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Results for “Optics and Refraction”

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At least 667 records · Page 37Linked to original sources

PubMed2006

Analysis of Gibbs monolayer adsorbed at the toluene/water interface by UV-visible partial internal reflection spectrometry.

Gibbs monolayers of lipophilic tetraphenylporphyrinatomanganese(III) and hydrophilic diacid of meso-tetrakis(4-sulfonatopheny)porphyrin adsorbed at the liquid-liquid interface have been analyzed by UV-visible external reflection (ER) and partial internal reflection (PIR) spectra measured at different angles of incidence. The angle-dependent ER and PIR spectra over the Brewster angles (thetaERB and thetaIRB) have readily been measured at the toluene/water interface. As preliminarily expected in our previous study, the present study has first proved that the reflection-absorbance of UV-visible PIR spectra quantitatively agrees with the theoretical calculations for the Gibbs monolayer over thetaIRB. In addition, it has also been proved that the absorbance of the PIR spectra is greatly enhanced in comparison to that of the ATR spectra. The enhancement is caused by an optical effect in the monolayer sandwiched between two phases of toluene and water that have different but refractive indices close to each other. This optical enhancement requires an optically perfect contact between the phases, which is difficult to prepare for a solid-solid contact. At the liquid/liquid interface, however, an ideal optical contact is easily realized, which makes the enhancement as much as the theoretical expectation. The PIR spectrometry will be recognized to be a new high-sensitive analytical tool to study Gibbs monolayer at the liquid/liquid interface.

Acids↗

PubMed2000

A fully automated remote refraction system.

Traditional methods of performing refractions depend on a trained refractionist being present with the subject and conducting an interactive form of subjective testing. A fully automated refraction system was installed in 13 optical dispensaries and after 15 months the patient and statistical information was gathered. The data from all operators were consistent and suggested a lack of operator effect on the refraction results. The mean of the SD of subjective sphere measurements was 0.2, or slightly less than a quarter dioptre, which would be an acceptable level of accuracy for ordering corrective lenses. The present study suggests an absence of operator influence on the results of the refractions and a degree of consistency and accuracy compatible with the prescription of lenses.

Humans↗

PubMed1992

[Heterotopic fundus. An easily missed abnormality].

This study demonstrates 12 patients with "tilted disc syndrome" which includes an inferior conus and inversion of the optic disc, sectorial ectasia of the fundus, and refractive scotoma. Knowledge of the anomaly can help to prevent the patient from repeated neurologic and neuroradiologic examinations to exclude a cerebral tumor.

Adolescent↗

PubMed2006

Refractive effects in coherent anti-Stokes Raman scattering microscopy.

Coherent anti-Stokes Raman scattering (CARS) microscopy with high sensitivity and high three- dimensional resolution has been developed for the vibrational imaging of chemical species. Due to the coherent nature of the CARS emission, it has been reported that the detection of epi-CARS and forward-CARS (F-CARS) signals depends on the size and shape of the sample. We investigate theoretically and experimentally the effects on the CARS signal of refractive index mismatches between the sample and its surroundings. Backward-CARS and F-CARS signals are measured for different polystyrene bead diameters embedded in different refractive index solvents. We show that index mismatches result in a backward-reflected F-CARS signal that generally dominates the experimentally backward-detected signal. Simulations based on geometrical and wave optics comparing forward- and backward-detected signals for polystyrene beads embedded in different index solvents confirm our findings. Furthermore, we demonstrate that the maxima of forward- and backward-detected signals are generated at different positions along the optical axis in the sample if refractive index mismatches are present between the sample and its surroundings.

Computer Simulation↗

PubMed1996

A wide-angle gradient index optical model of the crystalline lens and eye of the rainbow trout.

Trout lens external shape and internal refractive index gradient structure were measured and used to construct an optical lens model that predicts by ray tracing the average longitudinal spherical and chromatic aberration, focal length and image quality. The nearly spherical shape of the lens was measured from photographs, and the internal refractive gradient structure was measured directly with a special Pulfrich areal refractometer. Longitudinal spherical aberration and back focal length were measured using a simplified Hartmann test using laser beams and a Schlieren test which additionally made refractive index gradient fine structure visible and detected scattering, axial symmetry and structural irregularity. Axial focus shift caused by longitudinal chromatic aberration was measured using a star test. The model lens was then incorporated into a model trout eye based on vertical and horizontal eye frozen sections. Calculated model function yields insight into the relation between eye and lens structure and optical behaviour. Semi-random secondary structural features act as perturbations on the basic model, and will result in point image fine structure.

Animals↗

PubMed1980

Enhanced light collection in a flow cytometer.

A modified flow cell in a conventional flow cytometer is described. The refraction of light in the flow cell-to-air interface is analyzed. The analysis shows that much of the light that can be collected is refracted out of the collection optics. The efficiency of light collection is doubled by the addition of a plano-convex lens to the flow cell. Also, more stable operation of the flow cell is achieved with the addition of a secondary sheath.

Flow Cytometry↗

PubMed1997

Light scattering and morphology of cataract formation in transgenic mice containing the HIV-1 protease linked to the lens alpha A-crystallin promoter.

Two constructs of transgenic mice, TG61 and TG72, containing the HIV-1 protease linked to the lens alpha A-crystallin promoter develop cataract. The TG61 construct develop cataract in utero, while the TG72 construct exhibit frank opacities on the 24th day (homozygotes) and 26th day (hemizygotes) post natum. Polarized light scattering measurements were performed on cortical and nuclear sections of TG72 lenses from day 19 to day 26 as a function of scattering angle. The parallel components of the scattered light intensity increase gradually during opacification, the perpendicular components show very low values from day 19 to day 22 after which they increase exponentially. Analysis of the scattered light intensities yielded parameters describing the size of the protein aggregates, the size of the domains exhibiting optical anisotropy/birefringence, the difference in refractive index between (a) the protein aggregates and their surroundings and (b) the birefringent units and their surroundings. The last parameter accounts for the major portion of the increase in lens turbidity. The TG72 construct shows normal lens development on day 16. By day 21 the posterior cortex shows some disintegration, while the lens is still clear. By day 26 the lens nucleus migrates toward the posterior pole and there is a major alteration in the cortical fibers. Scanning electron microscopic studies reveal normal fiber cell organizations in control animals. In the TG72 construct the fiber cells are well organized at 16 days after birth but already develop some slight separation in the posterior cortical part of the lens. By post-natal day 21, the nucleus and the anterior cortex still exhibit well aligned fiber cell organization, but the posterior cortex shows disalignment. By day 26 in the TG72 construct, all areas of the lens show complete disintegration of the fiber cells and amorphous masses are present throughout. The light scattering parameters describing changes on the nanometer scale can be correlated with the changes in lens morphology during cataractogenesis that occur on the micrometer scale. In comparison, the light and scanning electron microscopic examinations of the postnatal TG61 construct show that the lens is severely disrupted and contains completely disintegrated fiber cell remnants at an early age.

Animals↗

PubMed1984

Dissimilar rates in molecular evolution.

In this work we present an evolutionary tree based on the differences in the physico-chemical properties involved in amino acid substitutions, instead of considering, for its construction, only the number of changes between species. Phylogenetic trees were constructed from the differences in bulkiness, refractivity index, hydrophobicity, polarity and optical rotation of 9 vertebrate calcitonins. A correlation of the form y = a xb was found between the number of changes (x) and the differences in any given physico-chemical property (y). This correlation implies that the evolutionary time can not be evaluated directly from the number of changes between species.

Amino Acid Sequence↗

PubMed1984

Pyramidal neurones of the dorsal cochlear nucleus: a Golgi and computer reconstruction study in cat.

The main projection neurones of the dorsal cochlear nucleus, termed pyramidal, bipolar or fusiform cells, have an apical dendritic arbor approaching the ependymal surface of the nucleus and a basal arbor oppositely directed. In Golgi-Del Rio-Hortega material these neurones were studied, with the light microscope, in nonconventional planes of sectioning oriented across or parallel to the main axis of the elongated nucleus. The pyramidal neurones were seen to be flattened across this axis. The size, shape and orientation of 21 cells from six blocks were studied in detail with computer-aided graphic reconstructions including stereo views. Camera lucida drawings of each cell (usually from several sections) were digitized to obtain x and y coordinates while z coordinates (depths in the tissue) were read from the fine focus knob during microscopy and typed interactively during digitization. The z values were corrected for the effects of refractive index differences in the optical system. Since it was the aim of this study to focus on some fundamental principles of structure and arrangement of pyramidal cells in the dorsal cochlear nucleus rather than on topographic variations, only the middle, regularly built part of the nucleus was examined. Towards the ends of the nucleus the architecture is less regular and will require separate analysis. Measurements of arbor and total cell height and of dendritic length are given. The height of the apical and basal arbor in individual cells showed considerable reciprocity. The total dendritic length was up to 8300 micron (average 6536 micron). The basal arbors always proved to be conspicuously flattened; roughly, the width varied between about 300 and 700 micron (average 489 micron) and the thickness between 65 and 105 micron (average 80 micron). The apical arbors were also often flattened but much less and with a greater variability than the basal arbors (average width 319 micron, thickness 115 micron). The two arbors of individual cells were practically coplanar, the arbor planes showing only moderate angularity (bend) and/or torsion relative to each other (angularity maximum 10 degrees, average 5 degrees; torsion maximum 18 degrees, average 6 degrees). The mutual orientation of cells from the same block was examined. The planes through the basal arbors proved to be very parallel, the differences in orientation angles being between 10 and 0 degrees with rare exceptions. Clearly flattened, apical arbors showed a somewhat greater spread.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2004

Wavefront corrections of intraocular lenses.

This article describes two currently available intraocular lenses (IOLs) that have special design features allowing for correction of optical aberrations other than spherical refractive errors. Although they are not yet fully "customized" lenses, their development has involved average aberrations measured with wavefront technology. An experimental IOL manufactured with a special technology is also described that, when used in conjunction with wavefront sensing, has the potential for full customization.

Animals↗

PubMed1994

Interferometric measurement of corneal thickness with micrometer precision.

The recently developed partial coherence laser Doppler interferometry technique was improved to measure central and peripheral corneal thickness with high precision. Corneal thickness profiles were measured on 18 eyes of health, volunteer subjects. All of these eyes were measurable at angles (between visual axis and measuring direction) ranging from 20 degrees nasal to 25 degrees temporal. At larger angles (up to 35 degrees) only part of the eyes was measurable. The thickness profiles of the 18 corneas have a nearly perfectly parabolic shape within the measured region. The precision (standard deviation) was 1.6 microns for central measurements and decreased somewhat to about 3.5 microns at measuring angles in the range of 25 to 30 degrees. No significant interobserver variability was found on 14 eyes measured by three different observers. This study indicates that the new technique is likely to be superior to currently used ultrasound and conventional optical pachymetry techniques, especially for refractive procedures.

Cornea↗

PubMed1996

Latanoprost, a prostaglandin analog, for glaucoma therapy. Efficacy and safety after 1 year of treatment in 198 patients. Latanoprost Study Groups.

PURPOSE: To determine efficacy and safety of latanoprost, a prostaglandin analog for glaucoma, during 1 year of treatment. METHODS: After baseline measurements, 0.005% latanoprost was topically applied once daily for 12 months in patients from Scandinavia, the United Kingdom, and the United States who had elevated intraocular pressure (IOP). Diagnoses included ocular hypertension, chronic open-angle glaucoma, exfoliation syndrome, and pigment dispersion syndrome. Treatment was masked for the first 6 months and open-label during the second 6 months. RESULTS: Of the 272 patients initially enrolled, withdrawals were due to inadequate IOP control (1%), increased iris pigmentation (5%), other ocular problems (3%), systemic medical problems (3%), and nonmedical reasons (14%). Latanoprost significantly (P < 0.0001) reduced diumal IOP from 25.3 +/- 3.0 mmHg (mean +/- standard deviation) at baseline to 17.4 +/- 2.7 mmHg (32% reduction) at 12 months in the 198 patients who completed 1 year of treatment. The IOP reduction was maintained at a consistent level throughout the 12 months without evidence of drift, and was not affected by sex, age, race, or eye color. Overall, latanoprost caused a possible or definite increase in iris pigmentation in 12% of the 272 patients, all of whom had multicolored irides at baseline. One half of these patients with increased pigmentation withdrew before completing 1 year of therapy. Visual field, optic disc cupping, visual acuity, refractive error, conjunctival hyperemia, aqueous flare, anterior chamber cellular response, lens examination, blood pressure, heart rate, blood tests, and urinalysis were not appreciably altered. CONCLUSION: Latanoprost safely and effectively reduces IOP for 1 year in patients of diverse nationalities, providing further evidence for its usefulness in chronic glaucoma therapy.

Administration, Topical↗

PubMed2000

Positive and negative dysphotopsia in patients with acrylic intraocular lenses.

PURPOSE: To report the incidence, management, and prevention of patient reports of glare and streaks around a point source of light or a dark shadow in the temporal field of vision after acrylic intraocular lens (IOL) implantation. SETTING: A private practice. METHODS: Cases in which patients complained vigorously of dysphotopsia were catalogued prospectively during the implantation experience in 6668 consecutive eyes having surgery between January 1995 and June 1999. The techniques of topical-intracameral anesthesia, temporal clear corneal incisions, and phacoemulsification were used in all cases. Alternate IOL styles were selected for use from July 1999 to April 2000. RESULTS: Fourteen cases (0.2%) were identified. The complaints resolved in 1, were diminished in 1, and were tolerated without change in 7. Five eyes of 4 patients required IOL exchange with capsular bag placement of a poly(methyl methacrylate) (PMMA) or silicone lens for resolution of symptoms. Selecting alternate IOL styles reduced the incidence of dysphotopsia. CONCLUSIONS: Glare and streaks from a point source of light represent positive photic expressions of dysphotopsia, and temporal dark shadows represent similar negative photic expressions. Both appear to be associated with shiny square-edge optics made of high-refractive-index acrylic polymer. Intraocular lenses of PMMA and silicone with rounded edges, along with square-edge acrylic IOLs with nonreflective edges, appear less likely to cause clinically significant pseudophakic dysphotopsia.

Acrylates↗

PubMed2003

Fibre optic coupler as a detector for microfluidic applications.

A new construction of a fibre optic coupler is presented in the paper. Two polymer optical fibres were used to build a coupler in which coupling efficiency of optical power depends on the refractive index of liquid delivered to a microchannel formed by the fibres. The coupler was tested as a detector in saccharose concentration measurements, and was used in absorbance measurements. A red light emitting diode and a spectrometer were used as a light source and a photodetector, respectively. Experiments confirmed that the coupler can be used for the real time monitoring of the changes in the refractive index of a saccharose solution exhibiting repeatable changes in the signal, with no hysteresis. Absorbance tests were performed with a solution of bromothymol blue at different pH.

Journal Article↗

PubMed2003

Computerized calculation scheme for bitoric eikonic intraocular lenses.

Despite full correction of the corneal astigmatism with toric intraocular lenses, the retinal image is distorted and the lateral image-object magnification is different in different meridians. The purpose of this study is to describe an iteration strategy for tracing an axial pencil of rays through the 'optical system eye' containing astigmatic refractive surfaces with their axes at random to calculate a thick bitoric lens implant which eliminates image distortion. The capabilities of this computing scheme are demonstrated with two clinical examples. We present a mathematically straightforward computer-based strategy for the calculation of thick bitoric eikonic lens implants. The iteration algorithm is initialized with a spherical front and a toric back surface and stepwise decreases the image distortion by adding cylinder lenses to the front lens surface corrected by the toric lens back surface. Total magnification can be modulated by varying the front-to-back surface power of the thick lens.

Algorithms↗

PubMed1993

[Properties of injectable intraocular lenses].

An aphakic eye can be corrected by injecting a liquid into the lens capsule following phacoemulsification and hardening the lens by UV irradiation. Another technique is to implant a thin casing of silicone rubber, that is then filled with liquid. The eye's resulting refraction depends strongly on the refractive index of the lens material. In either case, continuous control of the index of refraction is necessary while injecting the artificial lens material.

Humans↗

PubMed1992

[Etiology and occupational rehabilitation of late vision disorders].

Advising patients about means of rehabilitation is an important task for the ophthalmologist. There is a lack of up-to-date studies on the outcome of job measures for various ophthalmic disorders. In a retrospective study the charts of 334 patients (October 86-November 89) at the rehabilitation centre for adults with late onset visual impairment (Veitshöchheim) were analyzed. Retinitis pigmentosa, optic atrophy, diabetic retinopathy and refractive anomalies were the most frequent diseases (13-19%). In comparison to the other disorders the incidence of diabetic retinopathy is increasing. Other ophthalmic diseases (mainly traumatic injuries), macular degeneration, retinal detachment and primary and secondary cataract made up 6-9% of all cases. About half of the patients were legally blind (visual acuity 1/50 or worse), 20% severely visually handicapped with a visual acuity of 0.02-0.05, 24% had a visual acuity of 0.05-0.3. Regarding the age distribution the group of patients between 30 and 39 years of age was the largest followed by the group of the 25-29-year-old and, last, the group of the 20-24-year-old patients. Due to the high proportion of blind and severely visually disabled a basic rehabilitation (including mobility training, learning the Braille letters) was necessary in 62% of cases. The most popular job measure was the field of massage.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

[The parapapillary region of normal and glaucoma eyes. I. Planimetric values of 312 glaucoma and 125 normal eyes].

Magnification-corrected planimetry of the parapapillary region was performed according to Littmann's method in 312 unselected eyes with chronic primary open-angle glaucoma and in 125 normal eyes of an age- and refraction-matched control group using optic disk photographs. The glaucoma group was divided into five pathomorphologic subgroups. High myopics (less than -8.00 D) and "ocular hypertensives" had been excluded. The coefficient of variation ranged intraindividually from 0.0 to 0.17 and interindividually from 0.0 to 0.16. Two different morphologic variants were defined and examined: 1) Zone "Alpha" with incipient to advanced parapapillary chorio-pigmentepithelio-retinal atrophy - characterized by irregular hypo- and hyperpigmentation - was statistically proven in the control group (0.60 +/- 0.44 mm2; p less than 0.05; Wilcoxon-Mann-Whitney test) to be smaller than in the glaucoma group (0.81 +/- 0.70 mm2). It increased significantly (p = 0.0000) with advancing glaucoma stage. In the glaucoma and normal group it was broadest in the temporal horizontal sector (p less than 0.001; Wilcoxon test), followed by the temporal lower (p less than 0.001), temporal upper (p less than 0.001) and nasal sectors (p less than 0.001). There was no significant difference in prevalence between the two groups. 2) Zone "Beta" with subtotal to total parapapillary chorio-pigment-epithelio-retinal atrophy was also smaller in the normal eyes (0.18 +/- 0.52 mm2, prevalence: 20.0%; p = 0.0000) than in the glaucomatous ones (0.85 +/- 1.42 mm2, prevalence 66.7%) and was also, in both groups, broadest in the temporal horizontal sector, followed by the temporal lower, temporal upper and nasal sectors. In the control group it was smaller than zone "Alpha" (p less than 0.00001), while in the glaucoma group there was no difference. 3) The difference between normal eyes and earliest glaucoma stage I was for zone "Beta" (p = 0.0000); the difference between the normal eyes and those of glaucoma stage II was significant for both zones (p = 0.0000 and p less than 0.05, respectively). In both groups and in all glaucoma stages both zones were larger in the lower half of the optic disk than in the upper half. 4) "Conus pigmentosus" and the peripapillary scleral rim in normal and glaucomatous eyes showed no significant difference as regards their area and frequency. The parapapillary chorio-pigmentepithelio-retinal alterations are precursors of, or are equivalent to the so-called "halo glaucomatosus".(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗