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Amsler Grid
The Amsler grid, used since 1945, is a grid of horizontal and vertical lines used to monitor a person's central visual field. The grid was developed by Marc Amsler, a Swiss ophthalmologist. It is a diagnostic tool that aids in the detection of visual disturbances caused by changes in the retina, particularly the macula (e.g. macular degeneration, Epiretinal membrane), as well as the optic nerve and the visual pathway to the brain. Amsler grid usually help detecting defects in central 20 degrees of the visual field. In the test, the person looks with each eye separately at the small dot in the center of the grid. Patients with macular disease may see wavy lines or some lines may be missing. Amsler grids are supplied by ophthalmologists, optometrists or from web sites, and may be used to test one's vision at home. The original Amsler grid was black and white. A color version with a blue and yellow grid is more sensitive and can be used to test for a wide variety of visual pathwa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Normal Vision
Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an animal's ability to recognize small details with precision. Visual acuity depends on optical and neural factors. Optical factors of the eye influence the sharpness of an image on its retina. Neural factors include the health and functioning of the retina, of the neural pathways to the brain, and of the interpretative faculty of the brain. The most commonly referred-to visual acuity is ''distance acuity'' or ''far acuity'' (e.g., "20/20 vision"), which describes someone's ability to recognize small details at a far distance. This ability is compromised in people with myopia, also known as short-sightedness or near-sightedness. Another visual acuity is '' near acuity'', which describes someone's ability to recognize small details at a near distance. This ability is compromised in people with hyperopia, also known as long-sightedness or far-sightedness. A common optical cause of low visual acuity ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perimeter
A perimeter is the length of a closed boundary that encompasses, surrounds, or outlines either a two-dimensional shape or a one-dimensional line. The perimeter of a circle or an ellipse is called its circumference. Calculating the perimeter has several practical applications. A calculated perimeter is the length of fence required to surround a yard or garden. The perimeter of a wheel/circle (its circumference) describes how far it will roll in one revolution. Similarly, the amount of string wound around a spool is related to the spool's perimeter; if the length of the string was exact, it would equal the perimeter. Formulas The perimeter is the distance around a shape. Perimeters for more general shapes can be calculated, as any path, with \int_0^L \mathrms, where L is the length of the path and ds is an infinitesimal line element. Both of these must be replaced by algebraic forms in order to be practically calculated. If the perimeter is given as a closed piecewise ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Preferential Hyperacuity Perimetry
Preferential hyperacuity perimetry (PHP) is a psychophysical test used to identify and quantify visual abnormalities such as metamorphopsia and scotoma. It is a type of perimetry. Background Vision abnormalities such as metamorphopsia (distortions) and scotoma are symptoms of retinal diseases such as macular degeneration. In advanced stages of the disease, photoreceptor cells may be irreversibly damaged. Hence, if not treated, macular degeneration may lead to blindness. Awareness to early changes in vision, especially in high risk patients, leads to early treatment (such as intravitreal injection of anti-VEGF factors, e.g. bevacizumab or ranibizumab) and prevents loss of vision. Because of complex brain mechanisms such as filling-in, patients with small and peripheral defects in their vision are often unaware of such changes until late stages in the disease. Another problem is that minute visual aberrations can be normal and therefore should be distinguished from genuine visual ab ... [...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] |
Macular Sparing
Macular sparing is visual field loss that preserves vision in the center of the visual field, otherwise known as the macula. It appears in people with damage to one hemisphere of their visual cortex, and occurs simultaneously with bilateral homonymous hemianopia or homonymous quadrantanopia. The exact mechanism behind this phenomenon is still uncertain.Whishaw, I. Q., & Kolb, B. (2015). Fundamentals of Human Neuropsychology (7th ed.). New York, NY: Worth Custom Publishing. The opposing effect, where vision in half of the center of the visual field is lost, is known as macular splitting.Windsor, R. L. (n.d.). Visual Fields in Brain Injury - Hemianopsia.net Everything you need to know about Hemianopsia. Retrieved from http://www.hemianopsia.net/visual-fields-in-brain-injury/ Causes The favored explanation for why the center visual field is preserved after large hemispheric lesions is that the macular regions of the cortex have a double vascular supply from the middle cerebral artery ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glaucoma
Glaucoma is a group of eye diseases that can lead to damage of the optic nerve. The optic nerve transmits visual information from the eye to the brain. Glaucoma may cause vision loss if left untreated. It has been called the "silent thief of sight" because the loss of vision usually occurs slowly over a long period of time. A major risk factor for glaucoma is increased pressure within the eye, known as Intraocular pressure, intraocular pressure (IOP). It is associated with old age, a family history of glaucoma, and certain medical conditions or the use of some medications. The word ''glaucoma'' comes from the Ancient Greek word (), meaning 'gleaming, blue-green, gray'. Of the different types of glaucoma, the most common are called open-angle glaucoma and closed-angle glaucoma. Inside the eye, a liquid called Aqueous humour, aqueous humor helps to maintain shape and provides nutrients. The aqueous humor normally drains through the trabecular meshwork. In open-angle glaucoma, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cystoid Macular Edema
Cystoidea was defined as a class of extinct paleozoic blastozoan echinoderms established to encompass stalked taxa that were neither crinoids nor blastoids. It was shown to be polyphyletic in the late 1960s but continues to be used even in recent (as of 2022) literature to discuss both rhombiferans and diploporitans. History The concept of Cystoidea has a complex history, with many emendations from its original conception. Early versions included the homalozoans, eocrinoids, paracrinoids, blastoids, and edrioblastoids. By 1967 the modern usage encompassing only rhombiferans and diploporitans had been established, although questions remained regarding the possible inclusion of blastoids. Despite these removals, speculation continued as to whether cystoids were ancestral to blastoids, crinoids, or echinoids. Work published in 1967 and 1968 questioned whether Cystoidea formed a natural group, and in 1972 the former orders Rhombifera and Diploporita were elevated to class rank ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Macular Pucker
Epiretinal membrane or macular pucker is a disease of the eye in response to changes in the vitreous humor or more rarely, diabetes. Sometimes, as a result of immune system response to protect the retina, cells converge in the macular area as the vitreous ages and pulls away in posterior vitreous detachment (PVD). PVD can create minor damage to the retina, stimulating exudate, inflammation, and White blood cell, leucocyte response. These cells can form a transparent layer gradually and, like all scar, scar tissue, tighten to create tension on the retina which may bulge and pucker, or even cause swelling or macular edema. Often this results in distortions of vision that are clearly visible as bowing and blurring when looking at lines on chart paper (or an Amsler grid) within the macular area, or central 1.0 degree of visual arc. Usually it occurs in one eye first, and may cause binocular diplopia or Diplopia, double vision if the image from one eye is too different from the im ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Central Serous Chorioretinopathy
Central serous chorioretinopathy (CSC or CSCR), also known as central serous retinopathy (CSR), is an eye disease that causes visual impairment, often temporary, usually in one eye. When the disorder is active it is characterized by leakage of fluid under the retina that has a propensity to accumulate under the central macula. This results in blurred or distorted vision (metamorphopsia). A blurred or gray spot in the central visual field is common when the retina is detached. Reduced visual acuity may persist after the fluid has disappeared. The disease is considered of unknown cause. It mostly affects white males in the age group 20 to 50 (male:female ratio 6:1) and occasionally other groups. The condition is believed to be exacerbated by stress or corticosteroid use. Pathophysiology Recently, central serous chorioretinopathy has been understood to be part of the pachychoroid spectrum. In pachychoroid spectrum disorders, of which CSR represents stage II, the choroid, the hi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Near-sightedness
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 blurred vision, 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 (anatomy), lens being too strong. It is a type of refractive error. Diagnosis is by the use of Cycloplegic refraction, 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 Daylighting (architecture), natural light exposure. Myopia can be corrected with eyeglasses, contact lenses, or by refractive surgery. Eyeglasses are th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Presumed Ocular Histoplasmosis Syndrome
Presumed ocular histoplasmosis syndrome (POHS) is a syndrome affecting the eye, which is characterized by peripheral atrophic chorioretinal scars, atrophy or scarring adjacent to the optic disc and maculopathy. The loss of vision in POHS is caused by choroidal neovascularization. Presentation The diagnosis of POHS is based on the clinical triad of multiple white, atrophic choroidal scars, peripapillary pigment changes (dark spots around optic disc of the eye), and a maculopathy caused by choroidal neovascularization. Completely distinct from POHS, acute ocular histoplasmosis may rarely occur in immunodeficiency. Causes Despite its name, the "presumed" relationship of POHS to ''Histoplasma capsulatum'' is controversial and has been questioned by a number of medical professionals. The fungus has rarely been isolated from cases with POHS, Presumed Ocular Histoplasmosis Synd ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
