle Company) uses a multi-aspheric, center-distance design that's configured to ride slightly superior. Although this is a simultaneous vision lens, centration isn't necessary for a successful fit.
The Essential GP lens and the Boston Multivision (Bausch & Lomb) use similar near power with lower eccentricity values and more normal fitting relationships. They fit on alignment, much like a conventional single-vision GP.
SOFT MULTIFOCAL / BIFOCAL LENSES
The SofLens Multi-Focal (B&L) has an anterior aspheric surface, center-near design. The power varies gradually across the lens optic zone, and it's available in a low and high add power for early and late presbyopes.
Focus Progressives multifocal (CIBA Vision) offers a small zone of plus power placed centrally over the patient's line of sight. This front-surface aspheric uses a multi-addition progressive power profile.
The Acuvue Bifocal (Vistakon) is a five-zone concentric, annular, center-distance lens with a series of alternating distance and near images positioned over the pupil to maximize vision in varied lighting conditions.
The Frequency 55 Multifocal (CooperVision) offers a distance and a near lens. The distance lens uses a large spherical central zone to correct distance vision, surrounded by a smaller aspheric zone on the distance-dominant eye. The near lens uses a full central aspheric near correction, surrounded by a smaller spherical intermediate correction.
The UltraVue 2000 GP (Opti-Centre) employs a similar approach with GP lenses. The center-distance lens fits on the dominant eye and the center-near lens fits on the non-dominant eye to achieve a modified monovision effect.
While soft lens toric multifocals aren't widely available, laboratories such as Westcon, Acuity One and Unilens offer designs that correct both presbyopia and astigmatism.