Multifocal contact lens fits are not what they were a few years ago. The days of mental gymnastics and trial-and-error are going away. Success rates after the first or second trial lens can be greater than 90% when the right patient is paired with the right lens.1 This article summarizes the varied options available to eyecare practitioners (ECPs) and offers some reminders of what to consider to be as successful as possible.
A variety of options is available when fitting multifocal contact lenses. Each has a unique way of managing the optics to provide functional vision at varying distances. Most designs today utilize simultaneous vision, which is the concept that multiple powers (suited for clear vision at different distances) are presented to the eye at the same time. A patient subconsciously “chooses” the clearer prescription and ignores the blurred one depending on the visual demands of the task.2
Although the previous description used the verb “chooses,” the emphasis should be on “subconsciously.” ECPs should try some form of simultaneous vision lens before embarking on these types of contact lens fits. It is beneficial for providers to have a first-hand understanding of what this type of vision correction looks like. Many will likely be surprised by how clear the vision is, even immediately.
There are two commonly used multifocal designs. With aspheric lenses, the power spread smoothly transitions across the lens. With concentric lenses, distinct optical zones exist that alternate powers between distance and near in a concentric fashion.3 These lenses are designed as near- or distance-centered. Classic concentric designs have an abrupt change in power between the rings and can cause issues with ghost images or double vision. To combat this issue, lenses can also be designed to combine both distinct distance and near power zones with aspheric transition zones between them.4
The performance of multifocal contact lenses is dependent on design, add power, pupil size, and lens centration.5 The relative position of the line of sight to the power sections of a multifocal contact lens will ultimately determine the success or failure with regard to clarity of distance and near vision.4 This is important when recommending different designs to patients.
Most multifocal contact lenses have fixed parameters regarding zone size. Custom soft or rigid designs are available for patients falling outside of these parameters. These can be fabricated in any zone size, base curve, and diameter and also can be made with decentered optics to coincide with the line of sight.6 However, custom multifocal lenses are more expensive compared to other options, and this should be considered when recommending them to patients who otherwise are unsuccessful with more traditional lenses, which is a rarity today.
A cortical adaptation period is required for wearers to successfully adjust to multifocal lenses.7 Simultaneous vision can inherently degrade visual acuity. Reports show that patients may not be as sensitive to the change in real-world conditions, with patients generally scoring their multifocal contact lens experience as just as good if not better than other options—such as spectacle correction or monovision lenses (in which one eye wears the distance prescription and the other eye wears the near prescription).8
A line of lost Snellen acuity is insignificant if patients are happy with their vision for their specific daily demands. Use real-world examples such as cell phones, magazines, and pill bottles to test vision at near. In addition, educate patients that it is normal to see shadowing or mild blur for a few weeks while they adapt to this new way of viewing their environment.2,9
What happens during the cortical adaptation period is not fully understood. The concept is ambiguous and relies on anecdotal experiences in which patients’ visual acuity and lens tolerance improves after lenses have been worn for some time. Multifocal lens fits should not be declared successful or unsuccessful on the initial fitting day.
Certain patients make better candidates for multifocal contact lenses. Because of the potentially difficult nature of the cortical adaptation period, patient motivation is critical to success. Multitaskers and active people, as well as those frustrated with spectacles and over-the-counter readers, generally make good candidates for this reason.
Wearing contact lenses instead of spectacles gives wearers a wider field of view and can be advantageous when exercising or doing outdoor activities.9 Patients also have the flexibility to wear plano sunglasses over their lenses rather than being dependent on a prescription pair.7
Advances in material technologies are allowing previous “contact lens failures” back into the modality with significant improvements in comfort. Daily disposable soft contact lenses are increasing in popularity because they afford great convenience and ease of use (not to mention better compliance overall).
The option of being free from spectacles in the presbyopic years on a part-time or full-time basis can be very exciting. It can actually be very easy to describe the aforementioned advantages to patients and to deliver a highly motivated candidate.
Patients who have a lower amount of add typically have an easier time adapting to multifocal lenses compared with more advanced presbyopes.2 The more compacted design that comes with higher add powers can make adaptation more difficult.
Older presbyopes typically have smaller pupils and therefore can have trouble at near with center-distance concentric designs because the near zone is outside of the pupil during near tasks. Center-near designs have a compressed add power spread, which is advantageous with smaller pupils and can result in better distance vision when the pupil dilates in low-light conditions.6 This design also accounts for the natural miosis of the pupil when doing near work; when wearing them, patients do not need to tilt their head to view computer screens, which can be an issue with spectacle multifocal correction.7,10 For these reasons, simultaneous vision multifocals have increasingly been manufactured in a center-near design (and have experienced far greater success).
Intermediate visual demands have steadily increased in recent decades with the evolution of smart phones and increased computer time for all ages. Aspheric lens designs can be particularly useful here in established presbyopes in whom there may not be enough remaining accommodative facility to trigger intermediate vision when viewing through a concentric lens design.6
Most practitioners advise patients that a conservative goal for multifocal lenses is to provide adequate vision for 80% of tasks performed.9 Under certain conditions, such as dim illumination and reduced contrast, multifocal lenses do not provide the same clarity of vision when compared to spectacle lenses.8 In these instances, wearers can enhance their near vision with supplemental lighting, the addition of over-the-counter reading glasses over the lenses, or other magnification aids.5
Patients should be educated early about the fitting process and the time frame expected to find success. Allow substantial time for the lenses to settle and for patients to begin adapting to both distance and near powers in the lenses before evaluating them on the eye. Small changes in add power can alter the distribution of the add pattern on the lens surface, changing how the wearer’s eyes react to the design; so, it is critical to have an accurate refraction and to adjust the sphere power first when troubleshooting.2
Push the highest amount of plus power acceptable in the distance and the least amount at near to avoid excessive accommodation and adaptation issues from too high of an add.9 This step is critical for success. A carefully performed manual refraction (objective and subjective) eliminates confusion and accurately establishes an initial trial lens power. When habitual spectacle powers are used, over-minusing is a confounding error and can lead to greater chair time and far more trial lenses.
SOFT HYDROGEL MULTIFOCALS
As the available options for soft multifocal contact lenses (Figure 1) continue to grow, the decision of which to prescribe becomes increasingly difficult. There are several patient personality factors to consider when it comes to multifocal contact lenses. Individuals who are impatient, extremely critical of their vision, or who have critical visual demands may struggle to find success. Setting proper expectations for your patients at the very beginning is necessary.
Although these lenses should provide clarity for visual demands at all distances, some patients may require additional help in the form of readers for more demanding or finer near visual tasks (as previously described). It can be helpful to describe vision with multifocal lenses as having a softer focus and as finding the right balance between distance and near vision. The possibility of multiple visits to find the right fit and the adaptation period to the lenses should also be discussed ahead of time.
To minimize the number of visits for both you and your patients, follow the unique fitting guides with every brand of lens. Fitting guides are often based on tens of thousands of successful fits (more than most practitioners would have in their practices).
After selecting the right patient, the next question is which lens to choose. Like all contact lenses, daily disposable lenses tend to be the most comfortable and most hygienic choice. Currently, there are seven daily disposable multifocal soft lenses on the market. Only one of the seven designs is center-distance, with the remaining all being aspheric center-near designs. A center-near design allows the highest add power to overlap the visual axis as the pupils constrict with accommodation during near visual tasks.11
Ensuring lens centration over the pupil will maximize visual outcomes. Utilizing a topographer to obtain maps over the contact lens can help determine whether the lens is centered or not.12 If the lens is centered, the near zone of the lens will overlap the pupil ring on the map.12 Changing to a distance gaze dilates the pupils and allows for inclusion of the more minus peripheral power for distance clarity. With this concept taken a step further, there is one lens on the market that is designed to address the natural pupil variation with differing ages and refractive errors to optimize vision.
In addition to physiology, a patient’s visual tasks and demands need consideration when choosing a lens. If distance vision is a priority or a low add is required, a center-distance lens may be a better choice to meet patient needs.6 Several lens designs are made with two add powers—low or high, while others are made with three—low, medium, or high. There are only two available lenses that provide an add power of up to +3.00D. Due to the lack of consistency with add powers and effective add powers among contact lenses, it becomes difficult to replicate outcomes when comparing lenses. Providers can easily fall into the habit of selecting one lens and sticking with it, rather than choosing the best lens for each patient.
Fitting multifocal lenses is straightforward when the fitting guide is followed. Each lens is generally fit the same, with small tweaks to the process depending on the individual company. For example, some lenses require the differentiation between the dominant distance eye and the nondominant near eye, while others do not require such distinction. Each company will know the parameters of its lenses inside and out and can serve as an invaluable resource when troubleshooting fit issues.
Understanding the fitting guide for the selected lens is very important for success. For one multifocal lens, the first step in fitting it is to determine the most plus spherocylindrical refraction and near-point add (lowest tolerable). Once the lenses have settled, the patients’ vision should be assessed binocularly in a “real-world” setting. If patients are not 20/happy, perform a binocular, loose lens over-refraction at distance (using only plus power). The same steps are used for distance and near complaints. This can be confusing, but it is due to the unique optics in this particular lens’ design. Additional steps to fitting this lens are not commonly required but can be found in a supplemental fitting guide. This multifocal lens uses the same bifocal add power for both eyes. Matching add powers should enhance binocularity, whereas old habits of prescribing monovision or modified monovision can directly disrupt binocularity.
As for the other lenses, there are two in which the fit process is more unique. The first is a center-distance lens with a single universal add. Rather than an aspheric design, this center-distance lens acts to extend depth of focus up to +3.00D. This lens is simply fit in the same way as a spherical distance lens.
Another lens that has a unique fitting process is fit similarly to a monovision modality. The dominant eye is fit in a lens with the appropriate distance prescription, and the nondominant eye is given a “near boost” power added to the distance prescription depending on the patients’ near requirement.
Of all the soft multifocal lenses, each one has its own unique benefits, and knowing what your patients’ needs are will help you select a successful lens for them.
GP AND SPECIALTY MULTIFOCALS
The GP multifocal contact lens market has grown considerably and is no longer being dominated by small-diameter GP lenses. Newer hybrid and scleral contact lenses now offer multifocal designs, increasing the number of potential GP multifocal candidates. The biggest benefit of GP contact lenses is the clarity of vision versus a soft lens.13,14 Patients who are not currently satisfied with their vision in soft multifocal contact lenses are good candidates for GPs (Figure 2).13,14 For new wearers, good candidates are those who are more critical about their vision or who have a demand for fine detail during the day. And, as always, patients who are highly motivated make the best candidates.13,15
Evaluating good candidates comes down to their wants and visual needs as well as your professional judgement. The general checklist components for evaluating whether a patient is a contact lens candidate are consistent with what you will already be checking in a general examination. Perform a comprehensive history, both ocular and medical, and ask pointed questions about contact lens wear. For previous wearers, take time to understand what caused them to stop wearing lenses.
Dryness is a major factor in contact lens dropout, so a thorough evaluation of the ocular surface is always required. Start treatment immediately to prevent patients from dropping out of contact lenses.
Besides a refraction and keratometry values (Ks), the other elements of the examination that you may need are eye dominance, lid position and tonicity, pupil size, and vertical fissure size. These findings will end up playing a large role in guiding you through your lens selection.14,15
Corneal GP Multifocals These lenses can be divided into two main subgroups. One is the simultaneous or aspheric designs, and the other is the translating or alternating designs.16,17 When considering a patient’s needs, simultaneous and translating lenses often serve two different populations. Patients who have a need for good intermediate vision or younger presbyopes are stronger candidates for simultaneous lenses because they can often achieve all of their visual goals with this design.14,16 In contrast, they can have a more fluid transition when moving from the distance to near.
Simultaneous lenses tend to be center-distance, with the add achieved by a combination of some shifting or translating of the lens with near gaze and the gradual power transition within the lens.14 As multiple distances are being focused through the pupil at the same time, this can lead to visual compromise. The optical system of the simultaneous lens works best when centered over the pupil, so the lens needs to be able to position centered on the cornea.16 To achieve this central fitting, the base curve is fit steeper than a patient’s K value if a back-surface aspheric design is being utilized.16 The asphericity of the lens can be placed on either the back surface, the front surface, or both. The advantages of a front-surface aspheric design are that it allows the back surface to interact with the cornea more specifically (i.e., an alignment fitting relationship) while not resulting in corneal molding. In addition, a patient who has high corneal astigmatism can now have a toric back surface and an aspheric (simultaneous multifocal) front surface.14
Simultaneous lenses can be fit empirically or diagnostically. Both can instill confidence in your patient if performed correctly. The empirical fitting is simple initially. It usually entails obtaining Ks, manifest refraction, horizontal visible iris diameter (HVID), and lid anatomy measurements and then working with a laboratory to design the best lens for that patient. There are helpful online calculators to help in choosing the initial lens parameters. Using these parameters provides practitioners with an initial lens that already has a patient’s prescription and allows for clear vision from the start. An empirical fitting can reduce the time that patients are initially in the chair.13,16 However, if the fit is not correct or the vision is not adequate, this will lead to more follow-up examinations afterward.
The diagnostic trial lens route requires placing a trial lens on the eye during the office visit. Diagnostic fittings will take more time during the initial visit and may be frustrating to patients who cannot see the benefit immediately.13,16 However, fitters will have more confidence in ordering the first lens and often have a higher first lens success rate. Even though patients spend more time initially in the chair, this may result in fewer remakes and visits.
Be prepared to make modifications as necessary at progress evaluations. Keep in mind that lens position can be a big factor with the vision through the lens. If the lens is riding too high, they may be looking through the add power and thus have a minus power over-refraction.15,16 When checking the over-refraction, always keep in mind that the fit may be the reason for decreased vision. A complaint at near warrants a similar protocol.
After assuring that the power is correct, make sure the lens is centering correctly and that it is translating slightly.14,16 Remember, even though these are “simultaneous” lenses, they do need to translate some to allow for full near correction. Keep in mind your general rules of fitting a GP lens to troubleshoot other fit issues.
The other corneal GP design category is translating lenses, which are suited for patients who are more advanced presbyopes or who might be a little more critical with their vision.14,15,17 This is because it is more challenging for aspheric multifocal contact lenses to have large effective add powers, especially with patients having miotic pupils. With translating lenses that move optimally with downward gaze, you meet this challenge by allowing patients to alternately experience full distance focus and full near focus. These lenses appear more like a bifocal, with an add on the inferior portion of the lens in a crescent, executive, or D shape.14,15
While looking at distance, the lenses should stay settled on or near the lower lid, giving patients good distance vision as they look through the top portion of the lens. As a patient looks down, the lens translates upward, positioning the add in front of the pupil. Even though this may provide adequate vision at distance and near, patients may find themselves sacrificing in the intermediate zone.14,17 That said, there are a large number of trifocal designs, typically having either an aspheric, executive, or crescent intermediate zone.
Ideal patients for translating multifocal GP lenses need to have specific lid apposition. This would consist of a lower lid that is no higher than 1.5mm above the lower limbus or lower than 1.0mm below.14 If the lid sits too high, it does not leave enough room between the pupil and the lid for the add portion. If the lid is sitting too low, the lens will rest too far down and not allow for adequate translation in downgaze. This prevents the add from centering over the pupil.14,17 For this reason, a diagnostic fitting can be very helpful.
An in-office trial will allow you to assess the lens’ ability to translate and to decide whether to proceed with a segmented bifocal lens.14 As mentioned previously, this will also help you determine a more accurate starting lens. Even though a diagnostic fitting is recommended, practitioners can order empirically from the company with keratometry readings and a refraction. But, to have the best chance at a successful first trial, other measurements such as lower lid positioning, palpebral fissure width, pupil size, and HVID should be taken.14
When assessing the fit of a translating bifocal, the fluorescein pattern should be at alignment to slightly flat. It is satisfactory if the lens is picked up with blink as long as it returns to the bottom lid quickly. When at rest on the lower lid, the top of the bifocal segment should not intersect the pupil any higher than at the lower edge after settling.14,17 The lenses are often oriented by prism ballasting in the lower portion of the lens and may have a truncation of the lower edge to help with translation. When patients look at something closer, it is technically their eye that is translating down while the lens remains stable on the lid. A truncation is a flattening of the bottom edge, allowing it to align specifically with the lower eyelid. To save time and be confident in the over-refraction, take a look at the fit and make sure that patients are looking through the top portion in primary gaze.17
After you find the correct over-refraction, take time to make sure that the lens is translating to the add power, and use loose lenses to assess near vision power. If the near vision is poor, the lens might not be staying with the lower eyelid as patients look down.17 You can assess this either at the slit lamp by having them look down and lifting the top lid or outside of the slit lamp by using a direct ophthalmoscope set to the cobalt blue filter. A direct ophthalmoscope, or burton lamp, allows fitters to assess the translation in a more real-world, natural way.
Troubleshooting tips for a non-translating lens would be to flatten the base curve or peripheral curves if the lens is too tight and moving below the lower lid instead of moving superiorly via the lower eyelid.14,17 Moving to a larger lens will allow for more mass and more lid interaction. Adding a truncation to the lens will help align the inferior portion of the lens with the lower lid and, again, allow for more interaction.17
Watch out for lens rotation. If the lens rotates slightly nasal, this may not be a problem as we converge our eyes when we look at near. Otherwise, if the lenses are rotating too much or if they are rotating temporally, consider either flattening the base curve or increasing the prism in the lens to help orientate it better.14
Hybrid Multifocals Even though they may offer stable vision, small-diameter GP lenses can be very difficult for some patients to adapt to due to lid-lens interactions.18 If patients are having difficulty adapting to the comfort aspect of the lens or are currently wearing soft lenses, a hybrid lens can be a great option. With its central GP portion and soft lens skirt, it may offer the improved optics and comfort that patients demand. Like small-diameter GPs, they are great for patients who have corneal astigmatism.14,18 Unlike corneal GP lenses, however, they have center-near designs because, like soft lenses, they do not translate with the blink.
Besides comfort, the soft skirt allows the lens to center over the cornea, which keeps fitters from disqualifying patients because of lid tonicity or apposition. The multifocal design is dual aspheric, like some simultaneous GP lens designs, and should be fit directly over the pupil.18 The disadvantage of the soft skirt is the potential to exacerbate issues with dry eye.
Hybrid lenses are usually ordered empirically. The required information includes manifest refraction, add power, Ks, and eye dominance. When dispensing the lens, some saline in the bowl of the lens can add to initial comfort upon application.18 The fit of the lens should be similar to a soft lens. The hybrid lens should move slightly with the blink, up to 1mm.
Troubleshooting pertains specifically to fit and vision.18 If the lens is not centering over the pupil or is moving excessively, the steepness of the soft skirt may need to be adjusted. If there is no movement, start by flattening the soft skirt; if there is still no movement, the GP may need to be flattened as well.18 Once the fit is addressed, assess the vision. Check the over-refraction at distance and near. Additional plus power at distance that does not degrade the vision can help a patient’s near vision. If the vision is adequate, it is acceptable to dispense the lens and have patients return knowing that as the brain adapts, the vision will improve.18
Scleral Multifocals Lastly, scleral lenses are a good option because, like the hybrid lenses, they may provide good vision and improved initial comfort as compared to smaller-diameter GP lenses. They too are not affected by lid apposition, but have their own challenges with fitting.19 An ideal fit means approximate central vault over the cornea of 200 microns, with only 50 microns of vault over the limbus and a soft landing onto the conjunctiva that does not impinge blood flow. The optical systems are typically aspheric, allowing for simultaneous multifocal correction for distance and near. Depending on the design/manufacturer, the optical system may be a center-distance or -near design.18 Some can incorporate front-surface toricity to correct the corneal cylinder as well as any residual cylinder caused by the natural lens. For scleral lenses, a diagnostic lens needs to be put on the eye to determine the initial lens parameters. The lens will need to settle for at least 20 minutes before assessing.
Allow patients extra time for the dispensing of a scleral lens, as the application and removal process can create a steep learning curve for first-time wearers. Allow for 20 minutes of settling before assessing the fit, keeping in mind that the lens will likely continue to settle for the next few hours. After assessing the landing zone, central vault, and limbal vault, over-refract as you normally would for a multifocal lens. If the lens is positioning inferiorly, consider adding toric peripheral curves, decreasing the central clearance, decreasing overall diameter, or reducing central thickness. Every design is different regarding issues with vault, impingement, or vision; contact the laboratory consultant to help make the appropriate changes.18
CUSTOM SOFT MULTIFOCALS
When stock multifocal lenses do not provide adequate vision and patients are either unwilling or poor candidates for GP lenses, custom soft multifocal lenses can serve as an additional option. As always, the fit of the lens is very important.20,21 These soft multifocals have a simultaneous vision system with a distance or near center or aspheric optics. This allows distance and near objects to be focused on the retina at the same time. There is less margin of error for the lens to be moving or to decenter; if it does, however, the optics over the pupil will not be consistent.21 Inconsistency in the position of the lens will cause either inconsistent and fluctuating vision or overall poor vision at distance, near, or both. Custom soft multifocal lenses are ideal in this matter and can be manipulated for the best possible fit. You can choose the exact diameter, base curve, and even manipulate the optic zone and some secondary curves.21,22
Custom soft lenses increase your multifocal candidates by widening their parameters. They also can increase success with lens wear through the manipulation of the optic zones in the lenses. Additional parameters for these lenses include a wider range of sphere powers (±20.00D) as well as the ability to correct astigmatism.20-23 Unlike “stock” lenses, custom multifocal toric lenses can match the axis to 1° in some cases, and they offer more options for add powers. Low-distance sphere power, unmasked cylinder, dominant eye, and visual sensitivity are all reasons to upgrade your spherical multifocal to a custom toric multifocal.22 This opens doors for certain patients who wish to have the freedom from spectacles but still want the comfort and handling of a soft lens.
There has been significant advancement in contact lens multifocal technology. It should not be a surprise that, as technology has improved, so have success rates. ECPs who routinely fit contact lenses should add several types of multifocals to their routine of practice. The days of extensive chair time and trials galore are that of mythology today. What can result is an enormous generation of presbyopes back in contact lenses again. This can be of tremendous value to the practitioner, the practice, and the quality of life of presbyopic patients. CLS
- Bauman E, Lemp J, Kern J. Material effect on multifocal contact lens fitting of lenses of the same optical design with the same fitting guide. Presented at the British Contact Lens Association Clinical Conference & Exhibition, June 9-11, 2017.
- Pal S. Use Education and Empathy to Connect with Presbyopes. Rev Optom. 2016 Aug 15;153:34-38.
- Reindel B, Cairns G, China P. Improving Vision Outcomes for Presbyopic Patients. Contact Lens Spectrum. 2011 Nov;26:34-36.
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- Potter R, Pal S, Stiegemeier MJ. Avoiding the Soft Multifocal Failure. Contact Lens Spectrum. 2016 Mar;31:22-25.
- Lowe PA. Priorities for Presbyopes: Maintain Comfort and Continuity. Rev Optom. 2016 Aug 15;153:40-45.
- Dinardo A, Rosen CM. A Bright View of Soft Multifocal Contact Lens Optics. Contact Lens Spectrum. 2017 Nov;32:28-32.
- Lampa M. Multifocal Contact Lens Insights and Innovations. Presented at the 2018 Global Specialty Lens Symposium, Las Vegas.
- Ames K. Fitting the Presbyope with Gas Permeable Contact Lenses. Contact Lens Spectrum. 2001 Oct;16:42-45.
- Bennett E, Henry V. Clinical Manual of Contact Lenses. 4th ed. Lippincott Williams & Wilkins. 2013 Oct 1.
- Bennett ES. Contact Lens Correction of Presbyopia. Clin Exp Optom. 2008 May;91:265-278.
- Benoit DP. Aspheric Multifocal Gas Permeable Contact Lenses. In Optimizing Practice Success with GP and Custom Soft Multifocal Lenses. Supplement to Contact Lens Spectrum. 2017 Sep:8-11.
- Messer B. Segmented, Translating Multifocal Design: Fitting, Evaluation and Problem-Solving. In Optimizing Practice Success with GP and Custom Soft Multifocal Lenses. Supplement to Contact Lens Spectrum. 2017 Sep:12–14.
- Woo SL. Hybrid Multifocal Lenses: Design, Fitting, Evaluation, and Problem-Solving. In Optimizing Practice Success with GP and Custom Soft Multifocal Lenses. Supplement to Contact Lens Spectrum. 2017 Sep:20–22.
- Barnett M. Multifocal Scleral Lenses. Contact Lens Spectrum. 2015 Dec;30:26-31.
- Bennett ES, Henry VA. Bifocal Contact Lenses. In Clinical Manual of Contact Lenses. Wolters Kluwer/Lippincott Williams & Wilkins, 2013:396-422.
- Davis RL, Eiden SB, Sonsino J. Personalizing Vision with Custom Soft Lenses. Contact Lens Spectrum. 2014 Aug;29:28-33.
- Henry VA. Clinical Pearls for Fitting Soft Multifocals. Contact Lens Spectrum. 2008 July;22:32,31-36,38.
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