Cholera

Cholera, sometimes known as Asiatic cholera or epidemic cholera, is a contagious gastroenteritis caused by the bacterium Vibrio cholerae. Transmission to humans occurs through the process of ingesting contaminated water or food. The major reservoir for cholera was long assumed to be humans themselves, but considerable evidence exists those aquatic environments can serve as reservoirs of the bacteria.

Vibrio cholerae is a Gram-negative bacterium that produces cholera toxin, an enterotoxin, whose action on the mucosal epithelium lining of the small intestine is responsible for the characteristic massive diarrhoea of the disease.In its most severe forms, cholera is one of the most rapidly fatal illnesses known, and a healthy person may become hypotensive within an hour of the onset of symptoms; infected patients may die within three hours if treatment is not provided. In a common scenario, the disease progresses from the first liquid stool to shock in 4 to 12 hours, with death following in 18 hours to several days without oral rehydration therapy.

Blindness

Blindness is the condition of missing visual perception due to physiological or neurological factors.

Various scales have been developed to explain the extent of vision loss and define "blindness”. Total blindness is the entire lack of form and visual light perception and is clinically recorded as "NLP," an abbreviation for "no light perception”. Blindness is normally used to describe severe visual impairment with residual vision. Those described as having only "light perception" have no more sight than the capacity to tell light from dark. A person with only "light projection" can tell the common 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 difficult definitions referred to as legal blindness. In North America and most of Europe, legal blindness is defined as visual acuity (vision) of 20/200 (6/60) or less in the improved eye with best correction possible. This means that a officially blind individual would have to stand 20 feet (6.1 m) from an object to see it—with vision correction—with the same degree of clarity as a usually sighted person could from 200 feet (61 m). In many areas, people with average acuity who nevertheless have a visual field of less than 20 degrees (the norm being 180 degrees) are also classified as being legally blind. About ten percent of those deemed legally blind, by any measure, have no vision. The rest have some vision, from light perception alone to comparatively good acuity. Low vision is sometimes used to illustrate visual acuities from 20/70 to 20/200.