Evaluation of standardized performance test methods for biomedical Raman spectroscopy (Erratum)

The erratum corrects an error in Fig. 4 of the published article.

Evaluation of standardized performance test methods for biomedical Raman spectroscopy

SIGNIFICANCE

Raman spectroscopy has emerged as a promising technique for a variety of biomedical applications. The unique ability to provide molecular specific information offers insight to the underlying biochemical changes that result in disease states such as cancer. However, one of the hurdles to successful clinical translation is a lack of international standards for calibration and performance assessment of modern Raman systems used to interrogate biological tissue.

AIM

To facilitate progress in the clinical translation of Raman-based devices and assist the scientific community in reaching a consensus regarding best practices for performance testing.

APPROACH

We reviewed the current literature and available standards documents to identify methods commonly used for bench testing of Raman devices (e.g., relative intensity correction, wavenumber calibration, noise, resolution, and sensitivity). Additionally, a novel 3D-printed turbid phantom was used to assess depth sensitivity. These approaches were implemented on three fiberoptic-probe-based Raman systems with different technical specifications.

RESULTS

While traditional approaches demonstrated fundamental differences due to detectors, spectrometers, and data processing routines, results from the turbid phantom illustrated the impact of illumination-collection geometry on measurement quality.

CONCLUSIONS

Specifications alone are necessary but not sufficient to predict in vivo performance, highlighting the need for phantom-based test methods in the standardized evaluation of Raman devices.

3D-printed phantoms for characterizing SERS nanoparticle detectability in turbid media

Recent advances in plasmonic nanoparticle synthesis have enabled extremely high per-particle surface-enhanced Raman scattering (SERS) efficiencies. This has led to the development of SERS tags for in vivo applications (e.g. tumor targeting and detection), providing high sensitivity and fingerprint-like molecular specificity. While the SERS enhancement factor is a major contributor to SERS tag performance, in practice the throughput and excitation-collection geometry of the optical system can significantly impact detectability. Test methods to objectively quantify SERS particle performance under realistic conditions are necessary to facilitate clinical translation. Towards this goal, we have developed 3D-printed phantoms with tunable, biologically-relevant optical properties. Phantoms were designed to include 1 mm-diameter channels at different depths, which can be filled with SERS tag solutions. The effects of channel depth and particle concentration on the detectability of three different SERS tags were evaluated using 785 nm laser excitation at the maximum permissible exposure for skin. Two of these tags were commercially available, featuring gold nanorods as the SERS particle, while the third tag was prepared in-house using silver-coated gold nanostars. Our findings revealed that the measured SERS intensity of tags in solution is not always a reliable predictor of detectability when applied in a turbid medium such as tissue. The phantoms developed in this work can be used to assess the suitability of specific SERS tags and instruments for their intended clinical applications and provide a means of optimizing new SERS device-tag combination products.

Evaluation of Potential Optical Radiation Hazards from LED Flashlights

We performed optical radiation safety evaluations of LED flashlights to determine if they pose potential ocular hazards. Six commercially available flashlight samples were randomly selected from various vendors online. They were evaluated in accordance with specifications provided in the American National Standards Institute/Illuminating Engineering Society of North America (ANSI/IESNA) Standards RP 27.1 and RP 27.3. Four of the flashlights were found to have relatively high blue-light-weighted radiance values with short times (40 to 50 s) to reach the exposure limit specified in RP 27.1. These flashlights are in Risk Group 2 and present a moderate risk for retinal damage. Two of the flashlights are in Risk Group 1 and present a low risk for retinal damage. None of the flashlights present an ultraviolet (UV) radiation hazard or a retinal thermal hazard. Cautionary labeling on the packaging as required by RP 27.3 and on the flashlight handle is recommended for flashlights and on other handheld light sources that are in Risk Group 2 or Risk Group 3.

Experimental and analytical quantification of light scattering from vacuoles in intraocular lenses

PURPOSE

To develop an advanced test methodology for quantification of scattered light from intraocular lenses (IOLs) and to evaluate the correlation between IOL vacuole characteristics and measured scattered light.

SETTING

U.S. Food and Drug Administration, Optical Therapeutics and Medical Nanophotonics Laboratory, Silver Spring, Maryland, USA.

DESIGN

Experimental and analytical study.

METHODS

Twenty-four IOLs containing vacuoles were evaluated using a digital microscopy approach for identifying and characterizing the vacuoles present. A scanning light scattering profiler (SLSP) was used to evaluate and quantify the amount of scattered light from each IOL and from a 25th control IOL without any vacuoles. A variety of IOLs and vacuoles were also modeled in a Zemax simulation of the SLSP, and the simulated scattered light was modeled.

RESULTS

The scattered light as measured with SLSP was well correlated with vacuole characteristics, specifically density and size, as measured under the digital microscope for the 24 vacuole-containing IOLs. Additional correlations were found between vacuole sizes, orientations, and the angle at which light was scattered most severely. These correlations were also present in the Zemax model.

CONCLUSIONS

Vacuole optical characteristics can be well correlated with measured scatter, demonstrating an ability to predict scattered light based solely on microscope evaluation. Furthermore, the quantitative amount of scatter predicted with Zemax simulations trended closely with the experimentally measured trends.

Experimental investigation of parameters influencing plasmonic nanoparticle-mediated bubble generation with nanosecond laser pulses

Plasmonic nanoparticles (PNPs) continue to see increasing use in biophotonics for a variety of applications, including cancer detection and treatment. Several PNP-based approaches involve the generation of highly transient nanobubbles due to pulsed laser-induced vaporization and cavitation. While much effort has been devoted to elucidating the mechanisms behind bubble generation with spherical gold nano particles, the effects of particle shape on bubble generation thresholds are not well understood, especially in the nanosecond pulse regime. Our study aims to compare the bubble generation thresholds of gold nanospheres, gold nanorods, and silica-core gold nanoshells with different sizes, resonances, and surface coatings. Bubble generation is detected using a multimodality microscopy platform for simultaneous, nanosecond resolution pump-probe imaging, integrated scattering response, and acoustic transient detection. Nanoshells and large (40-nm width) nanorods were found to have the lowest thresholds for bubble generation, and in some cases they generated bubbles at radiant exposures below standard laser safety limits for skin exposure. This has important implications for both safety and performance of techniques employing pulsed lasers and PNPs.

Pulsed laser damage of gold nanorods in turbid media and its impact on multi-spectral photoacoustic imaging

Innovative biophotonic modalities such as photoacoustic imaging (PAI) have the potential to provide enhanced sensitivity and molecule-specific detection when used with nanoparticles. However, high peak irradiance levels generated by pulsed lasers can lead to modification of plasmonic nanoparticles. Thus, there is an outstanding need to develop practical methods to effectively predict the onset nanoparticle photomodification as well as a need to better understand the process during PAI. To address this need, we studied pulsed laser damage of gold nanorods (GNRs) using turbid phantoms and a multi-spectral near-infrared PAI system, comparing results with spectrophotometric measurements of non-scattering samples. Transmission electron microscopy and Monte Carlo modeling were also performed to elucidate damage processes. In the phantoms, shifts in PAI-detected spectra indicative of GNR damage were initiated at exposure levels one-third of that seen in non-scattering samples, due to turbidity-induced enhancement of subsurface fluence. For exposures approaching established safety limits, damage was detected at depths of up to 12.5 mm. Typically, GNR damage occurred rapidly, over the course of a few laser pulses. This work advances the development of test methods and numerical models as tools for assessment of nanoparticle damage and its implications, and highlights the importance of considering GNR damage in development of PAI products, even for exposures well below laser safety limits.

Noncontact method for sensing thickness and refractive index of intraocular lens implants using a self-calibrating dual-confocal laser caliper

We present a fiber-optic dual-confocal laser caliper method for noncontact high-precision sensing and measuring thickness and refractive index of intraocular lens (IOL) implants. The principle of the method is based on sensing and measuring the confocal intensity response of the laser beam reflection from the opposite object surfaces, which provides the advanced feature of having no limitations on the object shape, thickness, and transparency. Using single-mode optical fibers and a 658-nm laser source, the thickness measurement accuracy was assessed to be as high as 5  μm. In addition, refractive index of a transparent object with thickness smaller than the working distance of the focusing lenses can be measured. The thickness and refractive index of a planoconvex IOL were measured with a high accuracy.

Quantitative Evaluation of a Time-Dependent Eye Hazard Posed by Laser Pointers

A novel test methodology was developed for quantitative evaluation of critical radiant power characteristics as a function of time for diode pumped solid state (DPSS) laser pointers. It is based on a simultaneous measurement of time-dependent radiant power characteristics of multi-wavelength spectral components emitted by DPSS laser pointers. The authors tested green DPSS laser pointers, which emit three spectral components at the fundamental near-infrared (1064-nm), pumping near-infrared (808-nm), and second-harmonic green (532-nm) wavelengths. The obtained experimental results are employed for performing eye hazard evaluation according to U.S. and International laser safety standards. All tested green laser pointers demonstrated significant variability of radiant power as a function of time and wavelength. Thus, the severity of the potential eye hazard from DPSS laser pointers for a given exposure time depends on when a person was exposed after the pointer was turned on. Most laser pointers emitted radiation in excess of their classification limits, including unwanted infrared radiation that is not necessary for their intended use as laser pointers.

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light scattering from intraocular lenses (IOLs) using goniophotometer principles. This protocol describes the SLSP platform and how it employs a 360° rotational photodetector sensor that is scanned around an IOL sample while recording the intensity and location of scattered light as it passes through the IOL medium. The SLSP platform can be used to predict, non-clinically, the propensity for current and novel IOL designs and materials to induce light scatter. Non-clinical evaluation of light scattering properties of IOLs can significantly reduce the number of patient complaints related to unwanted glare, glistening, optical defects, poor image quality, and other phenomena associated with the unintended light scattering. Future studies should be conducted to correlate SLSP data with clinical results to help identify which measured light scatter is most problematic for patients that have undergone cataract surgery subsequent to IOL implantation.

Evaluation of the Potential Optical Radiation Hazards with Led Lamps Intended for Home Use

The authors evaluated the potential for ocular damage from optical radiation emitted by Light Emitting Diode (LED) based lamps used for general illumination. Ten LED lamps were randomly selected off the shelf from a local home improvement store. The LEDs were behind diffusers in half of these lamps, while in the other half, the LEDs were clearly visible. In addition, a battery powered LED lantern having a LED source behind a diffuser was measured. The optical radiation emissions from two common incandescent lamps were also measured to compare the relative hazards of LED and incandescent lamps. All lamp samples were evaluated in accordance with procedures specified in the American National Standards Institute/Illuminating Engineering Society of North America (ANSI/IESNA) Standard RP-27.3. For comparison purposes, the lantern and 100 W incandescent lamps were also evaluated according to ANSI RP-27.1. These measurements indicate that no lamp evaluated poses any photobiological hazard, and therefore, all lamps fall in the RP-27.3 category of Exempt Group. However, when evaluated in accordance with RP-27.1, the 100 W incandescent lamp would be classified in Risk Group 1 (low risk), while the LED lantern would be classified in Risk Group 2 (moderate risk).

Confocal laser method for quantitative evaluation of critical optical properties of toric intraocular lenses

PURPOSE

To present a proof-of-concept study on the development and implementation of an innovative confocal laser method platform for precise quantitative evaluation of critical optical properties unique to toric intraocular lenses (IOLs).

SETTING

U.S. Food and Drug Administration, Optical Therapeutics and Medical Nanophotonics Laboratory, Silver Spring, Maryland, USA.

DESIGN

Experimental study.

METHODS

The optical properties of hydrophobic toric IOLs were evaluated with a confocal laser method that was modified to isolate the 2 planes of focus that are observed with toric IOLs.

RESULTS

The results show the confocal laser method has the potential to measure the orthogonally separated optical powers and then calculate them to the commonly referenced spherical equivalent and cylinder powers of toric IOLs with high accuracy (≤1 μm of focal length measurement). Furthermore, the proposed confocal laser method design includes a new component for precise differentiation of the 2 focal planes and isolation of the 2 focal points, and thus for accurate measurement of the anterior cylinder axis of toric IOLs.

CONCLUSION

The modifications to the confocal laser method platform enabled the quantitative evaluation of optical properties attributed to toric IOLs.

FINANCIAL DISCLOSURE

None of the authors has a financial or proprietary interest in any material or method mentioned.

A novel full-angle scanning light scattering profiler to quantitatively evaluate forward and backward light scattering from intraocular lenses

Glare, glistenings, optical defects, dysphotopsia, and poor image quality are a few of the known deficiencies of intraocular lenses (IOLs). All of these optical phenomena are related to light scatter. However, the specific direction that light scatters makes a critical difference between debilitating glare and a slightly noticeable decrease in image quality. Consequently, quantifying the magnitude and direction of scattered light is essential to appropriately evaluate the safety and efficacy of IOLs. In this study, we introduce a full-angle scanning light scattering profiler (SLSP) as a novel approach capable of quantitatively evaluating the light scattering from IOLs with a nearly 360° view. The SLSP method can simulate in situ conditions by controlling the parameters of the light source including angle of incidence. This testing strategy will provide a more effective nonclinical approach for the evaluation of IOL light scatter.

Assessing the effect of laser beam width on quantitative evaluation of optical properties of intraocular lens implants

The design and manufacture of intraocular lenses (IOLs) depend upon the identification and quantitative preclinical evaluation of key optical properties and environmental parameters. The confocal laser method (CLM) is a new technique for measuring IOL optical properties, such as dioptric power, optical quality, refractive index, and geometrical parameters. In comparison to competing systems, the CLM utilizes a fiber-optic confocal laser design that significantly improves the resolution, accuracy, and repeatability of optical measurements. Here, we investigate the impact of changing the beam diameter on the CLM platform for the evaluation of IOL dioptric powers. Due to the Gaussian intensity profile of the CLM laser beam, the changes in focal length and dioptric power associated with changes in beam diameter are well within the tolerances specified in the ISO IOL standard. These results demonstrate some of the advanced potentials of the CLM toward more effectively and quantitatively evaluating IOL optical properties.

Impact of environmental temperature on optical power properties of intraocular lenses

Optical power properties of lenses and materials in general can be influenced by thermal changes of the material and surrounding medium. In the case of an intraocular lens (IOL) implant, the spherical power (SP), cylinder power, (CP), astigmatism, and spherical aberration are the critical fundamental properties that can significantly impact its efficacy. Directly evaluating how changes in temperature can affect these optical properties may show the importance of considering temperature when evaluating IOL optical characteristics. In this paper, we present a quantitative study on evaluating the impact of environmental temperature changes on IOL fundamental optical properties by testing IOL samples with different materials (e.g., hydrophobic and hydrophilic) and designs (e.g., monofocal and toric) to better encompass types of IOLs in conventional use today. The results from this study demonstrate that significant changes are observed as temperatures are changed from room temperature (20°C) to slightly above body temperature (40°C). Findings indicate that evaluating optical properties at arbitrary temperatures could significantly affect the characterization of IOLs that are already near the tolerance thresholds.

Assessing the phase retardation in corneal tissues using a femtosecond laser

We developed and validated a versatile test method for precise quantification of phase retardation in corneal tissues using a femtosecond laser. It is based on an experimental system for direct measurement of corneal phase rotation due to corneal birefringence effects using a dual-polarizer, computer-controlled, femtosecond laser design. It also includes a comprehensive analytical model using Jones matrices. The test method presented is used for quantification of phase retardation in corneal tissues by employing the experimental data obtained from corneal phase rotation measurements and using analytical model assessments. The experimental and theoretical results obtained, and thus, the system's high accuracy and repeatability potential for assessing the corneal phase retardation are validated using control phase retardation evaluation.

Quantification of glistenings in intraocular lenses using a ballistic-photon removing integrating-sphere method

An alternative method for quantification of glistenings in intraocular lenses (IOLs) using an integrating sphere with an adjustable back aperture to remove ballistic photons is presented. Glistenings in soft IOLs have been known for more than a decade; however, their severity and visual impact are still under investigation. A number of studies have been made to quantitatively describe glistenings in IOLs. Quantization and precise grading of IOLs will provide needed information to evaluate the severity and visual impact of glistenings in patients. We investigated the use of a simple modification of an integrating-sphere method to eliminate ballistic photons to quantitatively measure scattered light from glistenings in IOLs. The method described in this paper provides a simple and effective way to quantitatively characterize glistenings in vitro. It may be especially useful to quantify scattering associated with low-grade glistenings where the density of the scattering centers is low. Finally, the modified integrating-sphere method may also be generally applicable to quantitatively characterize scattering from other optical media.

Noncontact common-path Fourier domain optical coherence tomography method for in vitro intraocular lens power measurement

We propose a novel common-path Fourier domain optical coherence tomography (CP-FD-OCT) method for noncontact, accurate, and objective in vitro measurement of the dioptric power of intraocular lenses (IOLs) implants. The CP-FD-OCT method principle of operation is based on simple two-dimensional scanning common-path Fourier domain optical coherence tomography. By reconstructing the anterior and posterior IOL surfaces, the radii of the two surfaces, and thus the IOL dioptric power are determined. The CP-FD-OCT design provides high accuracy of IOL surface reconstruction. The axial position detection accuracy is calibrated at 1.22 μm in balanced saline solution used for simulation of in situ conditions. The lateral sampling rate is controlled by the step size of linear scanning systems. IOL samples with labeled dioptric power in the low-power (5D), mid-power (20D and 22D), and high-power (36D) ranges under in situ conditions are tested. We obtained a mean power of 4.95/20.11/22.09/36.25 D with high levels of repeatability estimated by a standard deviation of 0.10/0.18/0.2/0.58 D and a relative error of 2/0.9/0.9/1.6%, based on five measurements for each IOL respectively. The new CP-FD-OCT method provides an independent source of IOL power measurement data as well as information for evaluating other optical properties of IOLs such as refractive index, central thickness, and aberrations.

Alternative method for measuring effective focal length of lenses using the front and back surface reflections from a reference plate

We present a simple method for measuring the effective focal length without determining the location of principle plane of the lens. The method is based on the measurement of confocal backreflection axial responses from the front and back surfaces of a reference plate with known refractive index and thickness. We proved the concept by measuring the effective focal lengths of thin singlet lenses and complex microscope objectives. The theoretical limit of measurement precision varies depending on the numerical aperture of the lens. This method can provide an alternative focal length measurement method for complex lenses or lenses that are permanently attached to other structures. Measurement errors were analyzed theoretically and improvements in measurement accuracy were discussed.

Axial-scanning low-coherence interferometer method for noncontact thickness measurement of biological samples

We investigated a high-precision optical method for measuring the thickness of biological samples regardless of their transparency. The method is based on the precise measurement of optical path length difference of the end surfaces of objects, using a dual-arm axial-scanning low-coherence interferometer. This removes any consideration of the shape, thickness, or transparency of testing objects when performing the measurement. Scanning the reference simplifies the measurement setup, resulting in unambiguous measurement. Using a 1310 nm wavelength superluminescent diode, with a 65 nm bandwidth, the measurement accuracy was as high as 11.6 μm. We tested the method by measuring the thickness of both transparent samples and nontransparent soft biological tissues.

Investigation of gold-coated bare fiber probe for in situ intra-vitreous coherence domain optical imaging and sensing

We have investigated the usage of gold-plated bare fiber probes for in situ imaging of retinal layers and surrounding ocular tissues using time-domain common-path optical coherence tomography. The fabricated intra-vitreous gold-plated micro-fiber probe can be fully integrated with surgical tools working in close proximity to the tissue to provide subsurface images having a self-contained reference plane independent to the Fresnel reflection between the distal end of the probe and the following medium for achieving reference in typical common-path optical coherence tomography. We have fully characterized the probe in an aqueous medium equivalent to the vitreous humor in the eye and were able to differentiate various functional retinal tissue layers whose thickness is larger than the system's resolution.

Upconversion fiber-optic confocal microscopy under near-infrared pumping

We present a simple upconversion fiber-optic confocal microscope design using a near-infrared laser for pumping of a rare-earth-doped glass powder. The nonlinear optical frequency conversion process is highly efficient with more than 2% upconversion fluorescence efficiency at a near-infrared pumping wavelength of 1.55 microm. The upconversion confocal design allows the use of conventional Si detectors and 1.55 microm near-infrared pump light. The lateral and axial resolutions of the system were equal to or better than 1.10 and 13.11 microm, respectively.

A simple confocal fibre-optic laser method for intraocular lens power measurement

PURPOSE

To develop novel confocal fibre-optic laser method (CFOLM) for accurate and objective measuring of the dioptric power of both positive and negative intraocular lenses (IOLs).

METHODS

The CFOLM principle of operation is based on a simple apertureless single-mode fibre laser confocal design. The key element is a single-mode fibre coupler that serves simultaneously as a point light source (3-5 microm fibre diameter) used for the formation of a collimated Gaussian beam, and as a confocal point receiver that is highly sensitive to spatial displacements of the focused backreflectance laser emission. The basic CFOLM systems include IOL testing set-ups for the measurement of both positive and negative IOLs.

RESULTS

The CFOLM designs provide high accuracy (

CONCLUSIONS

The presented IOL power testing method offers a simple, accurate, objective, quick, and relatively inexpensive approach for dioptric power measurement of positive and negative IOLs. It provides an independent source of IOL power measurement data and information for evaluating the effectiveness and safety of novel IOL products.

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Key Words

• intraocular lens dioptric power
• confocal fibre-optic laser method
• single-mode fibre coupler

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MESH Headings

• Diagnostic Techniques, Ophthalmological/instrumentation
• Equipment Design
• Fiber Optic Technology/methods
• Humans
• Lasers
• Lenses, Intraocular
• Optics and Photonics

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Grants

• FD999999 Intramural FDA HHS

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Affiliation(s)

I K Ilev Division of Physics, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, US Food and Drug Administration, Rockville, MD 20857, USA.

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Characterizing reflections from intraocular lens implants

OBJECTIVE

To develop a test method for characterizing glare from intraocular lenses (IOLs) and to confirm a clinical finding that the haptic insertion in the optic of a three-piece IOL produces extraneous line images.

METHOD

The method consists of directing a collimated Gaussian laser beam to various parts of the IOL to be tested in a water-filled model eye. Reflected images produced in the retinal plane are photographed with a digital camera.

RESULTS

A test method was developed to characterize the source of glare images from IOLs. The test method developed was used to confirm a clinical finding that the haptic insertion in the optic of a three-piece IOL produces extraneous line images.

CONCLUSIONS

The method developed can be used to characterize and pin point the source of extraneous glare images from intraocular lens implants. The haptic insertion in the optic of a three-piece IOL has been identified as a source of line images.

Modification of the intrinsic fluorescence and the biochemical behavior of ATP after irradiation with visible and near-infrared laser light

In this work, the effects of visible (655 nm) and near-infrared (830 nm) light on ATP in solution were examined. The addition of irradiated ATP to the hexokinase reaction caused significant differences in the reaction rates and in the Michaelis-Menten kinetic parameters, k(m) and v(max). Irradiated ATP cleavage by hexokinase occurred in less time. Changes were wavelength and dose dependent. Excitation of ATP with a 260 nm wavelength ultraviolet light induced a fluorescence emission that was decreased when Mg2+ was added due to ion binding of the phosphates, which are the structures that modify the fluorescence produced by the adenine dipoles. The irradiation of this ATP.Mg2+ solution using 655 and 830 nm light increased the fluorescence by a possible displacement of Mg2+ from the phosphates. In conclusion, visible and near-infrared light modifies the biochemical behavior of ATP in the hexokinase reaction and the fluorescence intensity of the molecule thus altering the Mg2+ binding strength to the oxygen atoms in the phosphate group.

The electric field induced by light can explain cellular responses to electromagnetic energy: a hypothesis of mechanism

When cells are irradiated with visible and near-infrared wavelengths a variety of stimulatory effects are observed in their metabolism. To explain the observed light effects, researchers try to identify the chromophores that are involved in the processes. However, the mechanism of light absorption by a chromophore does not explain many of the experimental observations and therefore the primary mechanism for cellular light responses remains unproven. In addition to the ability of photons to produce electronic excitation in chromophores, light induces a wave-like alternating electric field in a medium that is able to interact with polar structures and produce dipole transitions. These dipole transitions are analyzed in the present article at different cellular and biochemical levels, leading to the proposal that the primary mechanism for the observed light effects is related to the light-induced electric field.

Light promotes regeneration and functional recovery and alters the immune response after spinal cord injury

BACKGROUND AND OBJECTIVES

Photobiomodulation (PBM) has been proposed as a potential therapy for spinal cord injury (SCI). We aimed to demonstrate that 810 nm light can penetrate deep into the body and promote neuronal regeneration and functional recovery.

STUDY DESIGN/MATERIALS AND METHODS

Adult rats underwent a T9 dorsal hemisection, followed by treatment with an 810 nm, 150 mW diode laser (dosage = 1,589 J/cm2). Axonal regeneration and functional recovery were assessed using single and double label tract tracing and various locomotor tasks. The immune response within the spinal cord was also assessed.

RESULTS

PBM, with 6% power penetration to the spinal cord depth, significantly increased axonal number and distance of regrowth (P < 0.001). PBM also returned aspects of function to baseline levels and significantly suppressed immune cell activation and cytokine/chemokine expression.

CONCLUSION

Our results demonstrate that light, delivered transcutaneously, improves recovery after injury and suggests that light will be a useful treatment for human SCI.

Low power laser irradiation alters gene expression of olfactory ensheathing cells in vitro

BACKGROUND AND OBJECTIVES

Both photobiomodulation (PBM) and olfactory ensheathing cells (OECs) transplantation improve recovery following spinal cord injury. However, neither the combination of these two therapies nor the effect of light on OECs has been reported. The purpose of this study was to determine the effect of light on OEC activity in vitro.

MATERIALS AND METHODS

OECs were purified from adult rat olfactory bulbs and exposed to 810 nm light (150 mW; 0, 0.2, or 68 J/cm(2)). After 7-21 days in vitro, cells underwent immunocytochemistry or RNA extraction and RT-PCR.

RESULTS

Analysis of immunolabeling revealed a significant decrease in fibronectin expression in the cultures receiving 68 J/cm(2). Analysis of gene expression revealed a significant (P < 0.05) increase in brain derived neurotrophic factor (BDNF), glial derived neurotrophic factor (GDNF), and collagen expression in the 0.2 J/cm(2) group in comparison to the non-irradiated and 68 J/cm(2) groups. OEC proliferation was also found to significantly increase in both light treated groups in comparison to the control group (P < 0.001).

CONCLUSIONS

These results demonstrate that low and high dosages of PBM alter OEC activity, including upregulation of a number of neurotrophic growth factors and extracellular matrix proteins known to support neurite outgrowth. Therefore, the application of PBM in conjunction with OEC transplantation warrants consideration as a potential combination therapy for spinal cord injury.

Photobiomodulation Improves Cutaneous Wound Healing in an Animal Model of Type II Diabetes

OBJECTIVE

We investigated the effects of photobiomodulation (PBM) on cutaneous wound healing in an animal model of type II diabetes, Psammomys obesus (Sand Rats).

BACKGROUND DATA

632-nm light has been established as the most effective wavelength for treatment of cutaneous wounds; however, the inconsistent efficacy of PBM may be due to inadequate treatment parameter selection.

METHODS

Using 632-nm light, an initial series of experiments were done to establish optimal treatment parameters for this model. Following creation of bilateral full-thickness skin wounds, non-diabetic Sand Rats were treated with PBM of differing dosages. Wound healing was assessed according to wound closure and histological characteristics of healing. Optimal treatment parameters were then used to treat type II diabetic Sand Rats while a diabetic control group received no irradiation. In order to elucidate the mechanism behind an improvement in wound healing, expression of basic fibroblast growth factor (bFGF) was assessed.

RESULTS

Significant improvement in wound healing histology and wound closure were found following treatment with 4 J/cm(2) (16 mW, 250-sec treatments for 4 consecutive days; p < 0.05). The 4 J/cm(2) dosage significantly improved histology and closure of wounds in the diabetic group in comparison to the non-irradiated diabetic group. Quantitative analysis of bFGF expression at 36 h post-injury revealed a threefold increase in the diabetic and non-diabetic Sand Rats after PBM.

CONCLUSIONS

The results demonstrate that PBM at an energy density of 4 J/cm(2) is effective in improving the healing of cutaneous wounds in an animal model of type II diabetes, suggesting that PBM (632 nm, 4 J/cm(2)) would be effective in treating chronic cutaneous wounds in diabetic patients.

Dual-confocal fiber-optic method for absolute measurement of refractive index and thickness of optically transparent media

We present a novel noncontact optical method for absolute measurement of refractive index and thickness of optically transparent media. The method is based on a simple dual-confocal fiber-optic sensor design. It includes two independent confocal channels consisting of two identical apertureless fiber-optic-type confocal microscopes constructed by use of a single 2x2 fiber coupler. A geometrical-ray model is used to obtain the analytical dependence between the sample's refractive index and its thickness. The measurement method provides high accuracy in spatially locating the specific imaging points that correspond to the backreflected intensity peaks of the confocal responses. Thus, a simultaneous measurement of the sample refractive index and thickness is achieved.

Attenuation measurement of infrared optical fibers by use of a hollow-taper-based coupling method

An alternative method for attenuation measurement of infrared (IR) fibers is described. The method includes a simple technique for direct laser-to-fiber coupling with an uncoated glass hollow taper. The operating principle of the hollow taper is based on the grazing-incidence effect of light reflection. The hollow taper forms a smooth Gaussian-shaped profile of the output laser emission and provides the proper conditions for equilibrium-mode distribution of optical power within the test IR fibers. The experimental hollow-taper-based coupling method is used for measurement of attenuation and bending losses of various kinds of IR fiber, including solid-core (fluoride, chalcogenide, and germanium-doped) and hollow fibers.

Simple autocollimation laser refractometer with highly sensitive, fiber-optic output

A simple autocollimation scheme for a laser refractometer with a highly sensitive, single-mode, fiber-optic output is described. It allows for the determination of the refractive index and dispersion of optical materials with an accuracy exceeding 10(-5), which is confirmed by both experimental and analytical investigations.

Simple fiber-optic autocollimation method for determining the focal lengths of optical elements

A novel simple fiber-optic autocollimation method for determining the focal lengths of lenses and objectives is presented. This method is based on the intensity sensing of reflected light, photoelectric measurement, and the use of single-mode optical fiber. This fiber serves simultaneously as a point light source for the formation of a collimated input laser beam and as a receiver that is highly sensitive to spatial displacements for the autocollimation backreflectance. The method permits us to locate the focal point spatially and to determine the back focal length of a focusing optical element with accuracies exceeding 1 and 2 microm, respectively, which are confirmed by both experimental and analytical investigations.