Visualization of the nucleoid in living bacteria on poly-lysine coated surfaces by the immersion technique.
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Bacteria↗
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Results for “Refractometry”
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Measurement of the optical thickness of transparent tissue layers.
The method of Duc de Chaulnes was employed to determine the mechanical and optical thickness, as well as the refractive index, of transparent tissue layers in living specimens. To this end the reproducible accuracy of the method and its dependence on the adjustment in focusing and on the numerical aperture of the objective was evaluated on test specimens using the procedures of transmitted light, phase-contrast (PC), and differential interference contrast (DIC) microscopy. The best working conditions were then applied to the actual measurements.
Animals↗
A quantitative interference light microscope study of human first trimester chorionic villi.
Using a Jamin-Lebedeff-type interference microscope an analysis of frozen sections of human first trimester chorionic villi reveals regional differences down to subcellular resolution. The evidence indicates compositional differences between villus cell types and shows that the syncytiotrophoblast is differentiated into at least three layers, one of which corresponds positionally to the previously described syncytioskeletal layer. Quantitative measurements have been made of specimen thickness, refractive index and dry mass of regions in the tissue. Local differences in syncytiotrophoblast have been noted with respect to the content of a population of organelles with distinctive optical properties. These may correspond to stored forms of steroid hormone or their precursors.
Chorionic Villi↗
Effect of refraction on optical microscopic measurement of internal blood-vessel diameter and its correction.
In optical microscopic measurement of internal blood-vessel diameters, the effect of refraction must be taken into account to ensure accuracy of the result. This effect is discussed and an analytical correction formula derived. Phantom blood vessels with known internal and external diameters were used to test the validity of the correction formula. The errors obtained prior to correction were reduced significantly after correction.
Blood Vessels↗
Measurement of specimen-induced aberrations of biological samples using phase stepping interferometry.
Confocal or multiphoton microscopes, which deliver optical sections and three-dimensional (3D) images of thick specimens, are widely used in biology. These techniques, however, are sensitive to aberrations that may originate from the refractive index structure of the specimen itself. The aberrations cause reduced signal intensity and the 3D resolution of the instrument is compromised. It has been suggested to correct for aberrations in confocal microscopes using adaptive optics. In order to define the design specifications for such adaptive optics systems, one has to know the amount of aberrations present for typical applications such as with biological samples. We have built a phase stepping interferometer microscope that directly measures the aberration of the wavefront. The modal content of the wavefront is extracted by employing Zernike mode decomposition. Results for typical biological specimens are presented. It was found for all samples investigated that higher order Zernike modes give only a small contribution to the overall aberration. Therefore, these higher order modes can be neglected in future adaptive optics sensing and correction schemes implemented into confocal or multiphoton microscopes, leading to more efficient designs.
Animals↗
Serum protein binding of furosemide in several species.
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Animals↗
Clinical experience with the Otago Photoscreener.
The Otago Photoscreener provides a sensitive indication of whether or not an infant is able to fix and focus binocularly on nearby objects. This instrument was designed for mass screening to identify infants with strabismus and/or amblyopia who do not fix and focus binocularly. This communication reports the authors' experience with the machine in the diagnosis and treatment of strabismus and amblyopia.
Amblyopia↗
Eccentric photorefraction: improving the predictive value and yield in detection of refractive errors.
Eccentric photorefraction (EPR) is a simple photographic technique for detecting amblyopiogenic conditions. Previous EPR studies to detect refractive errors (RE) have demonstrated high sensitivity but poor predictive value. We have established new criteria for detecting RE involving quantifying retinoscopic reflex crescent widths, thereby achieving 67% predictive value with 100% sensitivity for detecting RE greater than or equal to +3.5 D in a clinical study of 69 children. Optical analysis of EPR shows that anticrescent width (light crescent-free portion of the pupil) is independent of pupil diameter. Quantifying anticrescent widths in the above clinical trial increased the predictive value to 85%. Schematic eye and human eye EPR studies verify the theoretical prediction that similar ability to detect refractive errors is maintained when the working distance and eccentricity (distance of light source from lens edge) are reduced. These improvements in EPR reduce its cost and improve its yield; both are essential for its introduction as an acceptable community screening tool.
Adolescent↗
Varifocal spectacle lens surface power measurement.
An instrument is described for the assessment of varifocal lens surfaces based on a reflection technique. Results are also presented of measurements made on a series of lenses of the same design, illustrating some of the differences that exist between glass and plastics versions of the same lens.
Eyeglasses↗
Proposals for new reduced and schematic eyes.
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Cornea↗
Geometrical ray-tracing: a 'ray free' method.
A new geometrical method of determining the location of the image of an optical component is described. This method does not require rays to be drawn. It can be applied to refractive and reflective components as well as multi-component systems.
Mathematics↗
Thickness and weight of lenses for myopia.
High index lens materials have been introduced to minimize lens weight and thickness. By studying the best form lenses for different refractive indices and the effects of changing lens forms on thickness and weight, a method is proposed for comparing minus lenses in weight and thickness for different refractive indices and lens diameters.
Eyeglasses↗
Liquid crystal lens review.
Liquid crystal lenses are possibly the spectacle lenses of the future for presbyopic corrections. They present a variable refractive index which can be used to produce the necessary addition needed for presbyopia. The variability of the refractive index is due to the fact that these materials are optically anisotropic. This effect is obtained by the application of an electric or magnetic field through the liquid crystal layer. A review of the literature relating to the evolution, the preparation and the operation of these lenses is given. A discussion is also included of the practical problems and drawbacks, which at present limit their use, and possible solutions.
Eyeglasses↗
Determination of the nodal point position in the pseudophakic eye.
The optics of the schematic eye have been described by Gullstrand and Listing (System of Ophthalmology (ed. H. Kimpton), Vol. 5, C. V. Mosby, London (1970], data being averaged from a series of adult eyes with a crystalline lens. A ray of light from the height of any given object passing, undeviated, through the nodal point will determine the height of its image on the retina. The nodal point positions, therefore, are fundamental in determining image size, and any eye-to-eye variation in a patient will control the amount of aniseikonia. The optics of the pseudophakic eye are described together with a scientific method for determining the nodal point positions, and the implications are discussed.
Cornea↗
Aniseikonia: a method of objective assessment in pseudophakia using geometric optics.
There have been various reports in the literature regarding the limits that separate acceptable from disturbing aniseikonia. A criterion value of 5% is often quoted but actual values in pseudophakia may vary from 2% to 10%, depending on the type and position of implant used. In the accompanying paper we have reported a method by which image size can be calculated in the pseudophakic eye. Using this method a series of patients with anterior and posterior chamber implants were analysed and the image size for both eyes of each patient determined. This was compared with the patient's subjective appreciation.
Aniseikonia↗
Design of aspheric intraocular lenses.
The value of aspherizing intraocular lens surfaces for the purpose of improving retinal image quality of pseudophakic eyes was investigated. Surfaces were made as conicoids. Changes in primary wave aberrations and refractive errors were found to be proportional to changes in surface asphericity. The optimum asphericity depends markedly on ocular parameters, lens fitting position and how well lenses are centred within the eye. If lenses are not well centred, the asphericity that eliminates spherical aberration may result in poorer performance than that occurring with spherical surfaces. It is suggested that there is no general benefit in aspherizing surfaces of intraocular lenses.
Humans↗
On proximal effects in objective and subjective testing of dark accommodation.
This study investigated to what extent objective and subjective measurements of accommodation in darkness are affected by instrumentation or by flashed light stimuli that are arranged close to the subject's eye, and by the instructions given to the subjects. Subjects differed markedly in their susceptibility to these factors. Dark accommodation measured with an infra-red autorefractometer tended to be more distant by 0.2 D on the average if the autorefractometer allowed a free view into a large, but dark, room compared with a closed apparatus. When subjects were instructed to look into far or near distances during objective measurements, mean dark accommodation was more distant by 0.15 D and closer by 1.4 D, respectively, relative to the condition of 'relaxed eyes'. To find a simple screening test of dark accommodation, a 'number test' was investigated: subjects had to report which was the most sharply visible among a series of numbers that were simultaneously flashed at different optical distances in a Badal optometer. Objective measurements revealed that this test induced near shifts of 0.37 D on the average, relative to accommodation in a dark surround. Therefore, the results of the number test were only moderately correlated to objective measurements.
Accommodation, Ocular↗
Location of conjugate points in an optical system with particular reference to the estimation of aniseikonia in the pseudophakic eye.
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Algorithms↗