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About 1 mm decrease in axial length cause 3 diopters of hypermetropia. [2] One condition that cause axial hypermetropia is nanophthalmos. [12] Curvatural: Curvatural hypermetropia occur when curvature of lens or cornea is flatter than normal. About 1 mm increase in radius of curvature results in 6 diopters of hypermetropia. [2]
The number of people globally with refractive errors has been estimated at one to two billion. [4] Rates vary between regions of the world with about 25% of Europeans and 80% of Asians affected. [4] Near-sightedness is the most common disorder. [6] Rates among adults are between 15 and 49% while rates among children are between 1.2 and 42%. [7]
Other types of refractive errors may exist at the same time as presbyopia. [1] This condition is similar to hypermetropia or far-sightedness, which starts in childhood and exhibits similar symptoms of blur in the vision for close objects. Presbyopia is a typical part of the aging process. [4]
Other medical conditions may include refractive errors such as myopia, high hypermetropia, and astigmatism, amblyopia, presbyopia, pseudomyopia, diabetes, cataract, pernicious anemia, vitamin B 12 deficiency, thiamine deficiency, glaucoma, retinopathy, hypervitaminosis A, migraine, sjögren's syndrome, floater, macular degeneration, and can be ...
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]
Visual perception is the ability to interpret the surrounding environment through photopic vision (daytime vision), color vision, scotopic vision (night vision), and mesopic vision (twilight vision), using light in the visible spectrum reflected by objects in the environment.
Above a certain luminance level (about 0.03 cd/m 2), the cone mechanism is involved in mediating vision; photopic vision. Below this level, the rod mechanism comes into play providing scotopic (night) vision. The range where two mechanisms are working together is called the mesopic range, as there is not an abrupt transition between the two ...
(H52.2) Astigmatism — the cornea or the lens of the eye is not perfectly spherical, resulting in different focal points in different planes (H52.3) Anisometropia — the lenses of the two eyes have different focal lengths (H52.4) Presbyopia — a condition that occurs with growing age and results in the inability to focus on close objects