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The applicability of donor and recipient tissue matching in corneal transplantation ("harmonization") to reduce residual astigmatism after keratoplasty was simulated using Matlab software. The height profile of the donor and recipient corneas was measured using the anterior segment optical coherence tomography (AS-OCT) Casia 2. After best fit of the donor button in the recipient bed the mean height difference as the mismatch, which had to be minimized, was derived from the height profile of the donor and recipient corneal front and back surfaces. The donor button was rotated in the recipient bed to extract the best fit situation where the mean height difference was minimized. After successful simulation, the procedure will be transferred to real measurement data.

Zusammenfassung Hintergrund und Ziele Die ‚Descement Stripping Automated Endothelial Keratoplasty‘ (DSAEK) ist heute ein Standardverfahren fur die operative Therapie von Pathologien des Hornhautendothels. Dabei tritt in der Regel eine Hyperopisierung in der Refraktion auf. Ziel ist es, auf der Basis von Modelldaten die Geometrie nach DSAEK vorherzusagen und ein Verfahren anzugeben, wie der Hornhautbrechwert bestimmt werden kann, um z.B. bei einer spateren Kataraktoperation eine refraktive Uberraschung zu vermeiden. Material und Methoden Auf der Basis des Kooijman-Modellauges wurde fur den Spender parallel zur Hornhautvorderflache ein Mikrokeratomschnitt simuliert, so dass das radiale Dickenprofil der Spenderlamelle abgeleitet werden konnte. Diese Spenderlamelle wurde ruckseitig an die Wirtshornhaut angeschmiegt und so das Profil der Hornhaut nach DSAEK ermittelt. Aus dem Vergleich der Kurvatur des Wirtes ohne und mit aufgelegter Spenderlamelle konnte die klinisch nachgewiesene Hyperopisierung erklart werden und eine Vorschrift abgeleitet werden, wie der Hornhautbrechwert nach DSAEK zu ermitteln ist. Ergebnisse Aus den Modelldaten des Kooijman-Auges resultierte eine zentral um 150 μm erhohte Hornhautdicke durch das Aufbringen der Spenderlamelle, peripher um etwa 250 μm. Die Geometrie der Hornhautruckflache weist neben einem verringerten Krummungsradius (um etwa 0,9 mm) eine veranderte konische Konstante (um etwa -0,13) auf. Die klinisch beobachtete persistierende Hyperopisierung kann direkt mit der Geometrieanderung durch das Aufbringen der Spenderlamelle erklart werden und betragt mit den Modelldaten 0,88 D. Schlussfolgerung Die DSAEK fuhrt in der Regel zu einer Hyperopisierung des Patienten, die sich durch die Veranderung der Ruckflachengeometrie der Hornhaut beschreiben lasst. Fur den Fall einer nachgeschalteten Kataraktoperation sollte anstatt der Keratometrie oder Hornhauttopografie, die auf der Vermessung der Hornhautvorderflache basieren, die Brechungscharakteristik der gesamten Hornhaut auf der Basis einer Hornhauttomographiemessung einbezogen werden, um eine persistierende Hyperopie im pseudophaken Auge zu vermeiden. Bei einer Triple-DSAEK sollte auf -1,5 dpt gezielt werden, um einer postoperativen Hyperopisierung vorzubeugen.

Purpose To analyze corneal surface temperature profile in a young and healthy study population and to determine the impact of corneal thickness (CT), anterior chamber depth (ACD), and endothelial cell density (ECD) on surface temperature. Methods In this prospective, single-center study 61 healthy right eyes of 61 subjects without tear film pathologies (mean age 24.9 ± 6.7 years) were recruited. Ocular surface temperature (OST) was measured with the Ocular Surface Thermographer TG-1000. From Pentacam HR CT and ACD, and from specular microscopy ECD and central corneal thickness (CCT) were acquired. From the raw measurement data (OST, CT and ACD) we extracted a) local OST the corneal center and 3 mm away from the center at the 3, 6, and 9 o‘clock positions, and b) Zernike parameters Z1, Z2 and Z3 to evaluate the general temperature profile within a 6 mm circular area around the center. Results Overall, there was no correlation between OST and CT, ACD or ECD. Local OST did not correlate with CT at any measurement position. On average local OST was highest at measurement positions where CT was lowest, but without reaching statistical significance. Baseline OST was highest at thin corneal regions and temperature decay over time was smallest in those regions. Z1, Z2 and Z3 correlated well with CT. Conclusions In healthy subjects corneal thickness, endothelial cell density and anterior chamber depth have no effect on corneal surface temperature. The general temperature profile seems to be influenced by the corneal thickness profile effecting a higher temperature and lower decay at thinner corneal regions.

Background So-called aberration-free intraocular lenses (IOLs) are well established in modern cataract surgery. Usually, they are designed to perfectly refract a collimated light beam onto the focal point. Methods We show how much aberration can be expected with such an IOL in a convergent light beam such as that found anterior to the human cornea. Additionally, the aberration in a collimated beam is estimated for an IOL that has no aberrations in the convergent beam. The convergent beam is modelled as the pencil of rays corresponding to the spherical wavefront resulting from a typical corneal power of 43 m −1 . The IOLs are modelled as infinitely thin phase plates with 20 m −1 optical power placed 5 mm behind the cornea. Their aberrations are reported in terms of optical path length difference and longitudinal spherical aberration (LSA) of the marginal rays, as well as nominal spherical aberration (SA) calculated based on a Zernike representation of the wavefront-error at the corneal plane within a 6 mm aperture. Results The IOL designed to have no aberrations in a collimated light beam has an optical path length difference of −1.8 μm, and LSA of 0.15 m −1 in the convergent beam of a typical eye. The corresponding nominal SA is 0.065 μm. The IOL designed to have no aberrations in a convergent light beam has an optical path length difference of 1.8 μm, and LSA of −0.15 m −1 in the collimated beam. Conclusions An IOL designed to have no aberrations in a collimated light beam will increase the SA of a patient's eye after implantation.

This article presents a non-invasive sensor setup for objective analysis of the pre-corneal human tear-film involving a time-resolved videokeratoscopy and simultaneous imaging of the lipid layer of the tear-film by a second CMOS-camera. This paper describes in detail the mechanical and optical design of the sensor setup, the realization of the entire illumination component with an integrated Placido grid projection, and the calculation of the image formation using the Placido grid. This concept is demonstrated here with a test subject in the full inter-blink period. All images were taken under physiological conditions. The sensor can assist the ophthalmologist in diagnosing Dry-Eye Syndrome. Results and other potential applications are discussed.

Background and purpose Presbyopia is characterized by a decreasing ability of accommodation – the eye's ability to alter the focus between far and near distance objects. After cataract surgery, accommodation is completely lost. Several years ago, small aperture (pinhole) implants have been presented in order to increase the depth of focus providing functional vision at far and near distance without the need for spectacles. We simulated the theoretical depth of focus with three different pseudophakic eye models in order to investigate the potential benefit arising from the implantation of small aperture optical (SAO) implants. The purpose was to compare the achievable defocus range of a SAO intraocular lens with a SAO corneal inlay. Material and methods We created three pseudophakic eye models with an aberration correcting intraocular lens (IOL): one with a corneal SAO implant (M1), a second one with a SAO intraocular lens (M2) and a third one with a conventional intraocular lens of the same optical design but without SAO (M0). Defocus curves were created by varying the focal length of a thin lens in front of the eye – which mimics the clinical assessment of defocus curves. Results With a Strehl ratio threshold of 0.05, the reference design M0 provided a maximum defocus range of approximately 1.7 D (with a 2.0 mm pupil) whereas both pinhole implants (M1 and M2) showed a defocus range up to 3.0 and 3.3 D, respectively. With large natural pupil diameter, where light passes outside the SAO aperture, the defocus range drops to 0.8 D/0.7 D for M1 and M2 compared to 0.7 D with M0. Conclusions The SAO intraocular lens showed a similar defocus range as the SAO corneal inlay. Both concepts have the potential of increasing depth of focus compared to a conventional intraocular lens. In case of large physiological pupil diameters these advantages of SAO implants may be lost.

We propose a framework for the analysis of the repeatability and precision of corneal elevation and the repeatability of corneal thickness data measured by clinically used topographers and tomographers. The repeatability is given by the standard deviation of different measurements of the same eye for each data point. The differences between measurements can partially be explained by different positions of the eye at each measurement. The precision is given by the standard deviation of the data after correction for displacements (decentration, tilts, rotations). The applicability is demonstrated using measurements of the Pentacam HR [1] (Oculus Optikgerate GmbH, Wetzlar, Germany) Scheimpflug tomographer. It provides anterior corneal elevation data with a precision that was almost limited by the axial resolution of 1μm in the central 6mm zone. This is approximately five times better than the precision of the posterior elevation. The results can be applied to surface approximation of the exported corneal elevation data and give a measure for the goodness of the fit.

Descemet stripping automated endothelial keratoplasty (DSAEK) is an established treatment option for pathologies of the corneal endothelium. It is typically accompanied with a hyperopic shift in refraction. The purpose of this work is to predict corneal geometry after DSAEK based on model data and to present a concept how to determine corneal power, e.g. for intraocular power calculation to prevent a refractive surprise with a subsequent cataract surgery.Based on data of the Kooijman schematic model eye we simulated a microkeratome cut parallel to the corneal front surface for donor trephination to determine the radial thickness profile of the posterior corneal donor lamella. This donor lamella was tension-neutrally adapted to the back surface of the host and the profile of the cornea after DSAEK was derived and characterized by a quadric surface. Comparison with the curvature of the host without and with donor could resample hyperopic shift which was published in literature. A method was shown how to determine corneal power after DSAEK.From the data of the Kooijman schematic model eye and the donor characteristics central / peripheral corneal thickness was increased by 150 / 250μm due to adaptation of the donor lamella. Geometry of corneal back surface showed a reduced radius of curvature (by about 0.9mm) and a change in conic constant (by about -0.13). Persistent clinically observed hyperopic shift correlates to the change in geometry of the cornea due to adaptation of the donor lamella, which reduces corneal power by 0.88 D.DSAEK leads to a hyperopic shift in refraction, which can be explained by a change in corneal back surface geometry. In case of subsequent cataract surgery, the intraocular lens power should be calculated with consideration of both corneal surfaces rather than keratometry or corneal topography in order to minimize a systematic hyperopic shift due to misinterpretation of corneal power after DSAEK. In case of a Triple-DSAEK, a target refraction of -1.5 D should be chosen in order to safely prevent postoperative hyperopia.

As the average corneal shape can effectively be approximated by a conic section, a determination of the corneal shape by biconic parameters is desired. The purpose of the paper is to introduce a straightforward mathematical approach for extracting clinically relevant parameters of corneal surface, such as radii of curvature and conic constants for principle meridians and astigmatism. A general description for modeling the ocular surfaces in a biconic form is given, based on which an implicit parametric surface fitting algorithm is introduced. The solution of the biconic fitting is obtained by a two sequential least squares optimization approach with constrains. The data input can be raw information from any corneal topographer with not necessarily a uniform data distribution. Various simulated and clinical data are studied including surfaces with rotationally symmetric and non-symmetric geometries. The clinical data was obtained from the Pentacam (Oculus) for the patient having undergone a refractive surgery. A sub-micrometer fitting accuracy was obtained for all simulated surfaces: 0,08 μm RMS fitting error at max for rotationally symmetric and 0,125 μm for non-symmetric surfaces. The astigmatism was recovered in a sub-minutes resolution. The equality in rotational symmetric and the superiority in non-symmetric surfaces of the presented model over the widely used quadric fitting model is shown. The introduced biconic surface fitting algorithm is able to recover the apical radii of curvature and conic constants in principle meridians. This methodology could be a platform for advanced IOL calculations and enhanced contact lens fitting.

We present a biomechanical eye model to induce pseudophakic accommodative movement for evaluation of the focal shift of accommodative intraocular lenses. Therefore, an accommodative intraocular lens (IOL) was implanted into freshly enucleated porcine eyes. The eyes were glued into a mechanical apparatus to expand the ciliar body effectuating mechanical accommodation. An optical coherence tomographer was used to measure positional and geometrical changes of the IOL for different levels of expansion. The expansion unit allowed stretching of the globe of several millimeters. With the biomechanical eye model we were able to simulate the mechanical functionality of accommodation as well as to measure the lens vault and change in geometry. Accommodative vault could only be measured with an intact vitreous, indicating that the vitreous plays an important role for the functionality of accommodative IOLs.

Purpose Most of the protective eye wear devices currently on the market are manufactured on simple polycarbonate shields, produced by injection molding techniques. Despite high importance of optical quality , injection molds are rarely inspected for surface quality before or during the manufacturing process. Quality degradation is mainly monitored by optical testing of the molded parts . The purpose of this work was to validate a non-contact deflectometric measurement technique for surface and shape analysis of injection molds to facilitate deterministic surface quality control and to monitor minor conformity of the injection mold with the design data. Material and Methods The system is based on phase-measuring deflectometry with a operating measurement field of 80 × 80 mm2 (±18° slope), a lateral resolution of 60 μm and a local sensitivity of some nanometers . The calibration was tested with a calibration normal and a reference sphere. The results were crosschecked against a measurement of the same object with a tactile coordinate measuring machine . Eight injection molds for production of safety goggles with radii of +58 mm (convex) and -60 mm (concave) were measured in this study. The molds were separated into two groups (cavity 1 and 2 of the tool with different polishing techniques) and measured to test whether the measurement tool could extract differences. The analysis was performed on difference height between the measured surface and the spherical model. Results The device could derive the surface change due to polishing and discriminate between both polishing techniques, on the basis of the measured data. The concave nozzle sides of the first group (cavity 1) showed good shape conformity. In comparison, the nozzle sides of the second group (cavity 2) showed local deviations from design data up to 14.4 μm. Local form variations of about 5 μm occurred in the field of view. All convex ejector sides of both groups (cavity 1 and 2) showed rotational symmetric errors and the molds were measured in general flatter than design data. Conclusion We applied a deflectometric system for measuring and evaluating specular reflective injection molding tools to optimize the production process of occupational eye wear. The surface quality could be inline monitored in the production processes for actual spectacle models.

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 polynomial's 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.

This paper describes a general theoretical model for computing a broad beam excitation light transport in a 3D diffusion medium. The model is based on the diffusion approximation of the radiative transport equation. An analytical approach for the light propagation is presented by deriving a corresponding Green's function. A finite cylindrical domain with a rectangular cross section was considered as a 3D homogeneous phantom model. The results of the model are compared with corresponding experimental data. The measurements are done on solid and liquid phantoms replicating tissue-like optical properties.

This article describes a model eye created to mimic the three-layered human tear-film. The model replicates the properties of the mucin, liquid and lipid layer as well as the time-course behavior including blinking process and tear film break-up for measurements with the tear film sensor described in Part 1. The setup basically consists of a sphere that is moistened by a dilution of tear film substitute. Therefore, the time point of the first break-up strongly depends on the consistency of the dilution. By means of an integrated heater, the evaporation rate of the artificial tear-film can be increased. To illustrate the applicability of the model eye, exemplary images during tear-film simulation, taken with and without using the heater, are shown. All images were captured by the sensor. Results and other potential applications are briefly discussed.

A new method is described for obtaining a 2D reconstruction of a fluorescent source distribution inside a diffusion medium from planar measurements of the emission light at the surface after excitation by a plane wave. Point sources are implanted at known locations of a rectangular phantom. The forward model of the photon transport is based on the diffusion approximation of the radiative transport equation (RTE) for homogeneous media. This can be described by a hierarchical system of two time-independent RTE's, one for the excitation plane wave originating from the external light source to the medium and another one for the fluorescence emission originating from the fluorophore marker to the detector. A linear inverse source problem was solved for image reconstruction. The applicability of the theoretical method is demonstrated in some representative working examples. For an optimization of the problem we used least squares minimization technique.

In this article, a non-contact imaging setup for the acquisition of multiple 2D projections of fluorescent probes in tissue-like phantoms is described. The setup basically consists of a high-sensitivity CCD camera for the detection of fluorescence and a rotating broad-beam light source for the continuous illumination of a rotatable phantom located in the rotation center. This allows for imaging of various projections in a full angular projection range of 360°. Beside the detailed description of the system layout, important key characteristics of the setup are outlined. The setup is demonstrated with projectional measurements of a tissue-like phantom and the results are verified by comparison of the projection-dependent fluorescence intensity distributions with corresponding 2D simulations. It is shown that the instrument is suitable for the sensitive detection of fluorescence emanating from fluorescent objects in tissue-like phantoms. Such setup could facilitate the collection of large projection data sets as they are used in optical fluorescence tomography of small animals.