ONE OF THE BEST OPPORTUNITIES to improve a practice’s soft contact lens revenue, attract new patients, and stand out as a contact lens expert is to become proficient at fitting soft multifocal contact lenses. It may surprise some to know that soft multifocal lenses have been in the US market since the mid-1980s, with the first 2-week disposable bifocal launched in 1998.1-4 However, many practitioners in the United States seem reluctant to dive into this rewarding and profitable space, despite continued innovation and lens availability.5
Although 4 in 10 contact lens wearers in the typical US optometric practice are in or around their presbyopic years and greater than 90% wish to continue wearing lenses, a Gallup poll conducted in 2015 revealed that only 9% of adults in the multifocal age range received a recommendation for contact lenses as a means of vision correction.5,6 Another study that surveyed more than 1,500 adults over age 40 from several countries, including the United States, who wore or were willing to try contact lenses revealed that 50% of them were wearing contact lenses but only 25% of those wore multifocal lenses.7,8 These numbers suggest the potential annual loss of a good portion of a practice’s contact lens wearer base.
Becoming a multifocal expert requires understanding the optical approach of these lenses, following the fitting guides of the manufacturer, and picking materials and modalities that meet each patient’s needs in terms of comfort, vision, and lifestyle.
As patients age, their eyes lose their ability to accommodate. Multifocal lenses can correct this vision loss and allow patients to see comfortably from distance to near. Soft multifocal lenses employ various optical mechanisms that are based on the concept of splitting incoming light into multiple focal points to extend the depth of focus or the range of distances needed by the patient.
This concept of splitting the light allows the presentation of simultaneous images over the retina—presenting multiple powers to allow for multiple images to be created, typically at distance, intermediate, and near. Compared to the single focal point that single-vision lenses provide, this approach results in a larger blur circle at the retina and some level of visual compromise. As patients age and the near add component rises, the amount of light splitting increases, resulting in greater levels of visual compromise.1,9-11
Early multifocal lens designs were mostly concentric ring or zone designs, either center-near or center-distance.1 These early versions were plagued by patient complaints of halos and ghosting due to the optics’ interactions with pupil size, which negatively affected outcomes.1,10
Modern multifocal designs use aspheric center-near designs, which have helped reduce these negative issues. Aspheric designs use spherical aberration to extend the focus range of the optical system.9,12 These designs are still splitting light between images, so there is still some level of compromise, but they are much more effective than the multifocal lens designs made 20 years ago.9,12
Each manufacturer of soft multifocal lenses has a unique optical approach and a unique fitting guide.1 The fitting guide is specific to the optical design, so it is critical that the product and fitting guide be used together by the clinician. Although the initial lens selections and optimizing steps are different for each company, the basic initial data gathering should be the same among clinicians, and it’s the quality of these data that will make or break the outcomes for patients.
Because these lenses create some level of visual compromise, even small errors in the examination data used to fit a lens could have far-reaching ramifications. A refresher of the key steps, paired with some clinical pearls, can help achieve successful patient outcomes when fitting soft multifocal lenses.
Once the patient’s visual demands and lifestyle have been discussed and understood, there are 3 key components of examination data that should be acquired prior to beginning the fitting process:
• Best refraction with maximum plus acceptance, at distance
• Sensory ocular dominance
• Functional add at near
A summary and the importance of each step is below.
Best Refraction With Maximum Plus Acceptance
Refractive data are the foundation from which all other data are derived. If this data are not sound, then the accuracy of future data will be suspect. Because pupil size is an important consideration for these complex designs, refractions should be done in ambient lighting.13 Prescribing the maximum plus at distance for presbyopes is critical, as over-minusing at distance will result in the need for a higher add power—and higher adds result in higher amounts of spherical aberration and thus more visual compromise.
An easy and effective way to avoid over-minusing patients is to perform a duochrome test, or red/green balance. The test is based on the concept of chromatic aberration. Black letters are presented on a bipartite green (approximately 535 nm) and red (approximately 620 nm) background. The red and green are dioptrically equidistant, approximately 0.25 D from the yellow wavelength (570 nm). The longer red wavelength is refracted less than the shorter green wavelength. It is assumed that the best vision is attained when the yellow wavelengths are in focus on the retina, so optimal correction should occur when the red and green are balanced and equally clear to the patient.14
The authors believe that performing the red/green test monocularly eliminates the need for a binocular balance and will help achieve the maximum plus for each eye with a good binocular balance15 (Figure 1).
Step by Step
1. Create a block of letters 20/40 to 20/15 and apply the red/green filter.
2. Add +0.50 in both eyes. Adding plus should create a difference in clarity that can be appreciated by the patient.
3. Occlude the left eye.
4. Now tell the patient: “There are letters on the red side and letters on the green side. Tell me which letters look darker or clearer—the ones on the red side or green side?”
5. Since we added plus, the letters on the red side should look darker or clearer, so decrease the plus and continue to do so until you achieve balance.
6. For those cases in which you can’t get balance, the clinical pearl is to leave the presbyopic patient on the last red.
7. Now, occlude the right eye and open the left and repeat these steps.
A traditional method for binocular balance tells practitioners that both eyes are balanced, but not whether they have achieved a maximum-plus refraction. This quick test will assure practitioners that they have a perfect refraction upon which to base their multifocal contact lens fitting.
Sensory Ocular Dominance
Knowing the patient’s dominant eye is very important in situations when some level of disparity needs to be created to enlarge the depth of focus for the patient. As the intraocular (between the eyes) disparity is increased for many patients, there is a resulting reduction in the binocular summation.
One clinical study specifically noted that when +0.75 D or greater of disparity was prescribed, most patients went from binocular summation to binocular inhibition, explaining why monovision fails early on and why monovision patients complain of poor nighttime vision and have a reduction in stereopsis.16 The sensory dominant eye is the eye most sensitive to small amounts of defocus, so adding plus to this eye would further degrade objective and subjective binocular vision.
Many US doctors are still using the older sighting method to determine the dominate eye. The sighting method to determine the dominant eye indicates the patient’s motor dominance—which eye the patient prefers to sight with—but does not necessarily correspond with the patient’s sensory dominant eye, the eye that has the greatest sensitivity to plus defocus.
With this level of understanding, we are now ready to discuss how to determine dominance using the sensory method. It is interesting to note that sensory and motor dominance are reported to match only 50% of the time, which means using the sighting method to determine dominance may identify the incorrect eye in 50% of patients.17,18 In these cases, applying blur to the dominant eye could result in a reduction of binocular summation and a poor patient outcome. The sensory method is preferred for fitting multifocal contact lenses.
The following describes how to perform the sensory method for ocular dominance:
• After the red/green balance has been performed and the patient is still behind the phoropter, display a line of letters 1 line less (larger) than their best binocular VA.
• Select a +1.50 D handheld trial lens (or the retinoscopy lens on a standard phoropter) and say “I’m going to place a lens before each eye that will make the letters look a bit blurry. Please tell me when the letters appear blurrier or when you feel more uncomfortable.” Alternate the placement of the lens before each eye individually 1 or 2 times as they view the distance image.
Whichever eye is more uncomfortable or blurry is the dominant eye; this is the eye with the greatest sensitivity to plus defocus and the eye you never want to induce blur to. Completing this test behind the phoropter following your previously performed subjective refraction is quick and straightforward.
Functional Add
The final information required is the patient’s add power for near. The classical definition of a reading add is the amount of plus power needed allow the patient to comfortably see at their typical working distance. To objectively measure add, determine the patient’s working distance and then use either a binocular cross cylinder method or a plus build-up test to determine the amount of plus required at that working distance.19
It’s important to measure the add at the preferred working distance, because very few patients read or work at 16 inches (40 cm) while using computers, tablets, or phones. With today’s digital devices, a more typical working distance is in the range of 18 to 22 inches.20
A commonly used guide for determining add power based upon age was published in Clinical Refraction by Irving Borish: patients in their 40s should have an add power of +0.75 D to +1.25 D, those in their 50s +1.50 D to +1.75 D, and patients aged 60 and older +2.00 D and greater.21 Of course, there are always exceptions, and confirming your distance subjective refraction, followed by your determination of add power, independent of a patient’s previously prescribed spectacle correction, is crucial prior to the fitting of soft multifocal contact lenses.
Discussion
Following the steps presented above should provide the optimal data needed to select the initial multifocal lenses based on the manufacturer’s fitting guide. It is important to follow the instructions in the fitting guide for the chosen lens very carefuly to optimize the prescription. This will enable the clinician to overcome the typical reasons for less-than-desirable outcomes, which arise from 3 major areas: (1) not using an ideal refraction (most plus); (2) not using sensory dominance; and (3) excessively high add power.
Practitioners who follow these steps and the manufacturer’s fitting guide should expect to successfully fit many of their presbyopic patients, which likely will result in multiple patient referrals. Many expert fitters also proactively fit patients early in their presbyopic years and confidently suggest soft multifocal lenses to emmetropic presbyopes, as well as past contact lens dropouts.
Success with soft multifocals is achievable when adhering to a few basic tenets: a maximum plus distance refraction, using sensory dominance rather than sighting dominance to determine where plus can be added, and not overprescribing the add.
References
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