Multifocal and Extended Depth of Focus IOLs : Time to change the name ...

Multifocal and Extended Depth of Focus IOLs : Time to change the name of the game?

Radhika Rampat, MBBS BSc (hons), Moorfields Eye Hospital NHS Trust, radhika.rampat@, @radhikarampat

Damien Gatinel Author, MD, PhD, Departmental Head of Anterior Segment at Rothschild Foundation Hospital, gatinel@, @DocteurGatinel

Author's financial disclosures

Rampat: No Financial Disclosures

Gatinel: Consultant for Physiol, Nidek, Heidelberg Engineering

A little less than 15 years ago, there were already a wide range of intraocular lenses with their main characteristics being derived from the material used (hydrophobic or hydrophilic) and the degree of spherical aberration induction. Long gone are the days when a cataract surgeon was content with choosing a model and a power of monofocal intraocular lens for their patient. The refractive dimension of both cataract and clear lens extraction surgery has become so significant, that a majority of the pre-operative consultation is dedicated to discussing the desired correction strategy, depending on the patients' degree of expectation when it comes to spectacle independence postoperatively.

Diffractive bifocal implants such as Restor (Alcon Laboratories, Fort Worth, TX) and Tecnis bifocal (Johnson & Johnson, New Brunswick, NJ) have allowed patients to benefit from simultaneous correction of far and near vision. (1) Trifocal implants were introduced in 2010 to add intermediate vision, a need which had grown in importance as computers screens and digital tablets invaded our daily lives. (2) Previously we had to discourage patients with preexisting corneal astigmatism from premium lenses or accept unpredictable results of LRIs (Limbal relaxing incisions), but now with toric versions we are able to correct for both presbyopia and astigmatism.

As the multifocal platforms expanded, a subset of surgeons were occasionally dissatisfied with the multiple distinct foci, leading to varying degrees of photic phenomenon including glare. They wanted the advantages of multifocality, without the inherent disadvantages of splitting and sharing the light entering the eye across several foci. It is perhaps to satisfy these expectations, that a new category of lenses, known as "EDoF" short for "Extended Depth of Focus" were added to the panorama of so-called premium intraocular lens implants. Another abbreviation used for the same class was, ERoV or Extended Range of Focus IOLs.

In 2016, the Tecnis Symfony IOL (Abbott Medical Optics, now Johnson and Johnson, Santa Ana, California) became the first U.S. Food and Drug Administration (FDA) approved lens in its class. (3) This implant was immediately put forward as a solution to the problem of multifocality, with potential for reducing undesirable visual phenomena. It has since been joined by a plethora of intraocular lenses whose promoters claim an extension of the depth of focus, and portray this as an innovative technology - often distinct from diffraction. When this new class of IOLs were presented, there was a premise that they reduced dependence on glasses postoperatively, declaring better visual acuity across a wider range of distances. Officially, the American National Standards Institute (ANSI) define EDOF IOLs as implants that provide increased depth of focus compared to a monofocal IOL, with statistical superiority when it comes to photopic intermediate vision and being non inferior for distance vision.

There has been a degree of confusion ever since, fuelled by the creativity of some lens manufacturers to present their products in the best light whilst disclosing the least amount of technical information likely to identify the actual optical principles involved.

For example, the Tecnis Symfony was initially presented as an innovative concept, different from that of multifocal diffractive lenses, and based on an original diffractive mechanism making it possible to induce a "useful focus elongation" towards intermediate vision. It was certainly advantageous for the marketing team to bar the term "multifocal" from its sales pitch, which has now become associated with a higher risk of halos and glare. Studies have since revealed that the technology used to generate an increase in the depth of field with the Symfony implant was indeed multifocal diffractive, because it was based on the induction of an additional focal point in the intermediate vision, embellished with the induction of a

negative longitudinal chromatic aberration for the far and intermediate foci intended to compensate for the corneal chromatic aberration. Despite a marketing position aimed at differentiating itself from bi- or trifocal multifocal lenses, the Symfony, like other lenses introduced on the market since, is based on a diffractive technology which in principle generates a discrete distribution of light energy in several discrete foci.

Another source of confusion when it comes to these lenses is that EDOF IOLs are presented as a solution to presbyopia, whilst their near vision performance is notably insufficient to allow an eye corrected for distance vision to also benefit from independence from reading glasses for near vision. The challenges linked to conquering a market share and the desire to differentiate their own technology, by having an innovative facet, largely explains the confusion that currently reigns within the "premium" lens market.

Understandably, some manufacturers of these lenses are not very vocal about the precise description of the optical principles involved, whilst being creative on a marketing level to position themselves as completely original solutions. For example, the term `echellettes' is another word for diffractive gratings, another called `X-Wave technology' is presented as a "wavefront stretching and shaping technology " induced by a 1 micron plateau, supporting a curved zone. Insofar as it may actually be possible to stretch a wavefront ? which is a theoretical construct, this interesting description could only refer to a central sectoral zone effect with blended zones of an essentially bifocal lens. Similarly a newly coined `continuous transitional focus' lens really corresponds to a sectorial bifocal refractive lens.

If we study more carefully and as exhaustively as possible, what the term "EDoF" or "ERoV" encompasses today, we find that it covers a wide variety of optical principles. These include IOLs with reduced pupil aperture (pinhole effect), diffractive IOLs and aspherical and / or multizone refractive IOLs.

Lens (Manufacturer)

Commentary

Vivity (Alcon)

Isopure GF (Physiol)

EyHance (J&J)

LENTIS Comfort (Oculolentis) ReZoom (J&J, previously Abbott) MiniWell ready (SIFI Medtech) Triumf POD L/GF (Physiol)

AT LARA (Zeiss)

EDoF, Refractive, Monofocal, pupil independent, +1.53 defocus range EDoF, Refractive, Monofocal, pupil independent, +1.00 defocus range EDoF, Refractive, Monofocal, pupil dependent, +1.30 defocus range EDoF, Refractive, Bifocal, pupil independent, +1.5 D Add EDoF, Refractive, Bifocal, pupil dependent, +3.5 D Add EDoF, Refractive, Bifocal, pupil dependent, +2.5 D Add EDoF, Refractive-Diffractive, Trifocal, pupil dependent, +3.5 D Add, +1.75 D Intermediate EDoF, Diffractive, Trifocal, pupil dependent, +1.9 defocus range

Tecnis Symfony (J&J)

ERoV, Diffractive, Trifocal, pupil dependent, +1.5 defocus range

Synergy (J&J)

EDoF, Diffractive, Bifocal, pupil independent, +3.0 defocus range

Xact (Santen)

Diffractiva Diff-Aa (HumanOptics)

Artis Symbiose ? Mid and Plus (Cristalens) Lucidis (Swiss Advanced Vision) Eden (Swiss Advanced Vision) Harmonis (Swiss Advanced Vision)

EDoF, Diffractive, Monofocal, pupil independent, +1.5 defocus range EDoF, Refractive-Diffractive, Bifocal, pupil dependent, +3.0 defocus range, +3.5 D Add Diffractive EDoF and Bifocal lenses, bilateral implantation, binocular defocus range +3.75, pupil independent EDoF, Refractive, pupil dependent, +3.0 D Add EDoF, Refractive-Diffractive, pupil dependent EDoF, Refractive-Diffractive, pupil dependent, +2.5 to 3.5 D Add

LuxSmart (Bausch & Lomb)

EDoF, Refractive, pupil dependent

Acunex Vario (Topcon)

EDoF, Refractive sectoral Bifocal, +1.5 D Add

InFo (Vision Matrix)

EDoF, Refractive-Diffractive

Table 1: EDoF Lenses ? some of these intraocular lenses lack published or presented data

as far as we are aware, but are available on the market.

Further to this, it would be desirable to provide clarification regarding this class of IOLs. After presenting the data above, we believe there is a rationale for changing the terminology of this class of lenses. There is a growing consensus within the society of cataract and refractive surgeons internationally, that this is indeed required. We have disrobed each lens design into its basic components creating a classification system, in order to demystify this new class of Premium IOLs. We proposed this in our recent review article in Ophthalmology (4) and base it on the theoretical optical principles.

Proposed Classification EDoF effect

Effect Used Elongate continuous range of focus by refraction (e.g. negative spherical aberration, refractive zones) and/or induce intermediate foci by diffraction +/- reduction of chromatic aberrations

Examples Comfort (r), ReZoom (r), MiniWell Ready (r), Symfony (d), Synergy (d), Diff Aa (d), Triumf (d), AT LARA (d)

True EDoF Enhanced Monofocal

Elongate continuous range IC-8, Morcher

of focus by Pinhole effects

Diffractive or refractive

Vivity (r), Isopure*(r), Xact

technology

(d), EyHance*(r)

Table 2: EDoF proposed classification system (* = Aspherical continuous designs, r = refractive zonal, d = diffractive)

When we review the new nomenclature, it becomes clear that only the pinhole and aspheric lenses do not clearly belong to the category of "multifocal" IOLs. On the other hand, diffractive IOLs are by design providing distinct foci, linked to the diffraction orders that diffraction of light generates. Hence, they still belong under the "multifocal lenses" umbrella.

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