IT’S HAPPENED. The oldest of the millennials have turned presbyopic. The question is, will they wear multifocal (MF) contact lenses at a greater rate than previous generations? With proper education and the best technologies yet—both current and emerging—the answer will likely be “Yes.”

As for now, Generation X is our primary group of focus for fitting MF contact lenses. Unlike the baby boomers, who are moving into retirement, this generation is still young and image conscious enough to prefer contact lenses over glasses; and most in this generation are still enjoying excellent ocular health, making them good candidates for any contact lenses.

Born between 1965 and 1980, these patients are at their peak earning potential. This is important, as the MF fitting process and lens technologies both require higher fees than single-vision contact lenses, and rightfully so. A good understanding of the optics of these lenses—and how to troubleshoot them to obtain optimal vision—is important. And although more effort is required on the part of the eyecare practitioner compared with single-vision lenses, today’s designs and materials are easier than ever to fit.

MULTIFOCAL OPTIONS

MF contact lenses, when fit appropriately, provide greater stereopsis than monovision because both eyes are viewing together rather than separately.¹ In addition, various studies have found equal or better vision with MF contact lenses as compared with monovision.^2-5 As a result, more and more practitioners are selecting MFs as their first choice for presbyopic patients—50% versus 26% for monovision, according to Contact Lens Spectrum’s most recent annual report.⁶ Today, we have numerous lenses from which to choose: in total, 207 MF soft and GP lens designs.⁷

Soft Multifocal Contact Lenses Two of the most important determinants of success with MF contact lenses are to understand the optics and performance of the contact lens you are fitting and to understand your patient’s visual needs. Note that different lens brands within the same general optical design (for example, center-near) may perform differently on the eye because their material, parameters, and optics differ.

To expedite the fitting process, follow the manufacturer’s recommendations for initial lens selection. Always apply trial lenses and wait for the lenses to settle into place. Perform over-refractions in free space, not with the phoropter. Adjust light levels to mimic your patient’s real-life environment.

For an optimal endpoint, follow the manufacturer’s fitting guide for over-refraction and troubleshooting. Keep in mind that a 0.25D change in prescription can have a profound impact on success. The manufacturers have collected data from thousands of successful patients and their fitting guides are based upon this knowledge.

Whether aspheric or concentric, soft MFs provide “simultaneous” vision, i.e., both distance and near (and intermediate, if present) bundles of light are projected simultaneously onto the retina. The patient must ignore the unfocused image while viewing the properly focused image. The inability to do so will impair success with this modality.⁸

Pupil size plays an important role in fitting bifocal contact lenses. A very small pupil limits the view to only the central optics of the multifocal lens and impedes the use of the mid-peripheral optics. A very large pupil can prevent the eye from utilizing the central optics of the lens.

Most concentric designs are available in multiple central zone sizes. A center-distance design, for example, may not be optimal for patients who have small pupils. As the eyes accommodate and converge upon the reading material, the pupil naturally constricts. As a result, it is unable to utilize the mid-peripheral optics of the lens that contain the near correction.

By definition, monovision is the correction of one eye for distance and the other eye for near, utilizing single-vision contact lenses. The patient must suppress the blurred image of one eye while viewing with the other. Modified monovision, meanwhile, entails emphasizing one eye for distance and one eye for near, by utilizing MF contact lenses in one or both eyes⁸; some sources define the latter as the modified bifocal approach.⁹ Some manufacturers incorporate this approach into their fitting and troubleshooting guides. Modified monovision is often the key to success with MF contact lenses.

GP Multifocal Contact Lenses In general, the best candidates for GP MFs include current GP wearers, astigmats, and patients who require a high near addition. Rigid MF contact lenses typically provide better optics than soft lenses. One reason is their ability to correct astigmatism (if residual astigmatism is absent or low). Another advantage is a crisper front refracting surface due to the rigidity of the material.

In this day and age, most manufacturers recommend—given accurate initial measurements—that the first MF GP lens be ordered empirically.¹⁰ Most offer fair warranty periods and exchanges, and as a result, 86% of practitioners choose to fit this way.¹¹

Translating rigid lenses (Figure 1) are segmented and weighted to keep them in place. The advantage to this type of correction is that they can be manufactured with greater addition powers than aspheric designs. The latter (GP or soft) can be limited in add power by the technology that produces them.

In addition, alternating bifocal lenses are spherical, and as a result, optically similar to single-vision GPs. The best candidates for alternating GP bifocals have moderate to tight lid tension and a lower eyelid positioned at or above the lower limbus. Another advantage of alternating bifocal lenses is that they are less dependent on pupil size as compared with simultaneous designs. Trifocal segments are available, but it can take several visits to perfect their positioning.

Fitting translating designs requires knowledge of fitting single-vision GP contact lenses. The same optical relationships between contact lens and cornea exist; for example, to fit on the flat keratometer reading (K) for no-to-low astigmatism and between the flat and steep Ks for moderate-to-high corneal cylinder.

As their mechanism of action is translation, a tight fit is counterproductive and likely unhealthy. The lens is designed to sit on the lower eyelid. When the patient looks downward, the lower lid naturally pushes the contact lens upward, positioning the segment in front of the pupil for near viewing.

For many aspheric MF designs (soft or GP), centration is critical to ensure that the patient is looking through the proper point in the lens. As a result, many of the aspheric rigid MFs (especially back-surface optics) need to be fitted 1.00D to 5.00D steeper than keratometry readings to ascertain proper position. However, several of the front aspheric MFs (as well as low-eccentricity posterior aspheric designs) are designed for superior lid attachment. This simplifies the fitting process, resulting in an on-flat K fit similar to that of a spherical contact lens.

Scleral GP MFs offer many benefits as compared with corneal GPs, including improved comfort, centration, corneal protection, and a larger optic zone diameter. Candidates for scleral MFs include patients who have irregular corneas, against-the-rule corneal cylinder and/or dry eye, current scleral wearers, and those who require immediate comfort.

Scleral lenses, however, do not always center perfectly; the tendency is for the lens to position slightly inferior-temporally in most patients.¹² As scleral lenses do not move or translate, this means that the MF optics (most often center-near) are not aligning with the visual axis for optimal correction at all distances. In addition, the visual axis tends to be located slightly superior-nasal to the cornea’s optical center.¹³ These issues compound and can result in reduced acuity with a scleral MF lens.

To address both, some laboratories have incorporated offset optics into their MF lenses to ensure that the patient is looking through the center of the lenses’ optics, minimizing higher-order aberrations (HOAs).¹⁴ Some manufacturers have placed laser alignment grid marks on their trial lenses to facilitate measuring the angle and offset of the optics (Figure 2), while others use preset horizontal and vertical decentration amounts that can be modified if needed.^15,16 One laboratory even has an online tool with which the fitter can physically replicate the lens’s position, creating the series of values that need to be ordered.¹⁷

An important point to remember in fitting presbyopes with any type of contact lens is that these patients, being older, may have a number of physical characteristics that contraindicate contact lens wear. These include reduced tear quantity and quality, reduced eyelid tonicity, and small pupil size.

The key to successful contact lens fitting in this age group is a proper prescreening, good patient education, proper lens selection for that particular patient, and thorough knowledge of bifocal contact lens fitting. The patient needs to be educated that there are limitations to correcting presbyopia with contact lenses and that it may require multiple office visits to finalize the best fit and prescription.

TIPS FOR SUCCESS

• Educate all prospective patients—in terms they can understand—on how their lenses work. For example, patients accustomed to progressive-addition spectacles are trained to look down to read. With center-near MF contact lens designs, however, they may see better at near viewing straight ahead.
• Allow trial lenses to settle (per manufacturer’s recommendations). For simultaneous-vision lenses, excessive movement or decentration can affect over-refraction.
• Utilize real-world lighting for testing; many lens designs are dependent on pupil size.
• Over-refract outside of the phoropter with handheld lenses.
• Modified monovision may determine the difference between success and failure with the modality.
• Follow the manufacturers’ guides for fitting and troubleshooting and reach out to the GP laboratory consultants. The manufacturers know their lens designs in great detail and know just what to do to maximize lens performance. They want you to succeed.

Presbyopes desire contact lenses. MF contact lenses are the best they have ever been and are getting better. It’s our responsibility as eyecare professionals to help our patients achieve their goals. CLS

References

1. Back A. Factors influencing success and failure in monovision. ICLC. 1995;22:165-172.
2. Gromacki SJ, Nielsen E. Comparison of Multifocal Lens Performance to Monovision. Contact Lens Spectrum. 2001 May;16:34-38.
3. Gromacki SJ, Badowski L, Wicker D, Ventocilla M. A Clinical Study of an RGP Multifocal Contact Lens. Contact Lens Spectrum. 2001 Dec;16:36-41.
4. Schatz S. Improve Visual Performance with an Aspheric Multifocal. Contact Lens Spectrum. 2000 Aug;15:37-39.
5. Rajagopalan AS, Bennett ES, Lakshminarayanan V et al. Performance of Presbyopic Contact Lenses Under Mesopic Conditions. Invest Ophthalmol Vis Sci. 2003 May;44:3679.
6. Nichols JJ, Fisher D. Contact Lenses 2022. Contact Lens Spectrum. 2023 Jan;38:20-22, 24-26.
7. Tyler’s Quarterly. 2022;39(4):10-13, 24, 53-54.
8. Gromacki SJ. Monovision and Bifocal Contact Lenses. In Hom MM, Bruce AS, eds. Manual of Contact Lens Prescribing and Fitting. Butterworth Heinemann Elsevier, St. Louis, 2006:471-497.
9. Badowski L. Hydrogel options for the presbyopic patient. Contemp Optom. 2004;2:1-5.
10. Kauffman M. 21st Century Correction of Presbyopia. Contact Lens Spectrum. 2022 June;37:20-24.
11. Bennett ES. GP and Custom Soft Annual Report. Contact Lens Spectrum. 2022 Oct;37:24-31.
12. Kowalski LP, Collins MJ, Vincent SJ. Scleral lens centration: The influence of centre thickness, scleral topography, and apical clearance. Cont Lens Anterior Eye. 2020 Dec;43:562-567.
13. Abass A, Vinciguerra R, Lopes BT, et al. Positions of Ocular Geometrical and Visual Axes in Brazilian, Chinese and Italian Populations. Curr Eye Res. 2018 Nov;43:1404-1414.
14. Hastings G, Applegate R, Nguyen L, Kauffman M, Hemmati R, Marsack J. Comparison of Wavefront-guided and Best Conventional Scleral Lenses after Habituation in Eyes with Corneal Ectasia. Optom Vis Sci. 2019 Apr;96:238-247.
15. AccuLens. Available at acculens.com/scleral-designs/maxim-scleral . Accessed May 9, 2023.
16. Bausch + Lomb. Available at bauschsvp.com/lenses/zenlens . Accessed May 9, 2023.
17. CooperVision Specialty EyeCare. Available at prod.blcalculator.com/tools/all/en/ . Accessed May 9, 2023.