Perspectives from the Bench
We discuss the potential of adjustable lens technology with Liliana Werner, one of the world leaders in IOL research
What has driven the development of adjustable lens technologies?
Incorrect IOL power calculation resulting from incorrect measurements of the eye is the most likely cause of refractive errors after cataract surgery, and this may require explantation of the lens. Furthermore, as current standards regarding IOL power labeling allow a certain tolerance, the power in the label may not reflect the actual precise power of the lens. In the near future, the problem of incorrect IOL power will likely be exacerbated by the rising popularity of laser refractive surgeries, the increasing expectations that patients place on their physicians to give them ‘perfect’ vision, and the arsenal of IOLs currently available. All of these facts warrant the development of postoperative IOL adjustment technologies.
Which adjustable technologies hold the most potential?
Many technologies – which we described in a 2014 review (1) – have potential (see Examples of Adjustable Technologies). Although some of them are still far from reality, other examples of non-invasive technology are really promising and closer to reality, with upcoming clinical studies. For example, take the Perfect Lens femtosecond laser system, where in vitro and ex vivo studies have shown that the modulation transfer function (MTF) values obtained after inducing multifocality are similar to those of commercially available multifocal lenses. You cannot only choose the add power, but you can also choose how the light energy is going to be split for near and far.
What key results have come from your laboratory?
We have worked on several adjustable technologies. We have performed all the pre-clinical studies on the light adjustable lens (Calhoun/RxSight) to establish the biocompatibility of the adjustment and lock-in procedure, as well as assessing if irradiation of the lens was associated with any toxicity to intraocular tissues, such as the cornea or retina (2)(3).
We have also performed different pre-clinical studies on the Harmoni modular lens system (ClarVista Medical) to evaluate biocompatibility, and ease of explantation and exchange of the optic component (4)(5)(6). Through in vitro studies, we have evaluated the optical quality of commercially available lenses after power adjustment by the Perfect Lens femtosecond laser system, as well as pre-clinical in vivo studies to evaluate the biocompatibility of power adjustment (7)(8).
What are the notable benefits – and potential pitfalls – of adjustable technologies?
- Light adjustable lens: a clear benefit of this procedure is that the adjustment procedure is non-invasive. However, a specialized three-piece silicone lens is required, and patients have to wear UV protective glasses until the new lens power is ‘locked in’ – once the power is locked in, no more adjustments are possible.
- Harmoni modular IOL technology: with this system, the optical component can be easily exchanged, without manipulating the base and causing stress to the zonules. A secondary surgery is however required for the adjustment.
- Perfect Lens: the power adjustment can be performed in commercially-available lenses in a non-invasive manner using the femtosecond laser. The adjustment procedure is very fast and multiple adjustments are possible – and potentially reversible. Ongoing studies are so far very promising, but I am sure we will learn a great deal from upcoming clinical studies, including any possible side effects from lens modification.
Refractive Index Shaping (RIS) (1)
In RIS, a femtosecond laser is used to create a ‘lens’ inside the IOL. The femtosecond laser induces hydrolysis of polymeric material inside the IOL, which increases the hydrophilicity of the acrylic material and shifts the index of refraction. The laser is used to create a ‘pattern’ and 3D shape inside the lens, the shape of which determines which refractive properties are being applied to the lens – spherical correction, reversing multifocality, inserting multifocality, and so on. Through a process called ‘phase wrapping’, dioptric changes can be induced without changing the height of the IOL.
What key qualities should new lens technologies possess?
For adjustable technologies, the adjustment procedure has to be simple, fast, and preferably non-invasive, as well as reversible and open to multiple adjustments. For IOLs, I think key qualities are: biocompatibility, clarity, excellent optical quality, insertion through very small incisions, adjustability, and let us not forget accommodation!
Liliana Werner is Professor of Ophthalmology and Visual Sciences, and Co-Director of the Intermountain Ocular Research Center, at John A. Moran Eye Center, University of Utah, Salt Lake City, UT, USA.
- J Ford et al., “Adjustable intraocular lens power technologies”, J Cataract Refract Surg, 40, 1205–1223 (2014), PMID: 24957439.
- L Werner et al., “Corneal endothelial safety with the irradiation system for light-adjustable intraocular lenses”, J Cataract Refract Surg, 33, 873–878 (2007). PMID: 17466864.
- L Werner et al., “Retinal safety of the irradiation delivered to light-adjustable intraocular lenses evaluated in a rabbit model”, J Cataract Refract Surg, 36, 1392–1397 (2010). PMID: 20656165.
- KD MacLean et al., “Evaluation of stability and capsular bag opacification of a new foldable adjustable intraocular lens”, Clin Exp Ophthalmol, 43, 648–654 (2015). PMID: 25801178.
- JJ Guan et al., “Optic replacement in a novel modular intraocular lens system”, Clin Exp Ophthalmol, 44, 817–823 (2016). PMID: 27298269.
- J Ludlow et al., “Long-term uveal and capsular biocompatibility of a novel modular intraocular lens system”, Acta Ophthalmol, [Epub ahead of print], (2018). PMID: 29369535.
- J Nguyen et al., “Intraocular lens power adjustment by a femtosecond laser: In vitro evaluation of power change, modulation transfer function, light transmission, and light scattering in a blue light-filtering lens”, 44, 226–230 (2018). PMID: 29525614.
- L Werner et al., “Biocompatibility of intraocular lens power adjustment using a femtosecond laser in a rabbit model”, J Cataract Refract Surg, 43, 1100–1106 (2017). PMID: 28917413.
Liliana Werner is Professor of Ophthalmology and Visual Sciences, and Co-Director of the Intermountain Ocular Research Center, at John A. Moran Eye Center, University of Utah, Salt Lake City, UT, USA.
