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  • Accommodating IOLs: Current Technology, Limitations, and Future Designs

    Cataract/Anterior Segment, Comprehensive Ophthalmology
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    Accommodating IOLs may very well transform the practice of cataract and refractive lens surgery. This is because accommodative IOLs can potentially provide unaided near visual acuity without the optical aberrations and image degradation that may accompany multifocal IOL implantation. Not only will this enhance cataract surgery results, but it will also enable refractive surgeons to offer their patients a procedure that is unhindered by the restrictions of corneal refractive surgery and presbyopia. Accommodating lenses can currently be classified into 3 categories: (1) single-optic, (2) dual-optic, (3) and deformable optic IOLs. This article will explore the available accommodative technologies under these 3 headings including any limitations concerning lens excursion and accommodative amplitude and examine the potential impact of these IOLs on cataract and refractive surgeons and patients.

    Single-Optic IOLs

    The Morcher BioComFold Type 43E, HumanOptics 1 CU, Lenstec TetraFlex, and eyeonics crystalens are examples of single-optic IOLs. Single-optic, accommodating IOLs function by changing their position in the capsular bag during accommodative effort with a resulting increase in the effective power but not the inherent power of the lens. The limitations of these IOLs stem from their inability to move significantly enough to generate large amplitudes of accommodative power that would yield consistently acceptable near visual acuities.

    The Morcher BioComfold 43E is a single-optic/ring haptic lens. During accommodative effort, the ring haptics are brought together resulting in a forward axial movement of the optic with a resultant increase in the functional power of the lens. A recent study using pilocarpine 2% to simulate accommodation and partial coherence interferometry to measure the changes in anterior chamber depth (and, thus, forward movement of the IOL) revealed no more than 0.50 diopters (D) of accommodative amplitude in most cases (J Cataract Refract Surg. 2003;29:669-676). The Morcher BioComfold 43E is not approved by the United States Food and Drug Administration (FDA).

    The HumanOptics 1CU is a hydrophilic, acrylic, foldable, single-piece lens with a biconvex square-edge optic and 4 modified flexible haptics that allow for forward movement of the optic during accommodative effort (Figure 1). In a similar study as that performed with the Morcher BioComfold IOL, median anterior movement of the HumanOptics 1CU after pilocarpine 2% instillation was calculated to result in a refractive change of no more than 0.5 D in most patients (Ophthalmology. 2004;111:1515-1521). Although other studies have demonstrated much higher degrees of accommodative amplitudes, unfavorable results among European ophthalmologists who have utilized this lens will in all likelihood impair its success in the general market. The HumanOptics 1CU is also not FDA approved.

    Image courtesy Burkhard Dick, MD.
    Figure 1. SEM photograph of the HumanOptics 1CU accommodating IOL.

     

    The Lenstec TetraFlex is a square-edged, acrylic IOL with closed-loop haptics designed to move forward during accommodative effort. The lens is currently undergoing FDA clinical trials. Initial reports of close to 100 eyes implanted with this lens have demonstrated that more than 95% of eyes have accommodative amplitudes of more than 1 D, 70% have more than 2 D, and 20% have more than 3 D. There are currently no peer-reviewed publications to substantiate these promising reports.

    The eyeonics crystalens is a 10.5 mm, hinged plate haptic silicone lens with a 4.5 mm optic (Figure 2). It is the only accommodating IOL that has been approved by the FDA. One of the consistent findings in accommodative IOL studies is a disconnect between the measured axial movement of the IOLs and the unaided near acuities. In most studies, axial lens movement is much smaller than would be expected for the functional near vision outcomes. Marchini et al reported the mean anterior axial movement of 20 crystalens IOLs to be only 0.33 ± 0.25mm (J Cataract Refract Surg. 2004;30:2476-2482). Yet, despite a mean accommodative amplitude of 1.08 ± 0.54 D (range 0-2.25), 86% of patients in this study required no correction for near vision during routine daily activities. A more recent study further questioned the validity of this lens’s mechanism of action by demonstrating a mean 151 micron backward shift of the crystalens with pilocarpine 2% instillation (J Cataract Refract Surg. 2005;31:1290-1297).

    Image courtesy Richard S. Hoffman, MD, I. Howard Fine, MD, and Mark Packer, MD.
    Figure 2. Crystalens accommodating IOL in situ.

    Despite a lack of evidence supporting substantial axial movement of the crystalens, data from FDA clinical trials revealed that 26% of patients implanted bilaterally with this IOL were able to function completely without glasses, and 74% of patients were able to function either completely or mostly without glasses. These findings suggest that the accommodating crystalens is a viable alternative to multifocal IOLs in the appropriate patient.

    Dual-Optic IOLs

    The Sarfarazi Elliptical Accommodating IOL and the Visiogen Synchrony are examples of dual-optic lenses. Both of these IOLs utilize a positively powered biconvex front lens connected to a negatively powered concave-convex lens. During accommodative effort, the 2 lens components increase their distance from each other, resulting in increased effective power of the overall lens. The dual-optic design offers potential advantages over single-optic designs in that less lens excursion is necessary with the dual-optic in order to achieve a desired amount of accommodation (Figure 3)(Br J Ophthalmol. 2003;87:1083-1085 & Cataract Refract Surg. 2003;29:2284-2287). Investigators in South America and Europe have reported favorable results with the Visiogen Synchrony (Figure 4), measuring accommodative amplitudes between 0.5-2.5 D. The Synchrony is currently undergoing FDA clinical trials within the U.S. 

    Courtesy Visiogen
    Figure 3. Synchrony IOL versus single optic IOL. Relative accommodative amplitudes with associated forward IOL movement of 19 D.

    Image courtesy Visiogen.
    Figure 4. The dual-optic Synchrony accommodating IOL.

     

     

    Deformable IOLs

    The Medennium Smart IOL, Advanced Medical Optics (AMO) FlexOptic, NuLens, and Power Vision FluidVision IOL are examples of deformable optic IOLs. These types of lenses change their true power during accommodation, and hold the promise of providing higher amplitudes of power change than can be currently achieved with single and dual-optic accommodating lenses. Deformable IOLs are, for the most part, in the preliminary stages of development and animal research.

    The Medennium Smart IOL is a hydrophobic, acrylic IOL that has dimensions (9.5 x 3.5 mm) similar to the natural crystalline lens. The lens is unique, because it is packaged as a thin, solid rod that can be inserted into the eye at room temperature through a microincision (Figure 5). After being placed in the aqueous at body temperature, the Medennium Smart IOL transforms into a soft gel that completely fills the capsular bag and maintains some elasticity.

    Courtesy Medennium
    Figure 5. Schematic representation of the Medennium Smart IOL.

    The AMO FlexOptic IOL is an accommodating IOL that fills or conforms to the capsular bag and is designed to increase its anterior radius of curvature (and true power) in addition to changing its position in the capsular bag during accommodative effort. The NuLens accommodating IOL is designed to change its true power during accommodation and has been shown in an animal model to deliver over 40 D of accommodation. The NuLens incorporates a small chamber of silicone gel and a posterior piston with an aperture in its center that allows the gel to bulge relative to the forces generated by accommodation (Figure 6). The lens has been implanted in primates with encouraging results and is currently undergoing laboratory research and refinement before human studies are initiated.

    Image courtesy NuLens
    Figure 6. The NuLens accommodating IOL.

    The Power Vision FluidVision IOL is designed to change its shape and true power through a series of microscopic hydraulic actuators that are indirectly controlled by contraction and relaxation of the ciliary muscle (Figure 7). The lens is projected to deliver more than 10 D of power change.

    Courtesy Samuel Masket, MD
    Figure 7. Schematic representation of the Power Vision FluidVision IOL.

    Another new class of accommodating IOLs changes power through the mechanism of varying refractive indices within the lens. The Vision Solutions Technologies LiquiLens is an IOL containing 2 immiscible fluids in the center of the lens. Each fluid has a different refractive index. When the patient looks down to read, more of the higher refractive fluid is brought into the visual axis, increasing the effective power through the lens.

    Future Implications

    Currently available accommodating IOLs have their limitations. However, despite the inability to consistently generate large amounts of accommodative power, many surgeons have reported excellent results with many of these models. The limitations of these technologies should discourage surgeons from excessively promoting or guaranteeing independence from glasses following lens implantation. Yet, the potential benefits that have been reported should also encourage the ophthalmic community to continue using accommodative IOLs. As with any new technology, continued refinements and future developments will be necessary to achieve improved outcomes and to supply patients with the ideal lens implant.

    References
    1.

    Findl O, Kiss B, Petternel V, et al. Intraocular lens movement caused by ciliary muscle contraction. J Cataract Refract Surg. 2003;29:669-676.
    2. Findl O, Kriechbaum K, Menapace R, et al. Laserinterferometric assessment of pilocarpine-induced movement of an accommodating intraocular lens: a randomized trial. Ophthalmology. 2004;111:1515-1521.
    3. Mastropasqua L, Toto L, Nubile M, Falconio G , Ballone E . Clinical study of the 1CU accommodating intraocular lens. J Cataract Refract Surg. 2003;29:1307-1312.
    4. Marchini G, Pedrotti E, Sartori P, Tosi R. Ultrasound biomicroscopic changes during accommodation in eyes with accommodating intraocular lenses: pilot study and hypothesis for the mechanism of accommodation. J Cataract Refract Surg. 2004;30:2476-2482.
    5. Koeppl C, Findl O, Menapace R, et al. Pilocarpine induced shift of an accommodating intraocular lens: AT-45 Crystalens. J Cataract Refract Surg. 2005;31:1290-1297.
    6. McLeod SD , Portney V, Ting A. A dual optic accommodating foldable intraocular lens. Br J Ophthalmol. 2003;87:1083-1085.
    7. Rana A, Miller D, Magnante P. Understanding the accommodating intraocular lens. J Cataract Refract Surg. 2003;29:2284-2287.

    Author Disclosure

    Dr. Hoffman has no financial disclosures. Drs. Fine and Packer are consultants for Advanced Medical Optics, Inc. and Bausch & Lomb, Inc. They receive research and travel support from Eyeonics, Inc.