Modeling retinal detachment associated with hemorrhage by Monte Carlo simulation.

In this work we study fundus reflection in the case of retinal detachment. Vitreous humor builds up beneath the retina through a break in the retina or when there is traction on the retina. Further, we assume that this detachment is associated with hemorrhage in regions both above and below the retina. To investigate hemorrhage, we assume erythrocytes to be spheres of different radii. Then we apply Mie scattering theory to these spheres and calculate the scattering coefficient, the absorption coefficient, and the anisotropy factor. Using these parameters, we apply Monte Carlo simulation to calculate reflection. In order to model fundus reflection under retinal detachment, we define three types of reflection: reflection from the vitreous body, retinal reflection where photons are reflected from the retinal vitreous interface once, and retinal reflection where photons are reflected many times from the retinal vitreous interface.

Fourier transform spectrometer based on Fabry-Perot interferometer.

We analyze the Fourier transform spectrometer based on a symmetric/asymmetric Fabry-Perot interferometer. In this spectrometer, the interferogram is obtained by recording the intensity as a function of the interferometer length. Then, we recover the spectrum by applying the discrete Fourier transform (DFT) directly on the interferogram. This technique results in spectral harmonic overlap and fictitious wavenumber components outside the original spectral range. For this purpose, in this work, we propose a second method to recover the spectrum. This method is based on expanding the DFT of the interferogram and the spectrum by a Haar or box function. By this second method, we recovered the spectrum and got rid of the fictitious spectral components and spectral harmonic overlap.

Dispersion compensation in Fourier domain optical coherence tomography.

In this work, we propose a numerical technique to compensate for errors due to dispersion effects in Fourier domain optical coherence tomography. The proposed technique corrects for errors in depth measurements and resolution loss due to dispersion. The results show that, by using this technique, errors in thickness measurement are reduced from about 5% to less than 0.1% depending on the sample length and the amount of dispersion. Also, an improvement in the resolution from about 50 µm to less than 10 µm is demonstrated.

Symmetric moving-optical-wedge interferometer for Fourier transform spectroscopy: a step toward miniaturization.

In this paper we propose a modification to the ordinary moving-optical-wedge interferometer used for Fourier transform spectrometry. The ordinary wedge interferometer suffers from asymmetry in the visibility pattern, asymmetry in the interferogram, large volume, large weight, and greater motion of the wedge. Our proposed interferometer is based on using two pair of wedges. This results in symmetry in visibility pattern, symmetry in interferogram, halved size, halved motion, and more throughput.

Signal-to-noise ratio calculation in a moving-optical-wedge spectrometer.

In this paper we study the signal-to-noise ratio degradation in a moving-optical-wedge interferometer when used as an optical spectrometer. Both the mechanical vibration and temperature fluctuation effects are studied, and the effects are compared to their counterparts in a conventional Michelson interferometer. While the wedge interferometer is found to be more immune to linear translational vibration, it shows much higher sensitivity to rotational vibration.

Spot size effects in miniaturized moving-optical-wedge interferometer.

In this paper we study the effect of diffraction on the performance of a miniaturized moving-optical-wedge interferometer. By using the Gaussian model, we calculate the degradation of the interferometer visibility due to diffraction effects. We use this model to optimize the detector size required to obtain maximum visibility and study its effect on resolution of Fourier transform spectrometers based on a moving-optical-wedge interferometer. A comparison between these effects in Michelson and wedge interferometers is also presented showing the advantage of the moving-optical-wedge interferometer in suppressing the diffraction effects with respect to the Michelson interferometer.

Diffraction effects in optical microelectromechanical system Michelson interferometers.

We study the effect of diffraction on the performance of microelectromechanical system Michelson interferometers. By using a simple Gaussian model, we calculate the degradation of the interferometer visibility due to the diffraction effect. We then use this model to estimate the optimum detector diameter to maximize the fringe visibility at the interferometer output and study its effect on the resolution of Fourier transform spectrometers based on Michelson interferometers.

Dispersion compensation in moving-optical-wedge Fourier transform spectrometer.

In this paper we study the effect of material dispersion on the performance of a moving-optical-wedge Fourier transform spectrometer. The spectrum is thus evaluated numerically using a test spectrum source. The obtained numerical results show that the classical technique for numerical dispersion compensation, usually used with a Michelson interferometer, cannot be efficiently used with wedge interferometers as it is limited to the cases of weak dispersion. The error in this technique is thus evaluated in different cases and a new numerical technique is proposed to overcome this error. We also notice shrinkage in the interferogram spread in the spatial domain in contradiction with the normal dispersion effect in a Michelson interferometer.

A Method for Medical Diagnosis Based on Optical Fluence Rate Distribution at Tissue Surface.

Optical differentiation is a promising tool in biomedical diagnosis mainly because of its safety. The optical parameters' values of biological tissues differ according to the histopathology of the tissue and hence could be used for differentiation. The optical fluence rate distribution on tissue boundaries depends on the optical parameters. So, providing image displays of such distributions can provide a visual means of biomedical diagnosis. In this work, an experimental setup was implemented to measure the spatially-resolved steady state diffuse reflectance and transmittance of native and coagulated chicken liver and native and boiled breast chicken skin at 635 and 808 nm wavelengths laser irradiation. With the measured values, the optical parameters of the samples were calculated in vitro using a combination of modified Kubelka-Munk model and Bouguer-Beer-Lambert law. The estimated optical parameters values were substituted in the diffusion equation to simulate the fluence rate at the tissue surface using the finite element method. Results were verified with Monte-Carlo simulation. The results obtained showed that the diffuse reflectance curves and fluence rate distribution images can provide discrimination tools between different tissue types and hence can be used for biomedical diagnosis.

Modeling of vision loss due to vitreous hemorrhage by Monte Carlo simulation.

Vitreous hemorrhage is the leaking of blood into the vitreous humor which results from different diseases. Vitreous hemorrhage leads to vision problems ranging from mild to severe cases in which blindness occurs. Since erythrocytes are the major scatterers in blood, we are modeling light propagation in vitreous humor with erythrocytes randomly distributed in it. We consider the total medium (vitreous humor plus erythrocytes) as a turbid medium and apply Monte Carlo simulation. Then, we calculate the parameters characterizing vision loss due to vitreous hemorrhage. This work shows that the increase of the volume fraction of erythrocytes results in a decrease of the total transmittance of the vitreous body and an increase in the radius of maximum transmittance, the width of the circular strip of bright area, and the radius of the shadow area.