MULTI FOCAL LENSES
A Logical Approach to Multifocal Lens Fitting
With so many lens options for your many presbyopic patients, now is the time to hone your fitting strategy.
|Dr. Quinn is in group practice in Athens, Ohio. He is an advisor to the GP Lens Institute and an area manager for Vision Source. He is an advisor or consultant to Alcon and B+L, has received research funding from Alcon, AMO, Allergan, and B+L, and has received lecture or authorship honoraria from Alcon, B+L, CooperVision, GPLI, SynergEyes, and STAPLE program. You can reach him at email@example.com|
By Thomas G. Quinn, OD, MS, FAAO
Presbyopes are everywhere these days, and their numbers are growing. Simple supply and demand dictates we need to be in the game when it comes to satisfying the visual needs of this key demographic.
With so many presbyopic options now at our fingertips, perhaps the greatest challenge is devising a logical contact lens approach for this ever-growing population.
Know Your Patients
One very straightforward approach to assisting presbyopic contact lens wearers with near tasks is to prescribe reading glasses to be worn over single vision contact lenses corrected for distance vision. While simple and effective, it is inconvenient. Today’s presbyopes are “the wealthiest, most active and most physically fit generation” up to this time (Jones, 1980). Their multifaceted, on-the-go lifestyle necessitates a convenient form of visual correction.
Monovision and multifocal contact lenses offer the convenience demanded by an active population. Although we have learned much in recent years, the question persists: which is better?
Let Science Speak
While both have their strengths and weaknesses, science clearly favors multifocal contact lenses. Head-to-head crossover studies comparing both soft and GP multifocal lenses to monovision have consistently found about a 70-percent preference for multifocal contact lens correction (Johnson, 2000; Situ et al, 2003; Richdale et al, 2006; Woods et al, 2009).
Figure 1. A well-centered anterior-aspheric GP multifocal.
Some eyecare practitioners might respond to this information with something akin to, “that’s not been my experience.” Why is that? The problem may lie in what is used to measure success. Simply looking at visual acuity numbers during an eye examination may be misleading.
Woods et al (2009) found that, although visual acuity with monovision was sometimes better than with multifocal contact lenses, patients preferred multifocal contact lens correction over monovision for most activities. This was particularly true for driving (both during the day and at nighttime), watching television, and when changing focus from distance to near. So, while important, don’t rely on acuity measurements. Instead, bias your decision-making regarding level of success, or whether you should modify the lenses, on what patients tell you about their ability to do what they want to do in their daily lives.
Figure 2. A slightly superior-located bi-aspheric GP multifocal.
Another reason why some practitioners may persist in the belief that monovision is better compared to multifocals is related to multifocal lens performance at near in low light. Going back to science, some of the same studies that clearly show a preference for multifocals over monovision also find that near vision can be challenging when wearing multifocal contact lenses in a dimly lit environment (Richdale et al, 2006; Johnson, 2000; Woods et al, 2010). You can effectively manage this by making patients who are new to multifocal contact lenses aware of this fact, then arm them with the tools to manage the situation. Light and magnification will help. Light can be provided from a table lamp or a pocket light. A simple pair of over-the-counter reading glasses can provide magnification. The iRead app is a wonderfully convenient and effective aid for iPhone users, offering both a light source and a variable magnifier.
Once both patient and provider understand that multifocal contact lenses can meet most visual needs most of the time, with occasional assistance from other forms of aid, you are set to begin the fitting process.
Figure 3. A fairly high-riding posterior aspheric GP multifocal.
When to Modify the Modality
Patients already wearing contact lenses when presbyopia strikes are obvious candidates for multifocal contact lens correction. These individuals have enjoyed the benefits of contact lenses and usually want to continue to wear them into their presbyopic years. If they are generally happy with their current mode of correction (soft, GP, or hybrid), it makes sense to continue with that approach in a multifocal form.
However, sometimes performance can be improved by making a change in modality. Change always involves some risk. To ease patients into a modality change, it is helpful to review with them the reason why performance with their original form of correction is falling short and how the new approach will remedy it. Then, practice the “no surprise approach” by preparing them for how things (e.g., comfort, vision, lens handling) will be different with the new modality. You will now be working with patients as you move forward, rather than needing to refer back during the fitting process as to why things are different and why you recommended the new approach. Proactive education informs patients and helps you maintain their confidence should multiple modifications in fit or power be necessary.
Location Drives GP Design Selection
For patients already successfully wearing single vision GP lenses, use lens centration to guide your selection of GP multifocal design. Where a corneal GP lens positions on the cornea can be influenced by many factors, such as the base curve-to-cornea relationship, lens diameter, center thickness, and edge design. If a single vision GP lens aligns with the pupil, you have the option of fitting a number of multifocal GP designs (Figure 1). Perhaps the easiest would be a lens with multifocal optics on the front of the lens. This allows for simple duplication of the single vision lens parameters, with the addition of add power. This is not only very easy to order empirically, it avoids inducing changes in corneal curvature that could lead to spectacle blur. One caution with this approach: pay attention to lens center thickness, as it will sometimes increase with the introduction of a front-aspheric surface, potentially impacting lens centration.
In some patients it is quite difficult to get a GP lens of any design to center on the cornea. Some patients’ eye and eyelid anatomy promotes a high-riding lens. Many multifocal GPs are designed to position in a slightly superior location (Figure 2). Some of these designs have multifocal optics on both the front and back lens surfaces, allowing both to be manipulated to impact add power and thus allowing for greater add powers as compared to lens designs that rely on one surface or the other.
If a lens rides higher than ideal (Figure 3) and cannot be lowered by manipulating the fit, a low-eccentricity, back-surface aspheric design with a spherical front surface may perform best, as it is not dependant on aligning a front-surface add zone along the line of sight. The effective add power may be limited in these cases, sometimes necessitating over-plussing the nondominant eye to achieve satisfactory near vision.
If GP lenses ride extremely high, attempt to steepen the base curve, decrease the overall diameter, or increase the center thickness to lower the lens. If ineffective, a GP multifocal may not be a good option.
Low-riding GP contact lenses, whether single vision or multifocal, are problematic. Low-riding lenses, particularly ones that drop and don’t move, lead to problems with peripheral corneal desiccation, conjunctival injection, and discomfort. Low-riding multifocal lenses will not provide desired visual results due to optical misalignment. Attempt to improve centration by flattening the base curve, increasing lens diameter, decreasing lens center thickness, or modifying edge design to promote lid attachment (i.e., minus carrier lenticular edge).
If a lens is riding low due to high center thickness associated with high plus power, consider fitting a high-eccentricity posterior-aspheric design (Figure 4). These lenses are designed to be fit 4.00D to 6.00D steeper than K, creating a tear lens of corresponding power. This allows for less power in the contact lens itself, reducing lens thickness and mass.
Figure 4. A high-eccentricity posterior-aspheric GP multifocal.
Translating GP Designs
Translating, or alternating vision, bifocal GPs provide exceptional vision. They continue to play an important role for very discriminating visual observers. Trifocal designs are also available when it is necessary to provide correction for distance, intermediate, and near.
As these contact lenses are prism-ballasted and require an eyelid “shelf” to rest on, be sure to assess lower lid position relative to the lower limbus before proceeding with this approach. Ideally, the lower lid would rest tangent to the lower limbus (Figure 5). Slight coverage of the corneal limbus can also be acceptable, but the segment area will need to be lower to avoid interfering with distance vision.
Figure 5. A well-positioned translating GP bifocal.
GP Multifocal Resources
Specific designs and manufacturers of GP multifocal contact lenses are too numerous to be listed in this article. To find out more, a good place to start is by speaking with your favorite GP laboratory consultant. The GP Lens Institute (GPLI) also has a comprehensive list that is available on its website at www.gpli.info.
Soft Multifocal Lenses
Here’s a brief overview of today’s most widely available soft multifocal designs.
Acuvue Bifocal/Oasys for Presbyopia Vistakon introduced the Acuvue Bifocal lens in 1998. This center-distance, alternating ring design was the first soft multifocal design to enjoy widespread clinical success. It is scheduled to be discontinued in December 2013.
More recently, Vistakon introduced Acuvue Oasys for Presbyopia, a center-distance-biased design available in three add powers: Low, Mid, and High. The fitting guide for this lens recommends that patients who have a spectacle add of up to +1.25D be initially fit with a Low add on each eye. Those who have adds of +1.50D and +1.75D should be fit with a Mid add on each eye. Those who have spectacle adds of +2.00D to +2.50D should be fit with a Mid add on the dominant eye and a High add on the nondominant eye.
SofLens/PureVision Multi-Focal Bausch + Lomb’s SofLens (hydrogel) and PureVision (silicone hydrogel) Multi-Focal contact lenses have front-surface, center-near designs offered in a low and high add. Whereas most widely available soft multifocals are available in only one base curve, the SofLens Multi-Focal offers two base curves (8.5mm and 8.8mm), which may be helpful if lens centration is problematic. The fitting guide for these lenses recommends a low add design for each eye if the spectacle add is +0.75D to +1.25D. A high add design is recommended for each eye if the spectacle add is +2.00D and above. For patients who have spectacle adds of +1.50D or +1.75D, it is recommended that a high add design be employed OD and OS, but with −0.25D or −0.50D added to the distance power.
Air Optix Aqua Multifocal Alcon offers the Air Optix Aqua Multifocal, which has a front-surface, center-near aspheric design. It is available in three adds: Lo, Med, and Hi. Select a Lo add for spectacle adds up to +1.25D, a Med add for +1.50D to +2.00D, and a Hi add for +2.25D and +2.50D.
As do all the major contact lens manufacturers, Alcon emphasizes the importance of following its fitting guide, which in some ways differs from standard fitting approaches, and pushing plus to maximize near vision performance with the Air Optix Aqua Multifocal.
Proclear/Frequency 55/Biofinity Multifocal CooperVision offers two lens designs, a D and an N lens, each available in multiple add powers. This technology is currently available in three different lens materials.
The hydrogel contact lens options include the Proclear and Frequency 55 Multifocal. However, the Frequency 55 Multifocal lens is scheduled be discontinued, at least in the United States, in October 2013. The Biofinity Multifocal contact lens is manufactured in a silicone hydrogel material. CooperVision recommends that patients who have spectacle adds up to +1.50D be fit with a D lens on each eye. For adds above +1.50D, it is recommended to fit an N lens on the nondominant eye.
Daily Disposable Multifocals
CooperVision recently introduced the Proclear 1 Day Multifocal. This daily disposable contact lens is available in a single, front-surface, centernear add power.
For patients who have a spectacle add of +1.25D to +1.75D, it is recommended to provide a “near boost” to the lens worn on the nondominant eye of +0.75D. If the spectacle add is +2.00D to +2.50D, consider adding +0.75D or +1.00D to the lens power on the nondominant eye.
The Proclear 1 Day Multifocal joins Alcon’s long-offered Focus Dailies Progressive as the only widely available daily disposable multifocal soft lenses in the United States.
Custom-Design Soft Multifocals
Many small, custom labs also offer multifocal contact lens designs. Table 1 lists some of the labs in the United States that offer these lenses.
|Custom Laboratory Soft Multifocals|
|Advanced Vision Technologies||NaturaSoft Multifocal|
|Alden Optical||Astera Multifocal|
|Art Optical||Intelliwave Multifocal|
|Blanchard Contact Lenses, Inc.||Quattro Multifocal|
|Esstech Soft Multifocal|
|GP Specialists||iSight Multifocal|
|Metro Optics, Inc.||MetroFocal Multifocal Soft Lens|
|Unilens||C-Vue Customized Multifocals|
Choosing a Soft Multifocal
Having had the opportunity to participate in a number of multifocal soft contact lens workshops at schools and colleges of optometry across the United States, I have gained an appreciation of how many different designs can perform quite well on the same person. Recognizing this, it may be reasonable to choose your initial lens design based on your past clinical experience, price, availability, and relationship with the manufacturer.
Performance of a soft multifocal contact lens can be influenced by the lens design, add power, pupil size, and lens centration (Bakaraju et al, 2012). Consider these factors anytime that performance is less than desired.
As pupil size cannot be readily controlled and we have limited or no control over lens centration with the widely available soft multifocals, lens power and design are the most accessible variables to modify.
Always start any troubleshooting process by following the manufacturer’s fitting guide. If fitting guide recommendations for initial lens selection and troubleshooting lens power are not successful, change lens design.
Factoring in Astigmatism
One factor that can commonly lead to spherical soft multifocal contact lens failure is the presence of uncorrected astigmatism. Residual astigmatism tends to be more visually problematic when:
1. It is in the dominant eye.
2. It is 0.75DC or more.
3. The distance spherical refractive error is low.
4. The patient is visually sensitive.
The greater the degree of astigmatism and the number of these factors present, the more necessary it is to provide astigmatic correction.
When refractive astigmatism can be fully attributed to the toricity of the cornea, it is reasonable to consider a GP or hybrid multifocal lens option. In such cases, the firm rigid central optics will correct the astigmatism as well as provide multifocal correction. See the previous section for a discussion on corneal GP multifocal lens selection.
Multifocal contact lens designs are increasingly being offered in scleral lens designs as well (Potter, 2012). These designs, which are remarkably comfortable when fit properly, may be a great option for patients who demand the vision offered by a rigid lens but have difficulty adapting to the comfort of a corneal design.
Hybrid lenses (i.e., rigid center, soft skirt) also offer the promise of rigid lens optics with comfort more aligned with soft lenses. SynergEyes offers two hybrid multifocal lens options: the SynergEyes Multifocal and the Duette Multifocal.
Their original SynergEyes Multifocal is a true bifocal design, utilizing a central add zone of 1.9mm or 2.2mm in diameter. In addition to being fabricated with more oxygen permeable materials, the Duette Multifocal offers progressive optics by employing a centernear aspheric design.
The manufacturer’s recommended fitting approach for the Duette Multifocal has recently been revised as the Minutes-To-Fit 2.0 Fitting Guide (Quinn and Davis, 2012). Key differences include:
• No fluorescein is necessary; the central rigid fit can be indirectly assessed by examining final lens power, which is expected to be −0.50D to −1.50D more than the vertexed spectacle lens sphere power.
• Assess fit after at least 10 minutes of wear; choose the flattest soft skirt curve that provides comfort, centration, and good movement.
Soft Toric Multifocals
Quite a few toric soft multifocal contact lens designs are now available. Some manufacturers offering these lenses can be found in Table 2.
|Soft Toric Multifocals|
|Alden Optical||Astera Multifocal Toric|
|Art Optical||Intelliwave Multifocal Toric|
|Blanchard Contact Lenses, Inc.||Essential Soft Toric Multifocal|
|CooperVision||Proclear Multifocal Toric|
|Metro Optics, Inc.||MetroFocal Toric|
|SpecialEyes||54 Multifocal Toric|
|Unilens||C-Vue Customized Toric Multifocal|
|X-Cel Contacts||Horizon Progressive Toric|
Toric soft multifocal lenses can be fit on virtually any astigmatic presbyope, but are particularly useful when the vertexed refractive astigmatism does not match corneal cylinder, as residual astigmatism is present in such cases when fitting GP contact lenses or hybrid contact lens designs.
Due to the wide variety of power combinations that are possible with a soft toric multifocal lens, it is generally necessary to order diagnostic lenses during the fitting process. I start by ordering distance power based on the vertexed spectacle distance prescription. Remember that contact lens cylinder power will be lower than the spectacle cylinder power as high myopic powers are vertexed back to the corneal plane. Conversely, contact lens cylinder power will be higher than the spectacle cylinder power as high hyperopic powers are vertexed back to the corneal plane.
I order the available contact lens axis that is closest to the spectacle axis, assuming no rotation. If I am working with a design that tends to rotate, I will sometimes also order at axes +10 degrees of the spectacle axis. Base curve and diameter are chosen based on the recommendations of the manufacturer.
The first priority is to make sure the astigmatic error is corrected properly. Once a stable lens orientation is established with a lens of the correct axis, you can begin troubleshooting visual complaints as you would with a spherical soft multifocal lens.
Accept the Challenge
Today’s multifocal lenses are able to deliver exceptional visual performance to our presbyopic patients. Embrace this mode of correction with the confidence of knowing that science backs you up; multifocal lenses are preferred over other forms of contact lens correction by the majority of presbyopes.
Present-day presbyopes are known for pursuing activities and spending money on self-improvement services (Value Options, 2012). Recognize that you are offering them a service that has the potential to improve their quality of life, and charge appropriately. It will improve your attitude, which will in turn improve your service and success with multifocal contact lenses. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #208.