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REVIEW/UPDATE

Extended depth-of-focus technology in intraocular lenses

Kohnen, Thomas MD, PhD, FEBO; Suryakumar, Rajaraman BS Optom, PhD, FAAO

Author Information
Journal of Cataract & Refractive Surgery: February 2020 - Volume 46 - Issue 2 - p 298-304
doi: 10.1097/j.jcrs.0000000000000109
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The options for pseudophakic correction of presbyopia have historically been monofocal or multifocal intraocular lenses (IOLs).1,2 Each has strengths and weaknesses. Monofocal IOLs can provide patients with a full range of vision through monovision; however, there might be some loss of depth perception and these IOLs do not provide optimum visual acuity at intermediate distances.3–5 Multifocal IOLs have diffractive or refractive technology that allows patients to focus on images in multiple focal planes, achieving a fuller visual range and greater spectacle independence than monofocal IOLs.6–9 However, multifocal IOLs can affect contrast sensitivity and increase the likelihood of visual disturbances such as glare or halos, especially in low-light conditions.10,11

The extended depth-of-focus (EDOF) IOL is an emerging technology that is designed to improve range of vision, especially at intermediate distances (eg, distance needed for computer work).12 EDOF IOL technology could bridge the gap between monofocal IOLs and multifocal IOLs by providing improved visual acuity at intermediate distances and might also cause fewer or less severe visual disturbances and yield better contrast sensitivity.13 Although most EDOF IOLs share qualities, such as relatively good to excellent visual acuity at distance, improved intermediate visual acuity, and functional near visual acuity, attributes such as the degree of contrast sensitivity loss are specific to the design of the EDOF IOL.14

TYPES OF EDOF IOLS

This review is focused on the following 4 EDOF technologies: small-aperture design, bioanalogic IOL, diffractive optics, and via nondiffractive optical manipulations (ie, asphericity).14

Small-Aperture Design

An example of a small-aperture design is the IC-8 (AcuFocus, Inc.), which is a one-piece hydrophobic acrylic posterior chamber IOL.A The IC-8 IOL is implanted in 1 eye through a 3.5 mm corneal incision using a single-use injector system. The contralateral eye can receive a different type of IOL (ie, monofocal). The small-aperture design blocks unfocused peripheral light rays via its 3.23 mm wide opaque mask while allowing central and paracentral light rays through its 1.36 mm central aperture (Figure 1, A).15,A Patients with naturally large pupils might experience increased visual disturbances (eg, halo) under mesopic conditions or a drop in the defocus range as a result of the small diameter of the optic.16,17

Figure 1
Figure 1:
Types of extended-depth-of-focus IOL technology. A: The IC-8 IOL has 5-degree haptic angulation and small-aperture lens to block unfocused peripheral light rays via its nondiffractive opaque mask (dashed arrow) while allowing more focused central and paracentral light rays through its central aperture (solid arrow). B: The WIOL-CF is a bioanalogic one-piece polyfocal IOL with maximum refractive power in the center that continuously decreases without steps to its periphery. C: The Tecnis Symfony IOL (left) has a step structure with an achromatic diffractive echelette design and offset haptics. The AT LARA 829MP IOL (right) has a continuous diffractive surface profile and 0-degree haptic angulation. D: The SIFI Mini WELL IOL has fenestrated haptics with 5-degree angulation and uses asphericity, whereby opposite spherical aberrations in central zones and an external monofocal zone provide extended depth of focus. (Images used with permission from IC-8 Physician Information A [A], WIOL-CF Bioanalogic IOL Product Technology B [B], Cataract & Refractive Surgery TodayD [C, left], Zeiss AT LARA 829MP IOL Technical Specifications E [C, right], and Sifi G [D].) Copyright W2O Medizintechnik AG, Philippsburg, Germany, reprinted with permission. All permission requests for this image should be made to the copyright holder. (IOL = intraocular lens; WIOL-CF = Wichterle IOL-Continuous Focus).

Bioanalogic Design

The Wichterle IOL-Continuous Focus (WIOL-CF, Medicem) is a bioanalogic hydrogel IOL designed to emulate the crystalline lens with a similar shape, no haptics, and a refractive power that decreases from the center to the periphery (Figure 1, B).18,B The WIOL-CF is implanted via an injector through a 2.5 to 3.2 mm incision.B After the WIOL-CF is inserted, it is pushed inside the posterior capsular bag for 5 seconds to allow the IOL to adhere to the capsule.19 Because the WIOL-CF IOL is 8.9 mm in diameter with a larger surface area than conventional IOLs, this IOL might not be suitable for patients with very shallow anterior chambers.20

Diffractive Optics

Examples of diffractive EDOF IOLs include the Tecnis Symfony and Symfony toric (both Johnson & Johnson Vision Care, Inc.). These IOLs have a step structure design intended to provide improved visual acuity at intermediate distances (Figure 1, C, left).13,C,D The AT LARA 829MP and AT LARA toric 929M/MP (both Carl Zeiss Meditec AG) have a continuous diffractive surface profile from intermediate to distance focal points (Figure 1, C, right).21,E The Symfony is a foldable one-piece hydrophobic acrylic IOL that can be implanted with screw-style or syringe-style insertion instruments through an approximately 2.3 mm corneal incision.22–24 Patients might experience a reduction in contrast sensitivity or halos or glare in low-illumination conditions as a result of the IOL's elongated focus design.F For the toric model, misalignment greater than 30 degrees might reduce the astigmatic correction.F The AT LARA models are one-piece hydrophilic acrylic IOLs implanted with an injector through a 1.8 mm microincision.E The AT LARA has a plate-haptic design that might result in more tilt or displacement than IOLs with a loop-haptic design.25

Nondiffractive Optics

The SIFI Mini WELL (SIFI MedTech Srl) is a one-piece aspheric biconvex hydrophilic hydrophobic copolymer IOL implanted via a disposable injector through a 2.4 mm incision.G The IOL is available in a toric version for patients with astigmatism greater than 0.75 diopter (D). The IOL has a nondiffractive design that comprises the following 3 zones: a central zone with positive spherical aberration, a middle zone with negative spherical aberration, and an outer monofocal zone (Figure 1, D). Combined, these zones provide EDOF through asphericity.12,G Patients with small pupils might not be good candidates for the SIFI Mini WELL IOL.G

CLINICAL PERFORMANCE

Comparisons of the EDOF IOL technologies are challenging because of the variations in methodology and reported outcome measures across studies. However, despite differences in IOL design among models, in general EDOF IOLs provide good to excellent visual acuity at distance, improved intermediate visual acuity compared with monofocal IOLs, and functional near visual acuity (Table 1).13,15–24,26–34,F The clinical performance for each type of EDOF IOL technology is described in the following sections.

Table 1-a
Table 1-a:
Summary of extended depth-of-vision technologies and clinical outcomes. Only distance-corrected visual acuities are reported because uncorrected vision can be confounded by residual refractive errors.
Table 1-b
Table 1-b:
Summary of extended depth-of-vision technologies and clinical outcomes. Only distance-corrected visual acuities are reported because uncorrected vision can be confounded by residual refractive errors.

Small-Aperture Design

In a prospective case series of 12 patients who received the small-aperture IC-8 IOL,15 the percentages of patients achieving 20/32 monocular corrected distance visual acuity (CDVA), distance-corrected intermediate visual acuity (DCIVA), and distance-corrected near visual acuity (DCNVA) improved from 67%, 58%, and 8%, respectively, preoperatively, to 100%, 100%, and 83%, respectively, by 12 months after implantation. The defocus curve results showed that all patients had 20/40 or better visual acuity between +0.50 D and −1.50 D of defocus and more than 50% of patients had 20/40 or better visual acuity at +2.00 D and −2.00 D of defocus.15

In a comparative study of patients who received the IC-8 IOL in the nondominant eye (n = 105) and an aspheric monofocal IOL in the fellow eye (n = 105), most patients (>95%) achieved a binocular CDVA and DCIVA of 20/32 or better by 6 months and 54% achieved a binocular DCNVA of 20/32 or better.17 In that study, the monocular mesopic contrast sensitivity with and without glare was better in eyes with the monofocal IOL than in those with the IC-8 IOL (with glare, P < .001 for 1.5 cycles per degree [cpd], 3.0 cpd, and 6.0 cpd; without glare, P < .003 for 1.5 cpd, 3.0 cpd, 6.0 cpd, and 12.0 cpd).17 Differences in visual outcomes for bilateral implantation vs contralateral implantation of the IC-8 IOL were evaluated in a small number of patients (n = 17).16 The defocus curves showed better performance at intermediate and near distance for patients with bilateral implantation (n = 6) than for those with contralateral implantation (n = 11), although the difference in visual acuity was not significant.

Bioanalogic Design

At present, clinical data for the bioanalogic IOL WIOL-CF are limited. In a prospective study of 25 patients, 88% gained one line or more of CDVA during a 12-month postoperative period (mean CDVA 20/25 Snellen) and 72% achieved a UNVA and uncorrected intermediate visual acuity of 20/25 or better by the 12-month postoperative visit.20 A retrospective case series reported similar results for 20 patients who had an improvement from the preoperative CDVA; 70% of patients achieved a UNVA of 20/25 Snellen.19 Because the refractive target was unknown, it is not clear whether the improvement in visual acuity at near was a result of residual refractive errors. In a registry of 48 patients who received bilateral WIOL-CF IOLs, the mean binocular distance-corrected visual acuity was measured 6 months postoperatively; the mean CDVA was 0.01 logarithm of the minimum angle of resolution (logMAR) ± 0.02 (SD), the mean DCIVA at 70 cm was 0.11 ± 0.10 logMAR, and the mean DCNVA was 0.27 ± 0.12 logMAR.18 However, larger comparative studies of the WIOL-CF must be performed to fully characterize the performance at various distances.

Diffractive Optics

Several studies have evaluated the diffractive Tecnis Symfony EDOF IOL, and comparable results have been reported across studies for postoperative CDVA.13,23,27,28,30,G In a prospective noncomparative study of 26 patients who received bilateral implantation of the Symfony EDOF IOL, the binocular defocus curve between 0.00 D and −1.50 D showed a visual acuity range from −0.05 to 0.02 logMAR.22 In this study, the contrast sensitivity was 1.56 ± 0.37 Weber log units, 0.86 ± 0.12 Weber log units, and 0.78 ± 0.12 Weber log units for photopic, mesopic, and mesopic with glare conditions, respectively.22 The performance of the Symfony EDOF IOL was compared with that of a monofocal IOL in a prospective, randomized clinical trial (Symfony, n = 148; monofocal, n = 150).G The binocular CDVA was similar for the Symfony IOL and monofocal IOL, with all patients in each group achieving a CDVA of 20/32 or better at 6 months. A higher percentage of patients in the Symfony group (91%) than in the monofocal group (35%) achieved a binocular DCNVA of 20/40 or better. Overall, contrast sensitivity performance was worse with the Symfony IOL than with the monofocal IOL, with reduced contrast observed at spatial frequencies from 1.5 to 18.0 cpd. At 12.0 cpd under mesopic conditions with glare, the Symfony IOL had lower median contrast sensitivity scores than the monofocal IOL.G,H

In two prospective studies of patients who received the AT LARA 829MP IOL, a visual acuity of 0.3 logMAR or better was achieved between +1.00 D and −2.00 D of defocus.21,34 Contrast sensitivity was lower at 12.0 cpd and 18.0 cpd than at 3.0 cpd and 6.0 cpd; however, further clinical data are needed to assess the contrast sensitivity with the AT LARA IOL compared with that with monofocal IOLs.34

Nondiffractive Optics

Recently, the performance of the aspheric Mini WELL EDOF IOL was evaluated in a single-arm study and in two comparative studies (one monofocal comparison; one multifocal comparison).31–33 In all 3 studies, the defocus curve showed a gradual decline in visual acuity as the negative defocus was increased.31–33 In the single-arm prospective study (n = 97), the monocular defocus curve showed that visual acuity of 20/40 or better was obtained with the aspheric EDOF IOL between +1.00 D and −2.00 D of defocus.32 Similarly, patients in the monofocal comparative study who received the aspheric EDOF IOL (n = 25) had visual acuity of 20/30 or better between +1.00 D and −2.00 D of induced defocus, whereas those who received an aspheric monofocal IOL (n = 25) had a visual acuity of 20/30 or better between +1.00 D and −1.00 D.31

Compared with the aspheric monofocal IOL, the aspheric EDOF IOL provided better monocular and binocular near visual acuity (P < .01) and intermediate visual acuity (P < .001); however, the monocular CDVA was significantly better in the monofocal group (P < .05).31 The CDVA was similar for the aspheric EDOF IOL and a diffractive multifocal IOL.33 This result suggests that the depth-of-focus expansion might be accompanied by less-than-optimum distance vision compared with the results obtained with monofocal IOLs.

Contrast sensitivity at higher spatial frequencies was lower for patients with the aspheric EDOF IOL than for those who received an aspheric monofocal IOL, with a significant difference at 18 cpd (P = .01).31 However, no significant difference in contrast sensitivity was observed between the EDOF IOL and multifocal IOL.33

REGULATORY ASPECTS

In 2014, the U.S. Food and Drug Administration (FDA) convened a workshop to discuss establishing standardized endpoints, including patient-reported outcome measures and safety assessments, for all premium IOLs.I,J The workshop also introduced a new category of premium EDOF IOLs. Since then, the American National Standards Institute Z80 and International Organization for Standardization TC7 have begun drafting guidelines for demonstrating the safety and effectiveness of EDOF IOLs during clinical trials.35

The American Academy of Ophthalmology (AAO) convened a task force in 2016 to generate a consensus statement for EDOF IOLs that provided benchmarks and recommendations for classifying an implant as an EDOF IOL and evaluating its performance (Figure 2).36 An additional aim was for the application of standardized testing criteria to increase the availability of objective data for the FDA and clinicians, ultimately increasing the ease of device approval.I The criteria placed an emphasis on testing IOLs under conditions that reflected the daily activities of patients, such as intermediate vision and a range of lighting (photopic, mesopic, and glare).36 This set of standardized criteria established by the AAO will aid investigators in evaluating current and developing EDOF IOL technology.

Figure 2
Figure 2:
Summary of American Academy of Ophthalmology task force recommendations (ANSI = American National Standards Institute; DCIVA = distance-corrected intermediate visual acuity; EODF = extended depth-of-focus; IOL = intraocular lens; ISO = International Organization for Standardization; logMAR = logarithm of the minimum angle of resolution).

DISCUSSION

Extended depth-of-focus IOL technology constitutes an important addition to the IOL portfolio. Ideally, this technology will bridge the clinical shortcomings between monofocal and multifocal IOLs. Many types of EDOF IOL technologies are being developed to address this unmet need. The AAO consensus statement has provided a framework to test the performance of each type of EDOF IOL technology and generate clinically meaningful data that can be compared across IOL categories.

Extended depth-of-focus IOL technology is a welcome addition for surgeons worldwide to address the evolving visual needs of patients, and several existing technologies provide improvement in visual acuity at intermediate and near distances compared with monofocal IOLs. However, a review of published data shows that current technologies fall short in providing monofocal-like distance visual quality or provide contrast sensitivity that is significantly poorer than with monofocal IOLs. These factors might preclude these technologies from being optimum EDOF solutions for the correction of presbyopia.

It is becoming increasingly evident that the true test of the technology will be how well it provides monofocal-like distance visual quality, specifically visual disturbance profiles and EDOF at intermediate distance. From an optical standpoint, nondiffractive technologies that do not split light might be expected to best mitigate this gap; however, definitive clinical results from well-controlled studies are needed to confirm this hypothesis.

Catherine DeBrosse, PhD, and Lauriaselle Afanador, PhD, Complete Healthcare Communications, LLC (a CHC Group company), North Wales, Pennsylvania, USA, provided editorial support for development of this manuscript, funded by Alcon Vision LLC, Fort Worth, Texas, USA.

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