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At least 973 records · Page 54Linked to original sources
PubMed1986

[Aspherical single-strength eyeglasses with improved wearing comfort].

A new plastic single-vision lens series is presented with an aspherically designed front surface for the weak to medium-strength positive power range. With this lens the asphere is used to improve the non-optical properties and, at the same time, to maintain an image quality comparable to the high standard offered by regular spectacle lenses. The various factors which determine the optimization of so-called comfort in wear are discussed in detail.

Cataract↗
PubMed1976

Did Ptolemy understand the moon illusion?

Ptolemy is often wrongly credited with an explanation of the moon illusion based on the size-distance invariance principle. This paper elucidates the two Ptolemaic accounts: one in the Almagest, based on atmospheric refraction, and the other in the Optics, based on the difficulty of looking upwards. It is the latter passage which has been thought to refer to size-distance invariance, but it is more probable that it refers to the idea that the visual rays are diminished by the force of gravity (i.e. that the retinal image is reduced in size). Alhazen was probably the first author to explain the illusion by the size-distance invariance principle, and Roger Bacon the first to explain the enlarged apparent distance of the horizon by the presence of intervening objects. Della Porta was the first to credit Ptolemy with these explanations, and this mistake was repeated by many subsequent authors.

Astronomy↗
PubMed2005

Light scattered by model phantom bacteria reveals molecular interactions at their surface.

Testing molecular interactions is an ubiquitous need in modern biology and molecular medicine. Here, we present a qualitative and quantitative method rooted in the basic properties of the scattering of light, enabling detailed measurement of ligand-receptor interactions occurring on the surface of colloids. The key factor is the use of receptor-coated nanospheres matched in refractive index with water and therefore optically undetectable ("phantom") when not involved in adhesion processes. At the occurrence of ligand binding at the receptor sites, optically unmatched material adsorbs on the nanoparticle surface, giving rise to an increment in their scattering cross section up to a maximum corresponding to saturated binding sites. The analysis of the scattering growth pattern enables extracting the binding affinity. This label-free method has been assessed through the determination of the binding constant of the antibiotic vancomycin with the tripeptide l-Lys-d-Ala-d-Ala and of the vancomycin dimerization constant. We shed light on the role of chelate effect and molecular hindrance in the activity of this glycopeptide.

Bacteria↗
PubMed2006

Feasibility of cooling the Earth with a cloud of small spacecraft near the inner Lagrange point (L1).

If it were to become apparent that dangerous changes in global climate were inevitable, despite greenhouse gas controls, active methods to cool the Earth on an emergency basis might be desirable. The concept considered here is to block 1.8% of the solar flux with a space sunshade orbited near the inner Lagrange point (L1), in-line between the Earth and sun. Following the work of J. Early [Early, JT (1989) J Br Interplanet Soc 42:567-569], transparent material would be used to deflect the sunlight, rather than to absorb it, to minimize the shift in balance out from L1 caused by radiation pressure. Three advances aimed at practical implementation are presented. First is an optical design for a very thin refractive screen with low reflectivity, leading to a total sunshade mass of approximately 20 million tons. Second is a concept aimed at reducing transportation cost to 50 dollars/kg by using electromagnetic acceleration to escape Earth's gravity, followed by ion propulsion. Third is an implementation of the sunshade as a cloud of many spacecraft, autonomously stabilized by modulating solar radiation pressure. These meter-sized "flyers" would be assembled completely before launch, avoiding any need for construction or unfolding in space. They would weigh a gram each, be launched in stacks of 800,000, and remain for a projected lifetime of 50 years within a 100,000-km-long cloud. The concept builds on existing technologies. It seems feasible that it could be developed and deployed in approximately 25 years at a cost of a few trillion dollars, <0.5% of world gross domestic product (GDP) over that time.

Journal Article↗
PubMed2005

Modelling and validation of spectral reflectance for the colon.

The spectral reflectance of the colon is known to be affected by malignant and pre-malignant changes in the tissue. As part of long-term research on the derivation of diagnostically important parameters characterizing colon histology, we have investigated the effects of the normal histological variability on the remitted spectra. This paper presents a detailed optical model of the normal colon comprising mucosa, submucosa and the smooth muscle layer. Each layer is characterized by five variable histological parameters: the volume fraction of blood, the haemoglobin saturation, the size of the scattering particles, including collagen, the volume fraction of the scattering particles and the layer thickness, and three optical parameters: the anisotropy factor, the refractive index of the medium and the refractive index of the scattering particles. The paper specifies the parameter ranges corresponding to normal colon tissue, including some previously unpublished ones. Diffuse reflectance spectra were modelled using the Monte Carlo method. Validation of the model-generated spectra against measured spectra demonstrated that good correspondence was achieved between the two. The analysis of the effect of the individual histological parameters on the behaviour of the spectra has shown that the spectral variability originates mainly from changes in the mucosa. However, the submucosa and the muscle layer must be included in the model as they have a significant constant effect on the spectral reflectance above 600 nm. The nature of variations in the spectra also suggests that it may be possible to carry out model inversion and to recover parameters characterizing the colon from multi-spectral images. A preliminary study, in which the mucosal blood and collagen parameters were modified to reflect histopathological changes associated with colon cancer, has shown that the spectra predicted by our model resemble measured spectral reflectance of adenocarcinomas. This suggests that an extended model, which incorporates parameters corresponding to an abnormal colon, may be effective for differentiation between normal and cancerous tissues.

Algorithms↗
PubMedDate not supplied

Ophthalmic involvement in the fetal alcohol syndrome: clinical and animal model studies.

The fetal alcohol syndrome (FAS) is caused by maternal alcohol misuse during pregnancy and is characterized by pre- and postnatal growth retardation, central nervous system anomalies and a wide spectrum of malformations, the most typical being the craniofacial features. The eye is a sensitive indicator of the adverse effects of environmental agents, and the ocular abnormalities observed in children with FAS indicate that the developing eye is particularly affected by alcohol. The external signs include short palpebral fissures, telecanthus, epicanthus, blepharoptosis, microphthalmos and strabismus. Within the eyes, the signs and symptoms most commonly detected are optic nerve hypoplasia, increased tortuosity of the retinal vessels and impaired vision. Experimental models of FAS, closely reproducing characteristics of human FAS, have contributed to our understanding of the cellular and molecular basis of the action of alcohol in the developing visual system. As there is such a high frequency of eye signs and symptoms in FAS, an ophthalmological examination is important when making the diagnosis, as well as in the management of the disorder. Current knowledge of ophthalmological involvement in FAS in humans is presented, as well as a review of findings using animal models specially designed for studying ocular developmental changes induced by alcohol.

Animals↗
PubMed1971

Retinoscopy.

Explore the source record for details and available documents.

Humans↗
PubMed1975

Computer-assisted eye examinations IV. "Additive" lens systems in eye refractors.

After a brief introduction to the optical principles and terms, formulas are derived which demonstrate that with conventional methods and designs it is not possible to summate with accuracy the labeled power of three or more ophthalmic lenses in tandem. The effective power of sphero-cylindrical combinations in all currently available eye refractors, when powers of eight to ten diopters are exceeded, may differ from the summated labeled power by a quarter diopter or more, which can be clinically significant. This error can be directly and readily eliminated only in computer-actuated refractors by including a computer program which calculates the effective power and makes the necessary correction.

Diagnosis, Computer-Assisted↗
PubMed1976

A matrix formalism for decentration problems.

A matrix approach to decentration problems is presented which reduces the common decentration problems of ophthalmic optics to simple matrix multiplications. The formalism also leads to an alternative derivation of Thomson's formulas for obliquely crossed spherocylindrical lenses.

Lenses↗
PubMed1978

Changes in hydrogel contact lens power due to flexure.

When a hydrogel lens is placed on the eye, its power may change because of flexing of the lens. The correcting power of the lens when on the eye can be calculated by assuming that the lens flexes to the shape of the underlying cornea. Actual measurements of the correcting power of Hydrocurve lens on the eye were not in agreement with the calculated values. Assuming that the front and back surfaces of the lens flex by the same amount, the presence of a fluid lens between the hydrogel lens and the cornea would account for this discrepancy. For minus lenses of moderate and high power, it was found that the change in power was in the direction of more plus; for low minus and all plus lenses, the change was in the direction of more minus. Under the conditions of the present investigation, correcting power measured with the lens on the eye was in agreement with the calculated value for regular-thickness Hydrocurve lenses of -2.00 D and thin lenses of -0.75 D. This is interpreted to mean that lenses of these powers conform to the shape of the cornea so that the fluid lens is thin and plano. The clinical implications are discussed.

Contact Lenses, Hydrophilic↗
PubMed1978

Choosing the base curve for an ophthalmic lens.

Although optometrists can be expected to be responsible for the base curve, which determines the form of the lens they prescribe, they seldom specify the base curve to the optical laboratory. They may ask for a corrected-curve lens without specifying the kind of corrected-curve lens. If optometrists were to specify what they want in terms of a convex spherical base curve and allow the laboratory a leeway of p1.00 D, the laboratory could probably fill the order with an uncut lens from stock. With a series of semifinished lenses with convex spherical base curves spaced 2.00 D apart, the laboratory can supply a finished lens that will meet almost any need. For glasses to be used for distant objects, first consideration is usually given to minimizing the unwanted sphere and cylinder in the periphery of the lenses. For those who want to aim at this objective, I have worked out a series of convex spherical base curves that can be used for various combinations of spheres and cylinders.

Eyeglasses↗