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At least 1,405 records · Page 78Linked to original sources
PubMed1999

Light absorption by phototrophic bacteria: effects of scattering, cell concentration and size of the culture vessel.

This article analyzes how absorption of light by suspensions of phototrophic bacteria is modulated by changes in the biomass of the culture, the size of the culture vessel and by the presence of refractile structures within the cells. Increases in biomass and culture size result in higher rates of light absorption but in the decrease of the amount of energy available per cell. The presence of refractile structures has different consequences depending on the biomass concentration. In dense cultures, the accumulation of refractile structures increases the reflection of light, and also reduces specific light absorption. In diluted cultures, however, the effect is the opposite, and refractile structures seem to increase light absorption.

Bacteria↗
PubMedDate not supplied

Dental histology: study of aging processes in root dentine.

The amount of sclerotic root dentine increases with age, proceeding from the apex towards the crown. There are obvious optical changes in the tissue, which becomes translucent (dentine is normally opaque). Therefore, the sclerosis of root dentine could be a reliable indicator of age in anthropological studies of human remains. We studied the histological aspects of sclerotic dentine in longitudinal thin sections (70-140 microns) of undecalcified premolars, cut in the bucco-lingual plane. To quantify the sclerosis and to construct a reference standard, we sectioned 85 premolars from subjects of known age (70 from odontological extractions and 15 from a university collection). Another 10 teeth from medieval subjects were studied to assess the applicability of the method to ancient skeletal collections. The technique consists of embedding the tooth in a polyester resin (cold method), sectioning it with a diamond blade microtome. Qualitative analysis was performed with polarized light microscopy and measurements were made with a quote 2D x,y viewer and on digital images. The sclerotic root dentine was quantified with both linear and surface area parameters in order to assess the correlation with age. The quality of the sections was sufficient for the clear discernment and quantification of the sclerotic dentine. Indeed, the technique allowed us to obtain good results with a considerable saving of time and money compared with other dental histological techniques. The best correlation with age was obtained from the surface area parameter, particularly after exclusion of the cementum and pulp chamber. To produce comparable data from similar studies, we advise the use of cold resins, as used here, and digital computerized analyzers because of their accuracy, precision and quickness. The qualitative analysis of the ancient teeth indications that this dental aging techniques can be applied to both recent and ancient dental tissues.

Adolescent↗
PubMed2000

[Removal of inital cataract in high degenerative myopia--selection of surgical technique and planned refractive effect].

Visual function deteriorates additionally in high degenerative myopia in consequence of initial cataract causing increase of refractive index and refractive error. This paper presents indications for removal of initial cataract with posterior chamber lens implantation to improve visual acuity, colour perception, contrast sensitivity and to broaden visual field. Particular conditions of cataract surgery in myopic eye, selection criteria of operative technique and anaesthesia, power and diameter of implant and possible postoperative complications are discussed.

Anesthesia↗
PubMed2001

Lens growth and protein density in the rat lens after in vivo exposure to ultraviolet radiation.

PURPOSE: To investigate lens growth after different doses of ultraviolet radiation (UVR) and to investigate the long-term effect of a near-threshold UVR dose on the refractive index distribution in the lens. METHODS: Sprague-Dawley rats received UVR (lambda(MAX) = 300 nm) unilaterally during a 15-minute period. The exposure dose ranged from 0.1 to 20 kJ/m(2), and the rats were kept for up to 32 weeks after exposure. Intact lenses were photographed and lens wet and dry masses were measured. The protein density was estimated by quantitative microradiography. Freeze-dried lens sections were used for contact x-ray photographs. From the transmission of the microradiographs, protein density and refractive index profiles were calculated along the lens radius with a resolution of 2.5 microm. RESULTS: Lens dry mass in exposed eyes was lower than in nonexposed eyes at one week after exposure. Lens water content was decreased after low UVR doses but increased after high doses. The difference between exposed and nonexposed lenses in dry mass and water content increased with time after exposure. No significant difference was found for the mean protein density in exposed and nonexposed lenses. The protein density increased linearly in the lens cortex, from a minimum in the superficial cortex of 0.26 g/cm(3) to a maximum in the deep cortex of 0.81 g/cm(3). This corresponded to a refractive index of 1.38 and 1.48, respectively. CONCLUSIONS: Lenses exposed to UVR grew more slowly than their nonexposed contralaterals. This growth inhibition was dose dependent. Near-threshold doses led to decreased water content in the lens whereas high doses led to swelling. Six months after near-threshold UVR exposure, no global change of the refractive index was found. However, local variations of the refractive index caused a subtle cortical light scattering.

Animals↗
PubMed2001

[Myopia: frequency of lattice degeneration and axial length].

OBJECTIVE: To evaluate the relationship between lattice retinal degeneration and axial length of the eye in different grades of myopia. MATERIAL AND METHODS: A sample of 200 eyes from 124 myopic patients was collected by chance. The average age was 34.8 years (20-50 years) and the myopia was between 0.5 and 20 diopters (D). The eyes were grouped according to the degree of refraction defect, the mean axial length of each group (Scan A) and the frequency of lattice retinal degeneration and the relationship between these variables was studied. The possible influence of age on our results was also considered. For the statistical analysis, the SAS 6.07 program with the variance analysis for quantitative variables, and chi(2) test for qualitative variables with a 5% significance were used. A multivariable linear regression model was also adjusted. RESULTS: The highest frequency of lattice retinal degeneration occurred in those myopia patients having more than 15 D, and also in the group of myopia patients between 3 and 6 D, but this did not show statistical significance when compared with the other myopic groups. If the axial length is assessed, a greater frequency of lattice retinal degeneration is also found when the axial length is 25-27 mm and 29-30 mm, which correspond, respectively, to myopias between 3-10 D and more than 15 D. When the multivariable linear regression model was adjusted, the axial length showed the existence of lattice retinal degeneration (beta 0.41 mm; p=0.08) adjusted by the number of diopters (beta 0.38 mm; p<0.001). The determination coefficient (r(2)) was also 0.86. CONCLUSIONS: The highest number of cases of lattice retinal degeneration was found for myopias with axial eye length between 29-30 mm (more than 15 D), and 25-27 mm (between 3-10 D).

Adult↗
PubMed2000

Dielectric properties of some components of fruit aroma in carbon tetrachloride solution at 298.15 K.

The static electric permittivity and refractive index of carbon tetrachloride solutions of ethyl-2-methyl butanoate, 3-hexene-l-ol, 2-hexenal, ethyldecanoate, methyl anthranilate, anethole, damascenone and isoamyl propanoate were measured at 298.15 K in the concentration range up to 4.0 mol dm-3. The molar polarizations and refractions of the solutions, the partial molar polarizations and refractions of the solutes, as well as the dipole moments at infinite dilution of the solutes were calculated. On the basis of the concentration dependence of apparent values of the square of the molecular dipole moment, it was established that for the systems studied oligomeric species with low dipole moment were prevalent. With the assumption that the dipole moment of dimeric species amounts to zero (except for 3-hexene-l-ol and methyl anthranilate), the constant of dimerization was calculated and a weak molecular association was deduced.

Algorithms↗
PubMedDate not supplied

[Detection of the hepatitis B virus surface antigen with a biosensor].

A new method for detection of hepatitis B surface antigen (HBsAg) has been developed. It employees IAsys optical biosensor registration kinetics of HBsAg complexes with monoclonal antibodies. Detection of intermolecular interactions is accompanied by changes of the light refraction coefficient in the sensitive layer of the biosensor cuvette. The main advantage of this diagnostic technique consists in rapid registration of these interactions in real time, without any introduction of special labels into analysing molecules. The optical biosensor method was successfully employed for the detection of HBsAg in human blood serum. A comparative study of HBsAg detection by the optical biosensor and by immunoenzyme analysis demonstrated high specificity of HBsAg detection by this new method.

Antibodies, Monoclonal↗
PubMed2001

Accuracy of intraocular lens power calculations using the Zeiss IOL master. A prospective study.

PURPOSE: Partial Coherence Interferometry (PCI) is a fast, noncontact method to calculate lens implant power for cataract surgery. It has been reported as a potentially more accurate method than ultrasound biometry. Prospective study of the refractive outcomes of a consecutive series of patients undergoing phacoemulsification surgery with preoperative biometry by both ultrasound A-scan and PCI. METHODS: A series of 50 eyes of 35 patients underwent small-incision phacoemulsification cataract surgery and lens implantation by one single surgeon. All patients had preoperative biometry performed by both ultrasound using the Sonomed and IOL Master optical biometry. The IOL Master results were included in the SRK II formula to calculate the lens implant power. Postoperative refractive assessment was performed 4 weeks after surgery. RESULTS: The mean difference in axial length between ultrasound and optical biometry was 0.2 mm. The IOL Master measures a longer axial length. The mean keratometric power using the Javal instrument was 43.4 D and for the Zeiss IOL Master it was 42.9 D. At the week 4 postsurgery assessment, the overall refractive outcome was in the range of +/- 1D. Five patients were unable to undergo PCI biometry due to the density of cataract. CONCLUSIONS: Intraocular lens power calculations using the Zeiss IOL Master are easy to perform and result in excellent refractive outcomes. A-scan biometry is still needed in case of mature cataract.

Biometry↗
PubMed2001

[Improvement of vision in nursing home patients through eyeglasses].

Adequate refraction correction may contribute to the quality of life of elderly persons who will be less dependent on care in daily life and will be less prone to fall. In nearly 20% of 102 nursing home residents binocular visual acuity improved with at least one line on the Snellen Chart by adjustment of refractive correction.

Accidental Falls↗
PubMed2002

Temperature and composition dependence of the refractive indices of the 2-chloroethanol + 2-methoxyethanol binary mixtures.

Measurements of the refractive index n for the binary mixtures 2-chloroethanol + 2-methoxyethanol in the 0 < or = t/degree C < or = 70 temperature range have been carried out with the purpose of checking the capability of empirical models to express physical quantity as a function of temperature and volume fraction, both separately and together, i.e., in a two independent variables expression. Furthermore, the experimental data have been used to calculate excess properties such as the excess refractive index, the excess molar refraction, and the excess Kirkwood parameter delta g over the whole composition range. The quantities obtained have been discussed and interpreted in terms of the type and nature of the specific intermolecular interactions between the components.

Ethylene Chlorohydrin↗
PubMed2002

Opalescence of dental porcelain enamels.

OBJECTIVE: The objective of this study was to compare the microstructures of teeth, natural opals, and opal dental enamel porcelains to examine the mechanisms that cause opalescence. METHOD AND MATERIALS: Four dental porcelains, a natural opal mineral, and a human tooth were examined. Replicas were assessed in transmission electron microscopy for features that would cause opalescence. Enamel dental porcelains denoted as "light" were selected for the study. X-ray diffraction and color analyses of the porcelains were also performed. RESULTS: All the materials were opalescent, to varying degrees. The porcelains with fewer microscopic features were less opalescent. The presence of dispersed particles or a phase-separated glass was found to cause opalescence in dental porcelains. CONCLUSION: A phase-separated glass in one enamel porcelain best resembled the microstructure of natural opal mineral and teeth, and this was the most "opalescent" material.

Algorithms↗
PubMed2003

Near-field measurement of short-range correlation in optical waves transmitted through random media.

Two-dimensional near-field images of speckle patterns formed by optical waves transmitted through a disordered porous silica glass sample are measured. The corresponding 2D intensity correlation function, C, is extracted. The subwavelength spatial resolution of near-field microscopy allows us to resolve in the spatial distribution of C the expected subwavelength oscillations and to follow their dependence on the excitation wavelength. Finally, we deduce the effective refractive index of the material by fitting the theoretical spatial dependence of C to our experimental results.

Light↗
PubMed1992

Evaluation of two infrared autorefractors in pseudophakia.

We investigated the viability of using an objective infrared autorefractor to identify high corneal astigmatism (> 3.00 D) in a pseudophakic population. The eyes of 91 patients, who had recently undergone cataract extraction and intraocular lens implanation, were refracted manually and using two infrared autorefractors, a Canon RK-1 and a Nikon NR-2000. Autorefractor measurements were repeated to provide estimates of reliability for each instrument. LogMAR visual acuities were also recorded with both the manual and autorefractor corrections. Approximately 75% of repeat autorefractor measurements were within 0.50 D of the initial readings, and about 75% of measurements were within 1.00 D of the manual refractions. Visual acuities with manual corrections were, on average, one line better than with autorefractor corrections. By validating the autorefractors against manual refraction, the efficiency of the autorefractors for detecting astigmatism > 3.00 D was calculated. Setting the cut-off criterion to ensure high sensitivity (95%), so that almost all patients with > 3.00 D were detected, resulted in both instruments having a poor specificity of about 40%.

Adult↗
PubMed1992

Construction of a model eye and its applications.

Construction details are given of a model eye, based on the Bennett and Rabbetts schematic eye. It incorporates a cornea, lens, and spherical fundus. Distilled water filled the anterior and vitreous chambers. By means of a micrometer screw, the vitreous chamber depth can be precisely varied to produce axial ametropia from +11 to -17 D. Readings taken over the greater part of this range with a Topcon Autorefractor RM-A6500 were found to be repeatable and reproducible within +/- 0.25 D. The model eye was used to investigate the relationship between the actual size of a fundus feature and its photographic image in two different fundus cameras. With a Zeiss Oberkochen camera of telecentric design the magnification was found to remain constant whatever the degree of axial ametropia, whereas with a Carl Zeiss Jena camera the magnification varied linearly with ametropia. A technique developed by Littmann for determining the actual size of a retinal feature when using a fundus camera of telecentric design is discussed briefly.

Eye↗