IOL iterations abound, but shape-changing accommodating lens remains end goal
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Healio | OSN focuses on a topic dear to my heart, premium IOLs.
In 2013, Malvina B. Eydelman, MD, director of the FDA’s Division of Ophthalmic and Ear, Nose and Throat Devices, chaired an expert panel titled “Developing Novel Endpoints for Premium Intraocular Lenses Workshop.” The result of this workshop was the placement of all IOLs into five main categories.
In the first category were spherical and aspheric monofocal (M) IOLs that demonstrated less than 0.5 D depth of focus. In multiple well-controlled clinical trials, best corrected, a M IOL provides a patient with 20/20 vision at distance, 20/40 vision at intermediate and 20/70 vision at near. Enhancements to the early-generation spherical M IOLs include aspheric optics and hyper-aspheric optics, but depth of focus remains under 0.5 D.
In the second category, extended depth of focus (EDOF) IOLs, clinical trials including defocus curves must confirm an increased depth of focus measuring at least 0.5 D along with improved intermediate and near vision. In patients implanted with an EDOF IOL, when best corrected for distance, visual acuity generally measures 20/25 at intermediate and 20/40 at near.
In the third category are presbyopia-correcting multifocal (MF) IOLs, refractive, diffractive and refractive/diffractive, that provide even greater improvement in intermediate and near vision. In both EDOF and MF IOLs, some loss of distance vision, reduced contrast sensitivity and increased night vision symptoms such as glare, starbursts and halos are the penalty paid for improving intermediate and near vision.
The fourth category is an accommodating (ACC) IOL. Today, to be labeled as an ACC IOL, one must demonstrate at least 1 D of accommodation that improves intermediate and near vision and is dynamic under the patient’s control. The improved intermediate and near vision must be secondary to active accommodation and not so-called pseudoaccommodation.
In a fifth category is light adjustable IOLs, and potentially a light adjustable IOL optic could be utilized in any of the first four IOL categories.
The light adjustable, EDOF, MF and ACC IOLs are all premium IOLs eligible for an additional charge to the patient when astigmatism, presbyopia or significant higher-order aberrations are treated.
I will now share a few personal observations after 45 years of immersion in premium IOL design and clinical investigation.
From 1980 to 1992, I served as chief medical officer at 3M Vision Care. Together with an amazing team of scientists, we developed the 3M (model 815E) diffractive MF IOL, the first of many IOLs using diffractive optics and the first MF IOL. The clinical trial of the 3M MF IOL in the U.S. included 671 patients and collected a diverse set of information including personality profiles of the patients implanted using the validated Minnesota Multiphasic Personality Inventory. An important learning in this clinical trial was the fact that patient personality had no correlation with patient satisfaction. The most demanding patients could be happy with their MF IOL, and conversely, the least demanding patients could be unhappy. The only predictor of patient satisfaction in the 3M MF IOL clinical trial was the quality of the refractive outcome generated by the surgeon. The closer the patient was to plano postoperative with no residual sphere or cylinder, the higher the patient satisfaction. While controversial, I believe for refractive cataract surgery, the quality of the surgery performed is far more important than patient or even IOL selection. If a refractive cataract surgeon hits the patient’s preferred post-surgical refractive target, they can make even the most demanding patient happy.
The 3M MF IOL was a three-piece non-foldable PMMA biconvex posterior chamber IOL and was launched outside the U.S. in 1987. Because a 6-mm incision was required and biometry was less sophisticated than today, most patients had more residual refractive error than ideal, reducing patient satisfaction. Regulatory challenges including the requirement for objective data affirming night driving safety with a 3M MF IOL implanted discouraged 3M, and in 1992, 3M Vision Care was sold to Alcon.
The first MF IOL approved in the U.S. was the Allergan Medical Optics Array in 1997, which used refractive optics. Alcon continued research into diffractive optics for MF IOLs, resulting in FDA approval and launch of the Alcon AcrySof ReSTOR IOL in 2005. This MF IOL combined the benefit of small-incision foldable IOL technology allowing improved astigmatism management along with an apodized diffractive/refractive optic that improved quality of vision.
Today, MF IOLs with diffractive optics have garnered significant market share. Bifocal MF IOLs have been replaced by trifocal and even quadrifocal MF IOLs. However, a surgeon’s ability to generate a refractive outcome close to plano remains a critical factor in patient satisfaction. Improved biometry and the ability to enhance a patient’s refractive outcome with refractive corneal surgery, IOL exchange or more recently a light adjustable optic have greatly improved both surgeon and patient acceptance of premium IOLs.
The first IOL to achieve FDA approval in the EDOF IOL category was the Abbott Symfony IOL in 2016, and many more approvals have occurred in the past 7 years. The first and last accommodating IOL approved in the U.S. was the eyeonics Crystalens in 2003. Since that time, the requirements for an accommodating IOL label have been raised by the FDA. Attempts to achieve IOL accommodation through single- or dual-optic movement are not able to achieve the levels of accommodation required today for FDA approval.
At present, as discussed in the cover story, IOLs that achieve accommodation in a similar fashion to the natural lens through a change in shape show the most promise. While evidence confirms that the ciliary muscle continues to respond throughout life to an accommodative stimulus, the force and lever generated are small. As the natural lens ages, it becomes thicker and less malleable, reducing accommodation to zero by age 65 to 70 years. After removal and replacement of the natural lens with an IOL, the posterior capsule surrounding the lens also becomes less malleable with time as the retained capsule becomes fibrotic. If the force generated during accommodation is applied to an inelastic natural lens or an inelastic lens capsule, accommodation is reduced or eliminated.
Two key strategies are being employed to overcome this challenge. In one strategy, the remaining peripheral anterior capsule is kept separate from the posterior capsule to reduce capsular fibrosis. In another strategy, accommodative force is applied to a shape-changing in-the-bag IOL optic through a lever that impacts the ciliary muscle itself. Both strategies are showing promise.
I am optimistic a shape-changing accommodating IOL that can achieve 1 D or more of accommodation will be developed in the next 5 years. In my opinion, for it to replace the current market-leading diffractive trifocal and quadrifocal IOLs, a next-generation accommodating IOL will have to deliver visual acuities of 20/25 or better at distance, intermediate and near with higher quality of vision and reduced night vision symptoms when compared with a MF IOL. Ideally, the next generation ACC IOLs will eventually be manufactured with an easily exchangeable or adjustable power optic.
I have not undergone cataract surgery yet, and I remain hopeful that the IOL I receive will be an adjustable ACC IOL that can give me seamless 20/20 vision distance to near with M IOL-like quality of vision, contrast sensitivity, color perception and no night vision symptoms. Like my patients, I want to see after cataract surgery like I did at age 40 years as a pre-presbyopic emmetrope.
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