Optical and clinical simulated performance of a new refractive extended depth of focus intraocular lens.

OBJECTIVES: The purpose of this study is to evaluate the optical and expected clinical performance of a new refractive Extended Depth of Focus (EDF) intraocular lens (IOL) designed to maintain a monofocal-like dysphotopsia profile. METHODS: Simulated visual acuity (sVA) with varying defocus was calculated using the area under the Modulation Transfer Function measured in an average eye model and from computer simulations in eye models with corneal higher-order aberrations. Tolerance to defocus was evaluated using computer simulations of the uncorrected distance sVA under defocus. To evaluate the dysphotopsia profile, halo pictures obtained using an IOL-telescope, as well as simulated images in a realistic eye model under defocus were assessed. The results of the refractive EDF were compared to those of a diffractive EDF of the same platform. RESULTS: The refractive EDF IOL provides similar range of vision to the diffractive EDF IOL with the same distance, and similar intermediate and near sVA. The refractive EDF IOL provides the same tolerance to hyperopia as the diffractive EDF but more tolerance to myopia. Halo pictures and simulations showed that the refractive EDF provides comparable dysphotopsia profile to the monofocal IOL and better than the diffractive EDF. CONCLUSIONS: The results of this preclinical study in clinically relevant conditions show that the new refractive EDF IOL is expected to provide similar range of vision to the diffractive IOL of the same platform and higher tolerance to refractive errors. The refractive EDF provides a dysphotopsia profile that is better than the diffractive EDF and comparable to that of the monofocal IOL, also in the presence of residual refractive errors.

Enhancing the Intermediate Vision of Monofocal Intraocular Lenses Using a Higher Order Aspheric Optic.

PURPOSE: To describe and evaluate a new monofocal intraocular lens (IOL) designed to improve intermediate vision using a unique refractive technology. METHODS: The new monofocal lens is based on a higher order aspheric optic and is designed to improve intermediate vision. Simulated visual acuity from far to -2.00 diopters (D) was calculated using optical bench data. The effect of corneal higher order aberrations (HOAs) on simulated visual acuity, pupil size, and decentration was assessed using realistic computer eye models. The susceptibility to photic phenomena was evaluated by measuring preclinically the intensity of the light distribution in the retinal plane. The new lens design was compared to a standard aspheric monofocal IOL that shares the same platform, material, and primary spherical aberration as the new design. RESULTS: Simulated defocus curves showed increased simulated visual acuity in the intermediate range compared to a standard aspheric monofocal IOL with comparable distance vision, independently of the pupil size and corneal HOAs. At -1.50 D, the new IOL design provided a gain of approximately 0.1 logMAR, whereas at distance, the difference was less than 0.05 logMAR. The tolerance to decentration was also similar in both designs. Finally, experimental results indicate that the susceptibility to photic phenomena with the new lens design was similar to that of a standard aspheric monofocal IOL. CONCLUSIONS: Preclinical data showed that the new lens design improves intermediate vision while maintaining comparable distance image quality and keeping the same photic phenomena profile as a standard aspheric monofocal IOL. [J Refract Surg. 2020;36(8):520-527.].

Preclinical metrics to predict through-focus visual acuity for pseudophakic patients.

This study compares the clinical through-focus visual acuity (VA) in patients implanted with different intraocular lens (IOL) to optical bench testing of the same IOLs to evaluate the suitability of optical metrics of predicting clinical VA. Modulation transfer function and phase transfer function for different spatial frequencies and US Air Force pictures were measured using an optical bench for two monofocal IOLs, three multifocal IOLs and an extended range of vision IOL. Four preclinical metrics were calculated and compared to the clinical through-focus VA collected in three different clinical studies (243 patients in total). All metrics were well correlated (R(2)≥0.89) with clinical data and may be suitable for predicting through-focus VA in pseudophakic eyes.

From corneal shape to ocular wavefront in eyes with aspheric IOLs: the feasibility of IOL customisation.

PURPOSE: To determine if it is possible to predict the ocular wavefront aberrations of eyes with an aspheric IOL from the corneal shape and other readily available eye characteristics. A reliable prediction is a prerequisite for future IOL customisation. METHODS: Sixty pseudophakic eyes with aspheric IOLs of 60 patients were included. The corneal shape and the ocular wavefront aberrations were measured postoperatively with a Scheimpflug camera and an aberrometer, respectively. The elevation data of the anterior corneal surface were fitted by Zernike polynomials. Linear regression models for the Zernike coefficients describing the ocular wavefront aberrations up till the fourth order were determined, with as independent variables the Zernike coefficients describing the corneal shape, the eye (right/left), IOL power, and axial length. RESULTS: Linear regression equations with an explained variance (adjusted R-square) above 0.50 were found for five Zernike aberration terms: defocus (z(2,0); adjusted R-square 0.90), the astigmatism terms (0.81 for oblique astigmatism [z(2,-2)] and 0.88 for regular astigmatism [z(2,2)]), vertical coma (z(3,-1); 0.52), and spherical aberration (z(4,0); 0.71). CONCLUSION: The defocus, astigmatism, vertical coma, and spherical aberration terms of the ocular wavefront are strongly associated with the corneal shape in pseudophakic eyes and may thus be predicted from the corneal shape and other eye characteristics.

Extending the range of vision using diffractive intraocular lens technology.

PURPOSE: To describe and to experimentally assess a new intraocular lens (IOL) design using new diffractive technology. SETTING: AMO Groningen b.v., Groningen, Netherlands. DESIGN: Experimental study. MATERIALS AND METHODS: The basic principles of the new diffractive technology are described. The new IOL comprises two diffractive technologies; one is designed to extend the range of vision by elongating the focus, and the other increases the retinal image contrast by correcting chromatic aberration. To assess the potential visual performance, simulations were carried out in clinically verified eye models to predict the clinical defocus curves (visual acuity). The optical performance of the new lens design was evaluated by optical measurements in a model eye. The model eye had a cornea having the spherical aberration and chromatic aberration of an average cataract patient. The measurements were performed in white light and monochromatic light. RESULTS: The simulations suggested an increase in visual acuity of 0.27 logMAR as compared to an aspherical monofocal IOL in the range from -1 to -3 diopter defocus. The white light modulation transfer function in the far focus was identical to that of a monofocal IOL. The new lens demonstrated negative chromatic aberration, therefore showing the capability to actively reduce ocular chromatic aberration. The experiments also show retinal image characteristics of an extended light source that suggest that dysphotopsias (halos) of the new IOL are comparable to those associated with monofocal IOLs. CONCLUSIONS: The application of new IOL diffractive technology enabled optical characteristics that suggested that an extended range of vision can be obtained without compromising distance vision. FINANCIAL DISCLOSURE: All authors are employees of Abbott Medical Optics, Inc.

Binocular visual acuity for the correction of spherical aberration in polychromatic and monochromatic light.

Correction of spherical (SA) and longitudinal chromatic aberrations (LCA) significantly improves monocular visual acuity (VA). In this work, the visual effect of SA correction in polychromatic and monochromatic light on binocular visual performance is investigated. A liquid crystal based binocular adaptive optics visual analyzer capable of operating in polychromatic light is employed in this study. Binocular VA improves when SA is corrected and LCA effects are reduced separately and in combination, resulting in the highest value for SA correction in monochromatic light. However, the binocular summation ratio is highest for the baseline condition of uncorrected SA in polychromatic light. Although SA correction in monochromatic light has a greater impact monocularly than binocularly, bilateral correction of both SA and LCA may further improve binocular spatial visual acuity which may support the use of aspheric-achromatic ophthalmic devices, in particular, intraocular lenses (IOLs).

Theoretical performance of intraocular lenses correcting both spherical and chromatic aberration.

PURPOSE: To assess the performance and optical limitations of intraocular lenses (IOLs) correcting both longitudinal spherical aberration (LSA) and longitudinal chromatic aberration (LCA) compared to standard spherical and aspheric IOLs. METHODS: Using a set of 46 white light, pseudophakic eye models representing a population of cataract patients, retinal image quality was assessed for three IOL designs-standard spherical IOLs; aspheric IOLs, correcting a fixed amount of LSA; and aspheric refractive/diffractive IOLs, correcting a fixed amount of LSA and LCA. Depth of field and tolerance to IOL misalignments were also assessed. RESULTS: The improvement factor, based on the area under the radial polychromatic modulation transfer function (pMTF) curve of the IOL, correcting both average LSA and LCA over the aspheric IOL was 1.19±0.12, and over the spherical IOL was 1.43±0.29. Within the range of ±1.00 diopter of defocus, pMTF of the IOL correcting both LSA and LCA was equal or higher than both the spherical and aspheric IOLs. The IOL could be decentered up to 0.6 to 0.8 mm before the performance degraded below that of a spherical IOL. CONCLUSIONS: This is the first study that evaluates IOLs correcting both LSA and LCA in the presence of corneal higher order aberrations. Intraocular lenses that correct both LSA and LCA improve simulated retinal image quality over spherical IOLs and IOLs that correct LSA alone, without sacrificing depth of field or tolerance to decentration. Correction of LCA in combination with LSA shows the potential to improve visual performance.

Spherical aberrations of human astigmatic corneas.

PURPOSE: To evaluate whether the average spherical aberration of human astigmatic corneas is statistically equivalent to human nonastigmatic corneas. METHODS: Spherical aberrations of 445 astigmatic corneas prior to laser vision correction were retrospectively investigated to determine Zernike coefficients for central corneal areas 6 mm in diameter using CTView (Sarver and Associates). Data were divided into groups according to cylinder power (0.01 to 0.25 diopters [D], 0.26 to 0.75 D, 0.76 to 1.06 D, 1.07 to 1.53 D, 1.54 to 2.00 D, and >2.00 D) and according to age by decade. Spherical aberrations were correlated with age and astigmatic power among groups and the entire population. Statistical analyses were conducted, and P<.05 was considered statistically significant. RESULTS: Mean patient age was 42.6±11 years. Astigmatic corneas had an average astigmatic power of 0.78±0.58 D and mean spherical aberration was 0.25±0.13 µm for the entire population and approximately the same (0.27 µm) for individual groups, ranging from 0.23 to 0.29 µm (P>.05 for all tested groups). CONCLUSIONS: Mean spherical aberration of astigmatic corneas was not correlated significantly with cylinder power or age (P>.05). Spherical aberrations are similar to those of nonastigmatic corneas, permitting the use of these additional data in the design of aspheric toric intra-ocular lenses.

Population-based visual acuity in the presence of defocus well predicted by classical theory.

According to classical theory, visual acuity (VA) can be modeled using the intersection of the eye's modulation transfer function with a retinal threshold function. To date, there have been limited attempts to validate this methodology by comparing theory with actual measured data. We use the methodology to predict the visual acuity in the presence of defocus of a population of cataract patients implanted with diffractive multifocal intraocular lenses. For the prediction, we used a set of physiological eye models that include chromatic and higher order aberrations. We found that the simulations correlated strongly to the clinical outcomes (R(2)=0.93). While the simulated VA of the eye models was systematically 0.05 logMAR units lower (better acuity) than the clinical results, this difference was independent of defocus (p=0.98). These results show that when the simple and straightforward classical theory is applied using physiological eye models, accurate predictions of the VA, and through-focus VA of a population can be made. This method may be suited for predicting visual performance of new cataract and refractive treatments.

Visual effect of the combined correction of spherical and longitudinal chromatic aberrations.

An instrument permitting visual testing in white light following the correction of spherical aberration (SA) and longitudinal chromatic aberration (LCA) was used to explore the visual effect of the combined correction of SA and LCA in future new intraocular lenses (IOLs). The LCA of the eye was corrected using a diffractive element and SA was controlled by an adaptive optics instrument. A visual channel in the system allows for the measurement of visual acuity (VA) and contrast sensitivity (CS) at 6 c/deg in three subjects, for the four different conditions resulting from the combination of the presence or absence of LCA and SA. In the cases where SA is present, the average SA value found in pseudophakic patients is induced. Improvements in VA were found when SA alone or combined with LCA were corrected. For CS, only the combined correction of SA and LCA provided a significant improvement over the uncorrected case. The visual improvement provided by the correction of SA was higher than that from correcting LCA, while the combined correction of LCA and SA provided the best visual performance. This suggests that an aspheric achromatic IOL may provide some visual benefit when compared to standard IOLs.

Internal deformation of the human crystalline lens during accommodation.

PURPOSE: To describe the internal deformations in the crystalline lens that occur during accommodation. METHODS: A computer-based mechanical model of accommodation was created using the finite element method. The lens geometry of the model was based on in vivo measurements of human lenses in the accommodated state. The mechanical properties of the lens were based on ex vivo measurements of human lenses. To achieve a state of disaccommodation, the lens equator was stretched by 7%. The internal strains and displacements were calculated for a young accommodating lens, a lens of pre-presbyopic age and a lens of presbyopic age (20, 40 and 60 years old, respectively). RESULTS: The model showed that the radial strain was maximal in the nucleus for the young accommodating lens and minimal in the nucleus for the oldest non-accommodating lens. In the young lens the deformations occurred throughout the entire lens, whereas in the older non-accommodating lens the deformations were concentrated in the equatorial region. CONCLUSIONS: The model predicted that during accommodation, changes in lens thickness are mainly caused by deformation of the nucleus. In the older, non-accommodating lens, the deformations occur predominantly in the equatorial region and do not affect the central curvatures of the lens.

Visualization of the retinal image in an eye model with spherical and aspheric, diffractive, and refractive multifocal intraocular lenses.

PURPOSE: To present a method that visually demonstrates how spherical, aspheric, diffractive, and refractive multifocal intraocular lenses (IOLs) process light received from the cornea. METHODS: Monochromatic green light was projected through an Average Cornea Eye (ACE) Model with a cornea in front of the IOL. The model simulates a human cornea with average spherical aberration and visualizes the converging bundle of light leaving the IOL. Additionally, a US Air Force target was projected through the model, and the projected (retinal) image was captured. Various IOLs of differing designs were evaluated using this test setup. Multifocal IOLs included the aspheric diffractive Tecnis ZM900 and ZMA00 lenses; the refractive ReZoom NXG1 lens; the spherical AcrySof ReSTOR SA60D3 apodized diffractive lens; and the spherical diffractive CeeOn 811E lens. Monofocal IOLs included the spherical CeeOnEdge 911A IOL and the aspheric SofPort LI61AO, AcrySof IQ SN60WF, and Tecnis Z9000 and ZA9003 IOLs. RESULTS: The light paths of the different diffractive and refractive multifocal IOLs showed the variations in the processing of incoming light, illustrating the functional differences of IOL concepts. The US Air Force target projections in the ACE Model gave an impression of the functional optical quality of the different lenses. The value of this visualization method was demonstrated by comparing the results with modulation transfer function measurements. CONCLUSIONS: This visualization technique furthers the understanding of the working principles and quality of the retinal images produced by different mono- and multifocal IOLs.

On the relationship between lens stiffness and accommodative amplitude.

The purpose of this study was to investigate the relationship between the stiffness of the material comprising the lens and the loss of accommodative amplitude with age. We used a validated mechanical model to determine the changes in the shape of the lens during accommodation and disaccommodation. The relative contribution of lens stiffness to loss of accommodative amplitude with age was determined by varying lens stiffness in the model. The changes in lens stiffness with age were based on the results of two recently published studies. In the first study we showed that lens stiffness increases exponentially with age, and in the second study we showed that there is a considerable stiffness gradient within the lens that changes with age. The results of both studies were incorporated in the mechanical model. The model showed that it is not the increasing stiffness of the lens with age, but rather the changing stiffness gradient that influences accommodative amplitude. The results show that the changing stiffness gradient in the lens may be responsible for almost the entire loss of accommodation with age.

Theoretical comparison of aberration-correcting customized and aspheric intraocular lenses.

PURPOSE: To assess the performance and optical limitations of standard, aspheric, and wavefront-customized intraocular lenses (IOLs) using clinically verified pseudophakic eye models. METHODS: White light pseudophakic eye models were constructed from physical measurements performed on 46 individual cataract patients and subsequently verified using the clinically measured contrast sensitivity function (CSF) and wavefront aberration of pseudophakic patients implanted with two different types of IOLs. These models are then used to design IOLs that correct the astigmatism and higher order aberrations of each individual eye model's cornea and to investigate how this correction would affect visual benefit, subjective tolerance to lens misalignment (tilt, decentration, and rotation), and depth of field. RESULTS: Physiological eye models and clinical outcomes show similar levels of higher order aberration and contrast improvement. Customized correction of ocular wavefront aberrations with an IOL results in contrast improvements on the order of 200% over the control and the Tecnis IOLs. The customized lenses can be, on average, decentered by as much as 0.8 mm, tilted > 10 degrees , and rotated as much as 15 degrees before their polychromatic modulation transfer function at 8 cycles/degree is less than that of the Tecnis or spherical control lens. Correction of wavefront aberration results in a narrower through focus curve but better out of focus performance for +/- 0.50 diopters. CONCLUSIONS: The use of realistic eye models that include higher order aberrations and chromatic aberrations are important when determining the impact of new IOL designs. Customized IOLs show the potential to improve visual performance.

Stiffness gradient in the crystalline lens.

BACKGROUND: While the overall stiffness of the lens has been measured in a number of studies, the knowledge about the stiffness distribution within the lens is still limited. The purpose of this study was to determine the stiffness gradient in the human crystalline lens. A secondary purpose was to determine whether the stiffness gradient depends on age. METHODS: The local dynamic stiffness was measured in 10 human crystalline lenses (age range: 19 to 78 years). The lenses were stored at -70 degrees C before being measured. The influence of freezing on the mechanical properties has been determined in a previous study. A small oscillating probe was used to measure the local dynamic shear modulus as a measure of lens stiffness. The measurements were taken in the cross-sectional plane through the lens equator. RESULTS: The local dynamic shear modulus varied with location for all tested lenses. The central stiffness of the oldest lens (78 years) was 10(4) times higher than the youngest (19 years) lens. The equatorial stiffness of the oldest lens was 10(2) times higher than the youngest lens. For the older lenses, the centre was 5.8-210 times stiffer than the periphery, as opposed to earlier results described by Fisher (1971), who found that the periphery was up to 3 times softer than the centre for lenses younger than 70-years-old. For the three youngest lenses (19 to 49 years), the periphery was 2.2-16.6 times stiffer than the centre. CONCLUSIONS: The dynamic stiffness of the crystalline lens varies with location within the lens. The stiffness gradient depends on the age of the lens. The results of the 10 lenses indicate that the stiffness of both centre and periphery increase with age, but at a different rate.

Comment on "Scheimpflug and high-resolution magnetic resonance imaging of the anterior segment: a comparative study".

In a recent paper, Koretz et al. [J. Opt. Soc. Am. A 21, 346 (2004)] conclude that the results of the "corrected Scheimpflug technique" to obtain the shape of the human lens differ significantly from their magnetic resonance imaging (MRI) data. We demonstrate that the conclusions are based on incorrect statistical methods. A straightforward statistical comparison shows that there is no significant difference between the corrected Scheimpflug results and the MRI data.