The year of 2018 was, without any doubt, a fruitful one in terms of ophthalmology research. Regarding the specific area of intraocular lenses (IOL) – my area of expertise – I believe one of the most interesting and potentially ground-breaking advancements can be found in research on adjustable IOLs. Perfect Lens LLC (Irvine, CA, USA) has developed a femtosecond laser system for IOL power adjustment based on the concept of refractive index shaping (RIS) (1,2). It uses green light (520 nm), and operates with energy levels that are below the threshold for ablation or cuts. IOL power changes are obtained through laser-induced chemical reactions in targeted areas of the optic substance, with increase in hydrophilicity and decrease in refractive index, while the laser builds a RIS lens within the treated area. The technology can be applied to any commercially available hydrophobic or hydrophilic acrylic IOL, as a special IOL material is not necessary. Power adjustment is noninvasive, fast, and can be done under topical anesthesia. Multiple adjustments can be performed, as they change a very thin layer within the IOL optic substance, and they are potentially reversible.
We had the opportunity to evaluate this technology in our laboratory, at the John A. Moran Eye Center, University of Utah. In an in vitro study, IOL power, modulation transfer function (MTF), light transmission, and light scattering of a commercially available blue-light filtering IOL were assessed before and after power adjustment (3). After laser treatment, a mean power change of -2.037 D was associated with an MTF change of -0.064, and a light transmittance change of -1.4%. Back light scattering increased within the lens optic in the zone corresponding to the laser treatment, at levels that are not expected to be clinically significant. Treated areas within the optic could be well appreciated under light microscopy, without any damage to the IOLs. We concluded that the power adjustment by femtosecond laser produced an accurate change in dioptric power, while not significantly affecting the quality of the IOL.
We also had the opportunity to evaluate, for the first time, the biocompatibility of this technology in vivo in a rabbit model (4). The study showed that postoperative outcomes in terms of uveal and capsular biocompatibility were similar between treated and non-treated commercially available lenses. The laser power adjustment procedure did not induce inflammatory reactions in the eye, or do any damage to the IOL optic. The change in power obtained was consistent among the treated rabbit eyes.
In vitro and ex vivo studies by other researchers had already demonstrated the accuracy and repeatability of this process, without affecting the IOL optic quality (5,6). They also showed that this technology can be used to create multifocality in a monofocal lens, and to cancel the diffractive multifocal add of a traditional multifocal IOL, all without significant changes to the IOL optic quality (7,8). Furthermore, the hydrophilicity based refractive index change could be used to create a toric diopter change of up to 7.6 D in a monofocal hydrophobic acrylic lens (9).
Pre-clinical studies generated a lot of interest by the ophthalmology community on this promising technology, and we are now looking forward to learn more about it through clinical studies, which are set to start soon.
References
- 1. R Sahler et al., “Creation of a refractive lens within an existing intraocular lens using a femtosecond laser”, J Cataract Refract Surg, 42, 1207-1215 (2016). PMID: 27531298. 2. JF Bille et al., “Chemical basis for alteration of an intraocular using a femtosecond laser”, Biomed Opt Express, 8, 1390-1404 (2017). PMID: 28663836. 3. J Nguyen et al., “IOL power adjustment by a femtosecond laser: In vitro evaluation of power change, MTF, light transmission, and light scattering in a blue-light filtering lens”, J Cataract Refract Surg, 44, 226-230 (2018). PMID: 29525614. 4. 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. 5. D Koch et al., “Accuracy of IOL Spherical Power Modification Using RIS Technology”. Presented at the ASCRS Symposium, May 9, 2017, Los Angeles, CA, USA. 6. B Youssefzadeh et al., “Refractive Lens Diopter Adjustment in Rabbit Cadaver Eye”. Presented at the ASCRS Symposium, May 9, 2017, Los Angeles, CA, USA. 7. S Macdonald et al., “Creation of Multifocality in a Monofocal IOL That Has Been Implanted in a Cadaver Rabbit Eye”. Presented at the ASCRS Symposium, May 9, 2017, Los Angeles, CA, USA. 8. RJ Olson, “New Approach to Treat Postoperative Multifocal IOL Complications”. Presented at the ASCRS Symposium, May 9, 2017, Los Angeles, CA, USA. 9. R Sahler et al., “Large-Diopter Toric Change Inside a Hydrophobic IOL Using Refractive Index Shaping”. Presented at the ASCRS Symposium, April 2018, Washington, DC, USA.
