SEARCH · PubMed Health

Results for “Optics and Refraction”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 181 records · Page 10Linked to original sources

PubMed1997

The refractive group.

Spherocylindrical optical elements can be decomposed into a sphere-equivalent component and two cross-cylinder components, oriented at 45 degrees to one another. These components in turn can be represented with a simple matrix formalism. This matrix formalism allows it to be seen that the components also form members of an eight element group, designated the refractive group. The structure of this group is developed including its algebra and its representation with Cayley diagrams. The group is identified as the eight element dihedral group, D4, and is compared to another well-known eight element group, the quaternion group. An example is given using the group formal algebra to develop the transfer equations for spherocylindrical wavefronts. Certain properties of propagating spherocylindrical wavefronts, such as nonrotation of cylinder axes, are seen to come directly as consequences of the group properties.

Eyeglasses↗

PubMed1993

Optical crystallographic characteristics of some USP drugs.

Optical crystallographic data were determined on a variety of newer USP drugs for which data had not been previously obtained. The ingredients in an unknown sample can be identified by polarized light microscopy by mounting small amounts of the material in successive specific refractive index liquids and determining refractive indices, optic sign, type of extinction, estimated 2V angle, and other optical characteristics for each ingredient present. This information can then be compared with the data listed on known drugs and excipients and all of the ingredients can be identified. To aid in the identification of unknown drugs, optical crystallographic data obtained on 52 of the newer USP drugs are presented.

Crystallography↗

PubMed2006

Dielectric and optical properties of nanometric nickel silicides from valence electrons energy-loss spectroscopy experiments.

Valence and Core Electron Energy Loss Spectroscopy (VEELS and CEELS) experiments are performed from nanocrystallized nickel silicide thin films. Three different silicide compounds are identified in the films. Their chemical compositions are determined from Ni-L(2,3) to Si-K core edges quantification. The results obtained are coherent within less than 2% error with the pure Ni2Si, NiSi and NiSi2 phases. The analysis of the shape and energy position of Ni-L(2,3) near edge structures and volume plasmon peaks indicates that both are reliable signatures to identify unambiguously each compound. Nickel silicides low-loss spectra have been submitted as references to the EELS database (www.cemes.fr~eelsdb). Low-loss spectra are processed to extract single scattering spectra and determine the dielectric function. The results show that nickel silicides dielectric functions deduced from VEELS are in quite good agreement with epsilon1 and epsilon2 deduced from ellipsometry experiments. The optical properties (refractive index (n), absorption coefficient (k), reflectivity (R%) and resistivity (rho(opt))), calculated from VEELS dielectric function are then compared in details with the data resulting from others techniques available in the literature. We show that, except some minor divergences, the nickel silicides optical properties are generally well reproduced. This indicates that VEELS is a relevant technique for accessing reliably to physical properties and can be a successful alternative to conventional techniques when high spatial resolution is needed.

Journal Article↗

PubMed2003

Catheter for diagnosis and therapy with infrared evanescent waves.

We have developed an optical delivery device (catheter) capable of transmitting broadband infrared light (IR wavelengths from 2 to 10 microm) for both diagnostic and therapeutic applications. The catheter is 1.68 mm in outer diameter and 1 m in length. It consists of two hollow glass waveguides coupled to a high-refractive-index optic tip. The IR light interacts with the tissue at the optic-tissue interface to measure the spectral signatures and perform therapy on the tissue at this interface. Fourier-transform IR spectrophotometer light is used to obtain the spectral signatures, and an IR free-electron laser (FEL) is used to study the therapeutic interaction of evanescent waves with the tissue. We present our catheter design; preliminary IR spectroscopy of aorta, blood, fatty tissue, and muscle; and IR FEL therapy on atheroslerotic aorta.

Absorption↗

PubMed2003

[Stability of corneal optic power after photorefractive keratectomy].

Changes in the values of optical power of cornea in patients after photorefractive keratectomy (PRK) obtained by Fourier analysis of videotopographic picture of cornea were investigated. The authors compared changes of cornea surface (optical power) in patients with preoperation myopia up to 6 and more than 6 diopters. Moreover, the changes of absolute values of corneal optical power were compared with the development of refraction of the optical system as a whole. In patients with a lower degree of myopia the cornea optical power became stable up to 6 months after the operation. The cornea surface in patients with higher myopia was still changing one year after the operation. The changes of optical power of cornea in patients with a higher myopia were more marked, but the differences were not statistically significant (except for the period after cornea ablation). There was not any significant difference between the changes of objective refraction and the changes of cornea optical power. The main cause of fluctuating postoperative refraction is apparently the change of cornea surface associated with healing of cornea.

Adult↗

PubMed2006

Hybrid optics for focusing ultrashort laser pulses.

We present a specially designed hybrid optics comprising refraction and diffraction effects for tight spatial and temporal focusing of ultrashort laser pulses. Both aims can be put into practice by having a high numerical aperture (NA=0.45) and low internal dispersion at the same time. We are presenting what we believe is the first experimental realization of such a hybrid short plus focusing optics. The focusing properties are compared with a commonly used microscope objective (20 X, NA = 0.45) in theory and experimentally.

Journal Article↗

PubMed2003

Direct measurement of refractive-index dispersion of transparent media by white-light interferometry.

We report on a technique for measuring the refractive indices of nonabsorbing media over a broad spectral range from 0.5 to 5 microm. White-light interferometry based on a double-interferometer system consisting of a fixed Mach-Zehnder interferometer and a Fourier-transform spectrometer is used for direct measurement of the absolute rotation-dependent phase shift induced by an optical element. Refractive index n(lambda) over the whole investigated spectral range is thus obtained directly to an accuracy of 10(-4) without the need for any specific assumption about dispersion. Results for synthetic fused silica are presented and discussed.

Journal Article↗

PubMed1998

Effect of decreasing surface and interface irregularities after photorefractive keratectomy and laser in situ keratomileusis on optical and functional outcomes.

PURPOSE: To assess a new method for decreasing corneal ablated surface irregularities after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) by performing a final smoothing immediately after the treatment. METHODS: One hundred forty-seven eyes with ablation irregularities after PRK or LASIK using the Nidek ED-5000 excimer laser and examined with the Nidek EAS 1000, were randomized into two groups: 74 eyes had final smoothing and 73 eyes were patched immediately. Preoperative mean refraction for the smoothing group was -7.55 +/- 2.50 D and for the patched group, it was -7.30 +/- 1.90 D, (p = 0.04). RESULTS: AT 12 months after treatment, mean haze was 0.5 +/- 0.3 in the smoothing group and 1.2 +/- 0.4 in the patched group (p = 0.006); mean spectacle-corrected visual acuity was 1.1 +/- 0.25 in the smoothing group and 0.95 +/- 0.18 in the patched group (p = 0.02); the percentages of eyes within 1.00 D of the planned correction was 68% in the smoothing group and 33% in the patched group. CONCLUSION: Performing a final smoothing immediately after PRK or LASIK improves refractive and optical outcomes.

Adult↗

PubMed2002

Blindness, visual impairment and the problem of uncorrected refractive error in a Mexican-American population: Proyecto VER.

PURPOSE: To report the prevalence of blindness and visual impairment and the contribution of uncorrected refractive error to visual loss, in a population-based sample of Mexican Americans aged 40 and older. METHODS: Proyecto VER is a population-based study of blindness and visual impairment in Mexican Americans in Arizona. Block groups in Tucson and Nogales were randomly selected with probability proportional to the size of the Mexican-American population aged 40 and older. Participants had a complete ophthalmic evaluation, including assessment of presenting and best corrected visual acuity using standardized procedures. Those with presenting visual acuity worse than 20/30 had refraction to determine best corrected vision. A home questionnaire and a clinic examination provided data on education, perception of visual impairment, income, and acculturation. RESULTS: The prevalence of presenting visual acuity worse than 20/40 was 8.2%, with uncorrected refractive error accounting for 73% of the impaired acuity. In multivariate models comparing those who improved two or more lines on the acuity chart with proper refraction with those who had adequate optical correction, uncorrected refractive error showed a strong association with age, less than 13 years of education (odds ratio [OR] 1.6, 95% confidence interval [CI] 1.5-2.0), low acculturation index (OR 1.3, CI 1.1-1.3), lack of insurance coverage (OR 1.4, CI 1.1-1.7), and not having seen an eye-care provider in the past 2 years (OR 2.5, CI 2.1-3.0). Prevalence of best corrected acuity worse than 20/40 increased from 0.3% in those aged 40 to 49 years to 18% in those aged 80 years or more. CONCLUSIONS: Visual loss in this Mexican-American population is higher than has been reported in whites and is comparable to that in African Americans. Almost three quarters of those with visual acuity impairment would improve with optical correction. Socioeconomic factors that are probable markers of limited access to health care services were associated with uncorrected refractive error. These data suggest that education programs and interventions to improve access to eye care could significantly decrease the burden of visual loss among Mexican Americans.

Adult↗

PubMed2006

Double optical monitoring of dip coating with a time-varying refractive index.

A brief overview of optical monitoring for vacuum and wet-bench film-deposition processes is presented. Interferometric and polarimetric measurements are combined with regard to simultaneous monitoring of refractive index and physical thickness in real time. Monitoring stability and accuracy are verified during dip coating with a transparent oil standard. This double optical technique is applied to dip coating with a multicomponent zirconyl chloride aqueous solution, whose resulting temporal refractive-index and physical-thickness curves indicate good reproducibility as well as significant sensitivity to changes of film-flow properties during the dip-coating process.

Journal Article↗

PubMed1989

Effects of chronic optical defocus on the kitten's refractive status.

Lid closure initiated early in life produces axial myopia in a variety of species. However, it is currently not known what aspects of the anomalous visual experience associated with lid closure disrupt the emmetropization process and cause abnormal ocular axial elongation. This study was designed to determine if a degradation in the quality of the spatial characteristics of the retinal image was sufficient to produce an experimental myopia. Optical rearing procedures were employed to defocus one eye of developing kittens, and retinoscopic and ultrasonic procedures were used to evaluate the effects of chronic optical defocus on the kitten's refractive status. Different defocusing lens designs and rearing protocols were included to evaluate variables that may have confounded previous investigations. The major finding is that early chronic optical defocus results in axial myopia. The prevalence and magnitude of the induced refractive errors were dependent on the magnitude of optical defocus, but they were not affected by the sign or form of the defocusing lens. The results demonstrated that the potential for a clear retinal image is important for regulating normal ocular growth and maintaining a near emmetropic refractive status.

Animals↗

PubMed2006

Single-shot measurement of nonlinear absorption and nonlinear refraction.

A single-shot method for measurement of nonlinear optical absorption and refraction is described and analyzed. A spatial intensity variation of an elliptical Gaussian beam in conjugation with an array detector is the key element of this method. The advantages of this single-shot technique were demonstrated by measuring the two-photon absorption and free-carrier absorption in GaAs as well as the nonlinear refractive index of CS2 using a modified optical Kerr setup.

Journal Article↗

PubMed2006

Properties of porcine and recombinant human collagen matrices for optically clear tissue engineering applications.

Porcine and recombinant human atelocollagen I solutions were cross-linked with a water soluble carbodiimide at various stoichiometries and collagen concentrations (5-20 w/w %). The resulting hydrogels were clear and, when used as cell growth matrices, allowed cell and nerve visualization in vitro and in vivo. We have previously reported that, after six months of implantation in pigs' and rabbits' corneas, these robust hydrogels allowed regeneration of host cells and nerves to give optically clear corneas with no detected loss in thickness, indicating stable engraftment. Here, the biocompatible hydrogel formulations leading to this novel in vivo performance were characterized for amine consumption, gel hydration, thermal properties, optical clarity, refractive index, nutrient diffusion, biodegradation, tensile measurements, and average pore diameters. Gels with excellent in vitro (epithelial overgrowth, neurite penetration) and in vivo performance (clarity, touch sensitivity regeneration) had 4-11 nm pores, yet had glucose and albumin diffusive coefficients similar to mammalian corneas and allowed neurite extension through the gels.

Amines↗

PubMed2005

Visible and near-infrared characterization and modeling of nanosized holographic-polymer-dispersed liquid crystal gratings.

We have studied the electro-optical and angular behavior of holographic-polymer-dispersed liquid crystal gratings at different wavelengths, in the visible and in the near-infrared range. As usual in these kinds of materials, a strong polarization dependent behavior was observed. Our samples showed very high diffraction efficiency for p-polarized radiation at 1.55 microm, which is very interesting for many possible applications in the telecom field. However, we also observed a very unusual behavior for visible p-polarized light and we try to suggest some explanation for that. By analyzing the angular dependence of the diffraction efficiency, we could measure the components of the permittivity modulation tensor and infer important information about the main parameters involved in the grating structure: the degree of phase separation and the anisotropy in the liquid crystal droplet distribution. In our opinion, this simple and nondestructive methodology can be very useful for studying these kinds of materials and getting information on their morphology, in view of optimizing their properties. Finally, we discuss the role of the refractive index optical dispersion in order to describe the behavior of these materials at different wavelengths. These remarks are especially important when properties in the infrared range are extrapolated from measurements in the visible.

Journal Article↗

PubMed2005

Outcome of penetrating keratoplasty in patients with bilateral corneal blindness.

PURPOSE: To evaluate the outcome of penetrating keratoplasty in patients with bilateral corneal blindness. METHODS: Bilaterally blind patients who had undergone optical penetrating keratoplasty (PK) were evaluated on optical and refractive parameters and presence of complications if any. The results at 3 months, 6 months, and 1 year were compared with age-matched and indication-matched unilaterally blind controls. RESULTS: The most common indication for surgery in both the groups was the presence of a corneoiridic scar. Best corrected visual acuity of > or =6/18 was seen in five (16.66%) patients in the study group and in 11 (36.66%) patients in the control group (P = 0.14). In all, 15 (50%) grafts in the study group and six (20%) in the control group failed (P = 0.03). The most common cause of failure was graft infection (40%) in the study group and post-PK glaucoma (20%) in the control group. The percentage of graft rejection as a cause of graft failure was the same in both the groups. A composite socioeconomic status scale based on family literacy and income suggested that 70% of the cases in the study group and 30% in the control group belonged to the low socioeconomic group (P = 0.004). CONCLUSION: The outcome of optical penetrating keratoplasty in patients with bilaterally blinding corneal disease is poorer than those who are unilaterally blind. Low socioeconomic status may be a contributing factor for the poor outcome.

Adult↗

PubMedDate not supplied

Management of the ocular surface and tear film before, during, and after laser in situ keratomileusis.

PURPOSE: To identify evidence-based, best practice strategies for managing the ocular surface and tear film before, during, and after laser in situ keratomileusis (LASIK). METHODS: After a comprehensive review of relevant published literature, evidence-based recommendations for best practice management strategies are presented. RESULTS: Symptoms of ocular irritation and signs of dysfunction of the integrated lacrimal gland/ocular surface functional gland unit are common before and after LASIK. The status of the ocular surface and tear film before LASIK can impact surgical outcomes in terms of potential complications during and after surgery, refractive outcome, optical quality, patient satisfaction, and the severity and duration of dry eye after LASIK. Before LASIK, the health of the ocular surface should be optimized and patients selected appropriately. Dry eye before surgery and female gender are risk factors for developing chronic dry eye after LASIK. Management of the ocular surface during LASIK can minimize ocular surface damage and the risk of adverse outcomes. Long-term management of the tear film and ocular surface after LASIK can reduce the severity and duration of dry eye symptoms and signs. CONCLUSIONS: Strategies to manage the integrated ocular surface/lacrimal gland functional unit before, during, and after LASIK can optimize outcomes. As problems with the ocular surface and tear film are relatively common, attention should focus on the use and improvement of evidence-based management strategies.

Conjunctival Diseases↗

PubMed2002

Simultaneous refractive index and thickness measurements of bio tissue by optical coherence tomography.

This paper presents two techniques based on optical coherence tomography, the "focus tracking method" and the "optical path shifting method," for determining refractive index and thickness simultaneously, which are especially useful for bio tissues. From comparison of these two methods, it was found that the focus tracking method is suitable for in vivo measurement, but does not have high precision. The optical path shifting method is limited to in vitro measurement, but has high precision. Using the optical path shifting method, the refractive indices of cucumber were measured at the wavelength of 850 and 1300 nm.

Fiber Optic Technology↗

PubMed1998

Recent developments in capillary isoelectric focusing with whole-column imaging detection.

Capillary isoelectric focusing (CIEF) is a high resolution technique for protein separation. The on-column single point detector requires a mobilization step which lengthens the analysis time and causes an uneven resolution along the separation column. The real time and whole column imaging detection has been developed for performing CIEF without mobilization. Three types of imaging detection systems have been developed: optical absorption, refractive index gradient, and laser induced fluorescence. This technique provides a fast analysis speed (about 6 min) and a good resolution of 0.03 pH unit level. Using the absorption imaging detector, ampholyte-free IEF in tapered capillary is being demonstrated, which eliminates the interference of the expensive carrier ampholytes for protein detection in UV region. Recent advancements in this imaged CIEF technique as well as its applications are reviewed.

Electrophoresis, Capillary↗