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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 ]
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 ...
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]
Some people may have other visual problems, such as severe visual field defects, color blindness, reduced contrast, mild amblyopia, cerebral visual impairments, inability to track fast-moving objects, or one of many other visual impairments and still have "normal" visual acuity. Thus, "normal" visual acuity does not imply normal vision.
The resulting perception is also known as vision, sight, or eyesight (adjectives visual, optical, and ocular, respectively). The various physiological components involved in vision are referred to collectively as the visual system , and are the focus of much research in linguistics , psychology , cognitive science , neuroscience , and molecular ...
Tubular vision: Tubular vision Since macular fibers are the most resistant to glaucomatous damage, the central vision remains unaffected until end stages of glaucoma. Tubular vision or Tunnel vision is the loss of peripheral vision with retention of central vision, resulting in a constricted circular tunnel-like field of vision.
Graeco-Roman physician Galen first used the term "myopia" (from Greek words "myein" meaning "to close or shut" and "ops" (gen. opos) meaning "eye") for near-sightedness. [153] The first spectacles for correcting myopia were invented by a German cardinal in the year 1451. [ 154 ]
Visual decline progresses relatively quickly to the far peripheral field, eventually extending into the central visual field as tunnel vision increases. Visual acuity and color vision can become compromised due to accompanying loss of the cone photoreceptor cells, which are responsible for color vision, visual acuity, and sight in the central ...