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Night Blindness
Nyctalopia (; ), also called night blindness, is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition (for example, vitamin A deficiency). It can be described as insufficient adaptation to darkness. The most common cause of nyctalopia is retinitis pigmentosa, a disorder in which the rod cells in the retina gradually lose their ability to respond to the light. Patients with this genetic condition have progressive nyctalopia and, eventually, their daytime vision may also be affected. In X-linked congenital stationary night blindness, from birth the rods either do not work at all, or work very little, but the condition does not get worse. Another cause of night blindness is a deficiency of retinol, or vitamin A1, found in fish oils, liver, and dairy products. The opposite problem, the inability to see in bright light, is known as hemeralopi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
P360 Onderdendam Goed Nachtzicht Ns Nachtblind (), with a Cyrillic instead of a Latin P.
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P36 or P-36 may refer to: Vessels * , a ship of the Argentine Navy * , a P-class sloop of the Royal Navy * , a submarine of the Royal Navy * , a corvette of the Indian Navy Other uses * Curtiss P-36 Hawk, an American fighter aircraft * Papyrus 36, a biblical manuscript * Petrobras 36, a collapsed oil platform * Phosphorus-36, an isotope of phosphorus * Soviet locomotive class P36, a steam locomotive See also * R-36 (missile) The R-36 () is a family of intercontinental ballistic missiles (ICBMs) and space launch vehicles (Tsyklon) designed by the Soviet Union during the Cold War. The original R-36 was deployed under the GRAU index 8K67 and was given the NATO reportin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phenothiazines
Phenothiazine, abbreviated PTZ, is an organic compound that has the formula S(C6H4)2NH and is related to the thiazine-class of heterocyclic compounds. Derivatives of phenothiazine are highly bioactive and have widespread use and rich history. The derivatives chlorpromazine and promethazine revolutionized the fields of psychiatry and allergy treatment, respectively. An earlier derivative, methylene blue, was one of the first antimalarial drugs, and derivatives of phenothiazine are currently under investigation as possible anti-infective drugs. Phenothiazine is a prototypical pharmaceutical lead structure in medicinal chemistry. Uses Phenothiazine itself is only of theoretical interest, but derivatives of it revolutionized psychiatry, other fields of medicine, and pest management. Other derivatives have been studied for possible use in advanced batteries and fuel cells. Phenothiazine-derived drugs In 1876, methylene blue, a derivative of phenothiazine, was synthesized by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xerophthalmia
Xerophthalmia (from Ancient Greek () meaning "dry" and () meaning "eye") is a medical condition in which the eye fails to produce tears. It may be caused by vitamin A deficiency, which is sometimes used to describe that condition, although there may be other causes. Xerophthalmia caused by a severe vitamin A deficiency is described by pathologic dryness of the conjunctiva and cornea. The conjunctiva becomes dry, thick and wrinkled. The first symptom is poor vision at night. If untreated, xerophthalmia can lead to dry eye syndrome, corneal ulceration, and ultimately to blindness as a result of corneal and retinal damage. Xerophthalmia usually implies a destructive dryness of the conjunctival epithelium due to dietary vitamin A deficiency—a rare condition in developed countries, but still causing much damage in developing countries. Other forms of dry eye are associated with aging, poor lid closure, scarring from a previous injury, or autoimmune diseases such as rheumat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vitamin A Deficiency
Vitamin A deficiency (VAD) or hypovitaminosis A is a lack of vitamin A in blood and tissues. It is common in poorer countries, especially among children and women of reproductive age, but is rarely seen in more developed countries. Vitamin A plays a major role in phototransduction, so this deficiency impairs vision, often presenting with nyctalopia (night blindness). In more severe VAD cases, it can progress to xerophthalmia, keratomalacia, and complete blindness. Vitamin A deficiency is the leading cause of preventable childhood blindness worldwide and is a major cause of childhood mortality. Each year, approximately 250,000 to 500,000 malnourished children in the developing world go blind from a VAD, with about half of whom dying within a year of losing their sight. Addressing VAD has been a critical focus of global health initiatives, including Sustainable Development Goal 2: to end hunger, achieve food security and improved nutrition and promote sustainable agriculture. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visual Snow
Visual snow syndrome (VSS) is an uncommon neurological condition in which the primary symptom is visual snow, a persistent flickering white, black, transparent, or colored dots across the whole visual field. It is distinct from the ''symptom'' of visual snow itself, which can also be caused by several other causes; these cases are referred to as "VSS mimics." Other names for the syndrome include "scotopic sensitivity syndrome", "Meares-Irlen syndrome", and "asfedia." Other common symptoms are palinopsia, enhanced entoptic phenomena, photophobia, and tension headaches. The condition is typically always present and has no known cure, as viable treatments are still under research. Astigmatism, although not presumed connected to these visual disturbances, is a common comorbidity. Migraines and tinnitus are common comorbidities that are both associated with a more severe presentation of the syndrome. The cause of the syndrome is unclear. The underlying mechanism is believed to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Macular Degeneration
Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which may result in blurred vision, blurred or vision loss, no vision in the center of the visual field. Early on there are often no symptoms. Some people experience a gradual worsening of vision that may affect one or both eyes. While it does not result in complete blindness, loss of central vision can make it hard to recognize faces, drive, read, or perform other activities of daily life. Visual release hallucinations, Visual hallucinations may also occur. Macular degeneration typically occurs in older people, and is caused by damage to the macula of retina, macula of the retina. Genetic factors and smoking may play a role. The condition is diagnosed through a complete eye exam. Severity is divided into early, intermediate, and late types. The late type is additionally divided into "dry" and "wet" forms, with the dry form making up 90% of cases. The difference between ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retinitis Pigmentosa
Retinitis pigmentosa (RP) is a member of a group of genetic disorders called inherited retinal dystrophy (IRD) that cause loss of vision. Symptoms include trouble seeing at night and decreasing peripheral vision (side and upper or lower visual field). As peripheral vision worsens, people may experience " tunnel vision". Complete blindness is uncommon. Onset of symptoms is generally gradual and often begins in childhood. Retinitis pigmentosa is generally inherited from one or both parents. It is caused by genetic variants in nearly 100 genes. The underlying mechanism involves the progressive loss of rod photoreceptor cells that line the retina of the eyeball. The rod cells secrete a neuroprotective substance (rod-derived cone viability factor, RdCVF) that protects the cone cells from apoptosis. When these rod cells die, this substance is no longer provided. This is generally followed by the loss of cone photoreceptor cells. Diagnosis is through eye examination of the retina ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retinal Detachment
Retinal detachment is a condition where the retina pulls away from the tissue underneath it. It may start in a small area, but without quick treatment, it can spread across the entire retina, leading to serious vision loss and possibly blindness. Retinal detachment is a medical emergency that requires surgery. The retina is a thin layer at the back of the eye that processes visual information and sends it to the brain. When the retina detaches, common symptoms include seeing floaters, flashing lights, a dark shadow in vision, and sudden blurry vision. The most common type of retinal detachment is rhegmatogenous, which occurs when a tear or hole in the retina lets fluid from the center of the eye get behind it, causing the retina to pull away. Rhegmatogenous retinal detachment is most commonly caused by posterior vitreous detachment, a condition where the gel inside the eye breaks down and pulls on the retina. Risk factors include older age, nearsightedness ( myopia), eye injury, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radial Keratotomy
Radial keratotomy (RK) is a refractive surgery, refractive surgical procedure to correct myopia (nearsightedness). It was developed in 1974 by Svyatoslav Fyodorov, a Russian Ophthalmology, ophthalmologist. It has been largely supplanted by newer, more accurate operations, such as photorefractive keratectomy, LASIK, Epi-LASIK and the Intraocular lens#Intraocular lenses for correcting refractive errors, phakic intraocular lens. Procedure When performing RK, incisions are made with a diamond knife. The incisions relax the steep central cornea in patients with myopia in order to achieve a decreased need for correction. The original technique – consisting of incisions from periphery to center – was called the "Russian technique", while the later advances of performing controlled incision from center to periphery was called the "American technique".Gulani AC, Fyodorov S: Future Directions in Vision course, June 1997 RK may be performed with different types, numbers, and patterns of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LASIK
LASIK or Lasik (; "laser-assisted in situ keratomileusis"), commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and astigmatism. LASIK surgery is performed by an ophthalmologist who uses a femtosecond laser or a microkeratome to create a corneal flap to expose the corneal stroma and then an excimer laser to reshape the corneal stroma in order to improve visual acuity. LASIK is very similar to another surgical corrective procedure, photorefractive keratectomy (PRK), and LASEK. All represent advances over radial keratotomy in the surgical treatment of refractive errors of vision. For people with moderate to high myopia or thin corneas which cannot be treated with LASIK or PRK, the phakic intraocular lens is an alternative. As of 2018, roughly 9.5 million Americans have had LASIK and, globally, between 1991 and 2016, more than 40 million procedures were performed. However, the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Myopia
Myopia, also known as near-sightedness and short-sightedness, is an eye condition where light from distant objects focuses in front of, instead of on, the retina. As a result, distant objects appear blurry, while close objects appear normal. Other symptoms may include headaches and eye strain. Severe myopia is associated with an increased risk of macular degeneration, retinal detachment, cataracts, and glaucoma. Myopia results from the length of the eyeball growing too long or less commonly the lens being too strong. It is a type of refractive error. Diagnosis is by the use of cycloplegics during eye examination. Tentative evidence indicates that the risk of myopia can be decreased by having young children spend more time outside. This decrease in risk may be related to natural light exposure. Myopia can be corrected with eyeglasses, contact lenses, or by refractive surgery. Eyeglasses are the simplest and safest method of correction. Contact lenses can provide a rela ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oguchi Disease
Oguchi disease is an autosomal recessive form of congenital stationary night blindness associated with fundus discoloration and abnormally slow dark adaptation. Presentation Genetics Several mutations have been implicated as a cause of Oguchi disease. These include mutations in the arrestin gene or the rhodopsin kinase gene. The condition is more frequent in individuals of Japanese ethnicity. Diagnosis Oguchi disease present with nonprogressive night blindness since young childhood or birth with normal day vision, but they frequently claim improvement of light sensitivities when they remain for some time in a darkened environment. On examination patients have normal visual fields but the fundi have a diffuse or patchy, silver-gray or golden-yellow metallic sheen and the retinal vessels stand out in relief against the background. A prolonged dark adaptation of three hours or more, leads to disappearance of this unusual discoloration and the appearance of a normal reddish ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
