Timo Eppig

Tomography-based customized IOL calculation model.

Purpose: To provide a mathematical calculation scheme for customized intraocular lens (IOL) design based on high resolution anterior segment optical coherence tomography (AS-OCT) of anterior eye segment and axial length data. Material and Methods: We use the corneal and anterior segment data from the high resolution AS-OCT and the axial length data from the IOLMaster to create a pseudophakic eye model. An inverse calculation algorithm for the IOL back surface optimization is introduced. We employ free form surface representation (bi-cubic spline) for the corneal and IOL surface. The merit of this strategy is demonstrated by comparing with a standard spherical model and quadratic function. Four models are calculated: (1) quadratic cornea + quadratic IOL; (2) spline cornea + quadratic IOL; (3) spline cornea + spline IOL; and (4) spherical cornea + spherical IOL. The IOL optimization process for the pseudophakic eye is performed by numerical ray-tracing method within a 6-mm zone. The spot diagram on the fovea (forward ray-tracing) and wavefront at the spectacle plane (backward ray-tracing) are compared for different models respectively. Results: The models with quadratic (1) or spline (3) surface representation showed superior image performance than the spherical model 4. The residual wavefront errors (peak to valley) of models 1, 2, and 3 are below one micron scale. Model 4 showed max wavefront error of about 15 µm peak to valley. However, the combination of quadratic best fit IOL with the free form cornea (model 2) showed one magnitude smaller wavefront error than the spherical representation of both surfaces (model 3). This results from higher order terms in cornea height profile. Conclusions: A four-surface eye model using a numerical ray-tracing method is proposed for customized IOL calculation. High resolution OCT data can be used as a sufficient base for a customized IOL characterization.

Comparison of 3 biometry devices in cataract patients.

Purpose Accurate biometry is an obligatory preoperative measurement for refractive surgery as well as cataract surgery. A new device based on partial coherence interferometry was compared with 2 currently used biometry devices. Setting Department of Ophthalmology, Saarland University Medical Center, Homburg, Germany. Design Prospective case series. Methods Eyes of cataract patients were examined with a functional prototype of the new optical low‐coherence reflectometry (OLCR) biometer OA‐2000, the standard OLCR biometer Lenstar, and the partial coherence interferometry (PCI) biometer IOLMaster. The results were compared using a Wilcoxon‐Mann‐Whitney U test and Pearson correlation calculations. Results A total of 138 eyes of 74 cataract patients were examined. Pearson correlation showed excellent correlation for axial length, anterior chamber depth and keratometry among the 3 devices tested. The highest correlation was found between standard OLCR biometer and PCI biometer for AL, R1, and R2 (r = 1.0, r = 0.936, r = 0.952, respectively; all P ≤ .001). For anterior chamber depth (ACD), the highest correlation was found between the standard OLCR biometer and the new OLCR biometer (r = 0.943; P ≤ .001). The mean values of AL/ACD/R1/R2 differed very little, but the differences were significant (all P ≤ .05) (new OLCR biometer 23.31/3.21/7.74/7.64 mm; standard OLCR biometer 23.30/3.13/7.80/7.60 mm; PCI biometer 23.37/3.00/7.78/7.6 mm). Conclusions Compared with other clinical instruments, the new OLCR biometer generated the most accurate results. Differences especially in measurement of axial length were statistically but not clinically significant. The new OLCR biometer yielded results that correlated very well with the values of the PCI biometer and standard OLCR biometer. Financial Disclosure None of the authors has a financial or proprietary interest in any material or method mentioned.

Vignetting and field of view with the KAMRA corneal inlay.

Purpose. To evaluate the effect of the KAMRA corneal inlay on the retinal image brightness in the peripheral visual field. Methods. A KAMRA inlay was “implanted” into a theoretical eye model in a corneal depth of 200 microns. Corneal radius was varied to a steep, normal, and flat (7.37, 7.77, and 8.17 mm) version keeping the proportion of anterior to posterior radius constant. Pupil size was varied from 2.0 to 5.0 mm. Image brightness was determined for field angles from −70° to 70° with and without KAMRA and proportion of light attenuation was recorded. Results. In our parameter space, the attenuation in brightness ranges in between 0 and 60%. The attenuation in brightness is not affected by corneal shape. For large field angles where the incident ray bundle is passing through the peripheral cornea, brightness is not affected. For combinations of small pupil sizes (2.0 and 2.5 mm) and field angles of 20–40°, up to 60% of light may be blocked with the KAMRA. Conclusion. For combinations of pupil sizes and field angles, the attenuation of image brightness reaches levels up to 60%. Our theoretical findings have to be clinically validated with detailed investigation of this vignetting effect.

Staging of keratoconus indices regarding tomography, topography, and biomechanical measurements.

PURPOSE To derive limits of metric keratoconus indices for classification into keratoconus stages. DESIGN Validity and reliability analysis of diagnostic tools. METHODS A total of 126 patients from the keratoconus center of Homburg/Saar were evaluated with respect to Amsler criteria, using Pentacam (Keratoconus Index [KI], Topographic Keratoconus Classification [TKC]), Topographic Modeling System (Smolek/Klyce, Klyce/Maeda), and Ocular Response Analyzer (Keratoconus Match Probability [KMP], Keratoconus Match Index [KMI]). Mean value, standard deviation, 90% confidence interval, and the Youden J index for definition of the thresholds were evaluated. RESULTS For separation of keratoconus stages 0/1/2/3/4 we derived the following optimum thresholds: for KI 1.05/1.15/1.31/1.49 and for KMI 0.77/0.32/-0.08/-0.3. For Smolek/Klyce and Klyce/Maeda high standard deviations and overlapping confidence intervals were found; therefore no discrete thresholds could be defined. Nevertheless, for them we still found a good sensitivity and specificity in discriminating between healthy (stage 0) and keratoconus (stages 2-4) eyes in comparison with the other indices. CONCLUSIONS We derived thresholds for the metric keratoconus indices KI and KMI, which allow classification of keratoconus stages. These now need to be validated in clinical use. Smolek/Klyce and Klyce/Maeda were not sufficiently sensitive to allow classification into individual stages, but these indices did show a good specificity and sensitivity in discriminating between keratoconus and healthy eyes.

Effect of interface reflection in pseudophakic eyes with an additional refractive intraocular lens

Purpose To compare the surface reflections in a pseudophakic model eye with and without a monofocal additional refractive intraocular lens (add‐on IOL). Setting Department of Ophthalmology, Rudolf‐Virchow‐Klinikum Glauchau, Glauchau, and Experimental Ophthalmology, Saarland University, Homburg, Germany. Design Experimental study. Methods The Liou and Brennan model eye was used to determine the retinal surface reflections in a pseudophakic model eye with and without an add‐on IOL. The crystalline lens of the model eye was replaced by (1) a standard posterior chamber IOL (PC IOL) with a refractive power of 22.0 diopters (D) and (2) a PC IOL and an add‐on IOL with refractive powers of 19.0 D and 2.5 D, respectively. To theoretically estimate the impact of the reflected images to visual impression, the signal‐to‐noise ratio (SNR) was calculated under 2 conditions: without and with straylight and double reflection effects. Results Compared with the pseudophakic model eye without an add‐on IOL, the pseudophakic model eye with an add‐on IOL showed no relevant differences in the SNR under both conditions. Conclusion Findings indicate that implantation of monofocal add‐on IOLs will not induce relevant additional disturbing glare compared with conventional pseudophakia. Financial Disclosure Dr. Zoric is an employee of HumanOptics AG. Dr. Meßner is an employee of Dr. Schmidt Intraocularlinsen GmbH and HumanOptics AG. No other author has a financial or proprietary interest in any material or method mentioned.

Customized aspheric IOL design by raytracing through the eye containing quadric surfaces.

Purpose: The purpose of the present study was to demonstrate a method of how to calculate intraocular lenses with a customized asphericity and how to apply this strategy to clinical examples in cases where biometric data of the cornea (front and back surface topography) as well as distances in the eye are known. Methods: (1) we demonstrated an algebraic method for tracing a bundle of rays through a schematic eye containing surfaces which can be represented by 2nd order surfaces (quadric surfaces), and (2) we introduced a strategy for customization of the lens’ back surface for compensating the optical path length differences of the rays from object to image in terms of a wave front correction while predefining the lens front surface. Results: The presented method was applied to three working examples: example 1 referred to a centered optical system with a spherical cornea (front and back surfaces) and a predefined spherical lens front surface, example 2 referred to a centered optical system with aspherical surfaces for the corneal front and back surfaces and a predefined spherical lens front surface, and example 3 referrred to a non-centered system with a decentered aspherical cornea (front and back surface), and a predefined spherical lens front surface. The parameterized ray intersection points with the lens back surface were optimized in terms of equalizing the ray path lengths and a quadric surface was fitted to these ray intersection points to characterize the customized lens. The fitting error, ray spot diagram, and the optical path length of the rays are provided. Conclusion: This simple calculation strategy may be the first step in developing individual aspherical lenses, which have the potential to fully compensate spherical aberrations based on individual measures of the eye.

Additional multifocal sulcus-based intraocular lens: alternative to multifocal intraocular lens in the capsular bag.

Purpose To compare the visual outcomes of additional multifocal intraocular lenses (IOLs) for sulcus fixation with those of standard multifocal IOLs in the capsular bag. Setting Department of Ophthalmology, Rudolf‐Virchow‐Klinikum Glauchau, Glauchau, Germany. Design Prospective controlled clinical trial. Methods Eyes had phacoemulsification and implantation of a monofocal IOL in the capsular bag and an additional aberration‐free diffractive IOL in the ciliary sulcus (multifocal add‐on IOL group). Measurements of uncorrected and distance‐corrected distance, intermediate, and near visual acuities; contrast sensitivity; and defocus curve were performed 3 months postoperatively. Results were compared with those in eyes with an aberration‐correcting diffractive posterior chamber IOL (multifocal PC IOL group). Results The multifocal add‐on IOL group comprised 34 eyes of 20 patients and the multifocal PC IOL group, 31 eyes of 17 patients. Cataract surgery, IOL implantation, and the postoperative course were uneventful in all cases. There were no statistically significant differences in uncorrected and distance‐corrected distance, intermediate, or near visual acuities between the 2 groups. The median uncorrected distance visual acuity was 0.00 logMAR in both groups, and the median uncorrected near visual acuity was 0.10 logMAR in both groups. Contrast sensitivity testing yielded significantly better results in the multifocal add‐on IOL group, especially at spatial frequencies over 1.5 cycles per degree. Defocus curves were similar in the 2 groups. Conclusion Visual performance with a multifocal diffractive add‐on IOL was equivalent to that achieved with a commonly used multifocal diffractive PC IOL. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Iteratively re-weighted bi-cubic spline representation of corneal topography and its comparison to the standard methods.

PURPOSE The aim of this study is to represent the corneal anterior surface by utilizing radius and height data extracted from a TMS-2N topographic system with three different mathematical approaches and to simulate the visual performance. METHODS An iteratively re-weighted bi-cubic spline method is introduced for the local representation of the corneal surface. For comparison, two standard mathematical global representation approaches are used: the general quadratic function and the higher order Taylor polynomial approach. First, these methods were applied in simulations using three corneal models. Then, two real eye examples were investigated: one eye with regular astigmatism, and one eye which had undergone refractive surgery. A ray-tracing program was developed to evaluate the imaging performance of these examples with each surface representation strategy at the best focus plane. A 6 mm pupil size was chosen for the simulation. RESULTS The fitting error (deviation) of the presented methods was compared. It was found that the accuracy of the topography representation was worst using the quadratic function and best with bicubic spline. The quadratic function cannot precisely describe the irregular corneal shape. In order to achieve a sub-micron fitting precision, the Taylor polynomials order selection behaves adaptive to the corneal shape. The bi-cubic spline shows more stable performance. Considering the visual performance, the more precise the cornea representation is, the worse the visual performance is. CONCLUSIONS The re-weighted bi-cubic spline method is a reasonable and stable method for representing the anterior corneal surface in measurements using a Placido-ring-pattern-based corneal topographer.

Photodynamic inactivation of multidrug-resistant Staphylococcus aureus by chlorin e6 and red light (λ = 670 nm)

Multidrug-resistant Staphylococcus aureus (MDR-SA) are a frequent cause of antibiotic treatment refractory bacterial corneal infections. Photodynamic therapy (PDT) is being discussed as a putative treatment option to cure this type of bacterial infection. Here we tested the in vitro susceptibility of a set of 12 clinically derived MDR-SA isolates with differing genetic backgrounds and antibiotic resistance profiles against photodynamic inactivation (PDI) by the porphyrin chlorin e6 (Ce6) and red light (λ=670nm). All tested clinical isolates displayed a 5-log10 reduction in viable cells by Ce6 and red light, when cells were preincubated with the photosensitizer at concentrations ≥128μM for 30min in the dark, and a subsequent irradiation with light at λ=670nm (power density: 31mW/cm(2), absorbed dose: 18,6J/cm(2)) was applied. Similarly, cells of the laboratory strain Newman required the same Ce6 pre-incubation and light dose for a 5-log10 reduction in cell viability. Inactivation of crtM in strain Newman, which interferes with pigment production in S. aureus, rendered the mutant more susceptible to this PDT procedure, indicating that the level of resistance of S. aureus to this therapy form is affected by ability of the pathogen to produce the carotenoid pigment staphyloxanthin. Incubation of freshly explanted porcine corneas with a 0.5% Ce6 gel demonstrated that the photosensitizer can diffuse into and accumulate within the stroma of the cornea in concentrations found to be sufficient to yield a 5-log10 reduction of the S. aureus cell pool in vitro. These data suggest that PDI with Ce6 and red light might be a promising new option for the treatment of MDR-SA induced corneal infections.

Index of contrast sensitivity (ICS) in pseudophakic eyes with different intraocular lens designs

To evaluate the index of contrast sensitivity (ICS) in eyes after cataract surgery with various intraocular lens designs and to compare with the area under log contrast sensitivity curve (AULCSF).