Cyclotropia

	Cyclotropia Cyclotropia is a form of strabismus in which, compared to the correct positioning of the eyes, there is a torsion of one eye (or both) about the eye's visual axis. Consequently, the visual fields of the two eyes appear tilted relative to each other. The corresponding ''latent'' condition – a condition in which torsion occurs only in the absence of appropriate visual stimuli – is called cyclophoria. Cyclotropia is often associated with other disorders of strabism, can result in double vision, and can cause other symptoms, in particular head tilt. In some cases, subjective and objective cyclodeviation may result from surgery for oblique muscle disorders; if the visual system cannot compensate for it, cyclotropia and rotational double vision (cyclodiplopia) may result. The role of cyclotropia in vision disorders is not always correctly identified. In several cases of double vision, once the underlying cyclotropia was identified, the condition was solved by surgical c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Cyclovergence Cyclovergence is the simultaneous occurring cyclorotation (torsional eye movement (sensory), movement) of both human eye, eyes which is performed in opposite directions to obtain or maintain single binocular vision. Normal cyclovergence and cycloversion Conjugate cyclorotations of the eye (that is, cyclorotations in the same direction) are called ''cycloversion''. They mainly occur due to Listing's law, which, under normal circumstances, constrains the cyclorotation in dependence on the vertical and horizontal movements of the eye. Visually evoked cyclovergence Listing's law, however, does not account for all cyclorotations. In particular, in the presence of cyclodisparity (that is, when two images are presented which would need to be rotated in relation to each other in order to allow visual fusion to take place), the eyes perform cyclovergence, rotating around their gaze directions in opposite directions, as a motor response to cyclodisparity. Such additional, visually evoke ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Strabismus Strabismus is a vision disorder in which the eyes do not properly align with each other when looking at an object. The eye that is focused on an object can alternate. The condition may be present occasionally or constantly. If present during a large part of childhood, it may result in amblyopia, or lazy eyes, and loss of depth perception. If onset is during adulthood, it is more likely to result in double vision. Strabismus can occur due to muscle dysfunction, farsightedness, problems in the brain, trauma or infections. Risk factors include premature birth, cerebral palsy and a family history of the condition. Types include esotropia, where the eyes are crossed ("cross eyed"); exotropia, where the eyes diverge ("lazy eyed" or "wall eyed"); and hypertropia or hypotropia where they are vertically misaligned. They can also be classified by whether the problem is present in all directions a person looks (comitant) or varies by direction (incomitant). Diagnosis may be made by obser ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Torsion Torsion may refer to: Science * Torsion (mechanics), the twisting of an object due to an applied torque * Torsion of spacetime, the field used in Einstein–Cartan theory and ** Alternatives to general relativity * Torsion angle, in chemistry Biology and medicine * Torsion fracture or spiral fracture, a bone fracture when torque is applied * Organ torsion, twisting that interrupts the blood supply to that organ: Splenic torsion, causing splenic infarction Ovarian torsion ** Testicular torsion * Penile torsion, a congenital condition * Torsion of the digestive tract in some domestic animals: Torsion, a type of horse colic Gastric torsion, or gastric dilatation volvulus * Torsion (gastropod), a developmental feature of all gastropods Mathematics * Torsion of a curve * Torsion tensor, in differential geometry * Torsion (algebra), in ring theory * Torsion group, in group theory and arithmetic geometry * Tor functor, the derived functors of the tensor product of modules ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Human Eye The human eye is a sensory organ, part of the sensory nervous system, that reacts to visible light and allows humans to use visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm. The eye can be considered as a living optical device. It is approximately spherical in shape, with its outer layers, such as the outermost, white part of the eye (the sclera) and one of its inner layers (the pigmented choroid) keeping the eye essentially light tight except on the eye's optic axis. In order, along the optic axis, the optical components consist of a first lens (the cornea—the clear part of the eye) that accomplishes most of the focussing of light from the outside world; then an aperture (the pupil) in a diaphragm (the iris—the coloured part of the eye) that controls the amount of light entering the interior of the eye; then another lens (the crystalline lens) that accomplishes the remaining focussing of light into ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Double Vision Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often voluntary. However, when occurring involuntarily, it results in impaired function of the extraocular muscles, where both eyes are still functional, but they cannot turn to target the desired object. Problems with these muscles may be due to mechanical problems, disorders of the neuromuscular junction, disorders of the cranial nerves ( III, IV, and VI) that innervate the muscles, and occasionally disorders involving the supranuclear oculomotor pathways or ingestion of toxins. Diplopia can be one of the first signs of a systemic disease, particularly to a muscular or neurological process, and it may disrupt a person's balance, movement, or reading abilities. Causes Diplopia has a diverse range of ophthalmologic, infectious, autoimmune, neu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Head Tilt Torticollis, also known as wry neck, is a dystonic condition defined by an abnormal, asymmetrical head or neck position, which may be due to a variety of causes. The term ''torticollis'' is derived from the Latin words ''tortus, meaning "twisted"'' and ''collum, meaning "neck."'' The most common case has no obvious cause, and the pain and difficulty with turning the head usually goes away after a few days, even without treatment in adults. Signs and symptoms Torticollis is a fixed or dynamic tilt, rotation, with flexion or extension of the head and/or neck. The type of torticollis can be described depending on the positions of the head and neck. * laterocollis: the head is tipped toward the shoulder * rotational torticollis: the head rotates along the longitudinal axis * anterocollis: forward flexion of the head and neck * retrocollis: hyperextension of head and neck backward A combination of these movements may often be observed. Torticollis can be a disorder in itself as wel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Amblyopia Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amblyopia is the most common cause of decreased vision in a single eye among children and younger adults. The cause of amblyopia can be any condition that interferes with focusing during early childhood. This can occur from poor alignment of the eyes (strabismic), an eye being irregularly shaped such that focusing is difficult, one eye being more nearsighted or farsighted than the other (refractive), or clouding of the lens of an eye (deprivational). After the underlying cause is addressed, vision is not restored right away, as the mechanism also involves the brain. Amblyopia can be difficult to detect, so vision testing is recommended for all children around the ages of four to five. Early detection improves treatment success. Glasse ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Lancaster Red-green Test In the fields of optometry and ophthalmology, the Lancaster red-green test is a binocular, dissociative, subjective cover test that measures strabismus in the nine diagnostic positions of gaze. The test is named after Walter Brackett Lancaster, who introduced it in 1939. __TOC__ Test procedure The patient wears red-green glasses, and two lights (one red, one green) are used, so that the patient thus sees each light with a different eye. One light is held by the clinician, the other by the patient. The clinician points the light to a screen, requesting the patient to bring the second light to align on top of it. The patient's eye positions are measured while the patient performs the test. Advantageously, monocular occlusion is applied before the test for at least 30 minutes. This largely eliminates the neurologically learned fusional vergence tone ("vergence adaptation") that is present in patients who are able to achieve fusion in a limited area of gaze, as is often the case for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Cyclodisparity Cyclodisparity refers to the difference in the rotation angle of an object or scene viewed by the left and right eyes. Cyclodisparity can result from the eyes' torsional rotation (''cyclorotation'') or can be created artificially by presenting to the eyes two images that need to be rotated relative to each other for binocular fusion to take place. Human and animal vision The eyes and visual system can compensate for cyclodisparity up to a certain point; if the cyclodisparity is larger than a threshold, the images cannot be fused, resulting stereoblindness, and in double vision in subjects who otherwise have full stereo vision. When a human subject is presented with images that have artificial cyclodisparity, cyclovergence is evoked, that is, a motor response of the eye muscles that rotates the two eyes in opposite directions, thereby reducing cyclodisparity. Visually-induced cyclovergence of up to 8 degrees has been observed in normal subjects. Furthermore, up to about 8 degrees ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Dove Prism A Dove prism is a type of reflective prism which is used to invert an image. Dove prisms are shaped from a truncated right-angle prism. The Dove prism is named for its inventor, Heinrich Wilhelm Dove. Although the shape of this prism is similar to the shape described by a Dovetail joint, the etymology of the two is unrelated. A beam of light travelling parallel to the longitudinal axis, entering one of the sloped faces of the prism undergoes total internal reflection from the inside of the longest (bottom) face and emerges from the opposite sloped face. Images passing through the prism are flipped (mirrored), and because only one reflection takes place, the image is also inverted but not laterally transposed. Refraction at the entrance and exit surfaces results in substantial image astigmatism when used in convergent light. Thus the Dove prism is used almost exclusively for images appearing at infinity. If the flat hypotenuse surface of a Dove prism is cut into a roof shape, th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Hypertropia Hypertropia is a condition of misalignment of the eyes (strabismus), whereby the visual axis of one eye is higher than the fellow fixating eye. Hypotropia is the similar condition, focus being on the eye with the visual axis lower than the fellow fixating eye. Dissociated vertical deviation is a special type of hypertropia leading to slow upward drift of one or rarely both eyes, usually when the patient is inattentive. Presentation Associated defects Refractive errors such as hyperopia and anisometropia may be associated abnormalities found in patients with vertical strabismus. The vertical miscoordination between the two eyes may lead to * Strabismic amblyopia, (due to deprivation / suppression of the deviating eye) * cosmetic defect (most noticed by parents of a young child and in photographs) * Face turn, depending on presence of binocular vision in a particular gaze * diplopia or double vision - more seen in adults (maturity / plasticity of neural pathways) and suppress ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Harada–Ito Procedure The Harada–Ito procedure is an eye muscle operation designed to improve the excyclotorsion experienced by some patients with cranial nerve IV palsy. In this procedure, the superior oblique tendon is split, and the anterior fibers – the fibers most responsible for incyclotorsion – are moved anteriorly and laterally. This selectively stretches and tightens these fibers, enhancing the incyclotorsion power of the superior oblique. The most common indication for the Harada–Ito procedure is bilateral acquired cranial nerve IV palsy following closed head trauma (particularly automobile accidents). In this clinical situation the vertical imbalance is often less symptomatically bothersome to the patient than the induced excyclotorsion. Affected patients have a particularly annoying type of double vision (diplopia), wherein the images are twisted (excyclotorted). Patients with cranial nerve IV palsy whose complaints are not specifically limited to torsio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]