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At least 73 records · Page 4Linked to original sources

PubMed2004

Combining flat crystals, bent crystals and compound refractive lenses for high-energy X-ray optics.

Compound refractive lenses (CRLs) are effective for collimating or focusing high-energy X-ray beams (50-100 keV) and can be used in conjunction with crystal optics in a variety of configurations, as demonstrated at the 1-ID undulator beamline of the Advanced Photon Source. As a primary example, this article describes the quadrupling of the output flux when a collimating CRL, composed of cylindrical holes in aluminium, is inserted between two successive monochromators, i.e. a modest-energy-resolution premonochromator followed by a high-resolution monochromator. The premonochromator is a cryogenically cooled divergence-preserving bent double-Laue Si(111) crystal device delivering an energy width DeltaE/E approximately 10(-3), which is sufficient for most experiments. The high-resolution monochromator is a four-reflection flat Si(111) crystal system resembling two channel-cuts in a dispersive arrangement, reducing the bandwidth to less than 10(-4), as required for some applications. Tests with 67 and 81 keV photon energies show that the high-resolution monochromator, having a narrow angular acceptance of a few microradians, exhibits a fourfold throughput enhancement due to the insertion of a CRL that reduces the premonochromatized beam's vertical divergence from 29 micro rad to a few microradians. The ability to focus high-energy X-rays with CRLs having long focal lengths (tens of meters) is also shown by creating a line focus of 70-90 micro m beam height in the beamline end-station with both the modest-energy-resolution and the high-energy-resolution monochromatic X-rays.

Crystallography↗

PubMed2002

Thin film rheology and lubricity of hyaluronic acid solutions at a normal physiological concentration.

Using a surface forces apparatus to measure forces, and optical (multiple beam) interferometry to measure surface shapes and separations (to +/-1 A), the normal, viscous, and shear (lubrication) forces between smooth mica surfaces in aqueous hyaluronic acid (HA) solutions were measured. The experimental conditions of loading pressures, pH, and HA concentration were set to closely correspond to physiological human knee-joint conditions. From the force and optical (refractive index) measurements, it was concluded that, like other negatively charged polyelectrolytes, HA does not naturally adsorb on the mica surface which is hydrophilic and weakly negatively charged at physiological conditions: the polymer solution exhibits the bulk viscosity (22.5 +/- 1.5 cP) for films thicker than about 0.4 miccrom of the polymer, whereas for thinner films, the viscosity decreases monotonically toward the value of the pure electrolyte solution (1 cP) as HA is extruded from between the surfaces. This is indicative of a repulsive "depletion" interaction of HA with each mica surface and to a weakly attractive polymer-mediated force between the two surfaces. Thus, free HA in synovial fluid is not expected to act as a good "boundary lubricant." Relaxation measurements on approaching and receding surfaces in HA solutions were also performed, and it is shown that the presence of HA in the bulk solution can improve "hydrodynamic" modes of lubrication, for example, by assuaging the compression stroke. The study includes information that is beneficial to researchers working with biomaterials viscosupplementation devices.

Adsorption↗

PubMed1994

Ultrasonic spectroscopy of the porcine eye lens.

The purpose of the work is to measure and study the acoustic characteristics of the porcine eye lens and find correlations with chemical and optical parameters, obtained from literature. Ultrasonic spectroscopy was performed by using a scanning acoustic macroscope (frequency 20 MHz, resolution 150 microns). The transducer performed a two-dimensional scan over a central slice (1 mm thickness) of porcine lens (number of lenses = 10). A double transmission pulse-echo method was used to acquire the ultrasonic data from the lens. Two-dimensional images were reconstructed of the local ultrasound velocity and the frequency-dependent ultrasound attenuation. Axial and equatorial profiles of these parameters were calculated from the images. The acoustic parameters are not constant, but show a systematic dependence on the location within the lens. The profiles of the acoustic parameters are similar in shape to profiles of the protein and water contents of eye lens and to the profiles of the optical refractive index. A thorough quantitative correlation study is indicated, which should be based on detailed protein content data in porcine lenses.

Animals↗

PubMed2006

Laboratory findings in tear fluid analysis.

The tear film, composed of the lipid, aqueous and mucin layers, has many functions including defending the ocular surface. The tear film covering the ocular surface presents a mechanical and antimicrobial barrier and ensures an optical refractive surface. The lipid component originates from the meibomian glands of the tarsus and forms the superficial layer of the tear film. The aqueous component contains electrolytes, water, and a large variety of proteins, peptides and glycoproteins, and is primarily secreted by the lacrimal gland. Mucins are glycoproteins expressed by epithelial tissues of mucous surfaces. They protect tissues by functioning as antioxidants, providing lubrication, and inhibiting bacterial adherence. Quantitatively and qualitatively, its composition must be maintained within the fairly narrow limits to maintain a healthy and functional visual system. Abnormalities of the tear film, affecting the constituents or the volume, can rapidly result in serious dysfunction of the eyelids and conjunctiva and ultimately affect the transparency of the cornea. Many ocular surface tests have been developed for the clinical diagnosis of dry eye syndromes. This paper provides an overview on laboratory methods for the analysis of the tear film. Understanding the components of the tear film will aid in the treatment of dry eye syndromes and the ocular surface diseases.

Animals↗

PubMed2004

On the suitability of refractometry for the analysis of glucose in blood-derived fluids.

BACKGROUND: Refractometry is the determination of the optical refractive index of a substance or a mixture of substances. It is a very sensitive method for the detection and quantification of dissolved analytes, but it is incapable of distinguishing between different analytes. The aim of this investigation was to determine the principle suitability of refractometry for the quantification of glucose (blood sugar) in blood and various blood fluids which can readily be obtained for medical diagnosis, in particular blood plasma, blood serum, and their ultrafiltrates. METHODS AND RESULTS: After the oral intake of freshly dissolved alpha-glucose, the in vivo blood contents of the alpha and beta anomers of glucose were found to be in an at least approximate equilibrium at all times. This observation is a prerequisite for a refractometrical determination of glucose due to the fact that both molecule forms have different refractive index increments. An assessment of the glucose content in untreated blood fluids was not possible, since no suitable relationship to the refractive index was found, most probably due to the influence of the many other substances present in blood on this parameter. However, after removal of certain macromolecules by ultrafiltration, value pairs showed a high level of correlation, providing the nominal molecular weight limit (cut-off) of the ultrafilter used possessed a maximum of 300 kDa. Besides macromolecules, the osmolality of the fluids undergoing measurement also proved to be a considerable interfering factor, particularly when values were outside the normal physiological range between 285 and 293 mmol/L. CONCLUSIONS: If a clinical application of this method is to be contemplated it is imperative (1) that blood cells are separated and removed, (2) that macromolecules present in plasma or serum are removed, e.g. by ultrafiltration, and (3) that beyond the results presented the influence of all small molecules other than glucose on the overall refractive index be determined and included in the calculation of analysis results.

Adult↗

PubMed2002

Spatial optical solitons in nonlinear photonic crystals.

We study spatial optical solitons in a one-dimensional nonlinear photonic crystal created by an array of thin-film nonlinear waveguides, the so-called Dirac-comb nonlinear lattice. We analyze modulational instability of the extended Bloch-wave modes and also investigate the existence and stability of bright, dark, and "twisted" spatially localized modes in such periodic structures. Additionally, we discuss both similarities and differences of our general results with the simplified models of nonlinear periodic media described by the discrete nonlinear Schrödinger equation, derived in the tight-binding approximation, and the coupled-mode theory, valid for shallow periodic modulations of the optical refractive index.

Journal Article↗

PubMed2006

Accommodative lens refilling in rhesus monkeys.

PURPOSE: Accommodation can be restored to presbyopic human eyes by refilling the capsular bag with a soft polymer. This study was conducted to test whether accommodation, measurable as changes in optical refraction, can be restored with a newly developed refilling polymer in a rhesus monkey model. A specific intra- and postoperative treatment protocol was used to minimize postoperative inflammation and to delay capsular opacification. METHODS: Nine adolescent rhesus monkeys underwent refilling of the lens capsular bag with a polymer. In the first four monkeys (group A) the surgical procedure was followed by two weekly subconjunctival injections of corticosteroids. In a second group of five monkeys (group B) a treatment intended to delay the development of capsular opacification was applied during the surgery, and, in the postoperative period, eye drops and two subconjunctival injections of corticosteroids were applied. Accommodation was stimulated with carbachol iontophoresis or pilocarpine and was measured with a Hartinger refractometer at regular times during a follow-up period of 37 weeks in five monkeys. In one monkey, lens thickness changes were measured with A-scan ultrasound. RESULTS: In group A, refraction measurement was possible in one monkey. In the three other animals in group A, postoperative inflammation and capsular opacification prevented refraction measurements. In group B, the maximum accommodative amplitude of the surgically treated eyes was 6.3 D. In three monkeys the accommodative amplitude decreased to almost 0 D after 37 weeks. In the two other monkeys, the accommodative amplitude remained stable at +/-4 D during the follow-up period. In group B, capsular opacification developed in the postoperative period, but refraction measurements could still be performed during the whole follow-up period of 37 weeks. CONCLUSIONS: A certain level of accommodation can be restored after lens refilling in adolescent rhesus monkeys. During the follow-up period refraction measurements were possible in all five monkeys that underwent the treatment designed to prevent inflammation and capsular opacification.

Accommodation, Ocular↗

PubMed2006

Apochromatic telescope without anomalous dispersion glasses.

In order to correct secondary longitudinal chromatic aberration in conventional refracting optical systems, it is necessary to use at least one optical material having anomalous partial dispersion. A novel lens system with correction of the secondary spectrum by using only normal glasses is presented. The lens system comprises three widely separated lens components; both second and third components are subaperture. The presented example of an apochromatic telescope demonstrates secondary spectrum correction with the use of only crown BK7 and flint F2, which are among the most inexpensive optical glasses available at the market. Two more similar designs are presented, both with the use of low-cost slightly anomalous dispersion glasses. These telescopes have a higher relative aperture and a smaller tertiary spectrum.

Journal Article↗

PubMed1994

Changes in refractive trends and optical components of Hong Kong Chinese aged 19-39 years.

The distribution of refractive errors and its relationship to the optical components in 105 Hong Kong Chinese aged 19-39 years was studied. Myopia was most frequent (71%) in this population. The mean spherical equivalent was -3.00 DS. The trend of changes of the direction of refractive and corneal astigmatism from with-the-rule to against-the-rule with increasing age was shown. Significant correlations were found between age and anterior segment distance. Ultrasound examination showed that an increasing axial length was associated with higher myopia. Men had flatter corneal radii, but longer axial length. The prevalence of myopia in the Chinese population seems to be a new trend for the younger Hong Kong Chinese when compared with adults aged over 40 years. Thus the importance of genetics in determination of myopia is called into question by these findings.

Adult↗

PubMed2000

Optical rotation per refractive index unit, or enantiomeric (e) factor, for screening enantioselective catalysts through asymmetric activation or carbohydrates.

A super high-throughput screening (SHTS) system can be constructed by combining high-performance liquid chromatography (HPLC), optical rotation (OR), and refractive index unit (RIU) to determine not only the enantioselectivity of the addition of diethylzinc to an aliphatic aldehyde catalyzed by a binaphthol-zinc complex through asymmetric activation with chiral Schiff bases, but also the enantiopurity of a carbohydrate. The enantiomeric (e) factor, which we define here as optical rotation per refractive index unit, is linearly related to the percent enantiomeric excess (%ee) and is independent of concentration.

Acetonitriles↗

PubMed1990

The refractive structure and optical properties of the isolated crystalline lens of the cat.

Direct measurements of the shape and internal refractive index distribution of the isolated cat lens were used to construct individual optical models of the lenses from the left eyes of five cats. The right eyes were used in a companion study of the optics of the cat eye. The lens refractive index spatial distribution and dispersion were measured with a specially designed Pulfrich areal refractometer. Agreement of calculated ray paths through these models with the observed paths of laser beam fans incident parallel to, and at an oblique angle to the lens axis indicates that the models, which contain no freely adjustable parameters, are good physical and optical representations of the isolated (accommodated) crystalline lenses.

Accommodation, Ocular↗

PubMed2001

Power vector analysis of the optical outcome of refractive surgery.

PURPOSE: To demonstrate the power vector method of representing and analyzing spherocylindrical refractive errors. SETTING: School of Optometry, Indiana University, Bloomington, Indiana, USA. METHODS: Manifest and keratometric refractive errors were expressed as power vectors suitable for plotting as points in a 3-dimensional dioptric space. The 3 Cartesian coordinates (x, y, z) of each power vector correspond to the powers of 3 lenses that, in combination, fulfill a refractive prescription: a spherical lens of power M, a Jackson crossed cylinder of power J0 with axes at 90 degrees and 180 degrees, and a Jackson crossed cylinder of power J45 with axes at 45 degrees and 135 degrees. The Pythagorean length of the power vector, B, is a measure of overall blurring strength of a spherocylindrical lens or refractive error. Changes in refractive error due to surgery were computed by the ordinary rules of vector subtraction. RESULTS: Frequency distributions of blur strength (B) clearly demonstrate the effectiveness of refractive surgery in reducing the overall blurring effect of uncorrected refractive error. CONCLUSIONS: Power vector analysis also revealed a reduction in the astigmatic component of these refractive errors. Paired comparisons revealed that the change in manifest astigmatism due to surgery was well correlated with the change in keratometric astigmatism. Power vectors aid the visualization of complex changes in refractive error by tracing a trajectory in a uniform dioptric space. The Cartesian components of a power vector are mutually independent, which simplifies mathematical and statistical analysis of refractive errors. Power vectors also provide a natural link to a more comprehensive optical description of ocular refractive imperfections in terms of wavefront aberration functions and their description by Zernike polynomials.

Astigmatism↗

PubMed2002

Refractive compensation to optical defocus depends on the temporal profile of luminance modulation of the environment.

The refractive state of hatchling chicks rapidly compensates to applied optical defocus through alteration in eye growth. The mechanism is capable of sensing whether the plane of focus lies in front of or behind the photoreceptors, however, its nature and site of action within the retina are unknown. We attempted to create an imbalance in the adaptation of the retinal ON and OFF mechanisms previously implicated in refractive control through pharmacological interventions, by rearing chicks from 4 to 9 days of age with a monocular +10 D, 0 D or -10 D lens, in an environment illuminated by a moving or stationary plaid of luminance gradients. When the plaid moved in one direction a local Fast-ON sawtooth luminance modulation was produced, while plaid motion in the other direction resulted in a Fast-OFF sawtooth modulation. Significantly reduced refractive compensation accompanied +10 D lens/Fast-OFF and -10 D lens/Fast-ON rearing, but not for the other conditions. Thus the refractive compensation mechanism depends on the nature of the temporal contrast of the environment, suggesting a relationship between the sign of defocus and the state of adaptation of the retinal ON and OFF subsystems.

Adaptation, Ocular↗

PubMedDate not supplied

[Estimation of the size of bilayer liposome by optical density and refractive index].

A simple method for estimating a mean particles size in a suspension is suggested on the basis of an empirical correlation of a liposome size found by the optical shift method and on optic properties of the suspension. For liposome size characteristics only two parameters: optical density and refraction index increment are measured.

Biophysical Phenomena↗

PubMed1995

Non-arteritic anterior ischemic optic neuropathy and refraction.

A small cup-disk ratio has been reported as a risk factor in non-arteritic anterior ischemic optic neuropathy. Hyperopia is possibly related with a small cup-disk ratio. The purpose of the present study is to compare the refraction of 37 eyes with non-arteritic anterior ischemic optic neuropathy with a sex and age matched control group of 74 eyes. In our study, mild hyperopia was more frequently observed in the anterior ischemic optic neuropathy group than in the control group.

Adult↗

PubMed2002

Effect of interfacial refractive index on optical molecular orientation measurements.

The sensitivity of optical molecular orientation measurements to assumptions regarding thin film refractive index was investigated. Specifically, the influence of the interfacial refractive index on second harmonic generation (SHG) and linear dichroism measurements made in a total internal reflection (TIR) geometry was probed for five distinct molecular systems. The five molecular thin films ranged from weakly adsorbed species in equilibrium with solution to covalently bound molecules. Polarization data from the two techniques were fit using a range of assumed interfacial refractive indices. Surprisingly, a linear relationship between the difference in calculated apparent orientation angle and the difference in solvent-prism refractive index was observed. The trend indicates that for a TIR geometry, the error introduced by the thin film refractive index is negligible when the difference in solvent and prism refractive indices is less than approximately 0.08. However, there are clearly cases, such as a glass/air interface, in which assumptions regarding the thin film refractive index can result in significant error in the extracted orientation angle.

Journal Article↗

PubMed2005

Theoretical calculations of refractive indices and optical effects in spectra of nitric acid and nitric acid monohydrate crystals.

The theoretical infrared refractive indices of two systems related to atmospheric research, nitric acid (NA) and nitric acid monohydrate (NAM) crystals, have been computed using a methodology based on first-principles. The effects of lack of coherence in the infrared beam in RAIR and transmission spectra have also been treated using a model based on classical optics. The optical constants of NA crystals are presented for the first time; the results on NAM are compared to empirical values previously published with good general agreement. With the optical constants of NA, polarized reflection-absorption infrared spectra are predicted and compared to experimental spectra recorded also for the first time, for a set of varying film thickness. The global agreement is satisfactory. The effects of a number of experimental factors in transmission spectra of NAM are assessed, in an attempt to explain observed differences among experimental spectra. It is concluded that the spectral disparities are probably due to differences in the nature of the samples.

Journal Article↗

PubMed2005

Optic disk size correlated with refractive error.

PURPOSE: To evaluate for which range of refractive error the optic disk size depends on, or is independent of, the refractive error. DESIGN: Clinical observational study. METHODS: The study included 1999 eyes of 1011 subjects with a mean refractive error of -0.97 +/- 2.72 diopters (range, -24.25 to +9.4 diopters). Optic disk photographs were morphometrically evaluated. RESULTS: The relation between optic disk area and refractive error showed a curvilinear shape, with a steep increase toward high myopia starting at -8 diopters, and a decrease toward high hyperopia starting at +4 diopters. CONCLUSION: The optic disk size depends on the refractive error with an increase in highly myopic eyes beyond -8 diopters and a decrease in highly hyperopic eyes beyond +4 diopters. Confirming histomorphometric studies, the limits of -8 diopters and +4 diopters may be discussed to refine the definitions of high hyperopia and high myopia.

Chronic Disease↗