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Near Visual Acuity
Near visual acuity or near vision is a measure of how clearly a person can see nearby small objects or letters. Near vision is usually measured and recorded using a printed hand-held card containing different sized paragraphs, words, letters or symbols. Jaeger chart, N notation reading chart and Snellen's near vision test are the commonly used charts for measuring and recording near visual acuity. Near vision testing is usually done after correcting visual acuity at a distance. Eye conditions like presbyopia, accommodative insufficiency, cycloplegia etc. can affect the near visual acuity. According to the World Health Organization, the near visual acuity less than N6 or M0.8 at 40 cm is classified as near visual impairment. Physiology of near vision In human, near vision is obtained by a mechanism called accommodation. With the help of accommodation, a normal young human eye can change focus from distance (infinity) to as near as 6.5 cm from the eye. This change in foc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visual Acuity
Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e. (1) the sharpness of the retinal image within the eye, (2) the health and functioning of the retina, and (3) the sensitivity of the interpretative faculty of the brain. The most commonly referred visual acuity is the far acuity (e.g. 6/6 or 20/20 acuity), which describes the examinee's ability to recognize small details at a far distance, and is relevant to people with myopia; however, for people with hyperopia, the near acuity is used instead to describe the examinee's ability to recognize small details at a near distance. A common cause of low visual acuity is refractive error (ametropia), errors in how the light is refracted in the eyeball, and errors in how the retinal image is interpreted by the brain. The latter is the primary cause for low vision in people with a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bifocals
Bifocals are eyeglasses with two distinct optical powers. Bifocals are commonly prescribed to people with presbyopia who also require a correction for myopia, hyperopia, and/or astigmatism. History Benjamin Franklin is generally credited with the invention of bifocals. He decided to saw his lenses in half so he could read the lips of speakers of French at court, the only way he could understand them. Historians have produced some evidence to suggest that others may have come before him in the invention; however, a correspondence between George Whatley and John Fenno, editor of the ''Gazette of the United States'', suggested that Franklin had indeed invented bifocals, and perhaps 50 years earlier than had been originally thought. Despite this, the College of Optometrists concluded: :Unless further evidence emerges all we can say for certain is that Franklin was one of the first people to wear split bifocals and this act of wearing them caused his name to be associated with the ty ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Snellen Chart
A Snellen chart is an eye chart that can be used to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen, who developed the chart in 1862. Many ophthalmologists and vision scientists now use an improved chart known as the LogMAR chart. History Snellen developed charts using symbols based in a 5×5 unit grid. The experimental charts developed in 1861 used abstract symbols. Snellen's charts published in 1862 used alphanumeric capitals in the 5×5 grid. The original chart shows A, C, E, G, L, N, P, R, T, 5, V, Z, B, D, 4, F, H, K, O, S, 3, U, Y, A, C, E, G, L, 2. Description The normal Snellen chart is printed with eleven lines of block letters. The first line consists of one very large letter, which may be one of several letters, for example E, H, or N. Subsequent rows have increasing numbers of letters that decrease in size. A person taking the test covers one eye from 6 metres or 20 feet away, and reads aloud the letters of each row, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Herman Snellen
Herman Snellen (February 19, 1834 – January 18, 1908) was a Dutch ophthalmologist who introduced the Snellen chart to study visual acuity (1862). He took over directorship of the Netherlands Hospital for Eye Patients (Nederlandsch Gasthuis voor Ooglijders), after Franciscus Donders. Early life Snellen studied medicine at Utrecht University under Donders, Gerardus Johannes Mulder and Jacobus Schroeder van der Kolk. He earned his medical degree in 1858. He specialized in ophthalmology and worked as an assistant physician at the Netherlands Hospital for Eye Patients after he had completed his degree. Director He was named to succeed Donders as the institute's director in 1884, a position he served until 1903. In 1877, he was appointed as a professor of ophthalmology at Utrecht University. He did research on astigmatism, glaucoma and other eye diseases as well as research on correction of visual acuity using eyeglasses and ophthalmological surgery. Chart While alternative versio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ophthalmologist
Ophthalmology ( ) is a surgery, surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a medical degree, a doctor specialising in ophthalmology must pursue additional postgraduate residency (medicine), residency training specific to that field. This may include a one-year integrated internship that involves more general medical training in other fields such as internal medicine or general surgery. Following residency, additional specialty training (or fellowship) may be sought in a particular aspect of eye pathology. Ophthalmologists prescribe medications to treat eye diseases, implement laser therapy, and perform surgery when needed. Ophthalmologists provide both primary and specialty eye care - medical and surgical. Most ophthalmologists participate in academic research on eye diseases at some point in their training an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Times New Roman Font
Times New Roman is a serif typeface. It was commissioned by the British newspaper ''The Times'' in 1931 and conceived by Stanley Morison, the artistic adviser to the British branch of the printing equipment company Monotype Imaging, Monotype, in collaboration with Victor Lardent, a lettering artist in ''The Times's'' advertising department. It has become one of the most popular typefaces of all time and is installed on most desktop computers. Asked to advise on a redesign, Morison recommended that ''The Times'' change their text typeface from a spindly nineteenth-century face to a more robust, solid design, returning to traditions of printing from the eighteenth century and before. This matched a common trend in printing tastes of the period. Morison proposed an older Monotype typeface named Plantin (typeface), Plantin as a basis for the design, and Times New Roman mostly matches Plantin's dimensions. The main change was that the contrast between strokes was enhanced to give a cr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Text Size
In typography, the point is the smallest unit of measure. It is used for measuring font size, leading, and other items on a printed page. The size of the point has varied throughout printing's history. Since the 18th century, the size of a point has been between 0.18 and 0.4 millimeters. Following the advent of desktop publishing in the 1980s and 1990s, digital printing has largely supplanted the letterpress printing and has established the DTP point (DeskTop Publishing point) as the ''de facto'' standard. The DTP point is defined as of an international inch () and, as with earlier American point sizes, is considered to be of a pica. In metal type, the point size of the font describes the height of the metal body on which the typeface's characters were cast. In digital type, letters of a font are designed around an imaginary space called an '' em square''. When a point size of a font is specified, the font is scaled so that its em square has a side length of that particu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jaeger Chart
The Jaeger chart is an eye chart used in testing near vision acuity. It is a card on which paragraphs of text are printed, with the text sizes increasing from 0.37 mm to 2.5 mm. This card is to be held by a patient at a fixed distance from the eye dependent on the J size being read. The smallest print that the patient can read determines their visual acuity. The original 1867 chart had a text containing seven paragraphs and a corresponding seven-point scale. Jaeger cards are not standardized, and the variability of the actual size of test letters on different Jaeger cards currently in use is very high. Therefore, test results with different Jaeger cards are not comparable. More commonly, distance vision acuity is tested using the Snellen chart A Snellen chart is an eye chart that can be used to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen, who developed the chart in 1862. Many ophthalmologists and vision scientists now use an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypermetropia
Far-sightedness, also known as long-sightedness, hypermetropia, or hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blurred effect is due to incoming light being focused behind, instead of on, the retina wall due to insufficient accommodation by the lens. Minor hypermetropia in young patients is usually corrected by their accommodation, without any defects in vision. But, due to this accommodative effort for distant vision, people may complain of eye strain during prolonged reading. Some hypermetropes can see clear at distance, but near vision may be blurred due to insufficient accommodation. For this reason, this defect is referred as far-sightedness. If the hypermetropia is high, there will be defective vision for both distance and near. People may also experience accommodative dysfunction, binocular dysfunction, amblyopia, and strabismus. Newborns are almost invariably hypermetropic, but it gradually decreas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cycloplegia
Cycloplegia is paralysis of the ciliary muscle of the eye, resulting in a loss of accommodation. Because of the paralysis of the ciliary muscle, the curvature of the lens can no longer be adjusted to focus on nearby objects. This results in similar problems as those caused by presbyopia, in which the lens has lost elasticity and can also no longer focus on close-by objects. Cycloplegia with accompanying mydriasis (dilation of pupil) is usually due to topical application of muscarinic antagonists such as atropine and cyclopentolate. Belladonna alkaloids are used for testing the error of refraction and examination of eye. Management Cycloplegic drugs are generally muscarinic receptor blockers. These include atropine, cyclopentolate, homatropine, scopolamine and tropicamide. They are indicated for use in cycloplegic refraction (to paralyze the ciliary muscle in order to determine the true refractive error of the eye) and the treatment of uveitis. All cycloplegics are also mydriat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vision Therapy
Vision therapy (VT), or behavioral optometry, is an umbrella term for alternative medicine treatments using eye exercises, based around the pseudoscientific claim that vision problems are the true underlying cause of learning disabilities, particularly in children. Vision therapy has not been shown to be effective using scientific studies, except for helping with convergence insufficiency. Most claimsfor example that the therapy can address neurological, educational, and spatial difficultieslack supporting evidence. Neither the American Academy of Pediatrics nor the American Academy of Ophthalmology support the use of vision therapy. Definition and conceptual basis Vision therapy is based on the proposition that many learning disabilities in children are based on vision problems, and that these can be cured by performing eye exercises. Vision therapy lacks sound evidence, has been characterized as a pseudoscience and its practice as quackery. Vision therapy is a broad concept t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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