Researchers are increasingly focused on developing innovative presbyopia correcting intraocular lenses to satisfy the demands of patients.
There is a definite trend towards patients requesting, and being fitted with, presbyopia correcting intraocular lenses (IOLs) and this is expected to continue as the technology evolves. While initial prototypes of various technologies used for these IOLs had some significant side effects, newer designs have reduced side effects and their performance has been confirmed with clinical testing. A few areas of potential progress are emerging.
Custom Aspheric IOLs
As our patients become more demanding, the strategy of implanting an IOL with preset amount of spherical aberration is insufficient. This is due to the fact that asphericity in a standard IOL is not suitable for all eyes. Customisation of the IOL asphericity is especially important for cataract patients who have had previous corneal refractive surgery.
This IOL customisation depending on the asphericity needed, extends the range of vision and potentially improves the visual outcome. Oculentis is currently engaged in the study of IOL customisation on this front (the MyLentis project). It is hoped that these lenses will become available in the next few years.
all commercialised accommodating IOL designs to date have failed to translate into real accommodation
Continuous Transitional Focus IOLs
Recently, Precizon Presbyopic (Ophtec, Netherland) received CE certification. This new aspheric presbyopia-correcting IOL features an innovative proprietary continuous transitional focus (CTF) optical design.1
Ophtec claims that this IOL offers full range of vision and, due to its transitional zones technology, provides a smooth, continuous transition from near to infinity with low peaks (Figure 1). The light transmitting through the ‘natural’ positive corneal aberration is further bent by the aberration-neutral, aspherical lens forming a ‘broad beam’, which supposedly gives a zone with an increased depth of focus. This increased depth of focus produces uninterrupted, high-quality images for the brain to translate into clear vision at all distances. Moreover, apparently this technology makes the IOL forgiving for some degrees of lens tilt and decentration. This tolerance in misalignment reduces photic phenomena, which in turn should help patients adapt more naturally to their new vision. The CTF optic is also designed to be less dependent on pupil size under all lighting conditions.
Precizon Presbyopic is at post-marketing study stage with some promising data and the company is planning to commercially launch in 2018 during the European Society of Cataract and Refractive Surgeons Conference in Lisbon, Portugal. The product will initially be available in the European Union and a few selected markets.
Accommodating IOLs
Despite showing some initial promise and positive reports, all commercialised accommodating IOL designs to date have failed to translate into real accommodation. The human brain is not multifocal but monofocal with extended depth. Once a working accommodating IOL is available, the neural adaptation that we need to acquire with a multifocal IOL will not be needed.Therefore, interest in the potential for a truly accommodating IOL persists.
At least two electromechanical IOLs are in development: Elenza with the Sapphire AutoFocal IOL, and Vista Ocular with the VistaLens. These IOLs have the advantage that they do not require axial movement of the optic to achieve accommodative effect.
The Sapphire Autofocal IOL (Elanza) has a liquid crystal optic that responds to change in pupil size and automatically changes optical power for the near triad (Figure 2).2
When near, the pupillary photosensors are triggered and the stored charge from the photovoltaic cells adjusts the optic for near vision. The power cells can be recharged via encapsulated microcoils, which also function for two-way communication with the device and external programming. Recharging can be achieved at night through a mask over the orbits. The liquid crystal, electronics, and power cells are hermetically sealed in a glass wafer surrounded by an acrylic outer component. The downside is that the elasticity of the capsule is far from being demonstrated; rather, the contrary is the case, and the electro-activated process is complex; it depends on pupil size, which is highly variable and changes with age. An FDA trial is planned to begin soon.
Vista Ocular (Ohio, US), is developing an innovative technology to bypass pupillary and ciliary muscle movement, and target the muscle’s action potential as the accommodative signal. The technology is patented and more patents are pending. The company is currently in the process of testing an in-vivo sensor system for the detection of the ciliary muscle’s action potential. This design also incorporates rechargeable battery power with a flexible lens system to change optical power in a variable fashion (Figure 3).
The FluidVision IOL (PowerVision) incorporates a novel design with a 6-mm central optic surrounded by a peripheral reservoir that is filled with isorefractive index silicone oil (Figure 4).3 The hydrophobic acrylic lens is placed in the capsular bag. Upon the accommodative response, the fluid is displaced centrally into the lens, thereby expanding the central membrane of the optic and creating accommodative power. The company reports an average of 4.00 D of accommodative amplitude. With relaxation of the ciliary muscle, fluid returns to the periphery, and distance vision is created. The lens has been studied in South Africa, with accommodation reportedly lasting up to three years postoperatively. The company has just started a randomised clinical trial and hopes to initiate FDA trials in the next two years. Being a capsular bag IOL, the future performance of the FluidVision model is debatable due to some issues with capsular bag as in Sapphire IOL.
Based on evidence that forces in the sulcus dependent on the ciliary body persist over time, sulcus-based accommodating IOLs have a potential advantage. Lenses based on this approach have been implanted successfully in initial clinical trials.
Recently the Lumina IOL (Akkolens) has demonstrated accommodative capability in more than 50 eyes with one year of follow-up (Figure 5).4 This two-element varifocal lens is also designed for sulcus placement. It changes focal powers when its elements shift in the plane perpendicular to the optical axis. This lens holds major promise, and future experience will confirm the performance and safety of this device.
Similar in concept to the FluidVision but working in the sulcus, DynaCurve IOL achieves accommodation through use of a fluid or gel to change its shape (Figure 6). In theory, this lens could provide up to 10.00 D of accommodation. The DynaCurve IOL is implanted in front of the collapsed capsular bag, which is used as a component of a dynamic diaphragm. When this capsular diaphragm activates the lens’ components (a small chamber filled with silicone, a piston-like element, and a flexible membrane), the lens changes shape.5
Liquilens (Vision Solutions Technologies), has taken a completely different route for accommodation. Instead of relying on the body’s anatomical forces, the lens uses gravity.6 It uses the fluidics of two immiscible optically clear biocompatible fluids and their interplay to introduce an additional index of refraction into the line of sight that provides additional power when the patient looks down at a 60 to 70 degree angle (Figure 7). When the patient looks forward, the fluid is out of the way and the lens provides distance vision. Dr. Alan Glazier (optometrist and IOL developer) is seeking CE certification for the lens in Europe.
Diffractive Multifocal IOLs
Diffractive technology is, no doubt, the most commonly used approach to multifocality in the current IOL market. This technology has undergone major evolution in the recent past as it has expanded from bifocal (giving good distance and near vision) to trifocal which also provides additional functional intermediate vision. However, all these platforms still rely on diffraction technology that can result in complaints of visual disturbance and need neural adaptation. Therefore, there exists a definite clinical need to provide functional intermediate and near vision, while maintaining other qualities of a monofocal IOL. I have no doubt that IOL companies are working towards this goal, which when achieved, will provide the backbone for the platform of diffractive presbyopic IOLs for the near future.
Dr. Uday Bhatt was one of the first ophthalmic surgeons in the world to have implanted Trifocal intraocular lens in cataract surgery. Dr. Bhatt is a Cochrane reviewer and published author in many peer reviewed medical journals. He also regularly presents at national and international conferences. He specialises in cataract surgery and laser vision correction. He practises at Vision Eye Institute in Footscray, Camberwell and Coburg, Victoria.
References:
1. Holzer M et al. Functional outcomes of the new Precizon presby transitional continuous focus intraocular lens. Presentation European Society of Cataract and Refractive Surgeons (ESCRS) annual conference. Copenhagen Sept 10-14, 2016
2. CRSTEurope. (2017). An Autofocal Accommodating IOL. [online] Available at: https://crstodayeurope.com/articles/2015-jan/an-autofocal-accommodating-iol/. [Accessed 12 Sep. 2017].
3. FluidVision: Designed to Restore True Accommodation – OIS. [online] OIS. Available at: http://ois.net/fluidvision-designed-to-restore-true-accommodation/ [Accessed 12 Sep. 2017].
4. Alio JL, Simonov A, Plaza-Puche AB, Angelov A, Angelov Y, van Lawick W, Rombach M. Visual Outcomes and Accommodative Response of the Lumina Accommodative Intraocular Lens. Am J Ophthalmol. 2016 Apr;164:37-48. doi: 10.1016/j.ajo.2016.01.006. Epub 2016 Jan 29
5. Alió JL.Ben-nun J, Rodriguez-Prats JL, Plaza AB.Visual and accommodating outcomes 1 year after implantation of an accommodating intraocular lens based on a new concept. J Cataract Refract Surg.2009;35:1671-1678.
6. Walter Bethke, M. (2017). IOL Alternatives to Multifocality. [online] Reviewofophthalmology.com. Available at: https://www.reviewofophthalmology.com/article/iol-alternatives-to-multifocality [Accessed 12 Sep. 2017].
