Customized eye models for determining optimized intraocular lenses power

Generalised models of the vertebrate eye

PURPOSE

To present a set of closed-form analytical equations to create a consistent eye model balance based on clinically measured input parameters in a single step. These models complement the existing iterative approaches in the literature.

METHODS

Two different approaches are presented, both considering the cornea and lens as equivalent thin lenses. The first, called the Gaussian model, starts by defining the refractive error as the difference between the axial power (or dioptric distance) and the whole eye power, which can be expanded by filling in the formulas for each power. The resulting equation can be solved for either the refractive error, axial length, corneal power, lens power or the distance between the cornea and the lens as a function of the other four parameters. The second approach uses vergence calculations to provide alternative expressions, assuming that the refractive error is located at the corneal plane. Both models are explored for a biometric range typically found in adult human eyes.

RESULTS

The Gaussian and vergence models each instantly balance the input data into a working eye model over the human physiological range and far beyond as demonstrated in various examples. The equations of the Gaussian model are more complicated, while the vergence model experiences more singularities, albeit in trivial or highly unlikely parameter combinations.

CONCLUSIONS

The proposed equations form a flexible and robust platform to create eye models from clinical data. Possible applications lie in creating animal eye models or providing a generic reference for real biometric data and the relationships between the ocular dimensions.

Peripheral visual field shifts after intraocular lens implantation

PURPOSE

To assess whether intraocular lens (IOL) implantation induces shifts in the peripheral visual field.

SETTING

Department of Ophthalmology, Leiden University Medical Center, Leiden, the Netherlands.

DESIGN

Ray-tracing study.

METHODS

Nonsequential ray-tracing simulations were performed with phakic and pseudophakic versions of the same eye model to assess potential shifts in the visual field after IOL implantation. 2 different IOL designs were evaluated and for each design 5 different axial positions and 7 different intrinsic powers were tested. The relation between the physical position of the light source and the location where the retina was illuminated was determined for each eye model. Subsequently, these relations were used to calculate whether the visual field shifts in pseudophakic eyes.

RESULTS

The pseudophakic visual field shift was below 1 degree for central vision in all evaluated models. For peripheral vision, the light rays in the pseudophakic eyes were refracted to a more central retinal location compared with phakic eyes, resulting in a central shift of the peripheral visual field. The magnitude of the shift depended on the IOL design and its axial position, but could be as high as 5.4 degrees towards central vision.

CONCLUSIONS

IOL implantation tends to have little effect on the central visual field but can induce an over 5 degrees shift in the peripheral visual field. Such a shift can affect the perception of peripheral visual complaints.

Ray tracing optimization: a new method for intraocular lens power calculation in regular and irregular corneas

To develop a novel algorithm based on ray tracing, simulated visual performance and through-focus optimization for an accurate intraocular lens (IOL) power calculation. Custom-developed algorithms for ray tracing optimization (RTO) were used to combine the natural corneal higher-order aberrations (HOAs) with multiple sphero-cylindrical corrections in 210 higher order statistical eye models for developing keratoconus. The magnitude of defocus and astigmatism producing the maximum Visual Strehl was considered as the optimal sphero-cylindrical target for IOL power calculation. Corneal astigmatism and the RMS HOAs ranged from - 0.64 ± 0.35D and 0.10 ± 0.04 μm (0-months) to - 3.15 ± 1.38D and 0.82 ± 0.47 μm (120-months). Defocus and astigmatism target was close to neutral for eyes with low amount of HOAs (0 and 12-months), where 91.66% of eyes agreed within ± 0.50D in IOL power calculation (RTO vs. SRK/T). However, corneas with higher amounts of HOAs presented greater visual improvement with an optimized target. In these eyes (24- to 120-months), only 18.05% of eyes agreed within ± 0.50D (RTO vs. SRK/T). The power difference exceeded 3D in 42.2% while the cylinder required adjustments larger than 3D in 18.4% of the cases. Certain amounts of lower and HOAs may interact favourably to improve visual performance, shifting therefore the refractive target for IOL power calculation.

Effect of anatomical differences and intraocular lens design on negative dysphotopsia

PURPOSE

To assess the effect of ocular anatomy and intraocular lens (IOL) design on negative dysphotopsia (ND).

SETTING

Department of Ophthalmology, Leiden University Medical Center, Leiden, the Netherlands.

DESIGN

Ray-tracing study based on clinical data.

METHODS

Ray-tracing simulations were performed to assess the effect of anatomical differences and differences in IOL design on the peripheral retinal illumination. To that end, eye models that incorporate clinically measured anatomical differences between eyes of patients with ND and eyes of pseudophakic controls were created. The anatomical differences included pupil size, pupil centration, and iris tilt. The simulations were performed with different IOL designs, including a simple biconvex IOL design and a more complex clinical IOL design with a convex-concave anterior surface. Both IOL designs were analyzed using a clear edge and a frosted edge. As ND is generally considered to be caused by a discontinuity in peripheral retinal illumination, this illumination profile was determined for each eye model and the severity of the discontinuity was compared between eye models.

RESULTS

The peripheral retinal illumination consistently showed a more severe discontinuity in illumination with ND-specific anatomy. This difference was the least pronounced, 8%, with the frosted edge clinical IOL and the most pronounced, 18%, with the clear edge biconvex IOL.

CONCLUSIONS

These results show that small differences in the ocular anatomy or IOL design affect the peripheral retinal illumination. Therewith, they can increase the severity of ND by up to 18%.

Comparison of wavefront aberrations in the object and image spaces using wide-field individual eye models

Wavefront aberrations in the image space are critical for visual perception, though the clinical available instruments usually give the wavefront aberrations in the object space. This study aims to compare the aberrations in the object and image spaces. With the measured wavefront aberrations over the horizontal and vertical ±15° visual fields, the in-going and out-going wide-field individual myopic eye models were constructed to obtain the wavefront aberrations in the object and image spaces of the same eye over ±45° horizontal and vertical visual fields. The average differences in the mean sphere and astigmatism were below 0.25 D between the object and image spaces over the horizontal and vertical ±45° visual fields under 3 mm and 6 mm pupil diameter. The wavefront aberrations in the object space are a proper representation of the aberrations in the image space at least for horizontal visual fields ranging from -35°to +35° and vertical visual fields ranging from -15°to +15°.

Predictability of pseudophakic refraction using patient-customized paraxial eye models

PURPOSE

To determine whether patient-customized paraxial eye models that do not rely on exact ray tracing and do not consider aberrations can accurately predict pseudophakic refraction.

SETTING

Bascom Palmer Eye Institute, Miami, Florida.

DESIGN

Prospective study.

METHODS

Cataract surgery patients with and without a history of refractive surgery were included. Manifest refraction, corneal biometry, and extended-depth optical coherence tomography (OCT) imaging were performed at least 1 month postoperatively. Corneal and OCT biometry were used to create paraxial eye models. The pseudophakic refraction simulated using the eye model was compared with measured refraction to calculate prediction error.

RESULTS

49 eyes of 33 patients were analyzed, of which 12 eyes from 9 patients had previous refractive surgery. In eyes without a history of refractive surgery, the mean prediction error was 0.08 ± 0.33 diopters (D), ranging from -0.56 to 0.79 D, and the mean absolute error was 0.27 ± 0.21 D. 31 eyes were within ±0.5 D, and 36 eyes were within ±0.75 D. In eyes with previous refractive surgery, the mean prediction error was -0.44 ± 0.58 D, ranging from -1.42 to 0.32 D, and the mean absolute error was 0.56 ± 0.46 D. 7 of 12 eyes were within ±0.5 D, 8 within ±0.75 D, and 10 within ±1 D. All eyes were within ±1.5 D.

CONCLUSIONS

Accurate calculation of refraction in postcataract surgery patients can be performed using paraxial optics. Measurement uncertainties in ocular biometry are a primary source of residual prediction error.

Understanding In Vivo Chromatic Aberrations in Pseudophakic Eyes Using on Bench and Computational Approaches

Diffractive multifocal intraocular lenses (IOLs) modulate chromatic aberration and reduce it at certain distances due to interactions between the refractive and diffractive chromatic components. However, the extent to which computer modeling and on bench measurements of IOL chromatic aberration translate to chromatic aberration in patients implanted with these multifocal IOLs (MIOLs) is not yet fully understood. In this study, we compare the chromatic difference of focus and longitudinal chromatic aberrations in pseudophakic patients implanted with different IOL designs (monofocal and trifocal IOLs) and materials (hydrophobic and hydrophilic), and compared them with predictions from computer eye models and on bench measurements with the same IOLs. Patient data consisted of results from 63 pseudophakic eyes reported in four different studies and obtained psychophysically in the visual testing channel of a custom-developed polychromatic adaptive optics system. Computational predictions were obtained using ray tracing on computer eye models, and modulation transfer function (MTF) on bench measurements on physical eye models. We found that LCA (in vivo/simulated) for far vision was 1.37 ± 0.08 D/1.19 D for monofocal hydrophobic, 1.21 ± 0.08 D/0.88 D for monofocal hydrophilic, 0.99 ± 0.06 D/1.19 D for MIOL hydrophobic, and 0.82 ± 0.05 D/0.88 D for MIOL hydrophilic. For intermediate and near vision, LCA (in vivo/simulated) was 0.67 ± 0.10 D/0.75 D and 0.23 ± 0.08 D/0.19 D for MIOL hydrophobic and 0.27 ± 0.15 D/0.38 D and 0.15 ± 0.15 D/−0.13 D for MIOL hydrophilic, respectively. In conclusion, computational ray tracing and on bench measurements allowed for evaluating in vivo chromatic aberration with different materials and designs for multifocal diffractive intraocular lenses.

MRI-based 3D retinal shape determination

Objective

To establish a good method to determine the retinal shape from MRI using three-dimensional (3D) ellipsoids as well as evaluate its reproducibility.

Methods and analysis

The left eyes of 31 volunteers were imaged using high-resolution ocular MRI. The 3D MR-images were segmented and ellipsoids were fitted to the resulting contours. The dependency of the resulting ellipsoid parameters on the evaluated fraction of the retinal contour was assessed by fitting ellipsoids to 41 different fractions. Furthermore, the reproducibility of the complete procedure was evaluated in four subjects. Finally, a comparison with conventional two-dimensional (2D) methods was made.

Results

The mean distance between the fitted ellipsoids and the segmented retinal contour was 0.03±0.01 mm (mean±SD) for the central retina and 0.13±0.03 mm for the peripheral retina. For the central retina, the resulting ellipsoid radii were 12.9±0.9, 13.7±1.5 and 12.2±1.2 mm along the horizontal, vertical and central axes. For the peripheral retina, these radii decreased to 11.9±0.6, 11.6±0.4 and 10.4±0.7 mm, which was accompanied by a mean 1.8 mm posterior shift of the ellipsoid centre. The reproducibility of the ellipsoid fitting was 0.3±1.2 mm for the central retina and 0.0±0.1 mm for the peripheral retina. When 2D methods were used to fit the peripheral retina, the fitted radii differed a mean 0.1±0.1 mm from the 3D method.

Conclusion

An accurate and reproducible determination of the 3D retinal shape based on MRI is provided together with 2D alternatives, enabling wider use of this method in the field of ophthalmology.

Influence of lens position as detected by an anterior segment analysis system on postoperative refraction in cataract surgery

AIM

To predict postoperative intraocular lens (IOL) position using the Sirius anterior segment analysis system and investigate the effect of lens position and IOL type on postoperative refraction.

METHODS

A total of 97 patients (102 eyes) were enrolled in the final analysis. An anterior segment biometry measurement was performed preoperatively with Sirius and Lenstar. The results of predicted lens position (PLP) and IOL power were automatically calculated by the software used by the instruments. Effective lens position (ELP) was measured manually using Sirius 3mo postoperatively. Pearson's correlation analysis and linear regression analysis were used to determine the correlation of lens position to other parameters.

RESULTS

PLP and ELP were positively correlated to axial length (AL; r=0.42, P<0.0001 and r=0.49, P<0.0001, respectively). There was a weak correlation between the peLP (ELP-PLP) and the prediction error of spherical refraction (peSR; r=0.34, P<0.0001). The peLP of Softec HD IOL differed statistically from those of both the TECNIS ZCB00 and Sensor AR40E IOLs. Multiple linear regression was used to obtain the prediction formula: ELP=0.66+0.63×[aqueous depth (AQD)+0.6LT] (r=0.61, P<0.0001), and a new variable (AQD+0.6 LT) was found to have the strongest correlation with ELP.

CONCLUSION

The Sirius anterior segment analysis system is helpful to predict ELP, which reduces postoperative refraction error.

Determining the Theoretical Effective Lens Position of Thick Intraocular Lenses for Machine Learning-Based IOL Power Calculation and Simulation

Purpose

To describe a formula to back-calculate the theoretical position of the principal object plane of an intraocular lens (IOL), as well as the theoretical anatomic position in a thick lens eye model. A study was conducted to ascertain the impact of variations in design and IOL power, on the refractive outcomes of cataract surgery.

Methods

A schematic eye model was designed and manipulated to reflect changes in the anterior and posterior radii of an IOL, while keeping the central thickness and paraxial powers static. Modifications of the shape factor (X) of the IOL affects the thick lens estimated effective lens position (ELP). Corresponding postoperative spherical equivalent (SE) were computed for different IOL powers (-5 diopters [D], 5 D, 15 D, 25 D, and 35 D) with X ranging from -1 to +1 by 0.1.

Results

The impact of the thick lens estimated effective lens position shift on postoperative refraction was highly dependent on the optical power of the IOL and its thickness. Design modifications could theoretically induce postoperative refraction variations between approximately 0.50 and 3.0 D, for implant powers ranging from 15 D to 35 D.

Conclusions

This work could be of interest for researchers involved in the design of IOL power calculation formulas. The importance of IOL geometry in refractive outcomes, especially for short eyes, should challenge the fact that these data are not usually published by IOL manufacturers.

Translational Relevance

The back-calculation of the estimated effective lens position is central to intraocular lens calculation formulas, especially for artificial intelligence-based optical formulas, where the algorithm can be trained to predict this value.

Simulating Outcomes of Cataract Surgery: Important Advances in Ophthalmology

As the human eye ages, the crystalline lens stiffens (presbyopia) and opacifies (cataract), requiring its replacement with an artificial lens [intraocular lens (IOL)]. Cataract surgery is the most frequently performed surgical procedure in the world. The increase in IOL designs has not been paralleled in practice by a sophistication in IOL selection methods, which rely on limited anatomical measurements of the eye and the surgeon's interpretation of the patient's needs and expectations. We propose that the future of IOL selection will be guided by 3D quantitative imaging of the crystalline lens to map lens opacities, anticipate IOL position, and develop fully customized eye models for ray-tracing-based IOL selection. Conversely, visual simulators (in which IOL designs are programmed in active elements) allow patients to experience prospective vision before surgery and to make more informed decisions about which IOL to choose. Quantitative imaging and optical and visual simulations of postsurgery outcomes will allow optimal treatments to be selected for a patient undergoing modern cataract surgery.

Accuracy of Constant C for Ray Tracing: Assisted Intraocular Lens Power Calculation in Normal Ocular Axial Eyes

OBJECTIVE

To evaluate the effect of constant C for ray tracing-assisted intraocular lens (IOL) power calculation in patients with different refractive power, we compared the refractive outcome of the ray tracing method based on constant C and conventional IOL calculation.

METHODS

215 eyes which underwent phacoemulsification and IOL implantation were enrolled in the study. According to the average corneal power, patients were divided into 3 groups: high corneal power (K >45 D) group, medium corneal power (43 ≤ K ≤ 45 D) group, and low corneal power (K <43 D) group. The predicted sphero-equivalent refractive outcome for the IOL power implanted at surgery was calculated using the ray tracing method, SRK/T, and Haigis formulas.

RESULTS

On the basis of the corneal refractive power, there were 65 eyes of K >45 D (30.23%), 96 eyes of 43 ≤ K ≤ 45 D (44.65%), and 54 eyes of K <43 D (25.12%). In general, the ray tracing group had the smallest value of mean absolute error (MAE) and mean error, and the proportions of eyes with absolute error (AE) <0.50 and <0.75 D were significantly higher than those of the other 2 formulas (p = 0.010). In each group, the value of MAE was smallest in the ray tracing group; for the proportions of AEs <0.50 and <0.75 D, the values in the ray tracing group were higher than those in the SRK/T and Haigis groups. Especially in the high and low corneal refractive groups, the proportion of AE <0.25 D was also obviously higher, but only in the low corneal refractive power group, and the difference was statistically significant (p = 0.006).

CONCLUSIONS

Compared with the conventional formulas, C constant of the ray tracing-assisted IOL power calculation has more accuracy for the patients with different corneal refractive powers. Ray tracing could provide better guidance for IOL selection clinically.

Analytical solution of a personalized intraocular lens design for the correction of spherical aberration and coma of a pseudophakic eye

This manuscript reports on a closed-form solution determining the personalized required shape of a new intraocular lens able to remove spherical aberration and coma of a pseudophakic eye. The proposed analytical method, within the framework of the Seidel theory of third-order optical aberrations, considers corneal conicities, fourth-order aspheric surface of the intraocular optics, pupil-shift effect and ocular kappa angle.

Keratoconic eyes with stable corneal tomography could benefit more from custom intraocular lens design than normal eyes

We investigated whether eyes with keratoconic corneal tomography pattern could benefit more from aberration correction with custom intraocular lenses (IOLs) than normal cataractous eyes despite the effect of misalignment on the correction of aberrations. Custom IOLs (cIOLs) were calculated for twelve normal and twelve keratoconic eyes using personalized numerical ray tracing models. The Stiles-Crawford weighted root-mean-square spot-size (wRMS) at the virtual fovea was evaluated for cIOLs and aberration-neutral IOLs (nIOLs) in a simulated clinical study with 500 virtual IOL implantations per eye and per IOL. IOL misalignment (decentration, tilt, rotation) and pupillary ectopia (4.5 mm iris aperture) were varied upon each virtual implantation. The nIOLs achieved average wRMS of 16.4 ± 4.3 μm for normal, and 92.7 ± 34.4 μm for keratoconic eyes (mean ± standard deviation). The cIOLs reduced the average wRMS to 10.3 ± 5.8 μm for normal, and 28.5 ± 18.6 μm for keratoconic eyes. The cIOLs produced smaller wRMS than nIOLs in most virtual implantations (86.7% for normal and 99.4% for keratoconic eyes). IOL misalignment resulted in larger wRMS variations in the keratoconus group than in the normal group. Custom freeform IOL-optics-design may become a promising option for the correction of advanced aberrations in eyes with non-progressive keratoconic corneal tomography pattern.

Minimal smooth lenses for perfect imaging of two wavefronts

The problem of designing a lens for perfectly imaging two incident wavefronts into two respective refracted wavefronts is considered. In particular, the problem of deriving a unique such lens of prescribed smoothness is analyzed. Building upon an idea by Benitez and Minano et al., we propose a method for constructing such twice-differentiable lenses and derive equations for computing them. The theoretical considerations are supplemented by a few examples.

Ray-tracing Analysis of the Corneal Power From Scheimpflug Data

PURPOSE

To describe a method by which mapped corneal elevation data can be used for ray-tracing analysis of the effective corneal power.

METHODS

Mapped elevation data of the front and back surface of the cornea exported by a clinical Scheimpflug camera was triangulated into a polygonal format and imported into a commercial optical engineering software. The focal length of the cornea was determined by exact ray tracing analysis of the distance giving the sharpest point spread function (PSF) at the selected image plane. The effective corneal power could then be determined as the reciprocal of the observed focal length "reduced to air." The corneal power determined by the ray-tracing procedure was checked for reproducibility and effect of pupil size and finally compared with standard keratometry methods.

RESULTS

Twenty random cases referred for cataract or refractive lens surgery were investigated. The ray-traced corneal power was found to be highly reproducible with a maximum error of 0.023 diopters (D) between repeated ray-tracing experiments. The mean ray-traced corneal power of 42.34 D (assuming a 3-mm pupil) was found to be 1.02 D lower than the standard keratometry reading assuming a keratometric index of 1.3375 (P < .001). The ray-traced corneal power was found to be higher than the true net power (P < .01) but not significantly different from the total corneal refractive power reported by the Scheimpflug device (P > .05). The ray-traced corneal power increased 0.31 D when the pupil size increased from 3 to 5 mm, which was attributed to spherical aberration.

CONCLUSIONS

Exact ray tracing can be used on mapped tomography data to analyze for the effective corneal power. This technique was found to be highly reproducible and may be a promising tool in the analysis of the true power of the cornea of any shape. [J Refract Surg. 2018;34(1):45-50.].

Influence of material and haptic design on the mechanical stability of intraocular lenses by means of finite-element modeling

Intraocular lenses (IOLs) are used in the cataract treatment for surgical replacement of the opacified crystalline lens. Before being implanted they have to pass the strict quality control to guarantee a good biomechanical stability inside the capsular bag, avoiding the rotation, and to provide a good optical quality. The goal of this study was to investigate the influence of the material and haptic design on the behavior of the IOLs under dynamic compression condition. For this purpose, the strain-stress characteristics of the hydrophobic and hydrophilic materials were estimated experimentally. Next, these data were used as the input for a finite-element model (FEM) to analyze the stability of different IOL haptic designs, according to the procedure described by the ISO standards. Finally, the simulations of the effect of IOL tilt and decentration on the optical performance were performed in an eye model using a ray-tracing software. The results suggest the major importance of the haptic design rather than the material on the postoperative behavior of an IOL. FEM appears to be a powerful tool for numerical studies of the biomechanical properties of IOLs and it allows one to help in the design phase to the manufacturers.

Prediction of the true IOL position

PURPOSE

To develop algorithms for preoperative estimation of the true postoperative intraocular lens (IOL) position to be used for IOL power calculation.

SETTING

Moorfields Eye Hospital NHS Foundation Trust, London, UK.

METHODS

Fifty patients were implanted randomly with a 3-piece IOL model in one eye and a 1-piece model in the other eye. Preoperatively, the IOLMaster was used to determine axial length, anterior chamber depth and mean corneal radius. Lens thickness and corneal width were measured with the ACMaster. Postoperative IOL position was measured with the ACMaster. Partial least squares (PLS) regression analysis of IOL position in terms of preoperative parameters was performed with a commercially available software package.

RESULTS

The PLS regression analysis showed that age, refraction, corneal width, lens thickness and corneal radius are not significant predictors of postoperative position of the anterior IOL surface, while axial length and in particular anterior chamber depth are. Regression relationships in terms of the above-mentioned predictors were determined for the two models implanted. Surprisingly, it turned out that the position of the posterior IOL surface could be described by a single regression relationship valid for both models. The residual SD for prediction of IOL position was about 0.17 mm for all relationships.

CONCLUSIONS

Accurate relationships to determine the true postoperative IOL position were obtained. In addition to axial length and corneal radius, which are required for the IOL power calculation as such, they require measurement of preoperative anterior chamber depth only.

Extended depth of focus with induced spherical aberration in light-adjustable intraocular lenses

PURPOSE

To evaluate the quality of vision and depth of focus induced by controlled amounts of negative spherical aberration in patients implanted bilaterally with light-adjustable intraocular lenses.

DESIGN

Prospective, nonrandomized clinical trial.

METHODS

Seventeen patients were implanted and treated with appropriate spatial irradiance light profiles. One eye was set for emmetropia, and the fellow eye received an additional aspheric light treatment to induce controlled amounts of negative spherical aberration. We used a Hartmann-Shack sensor to measure the eye's refraction and aberrations for a 4-mm pupil diameter. Decimal visual acuity (VA) was measured using a micro-display placed at 10 m, 60 cm, 40 cm, and 30 cm.

RESULTS

Eyes treated with aspheric profiles were divided into 2 groups depending on the final amount of induced negative spherical aberration: low [-0.05, -0.10 μm] and high [-0.13, -0.23 μm]. In both groups, the mean uncorrected decimal VA at 60 cm was over 0.90. In the first group, distance VA was 0.97 ± 0.16, but in the second group it was lower (0.76 ± 0.16). As expected, the VA for nearer distances is higher in the eyes with a larger magnitude of spherical aberration (P value < .01): 0.94 ± 0.10 and 0.73 ± 0.16 at 40 and 30 cm, respectively, in comparison with 0.71 ± 0.15 and 0.50 ± 0.14. Binocular summation with the fellow eye, adjusted for emmetropia, produces an excellent binocular distance VA (>1.10) in both groups.

CONCLUSIONS

Controlled amounts of negative spherical aberration and defocus can be induced in eyes implanted with adjustable intraocular lenses to enhance near vision.

Full OCT anterior segment biometry: an application in cataract surgery

In vivo three-dimensional (3-D) anterior segment biometry before and after cataract surgery was analyzed by using custom high-resolution high-speed anterior segment spectral domain Optical Coherence Tomography (OCT). The system was provided with custom algorithms for denoising, segmentation, full distortion correction (fan and optical) and merging of the anterior segment volumes (cornea, iris, and crystalline lens or IOL), to provide fully quantitative data of the anterior segment of the eye. The method was tested on an in vitro artificial eye with known surfaces geometry at different orientations and demonstrated on an aging cataract patient in vivo. Biometric parameters CCT, ACD/ILP, CLT/ILT Tilt and decentration are retrieved with a very high degree of accuracy. IOL was placed 400 μm behind the natural crystalline lens, The IOL was aligned with a similar orientation of the natural lens (2.47 deg superiorly), but slightly lower amounts (0.77 deg superiorly). The IOL was decentered superiorly (0.39 mm) and nasally (0.26 mm).

Comparison of retinal image quality with spherical and customized aspheric intraocular lenses

We hypothesize that an intraocular lens (IOL) with higher-order aspheric surfaces customized for an individual eye provides improved retinal image quality, despite the misalignments that accompany cataract surgery. To test this hypothesis, ray-tracing eye models were used to investigate 10 designs of mono-focal single lens IOLs with rotationally symmetric spherical, aspheric, and customized surfaces. Retinal image quality of pseudo-phakic eyes using these IOLs together with individual variations in ocular and IOL parameters, are evaluated using a Monte Carlo analysis. We conclude that customized lenses should give improved retinal image quality despite the random errors resulting from IOL insertion.