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Optical quality and retinal quality are essential elements of the performance of any IOL. Physicians can define success by determining how much of each issue is involved in any procedure.
This article was reviewed by Dr. Jorge Alio, MD, PhD
Presbyopia-correcting IOLs are among the most important recent innovations in cataract and refractive surgery. A number of options are available to satisfy a growing patient population that demands spectacle-independent intermediate vision in addition to distance vision.
“These technologies have resulted in tremendous changes in clinical practice,” said Jorge Alio, MD, PhD. “Selecting the appropriate presbyopia-correcting IOL is now a challenge for most ophthalmologists.”
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Presbyopia-correcting IOL choices
The current trends in the new multifocals (mf) IOLs presbyopic IOLs are diffractive and refractive models. The former have reached a high standard of clinical performance and are designed to eliminate halos and glare by decreasing the near optical power, according to Dr. Alito, professor and chairman of ophthalmology, VISSUM, Instituto Oftalmologico de Alicante, Universidad Miguel Hernandez, Alicante, Spain.
“The new models combine manipulation of aberrations with multifocality and are referred to as a new hybrid mfIOL,” he explained.
Extended-depth-of-focus (EDOF) IOLs
This is the most recent technologic advance to become available for treating presbyopia.
According to Dr. Alio, these lenses manipulate the IOL’s spherical aberration (SA) so that the incoming light waves are elongated, which eliminates both the overlap of near and far images and the halos. These IOLs were designed to improve the intermediate vision. An associated limitation is the decreased retinal image quality, and for this reason the near vision add is limited to about 1 D.
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A number of companies have investigated this approach. Dr. Alio mentioned the Wichterle IOL (Medicem), a continuous-focus model that manipulates SAs. The idea behind this single-piece polyfocal hyperbolic optic with no haptics was that it mimicked the natural young crystalline lens, with the possibility of accommodation; however, poor visual quality forced the company to abandon this model. The Mini Well monofocal IOL (Sifl), another EDOF IOP, induces SAs in specific areas of the optic to increase the depth of focus and generate multifocality.
Another way of achieving the EDOF effect is use of the pinhole effect. The IC-8 (AcuFocus, Inc.), which uses a small aperture, achieves an extended and continuous range of vision using an embedded opaque annular mask of 1.36 mm that blocks unfocused paracentral light rays and permits paraxial light rays to enter. The XtraFocus Pinhole Implant (Morcher) is based on the same principle using a smaller pinhole of 1.3 mm.
The EDOF IOLs are approved only for distance and intermediate vision. Patients will need at least 1 D of correction for near vision. Postoperative patient dissatisfaction is attributed to intolerance of the total induced aberrations. If there is excessive EDOF, the quality of vision is affected. The explantation rate is higher.
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The disadvantages of the EDOP IOLs led to the development of mfIOLs with an EDOF system. “The multifocality and EDOF characteristics are not exclusive of each other,” Dr. Alio noted.
The hybrids balance three interrelated factors: visual acuity, depth of field, and dysphotopsias. The increasing depth of field and decreasing multifocality are tempered to avoid the negative impact on the near vision. The Tecnis Symfony (Johnson & Johnson Vision) was the first such IOL with a 1.75-diopter near add with increased depth of focus. The AcrySof IQ panoptix (Alcon) is a mfIOL that adds a negative SA on the anterior surface to compensate for the positive SA of the human cornea.
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New refractive mfIOLs
The refractive IOLs offer new optical profiles, as seen in the Precizon Presbyopic (Ophtec), and new materials, as exemplified by the Acunex Vario AN6V (Oculentis).
The former IOL offers constant progressive focus between two focal points and no light loss. The latter IOL uses the previous optical technology of focal IOLs without a varifocal lens with new biometry that results in a different profile and prevents opacification; the IOL incorporates changes in SA and haptics and offers EDOF.
“Some of the so-called EDOF IOLs available today are really mfIOLs with low power in which part of the rest of the power has been withdrawn to avoid the overlapping of images and the consequent halos and glare,” Dr. Alio explained. “IOLs should be referred to as EDOF only when they do not have either refractive or diffractive added multifocality. If so, they should be considered hybrid mf/EDOF IOL.”
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The Care Group introduced the Presby IPCL, a trifocal diffractive optic that is implanted in the sulcus to treat patients with advanced presbyopia.
Add-on piggyback mfIOLs are another option. The Sulcoflex (Rayner), a hydrophilic acrylic implanted in the sulcus. The results have shown that this IOL implanted atop a previously implanted monofocal IOL offers positive results. Other such IOLs include the Restor (Alcon), Trifocal (Zeiss), and Mplus (Oculentis).
An important question that remains unanswered is whether accommodation can be restored by an IOL. The bottom line thus far is that IOLs have not provided accommodation and have failed to provide an alternative to monofocal IOLs. “The question remains about whether these IOLs should be placed inside or outside the capsular bag. Answering this question could determine the future of accommodative IOLs,” he said.
Dr. Alio and colleagues have investigated this problem in a primate model and determined that there is no accommodative force in the capsular bag related to ciliary body stimulation 6 months postoperatively, which demonstrated that the sulcus and not the bag is the place for an accommodative IOL. The Lumina (Akkolens), an sulcus-based accommodative IOL has so far produced good results. The results indicated that this IOL restored visual function, accommodation, and contrast sensitivity after cataract surgery with no affect on the contrast sensitivity, he reported.
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Dr. Alio emphasized issues surrounding presbyopic IOLs.
“Optical quality and retinal quality are essential elements of the performance of any IOL, but visual performance involves neuroprocessing and is a cortical perception,” he said. “How much of each is involved? To address this, we must define success.”
Dr. Alio explained that the most relevant factor is the quality of the retinal image. Study of the defocus curves has made it clear that EDOF IOLs are insufficient for near vision and good for far vision. He noted that new presbyopic IOLs represent opportunities for the present and future, and urged clinicians to choose their IOLs carefully using evidence-based information.
“To use the EDOF, mfIOLs, and hybrids properly, we must be aware of what they offer and how they fit our patients’ needs,” he concluded. “There currently is confusion in terminology caused by an inappropriate commercial bias, leading to misinformation for practicing clinicians. Artificial intelligence IOLs are raising new expectations for near vision restoration in pseudophakia.”
Read more by Lynda Charters
Jorge Alio, MD, PhD
Dr. Alio is a consultant to numerous lens manufacturers, many of which have provided funds for research projects.