Light scattering from a diffractive-refractive intraocular lens: a goniometer-based approach for individual zone assessment

[Overview of intraocular lenses with optics for correcting presbyopia]

BACKGROUND

In recent years intraocular lenses (IOLs) for correcting presbyopia have been significantly improved and diversified. There are currently many different IOL models based on a wide variety of optical designs.

OBJECTIVE

The wide variety of available IOL solutions to correct presbyopia can be challenging for surgeons and patients. In everyday practice, the question is which IOL is best for which patient.

MATERIAL AND METHODS

This overview describes and categorizes the currently available implants. The respective optical properties are analyzed and clinical study results are discussed, in particular those evaluating visual performance and the occurrence of photic phenomena.

RESULTS

Monofocal-plus IOLs provide improved intermediate visual acuity with optimal distant visual acuity and minimal photic phenomena. Extended depth of field (EDoF) IOLs extend the depth of field through different optical principles and provide good distant and intermediate visual acuity. Trifocal lenses enable the greatest independence from spectacles at the price of a higher probability of dysphotopsia.

CONCLUSION

The selection of the most suitable IOL for correction of presbyopia requires a balance between the patient's visual needs and possible side effects. An adequate knowledge of the currently available implants allows a patient-oriented selection of IOLs.

[Optical benchtop evaluation of special intraocular lens optics]

Intraocular lenses (IOL) featuring complex optical designs can pose a challenge in understanding their performance, which may hinder making an informed decision when selecting suitable lenses for patients. This underlines the importance of collecting optical quality data of IOLs and making them available. The deployment of benchtop systems for IOL testing offers not only insights into the design features of various IOL solutions but also provides a platform for objective comparisons of special optics designs, including information about their susceptibility to photic phenomena. Recent advances in IOL testing have improved the ability to predict functional effects on visual acuity and contrast sensitivity from objective optical quality metrics. This, for instance, can be used to study monofocal lenses and the impact of asphericity on vision and IOLs tolerance to misalignment. Monofocal-plus IOLs consistently show only a slight improvement in the depth of focus when tested on the optical bench and in clinical settings. Although the pupil dependence found in this technology may limit the advantages of monofocal-plus over standard monofocal technology to extend the range of vision, it is the key to reduce photic phenomena. Refractive and diffractive extended depth of focus (EDOF) IOLs can effectively enhance intermediate vision, with the latter offering a slightly broader depth of focus but potentially increasing the risk of dysphotopsia. However, the limitation of EDOF IOLs is that they often fail to deliver spectacle independence for reading, which can be overcome by trifocal technology. Still, the available trifocal IOLs differ in their location of intermediate and near foci and the susceptibility to produce glare effects. Therefore, the knowledge from optical benchtop testing of IOLs can support optimizing the IOL selection by aligning the patient's visual needs with the IOL's properties, setting the right expectations, and assessing the risk profile for the occurrence of photic phenomena, potentially leading to improved decision-making.

Refractive Lens Exchange: A Review

In recent decades, technical advancements in lens surgery have considerably improved safety and refractive outcomes. This has led to a much broader range of indications for refractive lens exchange (RLE). Effective restoration of uncorrected distance and near visual acuity is possible with modern presbyopia correcting intraocular lenses (IOLs). Hyperopic patients who are fully presbyopic were identified as ideal candidates for RLE. For myopic patients, an increased risk of retinal detachment has been reported, which leads to a higher threshold to perform RLE in this patient group. The most frequent postoperative complications include posterior capsular opacification, deviation from the target refraction and cystoid macular edema. Thus, adequate planning of surgery, careful patient selection, as well as comprehensive counseling are crucial for successful RLE.

Characterizing glare effects associated with diffractive optics in presbyopia-correcting intraocular lenses

PURPOSE

To objectively quantify glare of intraocular lenses (IOLs) using a diffractive principle to extend the visual range and to identify models with increased susceptibility to inducing glare.

SETTING

David J Apple Laboratory, Heidelberg, Germany.

DESIGN

Laboratory investigation.

METHODS

Glare was assessed by means of a straylight parameter with a standard C-Quant intended for 7 degrees. In addition, 2 C-Quant modifications were used to test lower angles (ie, 2.5 degrees and 3.5 degrees). The following IOL models were assessed: PanOptix, AT Lisa Tri, Synergy, and Triumf, the latter 2 with chromatic aberration correction at distance. Straylight from trifocal IOLs was compared against a monofocal W-60R lens. The C-Quant test was performed through the studied IOLs by using additional optical components attached to their ocular.

RESULTS

Straylight (deg 2 sr -1 ) of the control was <1 at all tested angles, with the trifocal models showing comparable straylight at 7 degrees. At 3.5 degrees, Triumf's straylight increased to 15.5 ± 0.6, followed by Synergy (6.2 ± 1.1), PanOptix (4.1 ± 0.3), and AT Lisa Tri (2.0 ± 0.8). The chromatic aberration-correcting models demonstrated correspondingly higher straylight (Synergy: 18.8 ± 1.3; Triumf: 17.3 ± 0.5) at 2.5 degrees compared with PanOptix (4.3 ± 0.4), AT Lisa Tri (2.1 ± 0.1), and monofocal IOLs yielding minimal or no increase.

CONCLUSIONS

Trifocal IOLs induced increased straylight, but it was limited to lower angles, which may cause difficulties detecting these effects using a standard clinical approach. The latest IOL designs featuring chromatic aberration correction at far focus seem more susceptible than the established trifocal IOLs to inducing a glare phenomenon.

Optical-Quality Analysis and Defocus-Curve Simulations of a Novel Hydrophobic Trifocal Intraocular Lens

Purpose

The optical function of a novel refractive-diffractive trifocal intraocular lens (IOL) was tested in vitro to provide preclinical metrics that predict postoperative performance and may guide patient selection.

Methods

Fundamental optical characteristics of a trifocal hydrophobic-acrylic IOL with a C-loop haptic configuration (AT ELANA 841P, Carl Zeiss Meditec) were assessed using a fully automated optical test device under both monochromatic and polychromatic conditions combined with increased or compensated spherical aberration (SA). The area under the modulation transfer function (MTFa) was calculated across a defocus range from +1D to -3.5D and used to simulate visual acuity (VA). A polychromatic point spread function (PSF) was employed to assess the light distribution and identify photic phenomena.

Results

The highest MTFa values were obtained under monochromatic conditions using an SA-neutral corneal model. Nevertheless, after introducing SA and polychromatic light, the IOL performance remained good. Simulated VA values were 0.00 logMAR for distance, 0.1 logMAR at 100 cm, and progressively improving to 0.05 logMAR at 40 cm from the intermediate point. The light-spread analysis confirmed halos around the PSF center, which is a characteristic of trifocal technology.

Conclusion

AT ELANA 841P demonstrated good optical performance across various distances, independently of spectral and SA conditions, resulting in good simulated VA. Although light spread resembles standard trifocal IOLs, clinical studies are essential to confirm these laboratory results.

Chromatic aberration and spectral dependency of extended-range-of-vision intraocular lens technology

This study compared the optical quality and chromatic performance of refractive-diffractive intraocular lenses (IOLs) that are designed to extend the range of vision of pseudophakic patients and alter chromatic aberration. Five IOLs were evaluated, Tecnis Synergy and Triumf POD L GF, both intended to compensate for eye's chromatism, as well as Acriva Trinova Pro C-a lens that increases chromatic aberration, and AT Lisa Tri and AcrySof IQ PanOptix. An optical setup composed of a corneal model inducing monochromatic and chromatic aberrations and incorporating various spectral conditions was employed. The two chromatic-aberration correcting IOLs demonstrated the lowest far-focus dispersion, but it was negative only, with the Synergy indicating its ability to reduce eye's chromatic aberration. Although the Trinova increased far-point chromatism, it was close to the level of the PanOptix, but higher than that of the AT Lisa. All the studied models demonstrated varying optical quality in response to light color. Still, the strongest spectral dependency was associated with achromatizing technology. Therefore, chromatic aberration and wavelength dependency should be considered in IOL optimization and predicting visual function, particularly in non-white spectral conditions.

Combined finite-element and scalar diffraction simulation of light scattering on zone edges of diffractive intraocular lenses

A method has been developed to simulate the effects of scattered light on the image quality of optical systems. The coherent model is based on geometrical optics to take account of wavefront aberrations caused by lenses, applies finite-element calculation to solve Maxwell's equations around small scattering structures such as edges of diffractive surface zones, and uses scalar diffraction for free-space light propagation. The implementation is discussed in detail, and the operation is demonstrated on diffractive intraocular lenses. Point spread and modulation transfer functions are evaluated for an axial object point, taking account of scattered light as a function of slant angle and round radius of diffractive zone edges. Results show that, at a distance of ±200 Airy radius (i.e., ±2.1∘) from the axis, scattered irradiance is about 5 times more than without considering edge effects. Optimum round radius was found to be 7% of the step height, which agrees with simple geometrical optical estimations.

Spectral Effects and Range of Focus in a Multizonal-Refractive Intraocular Lens Compared with a Standard Trifocal Diffractive Design

INTRODUCTION

This study was performed to compare the optical performance of a multizonal presbyopia-correcting intraocular lens (IOL) and a conventional trifocal model.

METHODS

The optical quality and simulated visual acuity (VA) of 570 Precizon Presbyopic NVA (OPHTEC BV) and AcrySof IQ PanOptix (Alcon) were compared. The Precizon features a refractive design consisting of alternating optical zones that converge the incident light into two principal foci and a transitional zone for intermediate vision. By contrast, the PanOptix applies a diffractive (non-apodized) profile to achieve trifocality. Simulated VA was derived from the modulation transfer function. Chromatic aberration effects were also studied.

RESULTS

The diffractive and multizonal-refractive lenses yielded comparable simulated VAs at far focus (0.00 logMAR). All curves showed a reduction in expected VA with an increase in negative defocus. At - 1.0 D, the multizonal-refractive IOL's VA dropped by 0.05 logMAR, but for the diffractive model, it was one line (0.11 logMAR). The multizonal-refractive lens's VA prediction at the secondary peak was 0.03 logMAR-minimally better than the 0.06 logMAR of the diffractive lens at - 2.5 D. The refractive lens exhibited a 24% decrease in polychromatic optical quality due to material dispersion. The performance of PanOptix was more substantially affected, showing a 44% loss at 50 lp/mm at far, with minimal effects at other distances.

CONCLUSION

The multizonal-refractive lens does not fall short of the established trifocal IOL, and it can be used to extend the visual range of pseudophakic patients. Although the multizonal-refractive lens has lower material dispersion, the diffractive model corrects chromatism beyond far focus.

Trifocal Intraocular Lens Selection: Predicting Visual Function From Optical Quality Measurements

PURPOSE

To apply in vitro quality metrics to assess and compare three trifocal intraocular lenses (IOLs).

METHODS

The optical performance of the AT LISA tri 839MP (Carl Zeiss Meditec AG), AcrySof IQ PanOptix (Alcon Laboratories, Inc), and TECNIS Synergy (Johnson & Johnson Vision) was compared. The modulation transfer function (MTF) metrics were obtained using an optical bench set-up. A polychromatic light source and a model cornea inducing chromatic and spherical aberrations were used to mimic in vivo characteristics. The area under the MTF was calculated at each defocus position, which served as a parameter in a nonlinear formula applied to predict postoperative visual acuity (VA).

RESULTS

All of the studied IOLs had a predicted VA of 0.2 logMAR or better throughout the range of 0.00 to -3.00 diopters (D). Simulated VA differences between the IOLs were negligible (< 0.01 logMAR) at the far point. Although the three models were comparable at -1.00 D, at -2.00 D the AT LISA tri 839MP's VA was 0.06 and 0.08 logMAR worse than with the TECNIS Synergy and AcrySof IQ PanOptix, respectively. At near focus, the AcrySof IQ PanOptix's estimated VA was 0.06 logMAR (40 cm); for the AT LISA tri 839MP and TECNIS Synergy, it was 0.06 and 0.03 logMAR, respectively, at 36 cm.

CONCLUSIONS

Although simulated distance VA was comparable between the studied models, differences can be found in the intermediate focus' position and quality and the expected reading distance. Therefore, simulations of defocus curves from optical quality metrics provide insight into IOL characteristics and highlight differences between the IOLs, which may guide the selection of a trifocal lens based on patients' needs. [J Refract Surg. 2023;39(2):111-118.].