Analysis of a novel hydrophobic acrylic enhanced monofocal intraocular lens compared to its standard monofocal type on the optical bench
BMC Ophthalmology volume 22, Article number: 356 (2022)
The aim of this laboratory study is to objectively analyze the new hydrophobic, acrylic, enhanced monofocal intraocular lens Acunex Quantum (AN6Q) and compare it with the monofocal platform Acunex AN6.
Two IOL models were analyzed (Acunex Quantum AN6Q and Acunex AN6, Teleon Surgical, Spankeren, Netherlands), each having the same refractive power of + 22.0 D, on the optical bench with the OptiSpheric IOL PRO 2. The measurements followed the guidelines of the International Standard Organization with following parameters: ISO 2 cornea (+ 0,28 µ), ISO 11979/2, lens placement in situ in NaCl with 35° temperature, 546 nm and selection of different aperture sizes (3.0 mm vs 4.5 mm). The aberrations of each IOL were evaluated by the WaveMaster IOL 2, a high-resolution Shack-Hartmann sensor in reverse projection setup. An in-situ model eye was used according to ISO 11979 in NaCl (n = 1.337) with 546 nm, mask width 4.51. Zernike polynomials up to 10th order were determined by means of the measured wavefront that describe the optical properties of the IOL.
Through frequency modulation transfer function (mean) at 50 lp/mm (AN6Q/AN6 centered) was 0.687/0.731 (3.0 mm aperture) and 0.400/0.509 (4.5 mm aperture). The SR (mean) was 0.592/0.809 (3.0 mm) and 0.332/0.372 (4.5 mm). The MTF (mean) at 50 lp/mm (AN6Q/AN6 decentered by 1 mm) was 0.413/0.478 (3.0 mm) and 0.257/0.229 (4.5 mm). The SR (mean) was 0.393/0.404 (3.0 mm) and 0.183/0.212 (4.5 mm). The MTF (mean) at 50 lp/mm (AN6Q/AN6 tilted by 5°) was 0.508/0.710 (3.0 mm) and 0.337/0.513 (4.5 mm). The SR (mean) was 0.508/0.760 (3.0 mm) and 0.235/0.2372 (4.5 mm). AN6Q showed MTF peak of 0.55 with an enlarged depth of power of about 2.5 D and two cusps in the MTF curve. The spherical aberration Z 4–0 was about -0.21 µm and the secondary spherical aberration Z 6–0 was about 0.16 µm. No other relevant aberration showed up.
The new, enhanced monofocal AN6Q provides an extended range of focus with only slight decrease in contrast quality. Both types of the hydrophobic, acrylic Acunex IOL platform have its particular advantages in clinical settings and therefore its importance, respectively.
Recently, studies found that patients after cataract surgery with enhanced monofocal intraocular lenses (IOL) reported a better performance in activities that require intermediate vision [1,2,3]. These enhanced monofocal IOLs represent a very new type of IOLs in the market and can provide intermediate vision, and, at the same time similar far distance performance and photic phenomena compared with standard monofocal IOLs. By that, functional performance in daily life will be improved [4, 5].
These improvements and developments in monofocal IOL technology also offer new options to improve visual function in cases of multifocal IOL explantation due to adverse events and side effects of dysphotopsia like halo/glare [6, 7].
A variety of new and innovative lens designs have recently entered the market and the few studies made up to date are showing positive and promising clinical data.
However, in addition to clinical trials and long-term results, it seems also mandatory to evaluate new IOLs and their optical principles on the optical bench in a setting independent from IOL companies. This will help the clinician to better understand the optical properties of an IOL and, by that, to better decide which IOL to implant in a specific cataract case.
The aim of this study is to objectively analyze the new IOL Acunex Quantum (AN6Q) and compare it with the monofocal platform Acunex AN6.
The Acunex Quantum (AN6Q) by Teleon Surgical (Spankeren Netherlands) is a one-piece, foldable, hydrophobic acrylic IOL with a spherical aberration correction of -0.13 µm on the posterior surface (Fig. 1). The lens has a step vaulted C-loop design, an optical diameter of 6.0 mm and an overall diameter of 12.5 mm. The UV absorbing material with a water content of 4% has a high refractive index of 1.54 and a blue light filter is incorporated. A subtle modification of the very central part of the optics of the AN6Q (named “Q-Zone technology” by the manufacturer) is applied to increase depth of focus. Otherwise, material and basic geometry are identical to the monofocal counterpart, the Acunex IOL (AN6).
Two IOL models were analyzed (Acunex AN6 and Acunex Quantum AN6Q, Teleon Surgical, Spankeren, Netherlands), each having the same refractive power of + 22.0 D, on the optical bench with the OptiSpheric IOL PRO 2 and the Wavemaster IOL 2 (Trioptics company, Wedel, Germany).
All measurements were performed independently by Trioptics company on its own optical bench by a mandated, specialized optician who did not know the aim of the study. By that, an independent analysis was guaranteed. Results were confirmed with official certificates.
The measurements followed the guidelines of the International Standard Organization. The OptiSpheric IOL PRO 2 (Trioptics, Wedel, Germany) device was used to assess the optical quality of the two IOL models (AN6 and AN6Q). The following parameters were used: ISO 2 cornea (+ 0,28 µ), ISO 11979/2, lens placement in situ in NaCl (n = 1.337 solution index) with 35° temperature, 546 nm and selection of different aperture sizes (3.0 mm vs 4.5 mm). All measurements were repeated 3 times and performed on 2 different lenses of the same type. For each measurement, 5 tangential and 5 sagittal measurements were obtained and averaged. For rotational symmetrical IOLs, tangential and sagittal values generally are rather identical. The following settings were used: centered IOL, decentered IOL (1.0 mm) and tilted IOL (5°).
To simulate photopic and mesopic pupil conditions, measurements were performed with 3.0 mm and 4.5 mm aperture sizes. (Note: ISO standard 11,979–2 specifies MTF measurement at 1 mm decenter and 5 degrees tilt (annex C.7).
The following parameters were measured with the OptiSpheric IOL PRO 2 as the main criteria to describe the quality of the intraocular lens: The modulation transfer function (MTF) describes the contrast sensitivity of a lens system and is the imaging power of a lens at different spatial frequencies in the tangential and sagittal directions. Through frequency MTF were obtained for each IOL and each alignment. The Strehl number reflects the overall optical performance of an IOL as it takes into account the small oscillations that occur on the MTF curve. The Strehl Ratio (SR) is a measure of the imaging quality of an optical system over its entire spatial frequency range compared to the corresponding ideal (diffraction-limited) system.
Through focus MTF at 50 linepairs/mm were obtained additionally. To compare the depth-of-focus performance of both IOLs, an autofocus scan of the IOL was done. The through focus performance was defined as the distance between the foci of diopter powers showing a MTF better than 0.1.
The aberrations of each IOL were evaluated by the WaveMaster IOL 2 (Trioptics, Wedel, Germany), a high-resolution Shack-Hartmann sensor in reverse projection setup. An in-situ model eye was used according to ISO 11979 in NaCl (n = 1.337 solution index) with 546 nm, mask width 4.51, corresponding to standard settings and to a mesopic pupil. Zernike polynomials up to 10th order were determined by means of the measured wavefront that describe the optical properties of the IOL. It should be noted that spherical aberrations will be caused mainly by the lens’ optical design, while asymmetric aberrations such as Coma or Trifoil may partly result from lens errors. Zernike coefficients greater than 0.1 µm were defined as optical relevant.
Through frequency MTF
The through frequency modulation transfer function of all tested lenses, measured at the best focus through the 3.0 mm aperture (subsequently called “small”) and 4.5 mm aperture (subsequently called “large”), are shown (Figs. 2, 3 and 4). Centered: The through frequency modulation transfer function (MTF-mean) at 50 lp/mm (AN6Q/AN6) with small aperture was 0.687/0.731 and with large aperture 0.400/0.509. The Strehl Ratio (SR-mean) with small aperture was 0.592/0.809 and with large aperture 0.332/0.372. Decentered by 1 mm: The through frequency modulation transfer function (MTF-mean) at 50 lp/mm (AN6Q/AN6) with small aperture was 0.413/0.478 and with large aperture 0.257/0.229. The Strehl Ratio (SR-mean) with small aperture was 0.393/0.404 and with large aperture 0.183/0.212. Tilted by 5°: The through frequency modulation transfer function (MTF-mean) at 50 lp/mm (AN6Q/AN6) with small aperture was 0.508/0.710 and with large aperture 0.337/0.513. The Strehl Ratio (SR-mean) with small aperture was 0.508/0.760 and with large aperture 0.235/0.2372. Strehl findings are in accordance with MTF and all results are summarized in Tables 1 and 2.
Through focus MTF
The through focus results are presented in Fig. 5. For the aperture of 3.0 mm, AN6 showed a pronounced peak in MTF of about 0.72 with a depth of power of 1.25 D. AN6Q showed MTF peak of 0.55 with an enlarged depth of power of about 2.5 D and two cusps in the MTF curve.
As expected, for the aperture of 4.5 mm, the MTF values of AN6 and AN6Q were markedly reduced, with a shape of the through focus curves roughly similar to the aperture of 3 mm. AN6 showed a MTF peak of 0.51 and a depth of power of about 1 D. AN6Q showed a MTF peak of 0.39 and some reduced depth of power of about 1.5 D.
The wavefront maps and Zernike coefficients of AN6Q and AN6 are presented in Figs. 6 and 7. For Acunex Quantum AN6Q, the spherical aberration Z 4–0 was about -0.21 µm and the secondary spherical aberration Z 6–0 was about 0.16 µm. No other relevant aberration showed up. Peak-to-valley (PV) was 0.67 µm and root mean square (RMS) 0.12 µm.
For Acunex AN6, a spherical aberration Z 4–0 of about -0.31 could be revealed. No other relevant lower order aberrations (LOA) or higher order aberrations (HOA) were detected. Peak-to-valley (PV) is altered by pixel artifacts at the map’s margin.
The small cusp in the through frequency MTF curve of AN6Q represents the modification of the optical surface of this IOL. The monofocal AN6 proved to have a better through frequency MTF compared to AN6Q when centered and tilted. With decentration, both IOLs showed a similar pronounced decrease in MTF.
For the large aperture, corresponding to the mesopic pupil size of an elder person like a cataract patient, the MTF decreased for both IOLs, as expected. The apparently more pronounced decrease of the AN6 with large aperture is due to its very good performance with small aperture when centered or tilted. These results are in accordance with the expectations for our setting. With the positive spherical aberration of + 0.28 of the ISO-2 cornea, the aberration correcting AN6 can provide a very good image contrast.
The large aperture MTF is somewhat degraded because the spherical aberration (SA) of the IOL and model eye do not exactly match. However, real patients have a range of corneal SA, so this is a realistic simulation.
The optics of AN6 obviously are quite robust towards tilt which is advantageous for various anatomies of the patient’s eye, for complicated surgery but also in respect of the natural tilt of the lens and the IOL in the human capsular bag [8, 9].
The transfer of MTF results on the optical bench to clinical contrast visual acuity is always somewhat limited, of course. In clinical studies, there are various corneal asphericities of various patients, different geometries of the eyes, different pupil sizes, neuroadaptation effects and, especially, polychromatic light is present.
The improved depth of focus of AN6Q, claimed by the manufacturer, was confirmed in our study, although somewhat reduced for the big aperture corresponding to larger pupils. This could slightly affect the intermediate vision under mesopic conditions. However, in photopic conditions, a smaller pupil during pupillary near reaction will support the AN6Q IOL to provide a fairly convincing intermediate vision.
We could reveal that the Acunex Quantum AN6Q effectively generates this depth of focus seen in the through focus MTF curves by combining spherical aberration (Z 4–0) and secondary spherical aberration (Z 6–0) of opposite sign. This approach was proposed in literature in the last years and is applied to other novel IOL optics, like LuxSmart IOL (Bausch&Lomb) [10,11,12].
To know the underlying wavefront patterns of an IOL optics is extremely important for the clinician to understand the function of the particular IOL optics. Generally, no manufacturer will reveal the detailed aberrations of its IOLs. Therefore, our wavefront measurements can furnish important information for cataract surgeons. Wavefront patterns of both IOL are in accordance with the MTF results obtained.
Limitations of laboratory studies
To transfer the wavefront measurements to clinical settings, it has to be considered that any cornea will induce convergent light on the IOL and thus evoke aberrations of the IOL that are different from the nominal pattern. Furthermore, any laboratory measurement of IOL aberrations is done in air, water or NaCl with a central laser light beam of a defined wavelength. Different wavelengths will produce different wavefront errors. Finally, different diopters of an IOL with different lens thickness and thus material dispersion will produce some different wavefront . We also want to emphasize that only objective laboratory data of the new enhanced monofocal IOL and the monofocal counterpart is presented here trying to give the reader an overview and the chance to compare the two lenses with the same platform. Of course, clinical studies with high case numbers are very important to work out advantages and disadvantages of the different lens models in real life scenario. In addition, one should be careful when making comparisons to other EDoF or enhanced monofocal lenses of competitors with different optical principles.
The monofocal AN6 can provide a sharp contrast and a distinct image focus, while the enhanced monofocal AN6Q provides an extended range of focus with some minor decrease in contrast quality. Both types of the Acunex IOL platform have its particular advantages in clinical settings and therefore its importance, respectively.
The knowledge about the characteristics of both IOLs on the optical bench can help the cataract surgeon to better decide which type of IOL to implant in a specific patient’s eye up to the individual patient demands and expectations as well as the individual corneal asphericity.
Availability of data and materials
The authors confirm that the data supporting the findings of this study are available within the article.
Blancafort Alias S, Del Campo CZ, Salvador-Miras I, Luna Mariné S, Gómez Prieto MJ, Liñán Martín F, Salvà CA. Exploring Vision-Related Quality of Life: A Qualitative Study Comparing Patients’ Experience of Cataract Surgery with a Standard Monofocal IOL and an Enhanced Monofocal IOL. Clin Ophthalmol. 2022;16:1641–52. https://doi.org/10.2147/OPTH.S358386 PMID:35656389;PMCID:PMC9153939.
Alio JL, Plaza-Puche AB, Férnandez-Buenaga R, Pikkel J, Maldonado M. Multifocal intraocular lenses: An overview. Surv Ophthalmol. 2017;62(5):611–34. https://doi.org/10.1016/j.survophthal.2017.03.005 Epub 2017 Mar 31 PMID: 28366683.
Savini G, Balducci N, Carbonara C, Rossi S, Altieri M, Frugis N, Zappulla E, Bellucci R, Alessio G. Functional assessment of a new extended depth-of-focus intraocular lens. Eye (Lond). 2019;33(3):404–10. https://doi.org/10.1038/s41433-018-0221-1 Epub 2018 Sep 28. PMID: 30266985; PMCID: PMC6460699.
Auffarth GU, Gerl M, Tsai L, Janakiraman DP, Jackson B, Alarcon A, Dick HB, Quantum Study Group. Clinical evaluation of a new monofocal IOL with enhanced intermediate function in patients with cataract. J Cataract Refract Surg. 2021;47(2):184–91. https://doi.org/10.1097/j.jcrs.0000000000000399 PMID: 32932369.
Unsal U, Sabur H. Comparison of new monofocal innovative and standard monofocal intraocular lens after phacoemulsification. Int Ophthalmol. 2021;41(1):273–82. https://doi.org/10.1007/s10792-020-01579-y Epub 2020 Sep 6 PMID: 32893321.
Naujokaitis T, Zhao L, Scharf D, Khoramnia R, Auffarth GU. Monofocal intraocular lens with enhanced intermediate function as substitute for multifocal intraocular lens in positive dysphotopsia. Am J Ophthalmol Case Rep. 2022;26:101511. https://doi.org/10.1016/j.ajoc.2022.101511 PMID:35464676;PMCID:PMC9026612.
Chae SH, Son HS, Khoramnia R, Lee KH, Choi CY. Laboratory evaluation of the optical properties of two extended-depth-of-focus intraocular lenses. BMC Ophthalmol. 2020;20(1):53. https://doi.org/10.1186/s12886-020-1332-6 PMID:32059666;PMCID:PMC7023787.
Grzybowski A, Eppig T. Angle alpha as predictor for improving patient satisfaction with multifocal intraocular lenses? Graefes Arch Clin Exp Ophthalmol. 2021;259(3):563–5. https://doi.org/10.1007/s00417-020-05053-4.
Eppig T, Rawer A, Hoffmann P, Langenbucher A, Schröder S. On the Chromatic Dispersion of Hydrophobic and Hydrophilic Intraocular Lenses. Optom Vis Sci. 2020;97(4):305–13. https://doi.org/10.1097/OPX.0000000000001495 PMID: 32304541.
Yi F, Iskander DR, Collins M. Depth of focus and visual acuity with primary and secondary spherical aberration. Vision Res. 2011;51(14):1648–58. https://doi.org/10.1016/j.visres.2011.05.006 Epub 2011 May 17 PMID: 21609729.
Benard Y, Lopez-Gil N, Legras R. Optimizing the subjective depth-of-focus with combinations of fourth- and sixth-order spherical aberration. Vision Res. 2011;51(23–24):2471–7. https://doi.org/10.1016/j.visres.2011.10.003 Epub 2011 Oct 14 PMID: 22019797.
Schmid R, Borkenstein AF. Analysis of higher order aberrations in recently developed wavefront-shaped IOLs. Graefes Arch Clin Exp Ophthalmol. 2022;260(2):609–20. https://doi.org/10.1007/s00417-021-05362-2 Epub 2021 Aug 9 PMID: 34370067.
We would like to thank the company Trioptics (Wedel, Germany) which carried out all measurements according to their scientific standards and ISO guidelines and provided us with official certificates for the measurements.
There was no funding.
Ethics approval and consent to participate
Not applicable. The article is exempt from Ethical Committee approval as it is an optical bench analysis (in vitro study) without humans involved.
Consent for publication
All authors have no financial or proprietary interest in any material or method mentioned.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Borkenstein, A.F., Borkenstein, E.M. & Schmid, R. Analysis of a novel hydrophobic acrylic enhanced monofocal intraocular lens compared to its standard monofocal type on the optical bench. BMC Ophthalmol 22, 356 (2022). https://doi.org/10.1186/s12886-022-02584-8
- Enhanced monofocal intraocular lens
- Optical bench study
- Laboratory study
- Quality of intraocular lens