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Corrective Lens
A corrective lens is a lens (i.e. a transmissive optical device) that is typically worn in front of the eye to improve daily vision. 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). ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optometry
Optometry is a specialized health care profession that involves examining the eyes and related structures for defects or abnormalities. Optometrists are health care professionals who typically provide comprehensive primary eye care. In the United States and Canada, optometrists are those that hold a Doctor of Optometry degree. They are trained and licensed to practice medicine for eye related conditions, in addition to providing refractive (optical) eye care. In the United Kingdom, optometrists may also practice medicine (and provide refractive care) for eye related conditions. The Doctor of Optometry title can also be used in the UK for those that hold the postgraduate O.D. degree. Within their scope of practice, optometrists are considered physicians and bill medical insurance(s) (example: Medicare) accordingly. Moreover, many participate in academic research for eye related conditions and disease. Optometrists are the only health care professionals with a first professional ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Progressive Lens
Progressive lenses, also called multifocal lenses, progressive addition lenses (PAL), varifocal lenses, progressive power lenses, graduated prescription lenses, or progressive spectacle lenses are corrective lenses used in eyeglasses to correct presbyopia and other disorders of accommodation. They are characterised by a gradient of increasing 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 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. History The first patent for a PAL was British Patent 15,735, granted to Owen Aves with a 1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 be ... [...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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Human Nose
The human nose is the most protruding part of the face. It bears the nostrils and is the first organ of the respiratory system. It is also the principal organ in the olfactory system. The shape of the nose is determined by the nasal bones and the nasal cartilages, including the nasal septum which separates the nostrils and divides the nasal cavity into two. On average the nose of a male is larger than that of a female. The nose has an important function in breathing. The nasal mucosa lining the nasal cavity and the paranasal sinuses carries out the necessary conditioning of inhaled air by warming and moistening it. Nasal conchae, shell-like bones in the walls of the cavities, play a major part in this process. Filtering of the air by nasal hair in the nostrils prevents large particles from entering the lungs. Sneezing is a reflex to expel unwanted particles from the nose that irritate the mucosal lining. Sneezing can transmit infections, because aerosols are c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Accommodation (eye) Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image |
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