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Pattelli L, Mazzamuto G. Experimental imaging and Monte Carlo modeling of ultrafast pulse propagation in thin scattering slabs. JOURNAL OF BIOMEDICAL OPTICS 2022; 27:083020. [PMID: 35655345 PMCID: PMC9162504 DOI: 10.1117/1.jbo.27.8.083020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Accepted: 05/20/2022] [Indexed: 06/15/2023]
Abstract
SIGNIFICANCE Most radiative transport problems in turbid media are typically associated with mm or cm scales, leading to typical time scales in the range of hundreds of ps or more. In certain cases, however, much thinner layers can also be relevant, which can dramatically alter the overall transport properties of a scattering medium. Studying scattering in these thin layers requires ultrafast detection techniques and adaptations to the common Monte Carlo (MC) approach. AIM We aim to discuss a few relevant aspects for the simulation of light transport in thin scattering membranes, and compare the obtained numerical results with experimental measurements based on an all-optical gating technique. APPROACH A thin membrane with controlled scattering properties based on polymer-dispersed TiO2 nanoparticles is fabricated for experimental validation. Transmittance measurements are compared against a custom open-source MC implementation including specific pulse profiles for tightly focused femtosecond laser pulses. RESULTS Experimental transmittance data of ultrafast pulses through a thin scattering sample are compared with MC simulations in the spatiotemporal domain to retrieve its scattering properties. The results show good agreement also at short distances and time scales. CONCLUSIONS When simulating light transport in scattering membranes with thicknesses in the orders of tens of micrometer, care has to be taken when describing the temporal, spatial, and divergence profiles of the source term, as well as the possible truncation of step length distributions, which could be introduced by simple strategies for the generation of random exponentially distributed variables.
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Affiliation(s)
- Lorenzo Pattelli
- Istituto Nazionale di Ricerca Metrologica (INRiM), Torino, Italy
- European Laboratory for Nonlinear Spectroscopy (LENS), Sesto Fiorentino, Italy
| | - Giacomo Mazzamuto
- European Laboratory for Nonlinear Spectroscopy (LENS), Sesto Fiorentino, Italy
- Istituto Nazionale di Ottica (INO), CNR, Sesto Fiorentino, Italy
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Tomanič T, Rogelj L, Milanič M. Robustness of diffuse reflectance spectra analysis by inverse adding doubling algorithm. BIOMEDICAL OPTICS EXPRESS 2022; 13:921-949. [PMID: 35284194 PMCID: PMC8884198 DOI: 10.1364/boe.443880] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Revised: 11/12/2021] [Accepted: 12/14/2021] [Indexed: 06/14/2023]
Abstract
Analysing diffuse reflectance spectra to extract properties of biological tissue requires modelling of light transport within the tissue, considering its absorption, scattering, and geometrical properties. Due to the layered skin structure, skin tissue models are often divided into multiple layers with their associated optical properties. Typically, in the analysis, some model parameters defining these properties are fixed to values reported in the literature to speed up the fitting process and improve its performance. In the absence of consensus, various studies use different approaches in fixing the model parameters. This study aims to assess the effect of fixing various model parameters in the skin spectra fitting process on the accuracy and robustness of a GPU-accelerated two-layer inverse adding-doubling (IAD) algorithm. Specifically, the performance of the IAD method is determined for noiseless simulated skin spectra, simulated spectra with different levels of noise applied, and in-vivo measured reflectance spectra from hyperspectral images of human hands recorded before, during, and after the arterial occlusion. Our results suggest that fixing multiple parameters to a priori known values generally improves the robustness and accuracy of the IAD algorithm for simulated spectra. However, for in-vivo measured spectra, these values are unknown in advance and fixing optical parameters to incorrect values significantly deteriorates the overall performance. Therefore, we propose a method to improve the fitting performance by pre-estimating model parameters. Our findings could be considered in all future research involving the analysis of diffuse reflectance spectra to extract optical properties of skin tissue.
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Affiliation(s)
- Tadej Tomanič
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska ulica 19, 1000 Ljubljana, Slovenia
| | - Luka Rogelj
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska ulica 19, 1000 Ljubljana, Slovenia
| | - Matija Milanič
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska ulica 19, 1000 Ljubljana, Slovenia
- Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia
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Lee S, Wei S, Guo S, Kim J, Kim B, Kim G, Kang JU. Selective retina therapy monitoring by speckle variance optical coherence tomography for dosimetry control. JOURNAL OF BIOMEDICAL OPTICS 2020; 25:1-9. [PMID: 32061065 PMCID: PMC7019183 DOI: 10.1117/1.jbo.25.2.026001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2019] [Accepted: 01/29/2020] [Indexed: 05/29/2023]
Abstract
SIGNIFICANCE Selective retina therapy (SRT) selectively targets the retinal pigment epithelium (RPE) and reduces negative side effects by avoiding thermal damages of the adjacent photoreceptors, the neural retina, and the choroid. However, the selection of proper laser energy for the SRT is challenging because of ophthalmoscopically invisible lesions in the RPE and different melanin concentrations among patients or even regions within an eye. AIM We propose and demonstrate SRT monitoring based on speckle variance optical coherence tomography (svOCT) for dosimetry control. APPROACH M-scans, time-resolved sequence of A-scans, of ex vivo bovine retina irradiated by 1.7-μs duration laser pulses were obtained by a swept-source OCT. SvOCT images were calculated as interframe intensity variance of the sequence. Spatial and temporal temperature distributions in the retina were numerically calculated in a 2-D retinal model using COMSOL Multiphysics. Microscopic images of treated spots were obtained before and after removing the upper neural retinal layer to assess the damage in both RPE and neural layers. RESULTS SvOCT images show abrupt speckle variance changes when the retina is irradiated by laser pulses. The svOCT intensities averaged in RPE and photoreceptor layers along the axial direction show sharp peaks corresponding to each laser pulse, and the peak values were proportional to the laser pulse energy. The calculated temperatures in the neural retina layer and RPE were linearly fitted to the svOCT peak values, and the temperature of each lesion was estimated based on the fitting. The estimated temperatures matched well with previously reported results. CONCLUSION We found a reliable correlation between the svOCT peak values and the degree of retinal lesion formation, which can be used for selecting proper laser energy during SRT.
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Affiliation(s)
- Soohyun Lee
- Johns Hopkins University, Department of Electrical and Computer Engineering, Baltimore, Maryland, United States
| | - Shuwen Wei
- Johns Hopkins University, Department of Electrical and Computer Engineering, Baltimore, Maryland, United States
| | - Shoujing Guo
- Johns Hopkins University, Department of Electrical and Computer Engineering, Baltimore, Maryland, United States
| | | | | | - Gihoon Kim
- Lutronic Center, Goyang, Republic of Korea
| | - Jin U. Kang
- Johns Hopkins University, Department of Electrical and Computer Engineering, Baltimore, Maryland, United States
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4
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Inverse heat transfer analysis in detecting tissue optical properties using laser. Lasers Med Sci 2019; 34:1671-1678. [PMID: 30877489 DOI: 10.1007/s10103-019-02767-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2018] [Accepted: 03/06/2019] [Indexed: 10/27/2022]
Abstract
A new methodology has been proposed to measure optical properties of homogeneous tissue where a laser beam is used to induce heat to a tissue. The induced heat increased the temperature inside the tissue, which is detected by a thermocouple. These readings are compared with that obtained from the solution of the finite element solution that used iterative values of optical properties in determining temperature distribution. The two temperature distributions are used to determine tissue optical properties using the Levenberg-Marquardt iteration. An accurate result is obtained in determining absorption coefficient and reduced scattering coefficient. The work is extended to obtain three parameters (i.e., absorption coefficient, scattering coefficient, and anisotropy). The only limitation is that the temperature readings have to be measured with a high-accuracy thermocouple (i.e., less than 0.4% of maximum-recorded temperature).
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Singh R, Rajaraman S, Balasubramanian M. A Novel Nanoparticle Mediated Selective Inner Retinal Photocoagulation for Diseases of the Inner Retina. IEEE Trans Nanobioscience 2017; 16:542-554. [PMID: 28829313 PMCID: PMC5926191 DOI: 10.1109/tnb.2017.2741490] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
A novel nanoparticle mediated methodology for laser photocoagulation of the inner retina to achieve tissue selective treatment is presented. METHODS Transport of 527, 577, and 810 nm laser, heat deposition, and eventual thermal damage in vitreous, retina, RPE, choroid, and sclera were modeled using Bouguer-Beer-Lambert law of absorption and solved numerically using the finite volume method. Nanoparticles were designed using Mie theory of scattering. Performance of the new photocoagulation strategy using gold nanospheres and gold-silica nanoshells was compared with that of conventional methods without nanoparticles. For experimental validation, vitreous cavity of ex vivo porcine eyes was infused with gold nanospheres. After ~6 h of nanoparticle diffusion, the porcine retina was irradiated with a green laser and imaged simultaneously using a spectral domain optical coherence tomography (Spectralis SD-OCT, Heidelberg Engineering). RESULTS Our computational model predicted a significant spatial shift in the peak temperature from RPE to the inner retinal region when infused with nanoparticles. Arrhenius thermal damage in the mid-retinal location was achieved in ~14 ms for 527 nm laser thereby reducing the irradiation duration by ~30 ms compared with the treatment without nanoparticles. In ex vivo porcine eyes infused with gold nanospheres, SD-OCT retinal images revealed a lower thermal damage and expansion at RPE due to laser photocoagulation. CONCLUSION Nanoparticle infused laser photocoagulation strategy provided a selective inner retinal thermal damage with significant decrease in laser power and laser exposure time. SIGNIFICANCE The proposed treatment strategy shows possibilities for an efficient and highly selective inner retinal laser treatment.
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Coelho JMP, Freitas J, Williamson CA. Optical eye simulator for laser dazzle events. APPLIED OPTICS 2016; 55:2240-2251. [PMID: 27140558 DOI: 10.1364/ao.55.002240] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
An optical simulator of the human eye and its application to laser dazzle events are presented. The simulator combines optical design software (ZEMAX) with a scientific programming language (MATLAB) and allows the user to implement and analyze a dazzle scenario using practical, real-world parameters. Contrary to conventional analytical glare analysis, this work uses ray tracing and the scattering model and parameters for each optical element of the eye. The theoretical background of each such element is presented in relation to the model. The overall simulator's calibration, validation, and performance analysis are achieved by comparison with a simpler model based uponCIE disability glare data. Results demonstrate that this kind of advanced optical eye simulation can be used to represent laser dazzle and has the potential to extend the range of applicability of analytical models.
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Teussink MM, Cense B, van Grinsven MJ, Klevering BJ, Hoyng CB, Theelen T. Impact of motion-associated noise on intrinsic optical signal imaging in humans with optical coherence tomography. BIOMEDICAL OPTICS EXPRESS 2015; 6:1632-47. [PMID: 26137369 PMCID: PMC4467722 DOI: 10.1364/boe.6.001632] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Revised: 04/04/2015] [Accepted: 04/04/2015] [Indexed: 06/04/2023]
Abstract
A growing body of evidence suggests that phototransduction can be studied in the human eye in vivo by imaging of fast intrinsic optical signals (IOS). There is consensus concerning the limiting influence of motion-associated imaging noise on the reproducibility of IOS-measurements, especially in those employing spectral-domain optical coherence tomography (SD-OCT). However, no study to date has conducted a comprehensive analysis of this noise in the context of IOS-imaging. In this study, we discuss biophysical correlates of IOS, and we address motion-associated imaging noise by providing correctional post-processing methods. In order to avoid cross-talk of adjacent IOS of opposite signal polarity, cellular resolution and stability of imaging to the level of individual cones is likely needed. The optical Stiles-Crawford effect can be a source of significant IOS-imaging noise if alignment with the peak of the Stiles-Crawford function cannot be maintained. Therefore, complete head stabilization by implementation of a bite-bar may be critical to maintain a constant pupil entry position of the OCT beam. Due to depth-dependent sensitivity fall-off, heartbeat and breathing associated axial movements can cause tissue reflectivity to vary by 29% over time, although known methods can be implemented to null these effects. Substantial variations in reflectivity can be caused by variable illumination due to changes in the beam pupil entry position and angle, which can be reduced by an adaptive algorithm based on slope-fitting of optical attenuation in the choriocapillary lamina.
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Affiliation(s)
- Michel M. Teussink
- Department of Ophthalmology, Radboud University Medical Center, Nijmegen, P.O. Box 6500 HB,
The Netherlands
| | - Barry Cense
- Center for Optical Research and Education, Utsunomiya University, Utsunomiya, Tochigi, 321-8585,
Japan
| | - Mark J.J.P. van Grinsven
- Diagnostic Image Analysis Group, Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, P.O. Box 6500 HB,
The Netherlands
| | - B. Jeroen Klevering
- Department of Ophthalmology, Radboud University Medical Center, Nijmegen, P.O. Box 6500 HB,
The Netherlands
| | - Carel B. Hoyng
- Department of Ophthalmology, Radboud University Medical Center, Nijmegen, P.O. Box 6500 HB,
The Netherlands
| | - Thomas Theelen
- Department of Ophthalmology, Radboud University Medical Center, Nijmegen, P.O. Box 6500 HB,
The Netherlands
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Optical and spectroscopic properties of human whole blood and plasma with and without Y₂O₃ and Nd³⁺:Y₂O₃ nanoparticles. Lasers Med Sci 2013; 28:1559-66. [PMID: 23380906 DOI: 10.1007/s10103-013-1268-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2012] [Accepted: 01/08/2013] [Indexed: 10/27/2022]
Abstract
The optical properties of human whole blood and blood plasma with and without Y₂O₃ and Nd³⁺:Y₂O₃ nanoparticles are characterized in the near infrared region at 808 nm using a double integrating sphere technique. Using experimentally measured quantities of diffuse reflectance and diffuse transmittance, a computational analysis was conducted utilizing the Kubelka-Munk, the Inverse Adding Doubling, and Magic Light Kubelka-Munk and Monte Carlo Methods to determine optical properties of the absorption and scattering coefficients. Room temperature absorption and emission spectra were also acquired of Nd³⁺:Y₂O₃ nanoparticles elucidating their utility as biological markers. The emission spectra of Nd³⁺:Y₂O₃ were taken by exciting the nanoparticles before and after entering the whole blood sample. The emission from the ⁴F(3/2) → ⁴I(11/2) manifold transition of Nd³⁺:Y₂O₃ nanoparticles readily propagates through the blood sample at excitation of 808 nm and exhibits a shift in relative intensities of the peaks due to differences in scattering. At 808 nm, in both whole blood and plasma samples, a direct relationship was found with absorption coefficient and Y₂O₃ nanoparticle concentration. Results for the whole blood indicate a small inverse relationship with Y₂O₃ nanoparticle concentration and scattering coefficient and in contrast a direct relation for the plasma.
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9
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Akimov NP, Marshak DW, Frishman LJ, Glickman RD, Yusupov RG. Histamine reduces flash sensitivity of on ganglion cells in the primate retina. Invest Ophthalmol Vis Sci 2010; 51:3825-34. [PMID: 20207974 DOI: 10.1167/iovs.09-4806] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE. In Old World primates, the retina receives input from histaminergic neurons in the posterior hypothalamus. They are a subset of the neurons that project throughout the central nervous system and fire maximally during the day. The contribution of these neurons to vision, was examined by applying histamine to a dark-adapted, superfused baboon eye cup preparation while making extracellular recordings from peripheral retinal ganglion cells. METHODS. The stimuli were 5-ms, 560-nm, weak, full-field flashes in the low scotopic range. Ganglion cells with sustained and transient ON responses and two cell types with OFF responses were distinguished; their responses were recorded with a 16-channel microelectrode array. RESULTS. Low micromolar doses of histamine decreased the rate of maintained firing and the light sensitivity of ON ganglion cells. Both sustained and transient ON cells responded similarly to histamine. There were no statistically significant effects of histamine in a more limited study of OFF ganglion cells. The response latencies of ON cells were approximately 5 ms slower, on average, when histamine was present. Histamine also reduced the signal-to-noise ratio of ON cells, particularly in those cells with a histamine-induced increase in maintained activity. CONCLUSIONS. A major action of histamine released from retinopetal axons under dark-adapted conditions, when rod signals dominate the response, is to reduce the sensitivity of ON ganglion cells to light flashes. These findings may relate to reports that humans are less sensitive to light stimuli in the scotopic range during the day, when histamine release in the retina is expected to be at its maximum.
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Affiliation(s)
- Nikolay P Akimov
- Departments of Physiology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX, USA
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10
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Optical absorption and scattering of bovine cornea, lens and retina in the visible region. Lasers Med Sci 2009; 24:839-47. [PMID: 19495828 DOI: 10.1007/s10103-009-0677-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2008] [Accepted: 04/21/2009] [Indexed: 10/20/2022]
Abstract
Optical properties of bovine ocular tissues were determined at laser wavelengths in the visible region. The inverse adding doubling (IAD), Kubelka-Munk (KM), and inverse Monte Carlo (IMC) methods were applied to the measured values of the total diffuse transmission, total diffuse reflection, and collimated transmission to determine the optical absorption and scattering coefficients of the bovine cornea, lens and retina at 457.9 nm, 488 nm, and 514.5 nm laser lines from an argon ion laser. The optical properties obtained from these three methods were compared, and their validity is discussed.
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11
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Pocock GM, Aranibar RG, Kemp NJ, Specht CS, Markey MK, Rylander HG. The relationship between retinal ganglion cell axon constituents and retinal nerve fiber layer birefringence in the primate. Invest Ophthalmol Vis Sci 2009; 50:5238-46. [PMID: 19494208 DOI: 10.1167/iovs.08-3263] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To determine the degree of correlation between spatial characteristics of the retinal nerve fiber layer (RNFL) birefringence (Delta n(RNFL)) surrounding the optic nerve head (ONH) with the corresponding anatomy of retinal ganglion cell (RGC) axons and their respective organelles. METHODS RNFL phase retardation per unit depth (PR/UD, proportional to Delta n(RNFL)) was measured in two cynomolgus monkeys by enhanced polarization-sensitive optical coherence tomography (EPS-OCT). The monkeys were perfused with glutaraldehyde and the eyes were enucleated and prepared for transmission electron microscopy (TEM) histologic analysis. Morphologic measurements from TEM images were used to estimate neurotubule density (rho(RNFL)), axoplasmic area (A(x)) mode, axon area (A(a)) mode, slope (u) of the number of neurotubules versus axoplasmic area (neurotubule packing density), fractional area of axoplasm in the nerve fiber bundle (f), mitochondrial fractional area in the nerve fiber bundle (x(m)), mitochondria-containing axon profile fraction (m(p)), and length of axonal membrane profiles per unit of nerve fiber bundle area (L(am)/A(b)). Registered PR/UD and morphologic parameters from corresponding angular sections were then correlated by using Pearson's correlation and multilevel models. RESULTS In one eye there was a statistically significant correlation between PR/UD and rho(RNFL) (r = 0.67, P = 0.005) and between PR/UD and neurotubule packing density (r = 0.70, P = 0.002). Correlation coefficients of r = 0.81 (P = 0.01) and r = 0.50 (P = 0.05) were observed between the PR/UD and A(x) modes for each respective subject. CONCLUSIONS Neurotubules are the primary source of birefringence in the RNFL of the primate retina.
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Affiliation(s)
- Ginger M Pocock
- Biomedical Engineering Laser Laboratories, Department of Biomedical Engineering, The University of Texas at Austin, Austin, Texas 78712, USA
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Zhu D, Lu W, Zeng S, Luo Q. Effect of light losses of sample between two integrating spheres on optical properties estimation. JOURNAL OF BIOMEDICAL OPTICS 2007; 12:064004. [PMID: 18163820 DOI: 10.1117/1.2815691] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
A Monte Carlo algorithm is applied to simulate the measurements of a sample with glass slides sandwiched between the double integrating sphere (DIS) setup. The effects caused by various parameters, such as the sample port of integrating sphere, thicknesses, and optical properties of the sample, on light losses and optical properties estimated by the inverse adding-doubling method (IAD) have been investigated. The results show that the light loss greatly increases the estimated error of absorption coefficient and slightly affects the estimated scattering coefficient. When the increase of apparent absorption of the sample induced by the light loss is 59%, the relative error of the scattering coefficient is less than 2% and that of the absorption coefficient reaches 28%. Enhancing the sample port diameter or decreasing the thickness of the sample can reduce the error effectively, and the effect of the former is much greater than that of the latter. In addition, the IAD method is proved to be valid for estimating the optical properties of a highly scattering or highly absorbing sample. This study can not only evaluate the error of optical properties estimation, but also provide optimal ways for the design of DIS and a scheme for acquiring accurate optical properties of tissue.
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Affiliation(s)
- Dan Zhu
- Huazhong University of Science and Technology, Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics, Wuhan, 430074, China
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Sardar DK, Swanland GY, Yow RM, Thomas RJ, Tsin ATC. Optical properties of ocular tissues in the near infrared region. Lasers Med Sci 2006; 22:46-52. [PMID: 17143656 DOI: 10.1007/s10103-006-0421-y] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2006] [Accepted: 09/19/2006] [Indexed: 10/23/2022]
Abstract
Near infrared characterization of optical properties of aqueous humor and vitreous humor of healthy human and bovine eyes has been performed. The indices of refraction (n) of these ocular tissues were determined using a Michelson interferometer. The total diffuse reflection (R (d)) and total transmission (T (t)) measurements had been taken for individual ocular tissue by using a double-integrating sphere setup and infrared laser diodes. The inverse adding doubling (IAD) computational method based on the diffusion approximation and radiative transport theory was applied to the measured values of n, R (d), and T (t) to calculate the optical absorption and scattering coefficients of the human and bovine ocular tissues. The scattering anisotropy value was determined by iteratively running the IAD method program and a Monte Carlo simulation of light-tissue interaction until the minimum difference in experimental and computed value for T (t) was realized. A comparison between the optical characterization of human and bovine ocular samples was also made.
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Affiliation(s)
- Dhiraj K Sardar
- Department of Physics and Astronomy, The University of Texas at San Antonio, San Antonio, TX 78249-0697, USA.
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14
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Rylander HG, Kemp NJ, Park J, Zaatari HN, Milner TE. Birefringence of the primate retinal nerve fiber layer. Exp Eye Res 2005; 81:81-9. [PMID: 15978258 DOI: 10.1016/j.exer.2005.01.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2004] [Revised: 12/31/2004] [Accepted: 01/13/2005] [Indexed: 11/26/2022]
Abstract
The purpose of this study was to measure the peripapillary retinal nerve fiber layer (RNFL) thickness, phase retardation (PR), and depth-resolved birefringence (Deltan) of the normal primate eye using Enhanced Polarization-Sensitivity Optical Coherence Tomography (EPS-OCT). Both eyes of two rhesus monkeys were imaged with EPS-OCT. A multiple incident polarization state nonlinear fitting algorithm was used to determine RNFL phase retardation. RNFL thickness (RNFLT) was determined from the corresponding EPS-OCT intensity image and phase retardation per unit depth (PR/UD, proportional to Deltan) was calculated by dividing PR by RNFLT. Peripapillary area maps consisting of pixels uniformly distributed along a radius from 0.8 to 1.8 mm from the center of the optic nervehead were constructed for RNFLT, PR, and PR/UD. Average PR/UD in the superior and inferior quadrants was 18 degrees /100 mivrom (Deltan=4.2 x 10(-4)) and average PR/UD in the nasal and temporal quadrants was 6.3 degrees /100 microm (Deltan=1.5 x 10(-4)). Relative magnitude of PR radial gradient is similar to that of RNFLT radial gradient and no radial gradient was observed for PR/UD. Polarization-dependent amplitude attenuation per unit depth (PDAA/UD) was 0.02 rad/100 microm in thick RNFL regions. RNFL birefringence was higher in the arcuate bundles compared to nasal and temporal fibers (P=0.001). Birefringence was nearly equal in nasal and temporal quadrants. No statistically significant (P=0.01) radial gradient of birefringence was observed in any quadrant. RNFL birefringence is believed to originate from anisotropic structures within the cytoskeleton of the parallel axons. Birefringence differences presented in this study cannot be explained by the known axon diameter distribution around the optic nervehead and suggest other sources of the birefringence signal including neurotubules and neurofilaments.
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Affiliation(s)
- H Grady Rylander
- The Biomedical Engineering Laser Laboratories, Department of Biomedical Engineering, The University of Texas at Austin, 1 University Station #C0800, Austin, TX 78712, USA.
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Sardar DK, Yow RM, Tsin ATC, Sardar R. Optical scattering, absorption, and polarization of healthy and neovascularized human retinal tissues. JOURNAL OF BIOMEDICAL OPTICS 2005; 10:051501. [PMID: 16292945 DOI: 10.1117/1.2065867] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
The optical scattering, absorption, and polarization properties of human retinal tissues are investigated for a number of laser wavelengths in the visible range. The indices of refraction of these tissues are determined by applying Brewster's law. The inverse adding doubling method based on the diffusion approximation and radiative transport theory is applied to the measured values of total diffuse transmission, total diffuse reflection, and index of refraction to determine the optical absorption, scattering, and scattering anisotropy coefficients of the intact retinal tissues from healthy and diseased (neovascularized) human eyes. The polarization studies show that the retinal tissues possess significant intrinsic polarization characteristics, that are more pronounced in diseased tissues than in healthy tissues.
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Affiliation(s)
- Dhiraj K Sardar
- University of Texas at San Antonio, Department of Physics and Astronomy, San Antonio, Texas 78249-0697, USA.
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