|
Trifocal Lenses
Trifocals are eyeglasses with lenses that have three regions which correct for distance, intermediate (arm's length), and near vision. John Isaac Hawkins developed the trifocal lens in 1827. Trifocals are mostly used by people with advanced presbyopia who have been prescribed 2 diopters or more of reading addition. The intermediate addition is normally half the reading addition. So, for someone with a distance prescription of −4 diopters and a reading addition of +3, the reading portion of their trifocals would have a net power of −1, and the intermediate segment would be −2.5 diopters. Trifocal lenses are made in similar styles to bifocals, but with an additional segment for intermediate vision above the reading section. A common style is the 7×28 flat-top or D-shaped segment, 28 mm wide, with a 7 mm high intermediate segment. Larger intermediate segments are available, and are particularly useful for people who spend a lot of time using computers. Trifocals are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glasses
Glasses, also known as eyeglasses (American English), spectacles (Commonwealth English), or colloquially as specs, are vision eyewear with clear or tinted lenses mounted in a frame that holds them in front of a person's eyes, typically utilizing a bridge over the nose and hinged arms, known as temples or temple pieces, that rest over the ears for support. Glasses are typically used for vision correction, such as with reading glasses and glasses used for nearsightedness; however, without the specialized lenses, they are sometimes used for cosmetic purposes. Safety glasses are eye protection, a form of personal protective equipment ( PPE) that are worn by workers around their eyes for protection. Safety glasses act as a shield to protect the eyes from any type of foreign debris that may cause irritation or injury; these glasses may have protection on the sides of the eyes as well as in the lenses. Some types of safety glasses are used to protect against visible and n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lens (optics)
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), usually arranged along a common axis. Lenses are made from materials such as glass or plastic and are ground, polished, or molded to the required shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called "lenses", such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses. Lenses are used in various imaging devices such as telescopes, binoculars, and cameras. They are also used as visual aids in glasses to correct defects of vision such as myopia and hypermetropia. History The word ''lens'' comes from , the Latin name of the lentil (a seed of a lentil pla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Near Visual Acuity
Near visual acuity or near vision is a measure of how clearly a person can see nearby small objects or letters. Visual acuity in general usually refers clarity of distance vision, and is measured using eye charts like Snellen chart, LogMAR chart etc. 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Isaac Hawkins
John Isaac Hawkins (1772–1855) was a British American inventor and civil engineer who twice emigrated to and ultimately died in the United States, American state of New Jersey. Early life Hawkins was born on March 14, 1772 at Taunton, Somerset, England,R. L. Tafel, ''Documents Concerning Swedenborg'', p. 1217 the son of Joan Wilmington and her husband Isaac Hawkins, a watchmaker. The father, Isaac Hawkins, would become a Methodism, Wesleyan minister, but was expelled by John Wesley; and after moving the family to Moorfields in London he was a minister in the The New Church, Swedenborgian movement, which John Isaac would also follow. First emigration to America John Isaac emigrated to the United States about 1790, attending the Princeton University, College of New Jersey, where he studied medicine and later, chemical filtration. Hawkins married in New Jersey and lived at Bordentown, New Jersey, Bordentown and Philadelphia. In his own account, he was influenced by work of Geor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Presbyopia
Presbyopia is a physiological insufficiency of optical Accommodation (vertebrate eye), accommodation associated with the aging of the human eye, eye; it results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness (or as age-related long sight in the UK), it affects many adults over the age of 40. A common sign of presbyopia is difficulty in reading small print, which results in having to hold reading material farther away. Other symptoms associated can be headaches and eyestrain. Different people experience different degrees of problems. Other types of refractive errors may exist at the same time as presbyopia. 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. It occurs due to age-related changes in the Lens (anatomy), lens (decreased elasticity and increased h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diopter
A dioptre ( British spelling) or (American spelling), symbol dpt or D, is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, . It is normally used to express the optical power of a lens or curved mirror, which is a physical quantity equal to the reciprocal of the focal length, expressed in metres. For example, a 3-dioptre lens brings parallel rays of light to focus at metre. A flat window has an optical power of zero dioptres, as it does not cause light to converge or diverge. Dioptres are also sometimes used for other reciprocals of distance, particularly radii of curvature and the vergence of optical beams. The main benefit of using optical power rather than focal length is that the thin lens formula has the object distance, image distance, and focal length all as reciprocals. Additionally, when relatively thin lenses are placed close together their powers approximately add. Thus, a thin 2.0-dioptre lens placed close to a th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bifocals
Bifocals are eyeglasses with two distinct optical powers correcting vision at both long and short distances. 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. On the contrary, 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Progressive Lens
Progressive lenses are corrective lenses used in glasses, eyeglasses to correct presbyopia and other disorders of accommodation reflex, accommodation. They are characterised by a gradient of increasing optical power, lens power, added to the wearer's correction for the other refractive errors. The gradient starts at the wearer's distance prescription at the top of the lens (optics), lens and reaches a maximum addition power, or the full reading addition, at the bottom of the lens. The length of the progressive power gradient on the lens surface depends on the design of the lens, with a final addition power between 0.75 and 3.50 dioptres. The addition value prescribed depends on the level of presbyopia of the patient. In general the older the patient, the higher the addition. They are also known as multifocal lenses, progressive addition lenses (PAL), varifocal lenses, progressive power lenses, graduated prescription lenses, or progressive spectacle lenses. History The first paten ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Night-vision Device
A night-vision device (NVD), also known as a night optical/observation device (NOD) or night-vision goggle (NVG), is an Optoelectronics, optoelectronic device that allows visualization of images in low levels of light, improving the user's night vision. The device enhances Available light, ambient visible light and converts Infrared#Regions within the infrared, near-infrared light into visible light which can then be seen by humans; this is known as I2 (Image intensifier, image intensification). By comparison, viewing of infrared thermal radiation is referred to as Thermography, thermal imaging and operates in a different section of the infrared spectrum. A night vision device usually consists of an image intensifier tube, a protective housing, and an optional mounting system. Many NVDs also include a protective sacrificial lens, mounted over the front/Objective (optics), objective lens to prevent damage by environmental hazards, while some incorporat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Corrective Lenses
A corrective lens is a transmissive optical device that is worn on the eye to improve visual perception. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye. Intraocular lenses are surgically implanted most commonly after cataract removal but can be used for purely refractive purposes. Prescription of corrective lenses Corrective lenses are typically prescribed by an ophthalmologist or an optometrist. The prescription consists of all the specifications necessary to make the lens. Prescriptions typically include the power specifications of each lens (for each eye). Strengths are generally prescribed in quarter- diopter steps (0.25 D), because most people cannot generally distinguish between smaller increments (e.g., eighth-diopter steps / 0.125 D). The use of improper corr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
1827 Introductions
Eighteen or 18 may refer to: * 18 (number) * One of the years 18 BC, AD 18, 1918, 2018 Film, television and entertainment * ''18'' (film), a 1993 Taiwanese experimental film based on the short story ''God's Dice'' * ''Eighteen'' (film), a 2005 Canadian dramatic feature film * 18 (British Board of Film Classification), a film rating in the United Kingdom, also used in Ireland by the Irish Film Classification Office * 18 (''Dragon Ball''), a character in the ''Dragon Ball'' franchise * "Eighteen", a 2006 episode of the animated television series ''12 oz. Mouse'' Science * Argon, a noble gas in the periodic table * 18 Melpomene, an asteroid in the asteroid belt Music Albums * ''18'' (Moby album), 2002 * ''18'' (Nana Kitade album), 2005 * '' 18...'', 2009 debut album by G.E.M. * ''18'' (Jeff Beck and Johnny Depp album), 2022 Songs * "18" (5 Seconds of Summer song), from their 2014 eponymous debut album * "18" (One Direction song), from their 2014 studio album ''Four'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
