Functional Categorizations for Presbyopia-Correcting IOLs
Esteemed refractive cataract surgeons discuss how updated international classifications for IOLs will help them choose the best Alcon lenses for their patients’ needs.
INTRODUCTION
Since Sir Harold Ridley implanted the very first intraocular lens (IOL) in London in 1949,1 IOL technology has steadily progressed in design, materials, and surgical techniques. Recently, the International Organization for Standardization (ISO) reviewed and updated its standards for ophthalmic implants and IOLs for the correction of aphakia2 to include definitions of non-accommodative posterior chamber lenses (PCIOLs) with “simultaneous vision range.” Subtypes of these PCIOLs described in the guidelines include those with multifocal, extended-depth-of-focus (EDF), and full-range-of-vision optics.
Mercè Guarro, MD: I welcome the new ISO classifications for aphakic IOLs, which now includes an evaluation of these lenses’ functional vision outcomes after 6 months of implantation in at least 100 subjects, compared to that of an aspheric monofocal control. The updated standards require that IOLs with a simultaneous range of vision meet specific criteria for contrast sensitivity, superiority to controls for intermediate vision and defocus range, and noninferiority to controls for distance vision (Table 1), versus monofocal lenses. By having outcomes be the benchmark of these lenses, and not just their mechanisms of action, the ISO’s definition of EDF IOLs more closely matches that of the American National Standards Institute (ANSI).3
This panel, composed of ophthalmic colleagues from Germany, Spain, Norway, and the United States, will discuss the merits of these updated ISO standards. To my colleagues: what have been your clinical experiences with EDF IOLs, and do you think the ISO’s new definitions were warranted?
Kjell Gunnar Gundersen, MD, PhD: I think we benefit from having an objective, standardized means of assessing the advantages and disadvantages of IOL products that are currently available, and those in development. When designing optics, there are usually tradeoffs, whereby gains in one area necessitate sacrifices somewhere else. Such standardization will enable us to qualify these pros and cons and provide a useful tool by which patients and providers alike may choose an IOL.
Prof. Khoramnia: I appreciate being able to categorize IOLs based on their functional results. I think these new standards will eliminate confusion about the variations between types of IOLs—e.g., EDF versus enhanced monofocal IOLs.
Satish Modi, MD, FRCSC, CPI: I, too, am glad to have these updated guidelines for IOLs. Having evidence-based performance data from controlled, randomized trials will greatly assist our IOL selection.
DIFFERENTIATING IOLS
Prof. Khoramnia: In my opinion, it is critical for us surgeons to be able to differentiate between enhanced monofocal and EDF IOLs. Enhanced monofocal lenses are not the same as presbyopia-correcting IOLs such as EDF and trifocal lenses. Most patients cannot achieve spectacle independence with a monofocal or enhanced monofocal lens. Per the new ISO standards, the outcomes of a popular enhanced monofocal IOL4,5 do not meet the criteria for an EDF IOL (Table 2).
Dr. Gundersen: From a scientific standpoint, I believe the new ISO standards will clear up confusion about IOLs currently available and those in the pipeline. Clinical study data based on functional vision outcomes will give us a tool to better assess these lenses.
Prof. Khoramnia: This is a positive step towards having clear criteria to evaluate the pros and cons of new IOLs as they come to market. I expect the ISO classifications will impact the registration of new products when the European Medical Device Regulation (MDR) is in place.
IOL SELECTION FOR PATIENTS
Dr. Guarro: Experts will certainly benefit from these new ISO guidelines, but how should we talk to patients in our clinics about the differences between EDF and enhanced monofocal IOLs?
Prof. Khoramnia: I frame my IOL discussion with patients in terms of their visual goals: do they want to be free of spectacles, or do they not mind wearing glasses? For the patients who aren’t bothered by wearing glasses, I’ll prescribe a monofocal or enhanced monofocal lens and tell them to expect to need glasses for tasks that require near and intermediate focus.
Patients who state they prefer spectacle independence must not have any precluding comorbidities, and they must be willing to tolerate photic phenomena. I’ll choose a trifocal IOL for these qualifying individuals, and usually a non-diffractive EDF IOL for those who prioritize excellent visual quality and don’t mind reading glasses, in keeping with the ISO guidelines.
Two recently published comparison studies between the AcrySof IQ Vivity® IOL (Alcon) and various enhanced monofocal IOLs demonstrated that the AcrySof IQ Vivity® IOL gave patients greater depth of focus,6,7 a feature that further enhances the performance of an EDOF lens at intermediate viewing. Similarly, Sabur et al found a similar binocular defocus curve between the AcrySof IQ Vivity® IOL and the TECNIS® Eyhance™ IOL (Johnson & Johnson Vision),* up to -1.00 D.8 In the intermediate range, though, the AcrySof IQ Vivity® IOL clearly has the broader depth of focus—recipients of the AcrySof IQ Vivity® IOL needed much less spectacle correction compared to those who received the TECNIS® Eyhance™ IOL.* Studies like these demonstrate that, although some patients may experience better intermediate vision with enhanced monofocal IOLs versus some traditional monofocals, their optics are not equal to that of EDF IOLs.
Dr. Gundersen: I’d rather have all my patients’ outcomes be stable and consistent than have a few patients achieve above-average results. For cataract patients who do not request presbyopic correction, I will confidently prescribe a simple monofocal IOL. In patients who want to minimize dependence on glasses, I’ll use EDF or full-range IOLs.
Dr. Guarro: As practitioners, we must separate EDF IOL candidates from those who are suited to monofocal IOLs and even enhanced monofocal IOLs. I don’t promise patients that they’ll gain intermediate or functional near vision with the latter.
Prof. Khoramnia: I agree; I think the percentage of patients achieving functional intermediate vision from enhanced monofocal IOLs is still too low to set that expectation. Surgically, I must be able to deliver the results I describe to my patients preoperatively. I present monofocal IOLs and enhanced monofocal IOLs the same way—setting the expectation that patients will likely need to keep using glasses for various distance focal points.
My staff and I participated in a study that compared the ZCB00 lens with the TECNIS Eyhance™ lens.*,9 Although the TECNIS Eyhance™ lens* provided one additional line of intermediate distance viewing versus the ZCB00, that doesn’t make the TECNIS Eyhance™ IOL* superior to all other monofocal IOLs. Likewise, it is not necessarily true that all enhanced monofocal IOLs outperform all standard monofocal IOLs.
Dr. Modi: When I talk to patients about their choices of IOLs, I stress a lens’ value over its price. I want patients to understand the benefits they can potentially receive from an IOL, such as functionality, visual independence, and the freedom of doing the activities they enjoy.
PERFORMANCE BEYOND VISUAL ACUITY
Dr. Guarro: Visual disturbances of IOLs, which we do sometimes see clinically, were not considered in either the ISO standards or the ANSI criteria. The optics of various IOLs differ, and the lenses perform differently. We must be mindful of the potential for visual disturbances in our patients’ eyes.
Dr. Modi: Dysphotopsias, in fact, are a primary source of patients’ complaints after cataract surgery. Our IOL classifications shouldn’t ignore the potential for these phenomena among the various types of lenses.
Prof. Khoramnia: If photic phenomena were not an issue, most patients would receive a trifocal IOL after cataract surgery. Although some patients can see well enough without glasses at intermediate and distance viewing with diffractive EDF IOLs, they still need correction for near vision, and they still experience dysphotopsias. I don’t agree with that approach. For patients who can withstand some photic phenomena, I recommend a trifocal IOL so they may have a full range of glasses-free vision.
We can judge the performance of IOLs via clinical studies. A few years ago, colleagues and I published the results of an optical bench study on the propagation of light rays among four IOLs (one monofocal, two diffractive, and one non-diffractive).10 We stained water with a fluorescein solution and then shone a monochromatic green laser through it to view its rays. Our model cornea was a plano convex lens through which we recorded all images at 520 nm. We used dedicated software to record the light intensity profiles and compute the relative pixel values. The monofocal lens, unsurprisingly, created a single, distinct focal point. The non-diffractive lens, the AcrySof IQ Vivity® IOL based on wavefront-shaping X-WAVE™ technology, had a single focal point with an elongated focus. The two diffractive EDF IOLs, however, the AT Lara® (Zeiss)* and TECNIS® Symfony (Johnson & Johnson)*, performed differently. These both revealed two distinct focal points in close proximity—essentially, a low-add bifocal optic that produced the effect of an elongated focus (Figures 1 and 2).
Using point spread function (PSF), my coauthors and I illustrated each lens’ light distribution with a 0.1 mm pinhole. Whereas both of the diffractive lenses formed an extended halo pattern, the light spread of the AcrySof IQ Vivity® IOL was only slightly larger than that of the monofocal lens. Thus, we concluded that the AcrySof IQ Vivity® IOL extends patients’ focus yet with almost the same amount of photic phenomena as a monofocal IOL.
Dr. Guarro: What I see clinically with patients matches the results from your bench study, and both mirror results colleagues and I published from a study in which we compared the visual disturbances patients experienced with three EDF lenses against those from a monofocal IOL as a control.11 In a self-reported McAlinden Questionnaire, patients evaluated the visual phenomena they experienced from the TECNIS® Symfony* (Johnson & Johnson), the AcrySof IQ Vivity, or the AT LARA® (Zeiss)* IOLs compared to the monofocal. Under binocular conditions at 3 months, those who received an AcrySof IQ Vivity® noted visual phenomena on par with those who had received the monofocal implant, but those who had received the two diffractive EDOF IOLs reported significantly more phenomena (Figure 3). Then, we used a Light Distortion Analyzer (Halometer) to test the patients’ visual disturbances, and we again found statistically significantly fewer visual disturbances with the AcrySof IQ Vivity® lens compared with the AT Lara* and the TECNIS Symfony* IOLs.
It is common knowledge that IOLs with varying mechanisms of action can each meet the ISO guidelines and the ANSI standards for an EDF lens, yet they may impart different visual disturbances. The AcrySof IQ Vivity IOL meets the EDF criteria of both organizations12,13 using a nondiffractive design based on wavefront shaping technology, which produces less VD vs diffractive design. I feel comfortable implanting the AcrySof IQ Vivity®, but I feel less confident with diffractive EDFs, because they can produce the same problems with photic phenomena as with trifocals.
Dr. Gundersen: My patients’ satisfaction is the most important thing to me. I base their satisfaction with their vision not just on their visual acuities at all ranges, but the degree to which they experience visual phenomena, because, if they see dysphotopsias after I’ve promised them vision with no side effects, I’ll lose their trust. We clinicians must comprehend the complete optical capabilities of any IOL we implant. In my experience, a diffractive lens such as the TECNIS® Symfony IOL* produces visual phenomena on par with that of any diffractive trifocal optic.
Prof. Khoramnia: After my team and I took part in clinical trials in which we implanted diffractive EDF lenses, we saw a disappointing number of those recipients report postoperative visual disturbances. I ceased implanting diffractive EDF IOLs and instead recommend a trifocal implant for patients who can withstand some visual phenomena. I also like the non-diffractive EDF IOLs, which provide good intermediate and functional near vision with the optical quality of a monofocal implant. Thus, these lenses enable me to give a wider range of vision to patients who otherwise would have received a simple monofocal implant.
Dr. Guarro: Likewise, my volume of trifocal implants has remained steady, and I am choosing the AcrySof IQ Vivity® IOL instead of a monofocal lens in more patients. I would like to note that I still warn my monofocal recipients of the possibility that they may see visual disturbances caused by irregularities in the cornea or other ocular tissues that are not due to the lens.
Dr. Modi: I agree. Although I prefer to implant a trifocal IOL such as the PanOptix® IOL (Alcon) whenever possible, for patients who are not good candidates for that type of lens, I usually opt for the Vivity.®
Dr. Guarro: As we already mentioned previously, visual disturbances and dysphotopsias are excluded from the ISO standards, perhaps because there is not enough objective data. Combining data from various subjective questionnaires is challenging. Perhaps in the future, researchers will develop an objective and reliable method for evaluating the photopic phenomena of IOLs that will enable their inclusion in the classification systems, as was done with the Light Distortion Analyzer. I would like to be able to test IOLs with a halometer and then correlate those data with patients’ answers on subjective questionnaires. Again, this information might prove useful in clinical studies.
EVALUATING TRIFOCAL IOLS
Dr. Modi: As I said earlier, my first choice of IOL for most patients is a diffractive trifocal. Yet, not all brands of these IOLs perform identically; their visual performance is influenced by differences in design, sometimes significantly. Among the diffractive trifocal lenses available in the US, I served as lead author for the FDA registration study for the AcrySof® IQ PanOptix® IOL (Alcon), which gained FDA approval in 2019.14 Alcon’s PanOptix® IOL in fact features quadrifocal optics—the proprietary ENLIGHTEN® technology—which redistributes the 120-cm focal point toward distance viewing. This design emphasizes superb distance vision, with the intermediate focal point at 60 cm and near viewing at 40 cm. This differs from traditional trifocal IOLs, which offer three distinct focal points for distance viewing, intermediate vision at 80 cm, and near vision at 40 cm. In a paper published in 2022, Lwowski et al demonstrated a patient preference for superior visual performance at 60 cm versus 80 cm. When evaluating 94 patients at 3 months after they received either a diffractive EDoF lens or a trifocal/quadrifocal IOL, those who reported having stronger uncorrected distance and intermediate vision at 60 cm more often choose to receive the same implant again.15
The TECNIS® Synergy IOL* is what I consider to be a hybrid lens—the ZXR00 EDF optic combined with the bifocal optics of the ZM900, with +4.00 D of add located at the IOL plane.16 The lens’ hydrophobic material contains a chromophore that filters violet light and corrects chromatic aberrations, and it is also designed to minimize unwanted photopic disturbances. I participated in a randomized, prospective, investigator-initiated trial in which a total of 276 patients from 4 study sites received either the AcrySof IQ PanOptix® IOL or the TECNIS® Synergy* bilaterally.17,18 In assessing patients’ visual performance at three timepoints (1 month, 3 months, and 6 months), we investigators found that patients received a good range of vision with both lenses, and that the PanOptix was noninferior to the Synergy* implant. We expected the TECNIS® Synergy IOL* to perform better at near (33 cm) due to its 4.00-D add, but instead, we found no difference in visual performance between the two IOLs at any range (Figure 4).
Both lenses imparted high rates of spectacle independence: at 6 months postoperatively, more than 78% of the recipients of each lens reported that they never needed to use glasses. Contrast sensitivity, too, was comparable between the AcrySof IQ PanOptix® IOL and the TECNIS® Synergy*. Yet, those who received the PanOptix lens better withstood photopic phenomena, in particular with glare and starbursts (P<0.05)— almost twice as many PanOptix recipients as Synergy* recipients said they either did not see or were undisturbed by starbursts (Figure 5).
Dr. Guarro: As in Dr. Modi’s study, I have not seen differences in visual acuity between these two IOLs clinically, but I have noticed that their dysphotopsia profiles differ. In my experience, patients who receive the Synergy IOL* complain more about dysphotopsia than my PanOptix recipients.
Dr. Modi: Dr. Gundersen, how do you think the AcrySof IQ PanOptix® IOL performs against the trifocal lenses available on the market in the EU?
Dr. Gundersen: A colleague and I compared the visual acuity and long-term refractive outcomes (out to 2 years) of the AcrySof IQ PanOptix® IOL and the FineVision® IOL* (BVI Medical).19 The FineVision® IOL* features a trifocal design, a combination of two apodized bifocal diffractive profiles, which produces three focal points. Other specifications of this lens include a spherical optic with 26 diffractive steps, a near add of +3.50 D, and an intermediate add of +1.75 D. It designates 42% of the light for distance viewing, 15% of the light for intermediate vision, and 29% of the light for near viewing. The model of the FineVision® lens* we studied had a hydrophilic optic with a blue light filter;20 a hydrophobic model is now also available.
We noted statistically significant differences on the defocus curve between the two lenses at the 6-month timepoint. At 80 cm, the FineVision* lens performed better than the PanOptix IOL by a couple of letters on the logMAR chart. At 60 cm and 45 cm, PanOptix outperformed the FineVision* IOL by three logMAR letters. Other published studies comparing these two lenses found comparable results: in 2019, Martínez de Carneros-Llorente et al reported better intermediate vision between -1.50 and -2.00 D versus the FineVision,* TECNIS® Symfony,* and AT LISA (Zeiss)* lenses when measured at a contrast of 15%, 50%, and 100% (P<0.05).21 Similarly, Ribiero et al conducted a comparative study in 2020 between the FineVision* and AcrySof IQ PanOptix* lenses in which they demonstrated no statistical difference in visual acuity at 80 cm between the two implants (P=0.11), but statistically significantly better performance at 60 cm by the PanOptix lens (P=0.032).22
Prof. Khoramnia: Colleagues and I conducted a study to compare two versions of the FineVision IOL*, the hydrophilic one and the newer, glistening-free hydrophobic one.23 As far as visual acuity, we found similar outcomes between the two lenses.
Dr. Guarro: I see the greatest differences between trifocal IOLs in intermediate performance. Most trifocals place the intermediate focus at 80 cm, but the AcrySof IQ PanOptix* IOL places it at 60 cm. I live in Barcelona, and our native citizens generally are not tall—I’ve observed that most of my patients prefer intermediate vision at 60 cm much more than when it is at 80 cm. Dr. Modi, do you see greater patient satisfaction with intermediate vision at 60 cm or 80 cm?
Dr. Modi: I agree with you that intermediate vision is more functional at a range of 60 cm to 33 or 40 cm than it is at 80 cm to 33 or 40 cm.
Dr. Gundersen: For 5 years now, my staff and I have been considering patients’ height when we recommend an IOL. I believe that patients who are taller than 180 cm will be comfortable with 80-cm intermediate vision, but shorter people usually prefer intermediate vision at 60 cm.
CONCLUDING THOUGHTS
Dr. Guarro: To recap this discussion, the ANSI criteria and the new ISO standards for EDF IOLs align in their definitions, and the TECNIS Eyhance™ IOL* does not meet either. Commercially available EDF IOLs apply different mechanisms of action in their optics that produce variations in visual performance. We must remember that neither the ANSI nor the ISO definitions take into account IOLs’ visual disturbance profiles, although visual phenomena can greatly impact patients' vision. The nondiffractive AcrySof IQ Vivity® IOL, the diffractive TECNIS® Symfony IOL,* and the diffractive AT LARA IOL* are all classified as EDF lenses, although the AcrySof IQ Vivity® lens generally imparts much fewer photopic phenomena than the other two.11 Moreover, variations in the optic design of these diffractive lenses can greatly impact how they perform visually. For example, comparison studies have demonstrated that the PanOptix IOL induces much fewer photopic phenomena such as glare and starbursts than the Synergy*,17 lens, and it provides better intermediate vision (at 60 cm) than the FineVision trifocal IOL.*,21
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