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Arcus



An arcus cloud is a low, horizontal cloud formation, usually appearing as an accessory cloud to a cumulonimbus. Roll clouds and shelf clouds are the two main types of arcus clouds. They most frequently form along the leading edge or gust fronts of thunderstorms; some of the most dramatic arcus formations mark the gust fronts of derecho-producing convective systems. Roll clouds may also arise in the absence of thunderstorms, forming along the shallow cold air currents of some sea breeze boundaries and cold fronts.




arcus



A shelf cloud is a low, horizontal, wedge-shaped arcus cloud. A shelf cloud is attached to the base of the parent cloud, which is usually a thunderstorm cumulonimbus, but could form on any type of convective clouds. Rising cloud motion can often be seen in the leading (outer) part of the shelf cloud, while the underside can often appear as turbulent and wind-torn. Cool, sinking air from a storm cloud's downdraft spreads out across the land surface, with the leading edge called a gust front. This outflow cuts under warm air being drawn into the storm's updraft. As the lower and cooler air lifts the warm moist air, its water condenses, creating a cloud which often rolls with the different winds above and below (wind shear).


A roll cloud (Cloud Atlas name volutus) is a low, horizontal, tube-shaped, and relatively rare type of arcus cloud. They differ from shelf clouds by being completely detached from other cloud features. Roll clouds usually appear to be "rolling" about a horizontal axis. They are a solitary wave called a soliton, which is a wave that has a single crest and moves without changing speed or shape. One of the most famous frequent occurrences is the Morning Glory cloud in Queensland, Australia, which can occur up to four out of ten days in October.[2] One of the main causes of the Morning Glory cloud is the mesoscale circulation associated with sea breezes that develop over the Cape York Peninsula and the Gulf of Carpentaria. However, similar features can be created by downdrafts from thunderstorms and are not exclusively associated with coastal regions.


Arcus senilis (AS), also known as gerontoxon, arcus lipoides, arcus cornae, or corneal arcus, is a deposition of lipid in the peripheral corneal stroma. It is the most common peripheral corneal opacity. It frequently occurs with hyperlipidemia, especially in elderly individuals, and may be associated with dyslipidemia in younger patients (termed arcus juvenilis).[1]


Gross examination or a slit lamp examination are all that is needed to diagnosis AS. A study looking at corneal densitometry and systemic lipid levels on patients with arcus; there was a correlation found between high trigylceride levels and densitometry in the outer most zone of the cornea. [17]


Arcus senilis is common in people as they age. If these rings begin to appear around middle age or later, they are usually nothing to worry about. Almost everyone will eventually get arcus senilis. It is most common in men and in African Americans.


If you have a family history of high cholesterol you are more likely to have arcus senilis. But the appearance of arcus senilis in middle age or later does not necessarily mean you have high cholesterol.


Colored rings around the iris that begin to appear in childhood or early adulthood is called arcus juvenilis. Unlike arcus senilis, arcus juvenilis can be the sign of high cholesterol or other health problems. Children or young adults with these rings should see an ophthalmologist for an eye exam.


Babies can be born with a bluish hue to their sclera (the white of the eye) that can look like a ring along the edge of the iris. Their thin sclera allows structures below to show through. As babies gets older and their sclera matures, that coloration disappears. This is not arcus juvenilis and is not a concern.


An ophthalmologist can simply look at your eye to diagnose arcus senilis. Sometimes they will use a slit-lamp microscope as well. Arcus senilis has no symptoms. Arcus senilis does not cause vision problems, so no treatment is necessary.


Corneal arcus is a lipid-rich and predominantly extracellular deposit that forms at the corneoscleral limbus. It represents the most common peripheral corneal opacity and is not associated with tissue breakdown but rather with the deposition of lipids. The deposition of cholesterol in the peripheral cornea and arterial wall are similar in that both are accelerated by elevated serum levels of atherogenic lipoproteins, such as low-density lipoproteins (LDL). Corneal arcus is more prevalent in men than in women and in Blacks than in Whites. Its prevalence increases with advancing age. It has been associated with hypercholesterolemia, xanthelasmas, alcohol, blood pressure, cigarette smoking, diabetes, age, and coronary heart disease. Nevertheless, it is not clear whether or not corneal arcus is an independent risk factor for coronary heart disease (CHD). The present systematic review examines the relationship of corneal arcus and CHD to determine if corneal arcus is an independent CHD risk factor. We conclude that there is no consensus that corneal arcus is an independent risk factor. The presence of corneal arcus in a young person should prompt a search for lipid abnormalities. Also, because corneal arcus represents physical evidence of early lipid deposition, its presence suggests the need for aggressive lipid therapy.


ARCUS is a greentech start-up company founded in 2016. By means of its technology, it aims to use its technology to sustainably recycle plastic waste that cannot or only with difficulty be recycled in the carbon cycle and thus to use fewer fossil raw materials on the one hand and to master the global challenge of plastic waste on the other. ARCUS Greencycling Technologies GmbH is based in Ludwigsburg. For more information, see www.arcus-greencycling.com.


A relationship between corneal arcus and atherosclerosis has long been suspected but is controversial. The homozygous familial hypercholesterolemia patients in this study present a unique opportunity to assess this issue. They have both advanced atherosclerosis and corneal arcus.


This is a cross-sectional study of 17 patients homozygous for familial hypercholesterolemia presenting to the Clinical Center of the National Institutes of Health. Plasma lipoproteins, circumferential extent of arcus, thoracic aorta and coronary calcific atherosclerosis score, and Achilles tendon width were measured at the National Institutes of Health.


Patients with corneal arcus had higher scores for calcific atherosclerosis (mean 2865 compared to 412), cholesterol-year score (mean 11830 mg-yr/dl compared to 5707 mg-yr/dl), and Achilles tendon width (mean 2.54 cm compared to 1.41 cm) than those without. Corneal arcus and Achilles tendon width were strongly correlated and predictive of each other. Although corneal arcus was correlated with calcific atherosclerosis (r = 0.67; p = 0.004), it was not as highly correlated as was the Achilles tendon width (r = 0.855; p


Corneal arcus reflects widespread tissue lipid deposition and is correlated with both calcific atherosclerosis and xanthomatosis in these patients. Patients with more severe arcus tend to have more severe calcific atherosclerosis. Corneal arcus is not as good an indicator of calcific atherosclerosis as Achilles tendon thickness, but its presence suggests increased atherosclerosis in these hypercholesterolemic patients.


The German pathologist Rudolf Virchow is credited with the hypothesis that atherosclerosis reflects insudation of pathogenic agents into tissue. He also noted, in 1852, the association of corneal arcus and atherosclerosis, and hypothesized a similar mechanism of formation[1]. In contrast, William Osler, in 1892, suggested that arcus senilis had little utility in diagnosing "fatty degeneration" of the heart [2]. The attempt to relate corneal lipid deposits and vascular lipid deposits has been and remains controversial, despite continued interest[3, 4]. We investigate the relationship between corneal arcus (i.e. arcus senilis) and lipid deposition in other tissues in 17 patients homozygous for familial hypercholesterolemia (FH). This rare inborn error of metabolism is estimated to occur once in every million U.S. births [5]. However, the elucidation of the genetic basis of this metabolic disease has been central to understanding the role of particular lipoproteins in the pathogenesis of human atherosclerosis[6, 7]. Quantifying the extent of arcus and other lipid deposits in patients with such profound hypercholesterolemia provides a means of assessing the clinical issues raised by Virchow and Osler.


Corneal arcus. Four representative slides of corneal arcus. Arcus deposits tend to start at 6 and 12 o'clock and fill in until becoming completely circumferential. There is a thin clear section separating the arcus from the limbus known as the lucid interval of Vogt.


In 1974 David Cogan wrote "most attempts to correlate the degree of arcus formation with cardiovascular disease have been disappointing. The failure in correlation has been due in part to the inaccessibility of adequate criteria for analogous lipid deposit during life in other tissues of the body[20]." In this study we have used a non-invasive computed score to estimate calcified atherosclerosis in the thoracic aorta and coronary arteries of living patients. We have also calculated a dose-duration measure reflecting the patient's lifelong 'exposure' to the suspected pathogenic agent (i.e. elevated serum cholesterol). These measures were then compared with a measure of the circumferential extent of arcus in the peripheral cornea in an attempt to meet the challenge noted by Dr. Cogan.


Statistical analyses were performed using SPSS for Windows, 5.0, SPSSSV for Windows, 6.1 (SPSS Inc.), and Stata, 5.0 (Stata Corp.). For regression analysis the CYS, TC at diagnosis and calcific atherosclerosis scores were transformed in order to obtain a range and distribution better suited for analysis. The base 10 logarithm was taken for all CYS values, TC values at diagnosis, and for CA. Two tailed bivariate correlation coefficients were computed using the Pearson formula. Simple linear regression models were constructed to search for the single most significant predictor for the response of interest. Multiple linear regression models were also constructed to adjust for the confounding effects of age. Comparisons between FH homozygotes and normal control subjects, and comparisons between those patients with and without arcus, and males and females, were done with Student's t tests. 041b061a72


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