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At least 325 records · Page 18Linked to original sources
PubMed1994

Topographic evaluation of toric soft contact lens correction.

The anterior surface of the eye provides the greatest refracting surface to the optical system of the eye because of the large difference in refractive index between air and tissue. When a contact lens is placed on the eye, its anterior surface becomes the greatest refracting surface. Toric soft contact lenses have been designed to neutralize ocular astigmatism. We observed that topographic analysis of toric soft contact lenses on an astigmatic eye demonstrated residual astigmatism on the anterior surface of soft toric contact lenses. In this paper we show toric soft contact lens surface astigmatism by videokeratoscopy and interpret the origins of the astigmatism.

Astigmatism↗
PubMed2006

Optical properties of fluids for 248 and 193 nm immersion photolithography.

We present measured values of the refractive index, thermo-optic coefficient, and absorption coefficient of a number of common organic solvents and aqueous inorganic solutions that may have application in immersion photolithography at 248 or 193 nm wavelengths. The measurements were performed with a laser-based Hilger-Chance refractometer system whose design and operation are described. The optical properties of the sample fluids are compared with those of water, the currently favored immersion medium, and we discuss the potential for finding higher-index fluids that will be suitable for this application.

Journal Article↗
PubMed1982

High resolution DNA content measurements of mammalian sperm.

The high condensation and flat shape of the mammalian sperm nucleus present unique difficulties to flow cytometric measurement of DNA content. Chromatin compactness makes quantitative fluorescent staining for DNA difficult and causes a high index of refraction. The refractive index makes optical measurements sensitive to sperm head orientation. We demonstrate that the optical problems can be overcome using the commercial ICP22 epiillumination flow cytometer (Ortho Instruments, Westwood, MA) or a specially built cell orientating flow cytometer (OFCM). The design and operation of the OFCM are described. Measurements of the angular dependence of fluorescence from acriflavine stained rabbit sperm show that it is capable of orienting flat sperm with a tolerance of +/- 7 degrees. Differences in the angular dependence for the similarly shaped bull and rabbit sperm allow discrimination of these cells. We show that DNA staining with 4-6 diamidino-2-phenylindole (DAPI) or an ethidium bromide mithramycin combination allows resolution of the X and Y populations in mouse sperm. They have also been successful with sperm from the bull, ram, rabbit, and boar. Reliable results with human sperm are not obtained. The accuracy of the staining and measurement techniques are verified by the correct determination of the relative DNA content of these two populations in sperm from normal mice and those with the Cattanach [7 to X] translocation. Among the potential uses of these techniques are measurement of DNA content errors induced in sperm due to mutagen exposure, and assessment of the fractions of X and Y sperm in semen that may have one population artifically enriched.

Acriflavine↗
PubMed1994

Assembly and molecular organization of self-assembled lipid bilayers on solid substrates monitored by surface plasmon resonance spectroscopy.

The structural properties of lipid films, made from a squalene/butanol solution containing varying amounts (0-15 mg/ml) of egg phosphatidylcholine and deposited on a thin metallic silver layer, were investigated using surface plasmon resonance (SPR) spectroscopy. Optical parameters (thickness, refractive index and extinction coefficient) of such supported self-assembled lipid membranes were obtained from a theoretical analysis of the experimental SPR curves. The mass of the lipid membrane and the area and volume occupied by one lipid molecule were also calculated. The results were consistent with the formation of durable and homogeneous lipid bilayers on the solid substrate, and indicated similarities in structural properties between the present lipid bilayers and freely suspended and Langmuir-Blodgett bilayer membranes. Such bilayers represent a simple model for biological membranes, as well as providing a means of immobilizing proteins for various practical applications, including receptor-based sensors and molecular devices. The results confirm the value of the SPR technique for investigating the properties of thin biomolecular dielectric films deposited on a metal surface.

Lipid Bilayers↗
PubMed1991

Electroretinographic changes in aged pigeons.

Photopic electroretinograms, either to full-field light flashes (FERGs) or to contrast-reversal of square-wave gratings (PERGs) have been recorded in pigeons aged 2 years old (n = 5) and 10 years old (n = 5). Mydriatic pupil diameter, ophthalmoscopic appearance of the retinal fundus and optic media, and refractive state were comparable in the two groups. V/log I functions of individual FERG components (a-wave, b-wave and oscillatory potentials) displayed significantly lower slopes in the old birds than in the young, which suggests a reduction in retinal gain. PERG amplitude also was significantly lower in the older birds over a wide range of spatial frequencies (0.2-8.8 c/deg). Estimated visual acuity based on the extrapolated high-frequency cut off was 18 c/deg in the younger birds and 7.8 c/deg in the older birds. These results are in agreement with psychophysical data and retinal age-related losses in visual acuity, photoreceptors and retinal ganglion cells. Since these findings are comparable to those reported for humans, the results suggest that pigeons may serve as a useful model for human visual aging.

Aging↗
PubMed1990

Laser-based detectors in chromatographic analysis.

Advances in detection technology have been a vital part of the development of microscale chromatographic techniques. Separation techniques such as microbore liquid chromatography impose severe constraints on the permissible volume of detector cells. The use of lasers to construct a new generation of chromatographic detectors has satisfied the need for low volume detection and high sensitivity. The unique properties of laser radiation have been used to advantage in designing new approaches to the detection of optical absorbance through fluorescence emission and thermal effects. New approaches to monitoring refractive index changes and optical rotation have also been developed. Together, the combination of microscale-separation techniques and highly sensitive detection provide a powerful tool for analysing small quantities of samples. Yet, there are practical limitations arising from the cost and complexity of much of the instrumentation reported to date, as well as the difficulties of preparing small samples for analysis which have limited the wide-scale application of these methods to solve practical problems. Recent advances in laser technology such as the advent of diode lasers may be useful in overcoming some of these limitations.

Chromatography↗
PubMed2005

Approaches to improving the biocompatibility of porous perfluoropolyethers for ophthalmic applications.

Porous perfluoropolyether (PFPE) membranes for ophthalmic applications were prepared with a zwitterion monomer, 3-[[2-(methacryloxy) ethyl](N,N-dimethyl)ammonio]-propane-1-sulphonate, copolymerized in weight ratios of 0-10%. The polymer samples were assessed for a range of physical properties, including equilibrium water content, bovine serum albumin permeability, transparency, refractive index and the ability to support corneal epithelial cell and tissue attachment, growth and migration. In vitro assessment of the polymers using bovine corneal epithelial cells and tissue showed that a zwitterion incorporation level of between 0% and 6% in the PFPE membranes supported the migration of an intact sheet of epithelial tissue without compromising epithelial cell attachment and growth, with 4-6% being the optimal level for these properties. Binding patterns of the cell adhesion glycoprotein fibronectin were also found to reflect the cell and tissue response. Effective nutrient permeability, refractive index and optical transparency were also maintained by the porous PFPE polymers containing this concentration of zwitterionic monomer. The presence of amounts of zwitterion greater than 6% was inhibitory to both tissue migration and cell growth and was associated with increased optical haze. These results demonstrated that it is possible to achieve the potential for increased biocompatibility in zwitterion-containing PFPE polymers without compromising existing beneficial characteristics.

Animals↗
PubMed2005

Functional and structural outcomes following lensectomy for ectopia lentis.

PURPOSE: High refractive errors and optical aberrations reduce vision when the lens edge bisects the pupil. We studied outcomes of eyes with ectopia lentis following lensectomy. METHODS: Charts of 11 consecutive patients with bilateral ectopia lentis who underwent lensectomy-anterior vitrectomy in at least one eye from 1985 to 2004 were reviewed. Eighteen eyes were operated. One eye was excluded due to short-term follow-up (<2 years). RESULTS: Mean age at surgery was 7.7 years (2 to 17 years). Median follow-up after lensectomy was 10 years (range 2 to 16 years). Six eyes were followed for 6 to 10 years, and another six eyes were followed for 11 to 16 years. Patient diagnoses included Marfan syndrome (nine eyes), ectopia lentis et pupillae (three eyes), simple ectopia lentis (two eyes), homocystinuria (two eyes), and sporadic spherophakia (one eye). Preoperative best-corrected visual acuity (BCVA) ranged from 20/60 to light perception, and postoperative BCVA ranged from 20/20 to 20/100 (14 eyes were at least 20/30). Complications included posterior vitreous detachment (two eyes, 12%), glaucoma (one eye, 6%), transient ocular hypertension (one eye, 6%), wound dehiscence with iris incarceration (one eye, 6%), transient vitreous hemorrhage (one eye, 6%), and peripheral anterior synechiae (one eye, 6%). No retina detached. CONCLUSIONS: Our cohort of patients with long-term follow-up shows that pars plana lensectomy can be successful in restoring vision when conservative measures fail.

Adolescent↗
PubMed1997

Coupled plasmon-waveguide resonators: a new spectroscopic tool for probing proteolipid film structure and properties.

A variant of surface plasmon resonance (SPR) spectroscopy has been developed that involves a coupling of plasmon resonances in a thin metal film and waveguide modes in a dielectric overcoating. This new technique is referred to as coupled plasmon-waveguide resonance (CPWR) spectroscopy. It combines a greatly enhanced sensitivity (due to increased electromagnetic field intensities at the dielectric surface) and spectral resolution (due to decreased resonance linewidths), with the ability to directly measure anisotropies in refractive index and optical absorption coefficient in a dielectric film adsorbed onto the surface of the overcoating. Experimental data obtained with an egg phosphatidylcholine bilayer are presented to document these properties.

Anisotropy↗
PubMed2002

Comparison of the pupil card and pupillometer in measuring pupil size.

PURPOSE: To determine the difference in pupil size measured with the Colvard pupillometer in mesopic and scotopic luminance and with the Rosenbaum pupil card in mesopic luminance between 2 examiners. SETTING: Michel Pop Clinics, Montreal, Quebec, Canada. METHODS: Two examiners used the Colvard pupillometer and the Rosenbaum card to measure pupil size in 58 eyes. The Colvard pupillometer was used in mesopic and scotopic light conditions. The Rosenbaum card was used in mesopic luminance only. Pupil size was evaluated with a 1.0 mm interval scale at the nearest half millimeter. RESULTS: For the 3 sets of data, the limits of agreement and coefficient of interrater repeatability were calculated and a 2 x 2 factorial analysis of variance was performed. Because of interexaminer bias, measurements done in mesopic luminance with the Rosenbaum card were not statistically different from those with the Colvard pupillometer in scotopic luminance, although interrater repeatability of the Colvard pupillometer (0.8 mm) was superior to that of the Rosenbaum card (1.3 mm). CONCLUSIONS: Examiner bias was the greatest statistical bias in all sets of measures. Surgeons may want to opt for a "safe" limit of pupil size (ie, 0.5 to 0.8 mm greater than the measured size) when calculating optical zones in refractive surgery. Future devices for pupil measurement should be based on automatic adjustment sizing.

Diagnostic Techniques, Ophthalmological↗
PubMed2002

Reactive transport in porous media: a comparison of model prediction with laboratory visualization.

Groundwater transport models that accurately describe spreading of nonreactive solutes in an aquifer can poorly predict concentrations of reactive solutes. The dispersive term in the advection-dispersion equation can overpredict pore-scale mixing, and thereby overpredict homogeneous chemical reaction. We quantified this experimentally by imaging instantaneous colorimetric reactions between solutions of aqueous CuSO4 and EDTA4- within a 30-cm long translucent chamber packed with cryolite sand that closely matched the optical index of refraction of water. A charge-coupled device camera was used to quantify concentrations of blue CuEDTA2- within the chamber as it was produced by mixing of the two reactants at different flow rates. We compared these experimental results with a new analytic solution for instantaneous bimolecular reaction coupled with advection and dispersion of the product and reactants. For all flow rates, the concentrations of CuEDTA2- recorded in the experiments were about 20% less than predicted by the analytic solution, thereby demonstrating that models assuming complete mixing at the pore scale can overpredict reaction during transport.

Chelating Agents↗
PubMed2006

Electrochemical, spectroelectrochemical, and molecular quadratic and cubic nonlinear optical properties of alkynylruthenium dendrimers.

A combination of cyclic voltammetry (CV), UV-vis-NIR spectroscopy and spectroelectrochemistry, hyper-Rayleigh scattering (HRS) [including depolarization studies], Z-scan and degenerate four-wave mixing (DFWM) [including studies employing an optically transparent thin-layer electrochemical (OTTLE) cell to effect electrochemical switching of nonlinearity], pump-probe, and electroabsorption (EA) measurements have been used to comprehensively investigate the electronic, linear optical, and nonlinear optical (NLO) properties of nanoscopic pi-delocalizable electron-rich alkynylruthenium dendrimers, their precursor dendrons, and their linear analogues. CV, UV-vis-NIR spectroscopy, and UV-vis-NIR spectroelectrochemistry reveal that the reversible metal-centered oxidation processes in these complexes are accompanied by strong linear optical changes, "switching on" low-energy absorption bands, the frequency of which is tunable by ligand replacement. HRS studies at 1064 nm employing nanosecond pulses reveal large nonlinearities for these formally octupolar dendrimers; depolarization measurements are consistent with lack of coplanarity upon pi-framework extension through the metal. EA studies at 350-800 nm in a poly(methyl methacrylate) matrix are consistent with the important transitions having a charge-transfer exciton character that increases markedly on introduction of peripheral polarizing substituent. Time-resolved pump-probe studies employing 55 ps, 527 nm pulses reveal absorption saturation, the longest excited-state lifetime being observed for the dendrimer. Z-scan studies at 800 nm employing femtosecond pulses reveal strong two-photon absorption that increases significantly on progression from linear complex to zero- and then first-generation dendrimer with no loss of optical transparency. Both refractive and absorptive nonlinearity for selected alkynylruthenium dendrimers have been reversibly "switched" by employing the Z-scan technique at 800 and 1180 nm and 100-150 fs pulses, together with a specially modified OTTLE cell, complementary femtosecond time-resolved DFWM and transient absorption studies at 800 nm suggesting that the NLO effects originate in picosecond time scale processes.

Journal Article↗
PubMed2002

Red and/or blonde hair association with pigmentary glaucoma in Israel.

PURPOSE: To assess the prevalence of red and/or blonde hair in a defined pigmentary glaucoma (PG) population and to compare their clinical findings with those of PG patients with black or brown hair. METHODS: Hair color was studied in 35 consecutive PG patients and 35 consecutive primary open angle glaucoma (POAG) patients who served as controls. Patients were classified into red and/or blonde hair group or into black or brown hair group. Clinical characteristics were contrasted between PG patients of red and/or blonde hair with PG patients of black or brown hair. RESULTS: Of the 35 PG patients, 19 (54.3%) had red and/or blonde hair and 16 (45.7%) had black or brown hair. Of the 35 POAG patients, two (5.8%) had red and/or blonde hair and 33 (94.2%) had black or brown hair. This difference in prevalence of hair color is highly significant (P < 0.001; chi2). Clinical characteristics of the PG patients (age at initial diagnosis, gender, positive family history for glaucoma, initial IOP, refraction, severity of optic nerve damage and prevalence of retinal detachment) were similar in the red and/or blonde hair and the black or brown hair groups. CONCLUSIONS: A very high prevalence of red and/or blonde hair was found among PG patients in Israel. Should supportive evidence for this association accumulate subsequent to this report, screening of people with these hair colors for PG may be justified.

Adolescent↗
PubMed2003

Ophthalmic issues in hemangiomas of infancy.

Hemangiomas are the most common benign tumor of infancy. Although most hemangiomas remain asymptomatic, certain hemangiomas can cause significant morbidity and require treatment. Periocular hemangiomas require close observation and early therapy for those lesions with potential for visual impairment. Hemangiomas typically cause visual morbidity by induction of amblyopia, strabismus, significant refractive error or optic nerve compromise. Diagnosis is typically straightforward but occasionally other entities may cause diagnostic confusion and radiologic evaluation can be helpful. This is particularly important if the hemangioma is one component of the PHACES syndrome. Therapeutic options which may be useful include steroids (oral, intralesional or topical), interferon alpha (usually reserved for life- or sight-threatening lesions due to serious potential side effects), laser, embolization and surgery. Ophthalmic treatment using patching, atropine, glasses and stabismus surgery may be necessary.

Amblyopia↗
PubMed1996

A histochemical and x-ray diffraction study of keratoconus epikeratoplasty. Report of two cases.

Two epikeratoplasty lenticules (Epi-L) with keratoconus host corneas (Epi-H) were removed by penetrating keratoplasty because of poor visual acuity although they were clinically clear. Light microscopy showed that the keratocytes were underpopulated and unevenly distributed in Epi-L. Transmission electron microscopy showed that abnormal sized proteoglycans (PGs) were unevenly accumulated in the stromas of both Epi-L and Epi-H. The low-angle x-ray diffraction results from case 1 showed lower collagen interfibrillar spacings, compared with those from one keratoconus cornea, seven cryolenticules, and four normal human corneas. The fibril diameters and the collagen axial periodicity D were similar in all tissues. Allowing selected samples to swell, the interfibrillar spacing increased by 30.6-45.5% in Epi-H and by 29.8% in the keratoconus control. However, it increased by only 7.6-9.7% in Epi-L and by 11.4% in a cryolenticule. The uneven distribution of PGs and the lower interfibrillar spacings in the swollen lenticules suggest that there is an uneven distribution of water in different parts of the Epi-L and Epi-H stromas. This may lead to a variation of the refractive index or optical properties in the stroma and the deterioration of the visual image, which may explain the poor visual results.

Adult↗
PubMed2002

Refractive index measurements in a reentrant isotropic-calamitic nematic phase transition.

In this work the temperature dependence of the extraordinary/ordinary refractive indices and optical birefringence are determined near the reentrant isotropic (I(RE))-calamitic nematic (N(C)) and N(C)-isotropic (I) phase transitions in a lyotropic mixture of potassium laurate, decanol, and water. This reentrant isotropic phase is verified by our experimental data and discussed in terms of thermal variation of the micellar shape anisotropy. The results showed also, with basis in the Vuks's equation, that near the maximum optical birefringence in the range of N(C) phase the extraordinary coefficient of electronic polarizability (phi(parallel)) is equal to the ordinary coefficient (phi( perpendicular)).

Journal Article↗