Comparison of the Zeiss IOLMaster and applanation A-scan ultrasound: biometry for intraocular lens calculation

PURPOSE

A comparison of axial length estimates using applanation A-scan ultrasound and the Zeiss IOLMaster was conducted. The accuracy in predicting postoperative refraction determined by each method was also compared.

METHODS

A cross-sectional study was performed on 51 eyes in 46 patients presenting to clinical practice for cataract surgery assessment. Preoperative measurement of axial length was performed with applanation ultrasound and the IOLMaster. The IOLMaster measurements were used to determine the intraocular lens power based on the SRK/T formula. Postoperative refractive outcomes were obtained and spherical equivalent calculated and compared to the predicted refractive error with each biometric method.

RESULTS

On average the axial lengths measured by the IOLMaster were longer by 0.15 mm compared to ultrasound biometry (P < 0.01). Using the IOLMaster over applanation ultrasound biometry significantly improved the postoperative refractive outcome from 0.65 D to 0.42 D (P = 0.011).

CONCLUSIONS

The IOLMaster provides an accurate axial length measurement and results in accurate intraocular lens power calculation based on the SRK/T formula. It is quick and easy to use and provides a non-contact technique with no risk of infection or corneal abrasion.

Definition of the diffusion coefficient in scattering and absorbing media

We revisit the definition of the diffusion coefficient for light transport in scattering and absorbing media. From an asymptotic analysis of the transport equation, we present a novel derivation of the diffusion coefficient, which is restricted neither to low absorption nor to a situation in which the specific intensity is quasi-isotropic. Our result agrees with previous expressions of the diffusion coefficient in the appropriate limit. Using numerical simulations, we discuss the implications of the proper choice of the diffusion coefficient for time-dependent transport.

Accelerated Monte Carlo models to simulate fluorescence spectra from layered tissues

Two efficient Monte Carlo models are described, facilitating predictions of complete time-resolved fluorescence spectra from a light-scattering and light-absorbing medium. These are compared with a third, conventional fluorescence Monte Carlo model in terms of accuracy, signal-to-noise statistics, and simulation time. The improved computation efficiency is achieved by means of a convolution technique, justified by the symmetry of the problem. Furthermore, the reciprocity principle for photon paths, employed in one of the accelerated models, is shown to simplify the computations of the distribution of the emitted fluorescence drastically. A so-called white Monte Carlo approach is finally suggested for efficient simulations of one excitation wavelength combined with a wide range of emission wavelengths. The fluorescence is simulated in a purely scattering medium, and the absorption properties are instead taken into account analytically afterward. This approach is applicable to the conventional model as well as to the two accelerated models. Essentially the same absolute values for the fluorescence integrated over the emitting surface and time are obtained for the three models within the accuracy of the simulations. The time-resolved and spatially resolved fluorescence exhibits a slight overestimation at short delay times close to the source corresponding to approximately two grid elements for the accelerated models, as a result of the discretization and the convolution. The improved efficiency is most prominent for the reverse-emission accelerated model, for which the simulation time can be reduced by up to two orders of magnitude.

Fluorescence enhancement from an array of subwavelength metal apertures

We report the resonant excitation of a fluorescing molecular monolayer applied to a periodic array of subwavelength apertures in a metal film. The peak fluorescence occurs under conditions of maximum transmission of the excitation light, which indicates strong enhancement of the incident light within the apertures under resonant conditions. Fluorescence output normalized to the aperture fill fraction is enhanced by nearly 40 times, and the rate of photobleaching is increased by approximately a factor of 2, suggesting an increase in the fluorescence yield.

Finite-difference time-domain simulation of ultrashort pulse propagation incorporating quantum-mechanical response functions

A semiclassical implementation of the finite-difference time-domain method is used to simulate coherent linear propagation of ultrashort mid-infrared pulses through optically dense samples of isotropically diluted liquid water. Bloch equations for the density matrix are used as a simple model of the O--H oscillator relaxation, and the algorithm is extended to other response functions. Sensitivity of the field to the form of the response function is demonstrated, and the results are compared with experimentally determined electric fields in the same media [Rev. Sci. Instrum. 73, 2227 (2002)].

Polymer replicas of photonic porous silicon for sensing and drug delivery applications

Elaborate one-dimensional photonic crystals are constructed from a variety of organic and biopolymers, which can be dissolved or melted, by templating the solution-cast or injection-molded materials in porous silicon or porous silicon dioxide multilayer (rugate dielectric mirror) structures. After the removal of the template by chemical dissolution, the polymer castings replicate the photonic features and the nanostructure of the master. We demonstrate that these castings can be used as vapor sensors, as deformable and tunable optical filters, and as self-reporting, bioresorbable materials.

Optical bioluminescence and positron emission tomography imaging of a novel fusion reporter gene in tumor xenografts of living mice

Noninvasive imaging of reporter gene expression using various imaging modalitiesis playing an increasingly important role in defining molecular events in the field of cancer biology, cell biology, and gene therapy. In this study, a novel reporter vector was constructed encoding a fusion protein comprised of a mutant herpes simplex virus type 1 thymidine kinase (HSV1-sr39tk) (tk), a positron emission tomography (PET) reporter gene, and renilla luciferase (rl), a bioluminescence optical reporter gene joined by a 20 amino acid long spacer sequence. We validated the activity of the two enzymes encoded by the fusion protein (tk(20)rl) in cell culture. Then, tumors stably expressing the tk(20)rl fusion gene were imaged both by microPET and optically using a cooled charge coupled device camera in xenograft-bearing living mice. Using a single fusion reporter (PET/optical) gene should accelerate the validation of reporter gene approaches developed in cell culture for translation into preclinical and clinical models.

High-speed adaptive interferometer for optical coherence-domain reflectometry through turbid media

Two-wave mixing in a dynamic holographic film acts as the adaptive beam combiner in a short-coherence interferometer that performs optical coherence-domain reflectometry (OCDR) through turbid media. This approach combines the high spatial resolution and sensitivity of coherence-domain reflectometry with photorefractive quantum-well-based adaptive homodyne detection. A depth resolution of 28 microm and penetration through 16 mean free paths in a turbid medium have been obtained in this adaptive OCDR application.

Functional imaging of the retinal layers by laser scattering: an approach for the study of Leão's spreading depression in intact tissue

This paper presents a novel optical approach for the study of spreading depression in isolated retina. The method makes it possible to register the laser light scattered from each layer of the tissue, yielding a functional image of the retina during spreading depression. The tissue is kept intact, since histological cuts are not necessary. Measurements of other variables, such as extracellular potential, are also allowed by the described method. This is done simultaneously with the functional image in a high spatial resolution, with the positioning of the microelectrode tip being easily monitored. The information about temporal and spatial evolution of light was compacted in a single image. The image-processing technique used here enables the visualization of the light scattered by the inner plexiform layer (IPL), which is the most prominent scatter layer during spreading depression. The wavefront velocity and its increase as two wavefronts approach each other can then be determined, and it is also possible to observe the thickness variation of the tissue during the wave travel. The relationship between two peaks of light-scattering sequence during the phenomenon was studied at two wavelengths (632.8 and 543.5 nm). This relationship is shown to be dependent on the wavelength.

[Modeling light distribution in nasal tissue structures]

There are different applications in the field of optical diagnostics in which the theories explaining the light transport in tissue do not lead to simple solutions for complicate geometric conditions. In these cases the Monte Carlo method provides a powerful tool to solve this problem statistically. In order to simulate the light transport in the nasal region a model was created which includes the structure depending on the swelling of the mucous membrane as well as the Monte Carlo model. Using this model it is possible to evaluate the measured values qualitatively. However, due to the long distance between light source and detector the statistical error becomes a major problem for reliable statements.

LED-display for an intraocular microoptic system

In this paper the design and fabrication of an LED array usable for an intraocular vision aid (IOVA) is presented. IOVA is intended for people with vastly opaque cornea caused by explosion or chemical burns. The LED array consists of 1024 single GaP/GaAsP LEDs. In a first step an 8 x 8 pixel LED array has been fabricated. This LED array is bonded to a CMOS driver circuit performing a miniaturized display by using flip-chip-technique. Thus each LED pixel can be driven separately and the generated light passes the substrate.

[Development of a laser-optical tomograph for demonstration of CT imaging without ionizing radiation]

Computed X-ray tomography (CT) is one of the most powerful diagnostic procedures in medicine. In this study, we developed a laser-optical CT scanner for the use by students as part of their curriculum in biomedical engineering. Our CT set-up employs a linear-scan technique where the measurement objects (light absorbing phantoms embedded in immersion oil), the light emitter (modulated laserdiode), and the detector (photodiode) are moved by linear-step motors. The spatial resolution is limited by the width of the laser beam (2 mm) and the smallest achievable raster step size (0.02 mm). Optical tomographic images of various objects can be measured within a few minutes and allow the demonstration of imaging principles like extinction, scanning, projection, and reconstruction techniques.

New concept for the development of a confocal endomicroscope

It is one of modern medicine's top priorities to reduce the stress for the patient during diagnosis and therapy by designing minimally invasive applications of medical techniques. Microsystems technology has always held the key to minimally invasive solutions in surgery and micro-endoscopy. The new measuring system KOMED is currently developed for the application of in-vivo cellular microscopy. This approach is based on the concept of a miniaturised fibre-optical confocal microscope. The application range of this microsensor system includes the minimally invasive optical biopsy for purposes such as the early detection of tumour cells. In this paper the concept of the KOMED system is described, as well as technical challenges to be solved in the project.

Bifocal ultra thin intraocular lens--optical properties and clinical results

The therapy of the cataract with the implantation of intraocular lenses is a great success story over the last 20 years. However cataract patients cannot accommodate anymore and need additional glasses for the far and near view. In the last 10 years bifocal concepts for intraocular lenses have been investigated with little success. Our new bifocal diffractive bifocal lens showed in clinical trials with 150 Patients an excellent visual performance. Less than 10% of the patients still use additional glasses. Due to the diffractive principle the lens can be manufactured very thin. Therefore the lens can be easily implanted through very small incisions. The lens shows the potential for the replacement of multifocal glasses.

A CMOS clock and data recovery circuit for intraocular microsystems

This paper presents the implementation of a clock and data recovery circuit (CDR) for intraocular microsystems. The CDR was designed to minimize chip area and power consumption and to recover the clock and data signals from the incoming data stream. Since the CDR has been designed without any external components it is well suited for being integrated in an intraocular microsystem. Simulation results show that this CDR works with power dissipation of less than 2.4 mW with a single 3.3 V power supply. The simulations are based on a 0.6 micron n-well CMOS single-polysilicon, three-metal technology.

Polarimetric methods for measurement of intra ocular glucose concentration

Due to the increasing lifespan in the industrialized world the number of senior Diabetes patients is growing rapidly. Using non-invasive techniques, measurements of the blood sugar level could be done more frequently and hence diagnosis as well as therapy of type II Diabetes Mellitus can be improved especially for this group of senior patients. Especially polarimetric techniques measuring at the human eye offer promising properties for non-invasive and painless measurement. This article discusses different approaches for utilizing the polarizing properties of the Aqueous Humour (AH) for quantitative glucose measurements.

Micro displays as intraocular vision aid--design of an optical system

All over the world about 10 million people suffer from blindness caused by an opaque, irreversible damaged and inoperable cornea. Many of these people still have intact retinal functions. After Prof. Heimann of the University of Köln miniaturized and implantable displays might help such people to restore partially their vision. Optical and physiological constraints of such vision aids are discussed.

Near-field measurement of short-range correlation in optical waves transmitted through random media

Two-dimensional near-field images of speckle patterns formed by optical waves transmitted through a disordered porous silica glass sample are measured. The corresponding 2D intensity correlation function, C, is extracted. The subwavelength spatial resolution of near-field microscopy allows us to resolve in the spatial distribution of C the expected subwavelength oscillations and to follow their dependence on the excitation wavelength. Finally, we deduce the effective refractive index of the material by fitting the theoretical spatial dependence of C to our experimental results.

Utilizing lab-based CAD/CAM technology for metal-free ceramic restorations

This article describes 2 clinical cases using technology and materials that give the laboratory technician complete control over the timing, fit, and color of the restoration, while the dentist can rely on the consistent dependability of the technology and the aesthetic quality of the material.

Comparison of NIOSH 5040 method versus Aethalometer to monitor diesel particulate in school buses and at work sites

This study, undertaken initially to understand apparent differences between two recent reports of diesel particulate matter (DPM) inside school buses, involved side-by-side comparisons of two different methods for measuring ambient and occupational exposures to DPM. The NIOSH 5040 method yields time-weighted-average measurements of elemental carbon (EC) and organic carbon (OC), whereas the Aethalometer yields near-real time measures of carbonaceous particles (black carbon or BC) by optical absorption. The two methods were compared on three school buses and in three different work sites. Three side-by-side sampling configurations were used (open-faced filter with and without two different cyclones) in triplicate along with two or three Aethalometers. BC readings were correlated with results from open-faced cassettes, but there were statistically significant differences between the results of side-by-side Aethalometers. In addition, Aethalometer airflow rates were inaccurate, the instruments were sensitive to vibration, optical calibration could not be performed, and historically derived conversion factors to relate EC and BC were not appropriate. The Aethalometer could prove useful for monitoring of industrial work sites, but only after a method for external calibration and improvements in pump design and vibration isolation are developed.

Optimum pulse duration and radiant exposure for vascular laser therapy of dark port-wine skin: a theoretical study

Laser therapy for cutaneous hypervascular malformations such as port-wine stain birthmarks is currently not feasible for dark-skinned individuals. We study the effects of pulse duration, radiant exposure, and cryogen spray cooling (CSC) on the thermal response of skin, using a Monte Carlo based optical-thermal model. Thermal injury to the epidermis decreases with increasing pulse duration during irradiation at a constant radiant exposure; however, maintaining vascular injury requires that the radiant exposure also increase. At short pulse durations, only a minimal increase in radiant exposure is necessary for a therapeutic effect to be achieved because thermal diffusion from the vessels is minimal. However, at longer pulse durations the radiant exposure must be greatly increased. There exists an optimum pulse duration at which minimal damage to the epidermis and significant injury within the targeted vasculature occur. For example, the model predicts optimum pulse durations of approximately 1.5, 6, and 20 ms for vessel diameters of 40, 80, and 120 microm, respectively. Optimization of laser pulse duration and radiant exposure in combination with CSC may offer a means to treat cutaneous lesions in dark-skinned individuals.

Optically induced multispin entanglement in a semiconductor quantum well

According to quantum mechanics, a many-particle system is allowed to exhibit non-local behaviour, in that measurements performed on one of the particles can affect a second one that is far away. These so-called entangled states are crucial for the implementation of most quantum information protocols and, in particular, gates for quantum computation. Here we use ultrafast optical pulses and coherent techniques to create and control spin-entangled states in an ensemble of non-interacting electrons bound to donors (at least three) and at least two Mn2+ ions in a CdTe quantum well. Our method, relying on the exchange interaction between localized excitons and paramagnetic impurities, can in principle be applied to entangle an arbitrarily large number of spins.