Are extended-depth-of-focus IOLs hitting the visual sweet spot?

February 29, 2016

Article

Current IOL designs offer a variety of optical options for the correction of presbyopia. Regardless of the principal of correction, compromise is required. However, a new class of IOLs, currently referred to as extended-depth-of-focus IOLs (EDOF-IOLs), seems to be generating very satisfied patients.

Reviewed by Professor Sunil Shah

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I categorise presbyopia-correcting IOLs into three categories: multifocal, accommodating and EDOF-IOLs. The multifocal category encompasses diffractive optic lenses that split light between distance, intermediate and near. The user can focus on only one distance at a time, leaving the blur from the other focal points to sometimes cause halo and glare. The accommodating IOL needs either forward-backward axial movement or flexibility in lens shape or thickness to effect change in focal point from distance to near vision. However, capsular fibrosis can impact the presbyopia-correcting capability and induce asymmetric vaulting, leading to lens tilt. This makes the currently available accommodating IOL challenging to handle at times.

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Although premium multifocal lenses offer patients good results, market penetration of these lenses has remained relatively low, at 7.2% of cataract surgeries. In fact, monovision with standard IOLs is nearly three times more common than IOLs offering presbyopia correction,¹ most likely because of the shortcomings associated with multifocal IOLs, such as glare and halos.

The EDOF class of IOL is an emerging technology that employs new methods to improve the range of vision without splitting light rays. The goal of the EDOF-IOL is to address patient expectations and demand for presbyopia correction without compromising functional vision across all distances. As opposed to the single focal point of monofocal lenses or two distinct foci for multifocal lenses, an EDOF-IOL smooths out the dips in the defocus curve by creating one elongated focal point. There are currently three different lenses that can be classified as EDOF-IOLs, which employ radically different technology.

Small aperture design

Based on the KAMRA™ corneal inlay (AcuFocus, Inc., United States) technology, the IC-8™ lens (AcuFocus, Inc., United States) features an embedded opaque annular mask that blocks unfocused peripheral light rays while allowing paraxial light rays through its central aperture. The small aperture design creates an extended, continuous range of functional vision across all distances and is much more forgiving to a missed target refraction.

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Clinical trials demonstrated a mean visual acuity of 20/20 at distance and intermediate, with 100% of patients achieving 20/25 target-corrected intermediate visual acuity and target-corrected distance visual acuity.⁸ When combined with –0.75 D of myopia, patients can achieve the equivalent of 2.25 D of add power across an extended range of vision. Not only does this allow for natural visual adjustment, but the mask embedded in the IOL does not decrease binocular contrast sensitivity even under mesopic conditions.² In my experience, the lens is well tolerated, with patients reporting similar visual symptoms to those in their untreated fellow eye.

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Imaging through the IOL mask’s central aperture is possible, with minimal differences noted between the IC-8 IOL and fellow eyes with an implanted monofocal IOL.⁹ Technicians reported that ocular assessments were successful and required no different instructions for eyes with the IC-8 IOL. Vitreoretinal surgery in eyes implanted with the IC-8 IOL can be performed with ease and good visibility,^{10, 11} making the IC-8 IOL suitable for ametropic, emmetropic and post-LASIK presbyopes, as well as monofocal pseudophakic patients.

The IC-8 IOL has received CE Mark approval and is available in select European markets. It has not been approved for use in the United States.

Echlette

Echelette

The proprietary echelette design of the TECNIS® Symfony IOL (Abbott Medical Optics, Inc.) forms a step structure whose blaze angle elongates the focus of the eye to produce an extended range of vision.³ This enhanced design is combined with achromatic technology that corrects longitudinal chromatic aberrations. This results in sharper focus of light and increased contrast sensitivity. When combined with correction of spherical aberration, it increases retinal image quality without negatively affecting depth of focus.^4,5

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Studies conducted on the Symfony IOL showed sustained mean visual acuity of 20/20 or better at distance and intermediate, sustained through 1.5 D of defocus, and a 1.0 D increase in range of vision throughout the defocus curve.6 In one study, 97% of 31 subjects implanted with the Symfony IOL indicated that they would elect to have the lens implanted again.⁶

The Symfony has received the EU Mark of approval and is available in select European and Asian countries. It has not been approved for use in the United States.

Bioanalogic IOL

Unique in its design and use of materials is the WIOL-CF (Medicem) polyfocal IOL. Produced from a proprietary hydrogel designed to mimic the properties of the natural young crystalline lens, the clear lens enables polyfocal accommodation within a continuous range from near to distant focus.

Multicentre observational registry database studies indicated excellent visual acuity for far and intermediate vision, and contrast sensitivity exceeding population norms under all light conditions. Clinical studies indicate that the lens maintains its transparency for up to seven years following implantation. The registry recorded nearly 1.0 for uncorrected distance visual acuity, J1+ for uncorrected intermediate visual acuity, on average, and near vision within the range of social reading for all patients (mean uncorrected near visual acuity J2.6). Patient satisfaction is high, with only 4% of patients reporting optical phenomena such as halo/glare. Ninety-three per cent of patients report near spectacle independence and 89% were satisfied with their outcome.⁷

The WIOL-CF is currently under evaluation in Europe, Mexico and parts of Asia. It has not been approved for use in the United States.

Making the most of EDOF-IOLs

Because the EDOF-IOL does not split light, patients experience less glare and halos; however, the intensity of near vision does not match that provided by a multifocal lens. To compensate for the decrease in near vision in patients implanted with an EDOF-IOL, I often use a mini-monovision strategy, targeting one eye for distance and the other for slight myopia of –0.75 to –1.0. This gives good near vision, and the decrease in far vision from the low myopia is not as pronounced as the decreased contrast experienced by patients who are implanted with a multifocal IOL.

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Typically, patient complaints for the multifocal IOLs are centred on quality of vision: far vision is not sharp enough or they may experience decreased contrast, glare or halos. Contrast sensitivity testing in EDOF-IOLs demonstrates that, when the range of vision is extended, there is a slight decrease in contrast compared with a plain monofocal lens, but it is much better than that experienced with a multifocal lens. Most patients feel that this slight lack of contrast sensitivity is more than compensated by the extended range of vision possible. The EDOF-IOLs are also available to patients deemed unsuitable for multifocal lenses, such as those who have had previous LASIK surgery or those with diabetic retinopathy or glaucoma.

Conclusion

The emerging EDOF-IOL category of lenses has the potential to change presbyopia correction. In addition to taming the issue of halos and glare associated with multifocal lenses, these products offer exciting options to the patient previously excluded from the multifocal demographic. I expect the ongoing studies to further demonstrate the efficacy and versatility of these lenses, making limited spectacle dependence a possibility for a large population of patients.

References

1. ASCRS Clinical Survey. Eyeworld. http://eyeworld.org/supplements/2014_ASCRS_clinical_survey.pdf [Accessed December 20, 2014].

2. S. Manzanera et al., Presented at ESCRS, London, 2014.

3. TECNIS® Symfony DFU.

4. H.A. Weeber and P.A. Piers. J. Refract. Surg. 2012; 28(1): 48-52.

5. P. Artal et al., Opt. Express 2010; 18(2): 1637-1648.

6. 166 Data on file. Extended range of vision IOL 3-month study results (NZ).

7. D. Sivekova et al., ESCRS, Amsterdam, 2013.

8. Data courtesy of Robert Ang, MD

9. Data courtesy of Amadeo Veloso, MD.

10. Results from an animal study conducted by Dr Barry Kupperman, professor of ophthalmology and biomedical engineering; chief, Retina Service; vice-chair, Clinical Research, Ophthalmology at UC Irvine School of Medicine.

11. Personal experience in one patient from Professor Burkhardt Dick, MD.

Robert T. Ang, MD

E: rtang@asianeyeinstitute.com.

Robert T. Ang, MD, specialises in cornea and refractive surgery, glaucoma, and comprehensive ophthalmology at the Asian Eye Institute, located in the Philippines.