Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Refractometry”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16Linked to original sources
PubMed1993

[Apropos of preventive ophthalmologic interventions in the child population of compulsory school age. Authors' experience].

The results are reported of work carried out during the last five years by the Center of Social Ophthalmology, director Prof. G. Scuderi, which is part of the II Division of the Ophthalmologic Clinic of Rome University "La Sapienza" with the object of trying out together with territorial units a model of preventive intervention acting as a filter for specialized university facilities. In other words, already existing facilities and medical personnel were to be used and trained for specific methods and techniques. From 1985 through 1990, 787 children selected by ophthalmologic screening by school doctors among the compulsory school population of the RM 3 and 5 districts were seen and submitted to periodic checks. This cohort included children aged 5 to 14 without significant differences in sex distribution and with prevalence of the 8 to 10 year olds. Each subject was submitted to complete eye examination including refractometry and orthoptics, color vision, biomicroscopic and ophthalmoscopic examination. The principal findings show that about 36% of subjects examined have a natural vision of 11/10 while the high percentage of ametropia observed was mainly represented by astigmatism and hypermetropy, albeit of minor intensity. Strabismus was found in 2.79% and implied marked visual deficit that was often refractory to any type of treatment. In addition, the prevalence was determined of other abnormalities concerning eye motility, color vision and pathologies involving anterior segment and eyeground. In their conclusion, the authors stress the rarity of organic ocular pathology in children (mostly represented by inflammatory changes of the adnexes and conjunctiva) whereas amblyopia was one of the main causes of visual deficit in children. They stress the importance of early therapeutic intervention in order to allow complete visual rehabilitation. The results of the clinical model for prevention were excellent so that it can even be proposed for large scale prevention of amblyopia.

Adolescent↗
PubMedDate not supplied

[Intracapsular implantation of intraocular lenses in complicated cataracts].

A total of 75 patients with various types of cataracts, 35 of these (37 eyes) with complicated cataracts, were examined. Patients with a history of antiglaucoma surgery were not included in the study. Extracapsular extraction of complicated cataracts with intercapsular implantation and suture-free fixation of B. N. Alexeyev's IOL-IKB A004 were carried out after B. N. Alexeyev. The patients were examined using keratometry, ophthalmometry, visometry, echography and echobiometry, biomicroscopy, ophthalmoscopy, pupil test, tonometry, electron tonography, refractometry, gonioscopy, and entoptic phenomena. The results indicate the possibility of extracapsular cataract extraction with intracapsular implantation of IOLs after Alexeyev in patients with complicated cataracts. The incidence of intra- and postoperative complications in patients with complicated cataracts concomitant with myopia, glaucoma, uveitis, and diabetes mellitus did not differ from that in patients with uncomplicated cataracts concomitant with the same conditions. Moreover, the incidence of postoperative complications was far less in comparison with implantation of other lenses, as reported by some authorities.

Cataract↗
PubMedDate not supplied

[Structural transitions of serum proteins in solutions during high- and low-temperature dehydration].

Infrared and ultraviolet spectroscopy, potentiometric titration, and refractometry, as well as analysis of lysine, tryptophan, and tyrosine availability, and enzymic hydrolysis were used to establish that high-temperature and low-temperature dehydration of solutions of serum protein is accompanied by a rearrangement of its molecular structure, resulting in changes in the number of polar radicals and hydrophobic bonds, intermolecular and intramolecular interactions, and the formation of a new stable conformation. Comparison of the two methods of dehydration showed that cryoconcentration resulted in a greater accessibility of the protein molecule to chemical agents and proteolytic enzymes, whereas heating had an opposite effect.

Amino Acids↗
PubMed1997

[Computerized video-keratoscopic analysis and cataract surgery by phacoemulsification. Predictive calculation of the power of the intraocular implant].

PURPOSE: The authors present the results of a prospective study of 125 consecutive cases of phacoemulsification, performed by a single surgeon, to assess the benefit of computerised videokeratoscopy for the improvement of the predictive calculation of the power of intraocular lenses (IOL). METHODS: Preoperative keratometry was determined by means of 3 concurrent techniques, including automated kerato-refractometry (AKR 2000, Nidek) and videokeratoscopy by TMS-1 (Tomey) and CAS-1 (EyeSys). The results of the IOL calculation by these 3 methods was compared postoperatively to the power of the actual IOL yielding emmetropia as calculated by the optical method based on the postop, refraction at the various time-points. RESULTS: Simulated values obtained with videokeratoscopy significantly reduced the refractive error at 1 postop, week (p = 0.001), one month (p = 0.002) and 3 months (p = 0.002) for the CAS1 and at 3 months (p = 0.002) for the TMS1, as compared to values obtained with conventional automated keratometry. The refractive error was significantly reduced with the CAS1 at one month (p = 0.001) and 3 months (p = 0.019) as compared to TMS1. CONCLUSION: The determination of the anterior curvature of the entrance pupil by videokeratoscopy significantly improves the predictive calculation of the IOL power.

Aged↗
PubMed2000

Perish, then publish: Thomas Harriot and the sine law of refraction.

A talented young scientist, Thomas Harriot, wrote the first English account of the New World, "A Briefe and True Report of the New Found Land of Virginia," distinguished by its serious effort to describe and understand the American Indian. Harriot went on to make innovations in mathematics and was one of the first astronomers to use the telescope. His largely unappreciated contribution to the history of ophthalmology was the first formulation of the sine law of refraction of light, found in his unpublished papers long after his death in 1621. Willebrord Snell discovered the sine law in Holland in 1621 but also died without formally publishing it. Rene Descartes first published the sine law in 1637. The sine law of refraction became not only the prime law of all lens systems but ushered in a new world of physical laws.

Astronomy↗
PubMed1987

Refractive keratoplasty in monkeys using intracorneal lenses of various refractive indexes.

The refractive power of the cornea can be altered with an intracorneal lens when it is inserted within a freehand lamellar-pocket incision. The effectiveness of the implant in altering the refractive power of the cornea depends on the refractive index of the intracorneal lens, since little change in the anterior corneal curvature occurs. Thirteen nonhuman primate eyes received intracorneal lenses made of synthetic polymers with refractive indexes ranging from 1.3686 to 1.633. The lidofilcon-B hydrogel (refractive index, 1.3686) lenses created no significant alteration in the refractive power of the cornea. The polymethylmethacrylate (refractive index, 1.4900D) and polysulfone (refractive index, 1.633) lenses created a predictable and significant alteration of corneal power that increased with each implant with a successively higher refractive index. The polymethylmethacrylate lens created a refractive alteration that was approximately 31% of the lens power in air. The polysulfone lens created a corneal power alteration that was approximately 40% of the lens power in air.

Animals↗
PubMed1997

New anionic polyelectrolyte hydrogel for corneal surgery.

A new high-water-content (78%) anionic polyelectrolyte hydrogel was obtained by phase inversion (demixion) of a polymer solution containing 9.0% poly(acrylonitrile sodium methallylsulphonate), 85.0% dimethylformamide, and 6.0% saline solution (0.9% NaCl). The hydrogel is permeable to water, saline, urea, creatinine, glucose, human albumin, and saline-dissolved oxygen. Investigation of the interactions between human serum and surfaces prepared with the new yielded hydrogel, compared to serum interaction with silica-free silicone (RTV), regenerated cellulose (Cuprophan), MMA/PVP copolymer (Lidofilcon), PMMA (Perspex), FIFE (Gore-Tex), and poly(acrylonitrile sodium methallylsulphonate) hemodialysis membrane (AN-69), showed the hydrogel and hemodialysis membrane (both prepared with AN-69 copolymer) to be the only materials devoid of complement (C')-activating ability.

Biocompatible Materials↗
PubMedDate not supplied

Optical biosensors.

Explore the source record for details and available documents.

Biosensing Techniques↗
PubMedDate not supplied

Ligand loading at the surface of an optical biosensor and its effect upon the kinetics of protein-protein interactions.

Optical biosensors are finding increasing use in the determination of kinetic and equilibrium constants for a variety of biomolecular interactions. Usually these biosensors require one biomolecule, the ligand, to be covalently attached to a hydrogel matrix which itself is bonded to the sensing surface. The ligands partner, the ligate, then binds from solution resulting in a measurable change in response which the instrument records as a function of time. Although in many cases, optical biosensors are used in order to obtain parameters that relate to interactions in solution, it is becoming clear that measurements involving the interaction of ligate with immobilized ligands on surfaces require careful experimental design. Here we report on how the density of ligand loading within the hydogel matrix affects the measured interaction kinetics. It is found that crowding of ligand within this matrix results in a significant reduction in the measured association rate constant, with a corresponding effect in the calculated overall affinity. However, measurements at low ligand loadings show association rate constants that are comparable to those measured in solution. Clearly, where this comparison is required, it is important to perform measurements under such conditions.

Biosensing Techniques↗
PubMedDate not supplied

Detection and characterization of weak affinity antibody antigen recognition with biomolecular interaction analysis.

In biological systems, weak-affinity interactions (association constant, Ka, of less than approximately 10(4) M-1) between biomolecules are common and essential to the integrity of such units. However, studies of weak biological interactions are difficult due to the scarcity of analytical methods available for the bioscientist. In this communication, we report on the use of biosensors based on surface plasmon resonance to detect and characterize weak affinity antibody-antigen interactions. Monoclonal antibodies towards carbohydrate antigens were immobilized on sensor surfaces and were used to detect weak binding of the carbohydrate tetraglucose of dissociation constant, Kd, in the millimolar range. Sensorgrams were received in the form of square pulses where the kinetic rate constants were difficult to assess due to the rapid association and dissociation of the antigen to/from the immobilized antibody.

Antibodies, Monoclonal↗
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↗
PubMed2000

Reflection and absorption of millimeter waves by thin absorbing films.

Reflection, transmission, and absorption of mm-waves by thin absorbing films were determined at two therapeutic frequencies: 42. 25 and 53.57 GHz. Thin filter strips saturated with distilled water or an alcohol-water solution were used as absorbing samples of different thicknesses. The dependence of the power reflection coefficient R(d) on film thickness (d) was not monotonic. R(d) passed through a pronounced maximum before reaching its steady-state level [R(infinity)]. Similarly, absorption, A(d), passed two maximums with one minimum between them, before reaching its steady-state level [A(infinity)]. At 42.25 GHz, A(d) was compared with absorption in a semi-infinite water medium at a depth d. When d < 0.3 mm, absorption by the film increased: at d = 0.1 mm the absorption ratio for the thin layer sample and the semi-infinite medium was 3.2, while at d = 0.05 mm it increased up to 5.8. Calculations based on Fresnel equations for flat thin layers adequately described the dependence of the reflection, transmission, and absorption on d and allowed the determination of the refractive index (n), dielectric constant (epsilon), and penetration depth (delta) of the absorbing medium for various frequencies. For water samples, epsilon was found to be 12.4-19.3j, delta = 0.49 mm at 42.25 GHz, and epsilon = 9.0-19.5j, delta = 0.36 mm at 53.57 GHz. The calculated power density distribution within the film was strongly dependent on d. The measurements and calculations have shown that the reflection and absorption of mm-waves by thin absorbing layers can significantly differ from the reflection and absorption in similar semi-infinite media. The difference in reflection, absorption, and power density distribution in films, as compared to semi-infinite media, are caused by multiple internal reflections from the film boundaries. That is why, when using thin phantoms and thin biological samples, the specifics of the interaction of mm-waves with thin films should be taken into account.

Absorption↗
PubMed2000

Detection in capillary electrophoresis.

A review of the four major, on-line, capillary electrophoresis (CE) detection modalities is presented. It is shown that each detection method, fluorescence, absorbance (conventional and nonconventional), electrochemical and refractive index, have distinct advantages and limitations when applied to analysis in a CE format. Various aspects of CE detection are considered and a perspective regarding the applicability of the technique is provided. It is shown that because of widely varying detection limits (ranging from single molecule to 10(-5) M) and detection scheme complexity, the particular application should dictate the selection of detection methodology in CE.

Electrochemistry↗
PubMed1984

The molecular basis of cataract formation.

The theoretical and experimental basis for the transparency and opacification of the lens is reviewed. The microscopic mechanisms so far established which produce cataract are discussed. The use of quasielastic light scattering spectroscopy to measure in vivo the diffusivity of proteins and to sensitively detect the earliest stages of cataract formation is described.

Cataract↗