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A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision of the eye. [ 1 ] [ 7 ] Cataracts often develop slowly and can affect one or both eyes. [ 1 ] Symptoms may include faded colours, blurry or double vision , halos around light, trouble with bright lights, and difficulty seeing at night . [ 1 ]
Form deprivation myopia occurs when the eyesight is deprived by limited illumination and vision range, [79] or the eye is modified with artificial lenses [80] or deprived of clear form vision. [81] In lower vertebrates, this kind of myopia seems to be reversible within short periods of time.
The human eye can function from very dark to very bright levels of light; its sensing capabilities reach across nine orders of magnitude. This means that the brightest and the darkest light signal that the eye can sense are a factor of roughly 1,000,000,000 apart. However, in any given moment of time, the eye can only sense a contrast ratio of ...
One well-known example is the prophet Tiresias, whose blindness is ascribed to various causes. According to one story, it was a punishment for revealing the secrets of the gods; according to another, he was struck blind after accidentally witnessing Athena bathing; in a third, he was blinded by Hera after taking Zeus 's side in a dispute. [ 3 ]
Visual or vision impairment (VI or VIP) is the partial or total inability of visual perception.In the absence of treatment such as corrective eyewear, assistive devices, and medical treatment, visual impairment may cause the individual difficulties with normal daily tasks, including reading and walking. [6]
There is some confusion over how the focusing mechanism of the eye works. [clarification needed] In the 1977 book, Eye and Brain, [13] for example, the lens is said to be suspended by a membrane, the 'zonula', which holds it under tension. The tension is released, by contraction of the ciliary muscle, to allow the lens to become more round, for ...
For example, When undertaking critical activities, people with CVI should be prepared for their vision to fluctuate, by taking precautions such as always carrying a white cane, if they use one, even if they don't always use it to the fullest. Another example is having very large print available, just in case it's needed (For example, consider ...
In narratology, focalisation is the perspective through which a narrative is presented, as opposed to an omniscient narrator. [1] Coined by French narrative theorist Gérard Genette, his definition distinguishes between internal focalisation (first-person) and external focalisation (third-person, fixed on the actions of and environments around a character), with zero focalisation representing ...