China
Africa
Explore chapters and articles related to this topic
Visual field artefacts and errors of interpretation
Published in Fiona Rowe, Visual Fields via the Visual Pathway, 2016
An age and instrument appropriate plus correction should be worn during central visual field assessment and a cylinder prescription should be given where the prescription is ≥1 dioptre. Suggested sphere additions are shown in Table 13.1 for kinetic perimetry. Automated perimeters such as Humphrey and Octopus 900 will calculate the desired prescription on the basis of a distance prescription and the given age of the patient. It is inadvisable to use the patient’s own reading glasses, even if single lenses in a large frame, as the patient’s reading distance (for which their prescription is calculated) may not be the same as the testing distance of the perimeter (commonly 30-cm centrally). Use of a patient’s bifocal or varifocal spectacles is also contraindicated as optical defocus will occur between distance and near segments with differential threshold responses for corresponding superior and inferior visual fields.
Developmental Aspects of the Alveolar Epithelium and the Pulmonary Surfactant System
Published in Jacques R. Bourbon, Pulmonary Surfactant: Biochemical, Functional, Regulatory, and Clinical Concepts, 2019
Jacques R. Bourbon, Caroline Fraslon
The effects of mesenchyme upon epithelial cytodifferentiation are more complex to interpret. On one hand, the capacity to synthesize surfactant appears to be determined by the source of both the epithelium and the mesenchyme. Thus, prospective mouse alveolar epithelium produced abundant lamellar bodies with the condition to be cultivated in the presence of its homologous mesenchyme, whereas chick air sac epithelial cultures branched when reassociated with chick or mouse respiratory mesenchyme, but failed to produce surfactant.58 In other words, mesenchyme may control the degree of expression, but not the absolute presence or absence of the differentiated condition. In addition, regional differences in inductive influence appear to exist within pulmonary mesenchyme itself: bronchial mesenchyme is able to induce budding of tracheal epithelium, whereas tracheal mesenchyme suppresses branching of bronchial and distal bronchiolar epithelia.54,55 On the other hand, the form of cytodifferentiation of the pulmonary epithelium also appears to be dependent on the amount of mesenchyme.61 Thus, ciliated columnar cells indicative of bronchiolar cell differentiation were the only differentiated cell type observed in culture of mouse embryonic lungs from which three quarters or nearly all the mesenchyme had been removed, but were seen on exception only in cultivated intact rudiments. By contrast, cuboidal cells containing lamellar bodies indicative of alveolar cell differentiation were not seen when the rudiments contained less than one half of their mesenchyme; they were prominent when the mesenchyme was complete or when the epithelium was combined with several mesenchymal masses. Since the nature of the putative mesenchymal message is unlikely to change, depending on the amount of mesenchyme, these two differentiation patterns may reflect a differential threshold for epithelial responsiveness to mesenchymal inducing/stimulating activity. We suggest that during in vivo development, the type of cytodifferentiation could be directed by the relative distance of epithelial cells to alveolar mesenchyme, with the existence of a gradient of the putative differentiation-inducing factor(s). Explanting the tissue in vitro may suppress this gradient through reduction of the rudiment growth and of the elongation of bronchiolar channels, thus submitting the cells to conditions which favor type II pneumocyte differentiation.
ENTRIES A–Z
Published in Philip Winn, Dictionary of Biological Psychology, 2003
(from Greek, psyche: mind, physike: natural world) The study of the relationship between the physical world, including the brain, and the mind; founded by Gustav Teodor Fechner (1801-1887) in 1860. Also a collection of methods (many invented by Fechner) for precisely measuring sensory, perceptual and cognitive functioning in whole animals, especially humans. These include both measures of performance in various experimental paradigms as well as measures of subjective responses to stimuli. Characterized by four major problems: detection, discrimination, identification, and scaling. Absolute (detection) and differential (discrimination) thresholds (minimal stimulus levels or differences, respectively, that can be responded to) are measured by methods of constant stimuli, limits, or adaptive testing. Modern methods nearly always use forced-choice paradigms, based on SIGNAL DETECTION THEORY, in which decision bias is controlled. The signal detection theory measure of performance, d' (d prime) is often used in lieu of absolute or differential threshold measurements. Identification performance is measured in bits of information (base 2 logarithm of number of alternatives) successfully transmitted from stimulus to response. Subjective psychological magnitudes are measured by several scaling methods, the most popular of which is magnitude estimation in which numbers are assigned directly to perceived psychological magnitudes. Laws established using psychophysical methods include: Weber's law, AI = kl where AI is differential threshold, I is the stimulus intensity at which it is measured and k is a constant). A different value of k characterizes each sensory continuum, being relatively large for light and sound intensity and relatively small for painful stimuli. Fechner's law, S = (1/k) In (I/I0) where S is the magnitude of sensation given rise to by a stimulus of intensity I (relative to the absolute threshold intensity, I0), and k is the constant from Weber's law, incorporates an indirect scaling of sensation. Stevens's law, S= kIb (where b is different for different sensory continua and k is a scaling constant), is confirmed by direct scaling methods, such as magnitude estimation. Examples of laws describing the dependence of thresholds on stimulus conditions include the Bloch- Charpentier law, I0 t=b where t is stimulus duration less than about 100 msec and b is a constant that represents the minimal amount of light energy needed for detection, and Ricco's Law, IQ A=c where A (<10' of visual angle) is an area stimulated on the retina and c is a constant.
Histotripsy: the first noninvasive, non-ionizing, non-thermal ablation technique based on ultrasound
Published in International Journal of Hyperthermia, 2021
Zhen Xu, Timothy L. Hall, Eli Vlaisavljevich, Fred T. Lee
Different tissues have specific resistance thresholds to histotripsy-induced damage, requiring variable numbers of ultrasound pulses and/or ultrasound pressure levels to break down the tissue. Mechanically strong collagen-based tissues (e.g., large vessels, nerves, bile ducts, stroma, or the renal collecting system) have a higher ultimate tensile strength compared to more parenchymal structures (e.g., solid organs and tumors in the liver, kidney, and brain) [78–81]. Also, microbubbles appear constrained to expand to a smaller maximum diameter in stiffer collagen-based tissue compared to the softer cellular tissue, producing a lower strain [80,82,83]. Therefore, it takes a greater number of histotripsy pulses and/or modified pulsing parameters (e.g., lower frequency, higher pressure) to liquefy collagen-based tissue than non-collagenous tissue [69,70,82]. This differential threshold results in a tissue-selective dose-related ablation phenomenon observed in histotripsy [70]. For example, when treating the liver, cells can be completely destroyed, while bile ducts, larger vessels, nerves, and connective tissue within the ablation zone remain intact (Figure 3) [37,84,85]. When treating the kidney, renal cortical tissue can be completely liquefied, while the collecting system remains structurally intact [85,86].
Macular pigment optical density after panretinal photocoagulation
Published in Clinical and Experimental Optometry, 2021
Mustafa Doğan, Bünyamin Kutluksaman
After application of mydriatic agents to achieve pupil dilatation with a diameter of at least 7-mm, MPOD levels were measured using luminance differential threshold test (colour perimetry technique) at baseline, before PRP, and every month until the end of the study (Metrovision Inc, Nord, France).