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At least 37 records · Page 2Linked to original sources
PubMed1987

Evaluation of biangular reflection photometry for quantitative study of etched alloy surface roughness.

Biangular reflection photometry was correlated with quantitative stereology and direct pit-depth measurements for an electrolytically etched nickel-chromium-beryllium alloy. Effects of viewing angle, viewing aperture, and plane polarization of incident and viewing light were also studied. The results showed that architectural changes in the etched metal surface could be quantitatively described with the use of reflection photometry. An off-specular peak, located at an angle of reflection considerably different from the angle of incidence, was observed to have an intensity comparable with that of the specular reflection peak. Viewing aperture was found to affect one's ability to distinguish among degrees of surface roughness.

Acid Etching, Dental↗
PubMed2001

Macular pigment density measured by autofluorescence spectrometry: comparison with reflectometry and heterochromatic flicker photometry.

We present a technique for estimating the density of the human macular pigment noninvasively that takes advantage of the autofluorescence of lipofuscin, which is normally present in the human retinal pigment epithelium. By measuring the intensity of fluorescence at 710 nm, where macular pigment has essentially zero absorption, and stimulating the fluorescence with two wavelengths, one well absorbed by macular pigment and the other minimally absorbed by macular pigment, we can make accurate single-pass measurements of the macular pigment density. We used the technique to measure macular pigment density in a group of 159 subjects with normal retinal status ranging in age between 15 and 80 years. Average macular pigment density was 0.48 +/- 0.16 density unit (D.U.) for a 2 degrees -diameter test field. We show that these estimates are highly correlated with reflectometric (mean: 0.23 +/- 0.07 D.U.) and psychophysical (mean: 0.37 +/- 0.26 D.U.; obtained by heterochromatic flicker photometry) estimates of macular pigment in the same subjects, despite the fact that systematic differences in the estimated density exist between techniques. Repeat measurements over both short- and long-time intervals indicate that the autofluorescence technique is reproducible: The mean absolute difference between estimates was less than 0.05 D.U., superior to the reproducibility obtained by reflectometry and flicker photometry. To understand the systematic differences between density estimates obtained from the different methods, we analyzed the underlying assumptions of each technique. Specifically, we looked at the effect of self-screening by visual pigment, the effect of changes in optical property of the deeper retinal layers, including the role of retinal pigmented epithelium melanin, and the role of secondary fluorophores and reflectors in the anterior layers of the retina.

Adult↗
PubMed1985

Flicker photometry and achromatic-channel structure.

It is widely assumed that the near-perfect additivity of heterochromatic flicker photometry implies the existence of an achromatic channel in the visual system, which accurately sums R- and G-cone signals. For flicker photometry to be additive, the channel that detects the flicker stimulus need not add cone signals.

Color Perception↗
PubMed1996

Influence of sample temperature on reflectance photometry and electrochemical glucometer measurements.

OBJECTIVE: A study was conducted to determine the influence of sample temperature on manual reflectance photometers, automatic reflectance photometers, and electrochemical glucometers. RESEARCH DESIGN AND METHODS: Aqueous and blood-based control solutions were tested at temperatures ranging from 25 to 44 degrees C. With the Accu-Chek 3, One Touch, and Satellite G glucometers, multiple glucose determinations were performed on each sample. RESULTS: The results indicate that the manual reflectance photometry glucometer is prominently influenced by variation in sample temperature. The effect of sample temperature is greatest at high glucose levels. CONCLUSIONS: Caution may be required in the interpretation of manual reflectance photometry glucometer measurements in febrile or hypothermic diabetic patients.

Blood Glucose↗
PubMed2006

Toward a CIE supplementary system of photometry: brightness at any level including mesopic vision.

Photometry for brightness at any level including mesopic vision is described on the basis of the work conducted towards the development of a Commission Internationale de l'Eclairage (CIE) supplementary system of photometry in CIE technical committees. Several critical items in developing such a system are discussed: (1) how to scale brightness using the concept of equivalent luminance; (2) the basic vision model of brightness perception; (3) a description of the chromatic contribution to brightness at the photopic as well as at the mesopic level; (4) formulation of an adaptation coefficient for rod-cone interaction. A possible photometric model for brightness is described based on these considerations, together with a quantitative evaluation of the model using experimental data.

Adaptation, Ocular↗
PubMed1981

[Use and results of the microscope photometry in the virology (author's transl)].

Labelled preparations are scanned fluorometrically and absorptionsphotometrically qualitative and quantitative evaluation. Thereby dynamic characteristics can be found which may serve as markers for different virus types. The titre, probability of detection and the required dilution for complete detection of antigens can be determined. The microscope photometry is applicable for screening of potential virostatica as well as topographic analyses of virus synthetisizing cells. The distribution of computer operated scanning photometry is ensued by digital plotter as a 3 dimensional or mosaic print out. Moreover, cadastres of the immunity can be obtained by the fluorometric technique.

Adenoviruses, Human↗
PubMed1982

[Photometry of Mycobacteria and its application in sensitivity-testing of chemotherapeutic agents (author's transl)].

Using photometry in measuring the growth of mycobacteria in liquid medium 7 H 9 Middlebrook slightly modified, we could achieve a 5 to 8 fold increase of extinction values within 8 days. The reproducibility of these results were investigated by tenfold assay of the laboratory mycobacterial strain H37Rv and about 10 strains recently isolated from patients. As antituberculous chemotherapeutic agents require different pH for their optimal activity, the experiments were performed at pH 5.5, pH 6.8 and pH 7.3. By daily measuring the extinction values of all strains showed less growth at pH 5.5 compared to their behaviour at pH 6.8 and 7.3. Yet growth at pH 5.5 was sufficient to estimate the inhibitory effect of Pyrazinamide as later experiments could show. The variation coefficient at pH 5.5 revealed to be significantly lower than at pH 6.8 and pH 7.3. Isoniazid, Prothionamid and Rifampicin were tested at pH 6.8, Streptomycin, Ethambutol and Tetracyclin at pH 7.3 and Pyrazinamide at pH 5.5. The results of our calculations were expressed as growth percentages in relation to growth in the control tubes. Usüally the measurements of the last day of incubation were chosen for this evaluation. Inhibition of growth in 50% or more of the extinction values of the control tubes was the criterion for regarding a strain as sensitive to a given drug. All drugs were tested in two concentrations. In case of only one concentration effecting inhibition of growth in 50% ore more, the strain was reported to give a borderline result. Sensitivity testing with photometry was compared to conventionally performed tests on Loewenstein-Jensen-Medium which were in good agreement between 80 and 100%. Results being available within 8 days in an advantage of the photometric method of sensitivity testing. Furthermore Pyrazinamide and Tetracyclin can be tested without difficulties while these drugs give unsatisfactory results when tested on Loewenstein-Jensen-medium.

Antitubercular Agents↗
PubMed1989

A new test for endothelial viability. The Janus green photometry technique.

A new in vitro technique was developed to measure, by simple photometry, the amount of Janus green extracted with absolute alcohol from isolated corneas after vital staining. The amount of stain corresponded to the percentage of damaged endothelial cells and was a reliable parameter of endothelial viability. More rapid and easier to perform than the usual cell counting of devitalized cells, this technique can be used to study the endothelial damage induced, for example, by experimental surgery, intraocular solutions, intraocular lens material, corneas storage solutions. As an example of application, results of the endothelial status after medium-term preservation of pig corneas (n = 40) in a modified McCarey-Kaufman medium at 4 degrees C were determined. The mean +/- endothelial damage was 8.5% +/- 1.8% (mean +/- SD) after 4 days, 29.5% +/- 3.7% after 7 days, 45.5% +/- 5.5% after 10 days, 69.3% +/- 3.7% after 14 days, and 100% after 20 days of storage in McCarey-Kaufman medium.

Animals↗
PubMed1983

Fluoro-photometry in myotonic dystrophy.

We found pigment alterations in the anterior segments of the eyes of patients with myotonic dystrophy. We therefore performed fluoro-photometry in a group of ten myotonic patients and the results were compared with those of a group of normal persons. The fluorescence levels in the aqueous and vitreous of the myotonic eyes appeared to be two or three times higher than in the normal eyes. This brings us to the conclusion that myotonic eyes have a defect in the blood-ocular barriers.

Aqueous Humor↗
PubMed1977

Use of a wedge cuvette in thin layer photometry and its application to oximetry.

A wedge cuvette was constructed by fixing 2 glass plates at a known angle with a spacer at one end. This resulted in a thin layer with thickness varying from 0 to 250 micrometer. By measuring the intensity of a beam of light through the thin layer as a function of distance along the wedge (and thus layer thickness), the absorption coefficient at the light wavelength used could be obtained without a separate measurement of I0, the reference light intensity. In addition, the difficult problem of determining accurate layer thickness as encoutered in conventional thin layer photometry has been avoided. Tests of the wedge cuvette method with Evans Blue and Malachite Green serial dilutions as well as with haemoglobin solutions at several oxygen saturations demonstrate that accuracy of the order of 1% can be obtained. Application of the wedge cuvette in experiments on oxygen uptake by layers of haemoglobin solution are discussed.

Hemoglobins↗
PubMed2002

Opponent and nonopponent contributions to the zebrafish electroretinogram using heterochromatic flicker photometry.

While some lower vertebrates, such as zebrafish, do not appear to possess anatomically separate pathways of processing visual information (such as M-pathways and P-pathways), it is believed that separate processing of the visual stimulus (such as luminance and chromatic processing) is a basic requirement of vertebrate vision. In this study, spectral sensitivity functions were obtained from electroretinogram responses to heterochromatic flicker photometry stimuli at several flicker rates, including a low flicker rate (2 Hz), in an attempt to predominantly stimulate chromatic processes and a high flicker rate (16 Hz), in an attempt to predominantly stimulate luminance processes. In addition, chromatic adaptation was used to isolate and examine the temporal properties of the different cone-type contributions to the electroretinogram response. Spectral sensitivity functions based on responses to heterochromatic stimuli of a low flicker rate appeared to receive both opponent and nonopponent contributions; however, when the stimulus flicker rate was high, spectral sensitivity appeared to be a function of only nonopponent mechanisms. Also, the differences in cone contributions to the spectral sensitivity functions across the different flicker rates appear to be related to the temporal properties of the cone contributions to the electroretinogram response.

Animals↗
PubMed2003

Evaluation of the blood-aqueous barrier by laser flare cell photometry following retinal cryocoagulation.

PURPOSE: To evaluate the influence of peripheral 360 degrees retinal cryocoagulation on the blood-aqueous barrier of patients with retinal vascular disorders. METHODS: The aqueous of 50 eyes of 50 patients with diabetic retinopathy or central vein occlusion was measured by laser flare photometry (FC-2000, Kowa) before peripheral 360 degrees retinal cryocoagulation and 1 day, 1 week, and 1 month thereafter. RESULTS: Mean aqueous flare values before treatment were 15.7 (+/-8.2) photon counts/ms; mean cell count was 9.8 (+/-14.8) cells/0.5 mm(3). One day after retinal cryocoagulation flare values had increased statistically significantly to a mean of 39.2 (+/-85.8) photon counts/ms, while the increase in mean cell number to 15.0 (+/-37.2) cells/0.5 mm(3) did not reach statistical significance. One week following treatment, mean flare values had dropped to 30.9 (+/-49.6) photon counts/ms and were no longer significantly elevated compared with baseline, while the mean cell count of 11.1 (+/-27.0) cells/0.5 mm(3) was now statistically significantly elevated compared with baseline. One month after treatment the flare values had decreased to a mean of 19.7 (+/-12.0) photon counts/ms, and mean cell count had decreased to 8.1 (+/-10.4) cells/0.5 mm(3); at this point neither parameter showed a statistically significant difference from baseline values. CONCLUSION: Peripheral 360 degrees retinocryocoagulation does not lead to permanent disturbance of the blood-aqueous barrier.

Aqueous Humor↗
PubMed1995

Spectral efficiency measured by heterochromatic flicker photometry is similar in human infants and adults.

Spectral efficiency functions based on heterochromatic flicker photometry (HFP) were measured for three adults and 42 infants using a rapid visually-evoked potential (VEP) method. A 5 degrees-diameter, broadband standard (0.6 cd/m2) was presented in square-wave counterphase (15 Hz) with one of 13 monochromatic lights (420-660 nm; 20 nm steps). The intensity of the monochromatic light was continuously varied while extracting the phase-locked VEP amplitude of the fundamental component. HFP functions measured psychophysically by the method of adjustment were also obtained for the adults. Adult HFP functions from the two methods were found to be essentially the same. Both of these functions were compared to Vos'-modified 2 degrees V(lambda) function and the 10 degrees CIEV(lambda) function. The mean adult data were slightly better fit to the 2 degrees V(lambda) function than to the 10 degrees CIEV(lambda) function, although there was an elevation in sensitivity at 420 and 440 nm. Infant HFP functions were similar to Vos' modified V(lambda) except for an elevation in efficiency at short wavelengths. The mean infant HFP function agreed better with the 10 degrees CIEV(lambda) function than Vos'-modified V(lambda) function, but infant sensitivity was elevated by 0.4 log units at 420 nm compared to the 10 degrees CIE observer. The elevation found at short wavelengths for both adults and infants is attributed to individual and age-related variation in the density of the ocular media, and to reduced macular pigment screening resulting from use of a 5 degrees field size.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Interactions of hyaluronan (hyaluronic acid) with phospholipids as determined by gel permeation chromatography, multi-angle laser-light-scattering photometry and 1H-NMR spectroscopy.

The chain flexibility of solutions of hyaluronan (HA) of different molecular weights was determined by 1H-NMR spectroscopy in the absence and presence of the phospholipid dipalmitoyl-D,L-alpha-phosphatidylcholine (DPC). Sonication of high- or low-molecular-weight HA with DPC for periods of up to 120 min markedly increased HA chain flexibility as determined by observing the half-peak linewidths (delta V1/2) for the methyl protons of the acetamidodeoxyglucose residues of the HA molecules. Gel permeation chromatography of mixtures of purified high-molecular-weight HA (Healon) with 3H-DPC or 3H-platelet activating factor (PAF) showed exclusion of these radioactively labelled molecules from the gel in the presence of HA but not in its absence. Studies using multi-angle laser-light-scattering (MALLS) photometry of sonicates of DPC and Healon after Superose 6 chromatography revealed increases in HA Mw, Mn, Mz and their corresponding root mean square radii relative to control sonicates of HA without DPC. From these data, we have deduced that DPC binds to HA by competing for those hydrophobic centres along the HA chain which are normally responsible for the inter- and intra-chain interactions and which confer stiffness to the HA molecule. It is proposed that such interactions in arthritic joints could reduce synovial fluid viscoelasticity thereby diminishing the ability of this medium to protect articular cartilage from mechanical injury.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1994

Semiautomated HLA-DQB1 typing by fluorescent dye photometry of amplified DNA on microtiter plates.

We report a simple semiautomated HLA class II typing method that suits the demands of a 24-hour-duty transplantation service for preorgan retrieval donor typing. The procedure consists of sequence-specific amplification of HLA alleles by the polymerase chain reaction (nested PCR-SSP) followed by fluorescent dye photometry of the resulting PCR products on microtiter plates. The entire typing procedure is semiautomated and completed in less than 90 minutes after DNA isolation. The test was evaluated for the definition of the specificities DQ1-DQ9 (generic HLA-DQB1 typing). Sensitivity and specificity as judged by DNA reference typing in a different laboratory was 99.5% (n = 202 alleles).

Alleles↗
PubMed2004

Heterochromatic flicker photometry.

Measurement of the macular pigment optical density (MPOD) by heterochromatic flicker photometry (HFP) is accomplished by viewing a small circular stimulus that alternates between a test wavelength that is absorbed by the MP (typically--blue, 460 nm) and a reference wavelength that is not absorbed (typically-green, 540 nm). Flicker observed by the subject is reduced to a null point by adjusting the intensity of the former while viewing the stimulus centrally, and then peripherally. A higher intensity, I, of the blue component of the stimulus is needed under central viewing conditions owing to attenuation by the MP. The MPOD at the test wavelength is given by log (Icentral/Iperipheral). Variation of the test wavelength has been used to measure the MPOD spectrum. This in vitro MPOD spectrum matches that of the carotenoids present in the macular region of the retina and demonstrates the validity and specificity of this methodology. The distribution of MPOD in the retina can be determined with HFP using a series of annular stimuli of different diameters.

Carotenoids↗
PubMed2004

Macular pigment assessment by motion photometry.

A Moreland anomaloscope was modified to measure macular pigment optical density (MPOD) profiles by motion photometry. A grating (spatial frequency 0.38 c deg(-1)), whose alternate bars were filled, respectively, with 460 nm (maximum MP absorption) and 580 nm (zero MP absorption) lights, drifted steadily at 37 degrees s(-1). The subject adjusted the 580 nm radiance to minimise perceived motion (equiluminance between 460 and 580 nm). Five or more settings were made for two foveal fields (0.9 degrees and 2.2 degrees diameter) and 11 extrafoveal annular fields (0.8 degrees -7.5 degrees eccentricity). Twenty subjects made measurements for both eyes: some with replications. MPOD profiles varied in scale (0.18-0.75 for the 0.9 degrees foveal field) and in shape. A mean profile was derived. Foveal data were optimally aligned with annular data in that profile when plotted at 0.71 of the foveal field radius. Factors that limit precision were identified, such as fixation errors foveally and Troxler's effect parafoveally.

Humans↗
PubMed2004

Macular pigment and the edge hypothesis of flicker photometry.

Heterochromatic flicker photometry is commonly used to measure macular pigment optical density (MPOD) in the human retina. It has been proposed, and accepted by many, that the MPOD so measured represents the value at a retinal location corresponding to the edge of the flickering, circular stimulus. We have investigated this proposal by using a series of annular stimuli to determine the MPOD distribution in the central 1.5 degrees of the retina for both eyes of 10 subjects. The MPOD obtained using a 1.5 degrees circular stimulus matched the MPOD distribution at a retinal eccentricity that was always less than the stimulus radius, and averaged, for the 10 subjects, 51% of the stimulus radius. Similar results were obtained using a 1 degrees stimulus. Thus the edge hypothesis is inconsistent with our data. We suggest that involuntary eye movements may be responsible for an apparent edge effect.

Eye Movements↗