This PDF file contains the editorial “Editorial: A Letter from the Editor” for JBO Vol. 1 Issue 02

The cornea and the lens are the optical elements of the eye, responsible for correctly focusing light rays on the retina. As the eye ages, both the cornea and the lens undergo structural changes, some of which affect function. This review deals with such age-related changes and any functional manifestations arising from them.

This paper gives an introduction to optical coherence tomography (OCT), explains its basic principles, and discusses the information content of OCT images. Various interferometric techniques used in OCT are reviewed and a short survey of results obtained so far in different fields of application and possible future developments are presented.

A new noninvasive technique for monitoring capillary blood flow has been developed. Based on the phenomenon of time-varying laser speckle, it is a digital version of single-exposure speckle photography. It provides a velocity map of the area of interest in real time without the need for scanning. The results of some initial experiments on volunteers are presented.

We present a formal, microscopic, solution of the wave propagation problem for an inhomogeneity embedded in an isotropically disordered, multiple scattering, homogeneous background. The inhomogeneity is described by a local change in the complex, dielectric autocorrelation function B(r,r8) [v4/c4^e*(r)e(r8)&ensemble for a wave of frequency w and velocity c. For the homogeneous background, we consider a dielectric autocorrelation function Bh(r−r8) arising from a colloidal suspension of small dielectric spheres. This autocorrelation function can be determined using a newly developed technique called phase space tomography for optical phase retrieval. This technique measures the optical Wigner distribution function I(R,k) defined as the Fourier transform, with respect to r, of the electric field mutual coherence function ^E*(R+r/2)E(R −r/2)&ensemble. The Wigner distribution function is the wave analog of the specific light intensity, Ic(R,k ˆ ), in radiative transfer theory which describes the number of photons in the vicinity of R propagating in direction k ˆ. The Wigner function describes coherence properties of the electromagnetic field which can propagate much longer than the transport mean-free-path l* and which are not included in radiative transfer theory. Given the nature of the homogeneous background, repeated light intensity measurements, which determine the optical phase structure at different points along the tissue surface, may be used to determine the size, shape, and internal structure of the inhomogeneity. In principle, this method improves the resolution of optical tomography to the scale of several optical wavelengths in contrast to methods based on diffusion approximation which have a resolution on the scale of several transport mean-free-paths.

We report preliminary clinical testing of elastic-scattering spectroscopy for the detection of pathologies of the gastrointestinal tract. Tissue pathologies are detected and diagnosed using spectral measurements of elastically scattered light in an optical geometry that results in sensitivity to both the absorption and scattering properties of the tissue, over a wide range of wavelengths (300 to 750 nm). The system employs a small fiber optic probe, which is amenable to use with most endoscopes or catheters, or to direct surface examination, as well as interstitial needles. In this paper we report the results of preliminary clinical measurements on various organ sites of the gastrointestinal tract. In several instances the data indicate promise for this diagnostic method to distinguish malignant and dysplastic conditions from normal or other diagnoses.

Additions of a solute/carbohydrate in tissue affect the size of tissue cells and the refractive indexes of the extra- and intracellular fluids, and thus the overall tissue scattering properties. We use both the Rayleigh- Gans and Mie theory approximation in calculating effects of the osmolarity and refractive indexes on the reduced scattering coefficient of tissue, and employ photon diffusion theory to associate the reduced scattering coefficient to the mean optical path length. The calculations show that changes of scattering in tissue depend not only on the change in extracellular refractive index but also on the change in osmolarity, and thus on the change in cell size and volume fraction. Experimentally, we have utilized time-domain and frequencydomain NIR techniques to measure the changes of optical properties caused by an addition of a solute in tissue models and in perfused rat livers. The temperature-dependent path length measurement of the perfused liver confirms the dependence of tissue scattering on the tissue cell size. The results obtained from the liver with three kinds of carbohydrate perfusion display different scattering aspects and can be well explained by changes in cell size and in extracellular as well as intracellular refractive indexes. The consistency between the theoretical and experimental results confirms the dependence of optical properties in (liver) tissue on both tissue osmolarity and relative refractive indexes between the extracellular and intracellular compartments. This study suggests that the NIR technique is a novel and useful tool for noninvasive, physiological monitoring.

The group refractive index and physical thickness of dry and hydrated type I collagen films are measured using optical low-coherence reflectometry. The average value for the group refractive index of dry and fully hydrated collagen films at lo = 850 nm is, respectively, 1.53 6 0.02, and 1.43 6 0.02. The physical thickness of type I collagen films nearly doubles when going from the dry (56 mm) to hydrated (118 mm) state.

Cell damage by low-power 365-nm radiation of a 50-W high-pressure mercury microscopy lamp was studied. Exposure of Chinese hamster ovary (CHO) cells to ultraviolet-A (UVA) radiation .10 kJ/m2 resulted in significant modifications of nicotinamide adenine dinucleotide (NADH) attributed autofluorescence and inhibition of cell division. Single-cell gel electrophoresis (comet assay) revealed UVA-induced single-strand DNA breaks. According to these results, UVA excitation radiation in fluorescence microscopy may damage cells. This has to be considered in vital cell microscopy, e.g., in calcium measurements.

Besides heart rate and arterial blood pressure, several parameters of the cardiovascular system fluctuate spontaneously. In the current study, the fluctuations of tissue blood content and blood volume pulse were investigated using two parameters of the photoplethysmographic (PPG) signal: the parameter BV, defined by: BV=Const−BL where BL is the baseline of the PPG signal, and the amplitude (AM), which are related to the blood volume and to the systolic blood volume increase, respectively. The PPG measurements were performed on the fingertips of ten healthy male subjects for 5 to 10 min and the PPG signal was digitally analyzed. Both BV and AM show low frequency fluctuations, which, for 23 out of 26 examinations, were positively correlated, with a lag of BV relative to AM. In three examinations, however, the two parameters were inversely correlated. A lower correlation was found between each of these parameters and the PPG period, which is actually the cardiac period. The results show that several mechanisms are involved in the spontaneous periodic fluctuations in the vascoconstriction level, which are known to be mediated by the sympathetic nervous system. The digital PPG provides, therefore, a potential tool for evaluating the role of the sympathetic nerves in the regulation of the microcirculation.

The effects of Holmium:YAG laser energy with and without a topical fluoride mixture (resin to NaF) was compared with two types of topical fluorides on surface topography and resistance to acid destruction of root surfaces. Scanning electron microscopy (SEM) was used to evaluate the effects of the selected treatments on surface topography before acid exposure. Toluidine blue dye was used to test the permeability of root surfaces after acid exposures. SEM examinations of the dentinal root surfaces showed consistently smooth surfaces with tubule closures when using topical resin to fluoride and HO:YAG laser treatment; in contrast, HO:YAG laser energy treatment alone exhibited increased roughness of root surfaces. Topical fluoride applications alone presented surfaces similar to untreated control sites. Toluidine blue dye penetration into root surfaces of the fluoride/laser-treated root surfaces showed significantly less dye penetration after acid exposures than controls and other treatment protocols. The results of this study indicate that the resin–fluoride application and holmium:YAG irradiation effectively produced increased smoothness and increased resistance to destruction of root surfaces in human extracted teeth under these in vitro conditions.