Blindness is the condition of lacking visual perception Visual perception is the ability to interpret information and surroundings from visible light reaching the eye. The resulting perception is also known as eyesight, sight or vision. The various physiological components involved in vision are referred to collectively as the visual system, and are the focus of much research in psychology, cognitive due to physiological Physiology is the science of the functioning of living systems. It is a subcategory of biology. In physiology, the scientific method is applied to determine how organisms, organ systems, organs, cells and biomolecules carry out the chemical or physical function that they have in a living system. The word physiology is from Greek φύσις, physis, or neurological Neurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue, such as muscle. The corresponding surgical specialty factors.
Various scales have been developed to describe the extent of vision loss Vision loss or visual loss is the absence of vision where it existed before, which can happen either acutely or chronically (i.e. over a long period of time) and define blindness.[1] Total blindness is the complete lack of form and visual light perception and is clinically recorded as NLP, an abbreviation for "no light perception."[1] Blindness is frequently used to describe severe visual impairment Visual impairment is vision loss (of a person) to such a degree as to qualify as a handicap through a significant limitation of visual capability resulting from either disease, trauma, or congenital or degenerative conditions that cannot be corrected by conventional means, such as refractive correction, medication, or surgery. This functional loss with residual vision. Those described as having only light perception have no more sight than the ability to tell light from dark and the general direction of a light source.
In order to determine which people may need special assistance because of their visual disabilities, various governmental jurisdictions have formulated more complex definitions referred to as legal blindness.[2] In North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific Ocean; South America lies to the southeast. North and most of Europe Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural River, the Caspian Sea, the Caucasus Mountains (or the Kuma-Manych Depression), and the Black Sea to the southeast. Europe is bordered, legal blindness is defined as visual acuity Visual acuity is acuteness or clearness of vision, especially form vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain (vision) of 20/200 (6/60) or less in the better eye with best correction possible. This means that a legally blind individual would have to stand 20 feet (6.1 m) from an object to see it—with corrective lenses A corrective lens is a lens worn in front of the eye, mainly used to treat myopia, hyperopia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye. Intraocular lenses are surgically implanted most commonly after cataract—with the same degree of clarity as a normally sighted person could from 200 feet (61 m). In many areas, people with average acuity who nonetheless have a visual field The term visual field is sometimes used as a synonym to field of view, though they do not designate the same thing. The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments", while 'field of view' "refers to the physical objects and light sources in the of less than 20 degrees A degree , usually denoted by ° (the degree symbol), is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians. When that angle is with respect to a reference meridian, it indicates a location along a great circle of a sphere, such as Earth (see Geographic coordinate system), Mars, or the (the norm being 180 degrees) are also classified as being legally blind. Approximately ten percent of those deemed legally blind, by any measure, have no vision. The rest have some vision, from light perception alone to relatively good acuity. Low vision Low vision is a subspecialty within the professions of optometry and ophthalmology and opticianry dealing with individuals who have less than normal vision even with the most accurate conventional prescription available. It can be a result of either congenital or acquired factors. An example of the former is Leber's congenital amaurosis and of the is sometimes used to describe visual acuities from 20/70 to 20/200.[3]
By the 10th Revision of the WHO The World Health Organization is a specialized agency of the United Nations (UN) that acts as a coordinating authority on international public health. Established on 7 April 1948, and headquartered in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health Organization, which had been an agency of the International Statistical Classification of Diseases, Injuries and Causes of Death, low vision is defined as visual acuity of less than 6/18 (20/60), but equal to or better than 3/60 (20/400), or corresponding visual field loss to less than 20 degrees, in the better eye with best possible correction. Blindness is defined as visual acuity of less than 3/60 (20/400), or corresponding visual field loss to less than 10 degrees, in the better eye with best possible correction.[4][5]
It should be noted that blind people with undamaged eyes may still register light non-visually for the purpose of circadian A circadian rhythm is a roughly 24-hour cycle in the biochemical, physiological or behavioral processes of living entities, including plants, animals, fungi and cyanobacteria . The term "circadian", coined by Franz Halberg, comes from the Latin circa, "around," and diem or dies, "day", meaning literally " entrainment In chronobiology, entrainment of a circadian system is the alignment of its own period and phase to the period and phase of an external rhythm. A common example is the entrainment of endogenous circadian rhythms to the daily light-dark cycle. Of the several possible cues, called zeitgeber (German for time-giver, synchronizer), which can contribute to the 24-hour light/dark cycle. Light signals for this purpose travel through the retinohypothalamic tract The retinohypothalamic tract is a photic input pathway involved in the circadian rhythms of mammals. The origin of the retinohypothalamic tract is the intrinsically photosensitive Retinal Ganglion Cells , which contain the photopigment melanopsin. The axons of the ipRGCs belonging to the retinohypothalamic tract project directly to the, so a damaged optic nerve beyond where the retinohypothalamic tract exits it is no hindrance.
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Blind horses. Dogs with three legs, or neurological or orthopedic issues, or blindness . Cats that are blind or can't walk well because of congenital or ...
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Feds Investigate Blindness ED Drug Link
Laurel Jean
Wed, 06 Jan 2010 20:27:00 GM
To make things a bit more interesting, I have also been . blind. since birth. I consider my . blindness. to be a unique gift from God, an opportunity to serve as an ambassador among . blind. and sighted folks of all ages, on all walks of life. ...
