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Floater
Floaters or eye floaters are sometimes visible deposits (e.g., the shadows of tiny structures of protein or other cell debris projected onto the retina) within the eye's vitreous humour ("the vitreous"), which is normally transparent, or between the vitreous and retina.Cline D; Hofstetter HW; Griffin JR. ''Dictionary of Visual Science''. 4th ed. Butterworth-Heinemann, Boston 1997. They can become particularly noticeable when looking at a blank surface or an open monochromatic space, such as blue sky. Each floater can be measured by its size, shape, consistency, refractive index, and motility. They are also called ''muscae volitantes'' (Latin for 'flying flies'), or ''mouches volantes'' (from the same phrase in French). The vitreous usually starts out transparent, but imperfections may gradually develop as one ages. The common type of floater, present in most people's eyes, is due to these degenerative changes of the vitreous. The perception of floaters, which may be annoying ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Entoptic Phenomenon
Entoptic phenomena () are visual effects whose source is within the human eye itself. (Occasionally, these are called entopic phenomena, which is probably a typographical mistake.) In Helmholtz's words: "Under suitable conditions light falling on the eye may render visible certain objects within the eye itself. These perceptions are called ''entoptical''." Overview Entoptic images have a physical basis in the image cast upon the retina. Hence, they are different from optical illusions, which are caused by the visual system and characterized by a visual percept that (loosely said) appears to differ from reality. Because entoptic images are caused by phenomena within the observer's own eye, they share one feature with optical illusions and hallucinations: the observer cannot share a direct and specific view of the phenomenon with others. Helmholtz commented on entoptic phenomena which could be seen easily by some observers, but could not be seen at all by others. This variance is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vitrectomy
Vitrectomy is a surgery to remove some or all of the vitreous humor from the eye. Anterior vitrectomy entails removing small portions of the vitreous humor from the front structures of the eye—often because these are tangled in an intraocular lens or other structures. ''Pars plana'' vitrectomy is a general term for a group of operations accomplished in the deeper part of the eye, all of which involve removing some or all of the vitreous humor—the eye's clear internal jelly. Even before the modern era, some surgeons performed crude vitrectomies. For instance, Dutch surgeon Anton Nuck (1650–1692) claimed to have removed vitreous by suction in a young man with an inflamed eye. In Boston, John Collins Warren (1778–1856) performed a crude limited vitrectomy for angle closure glaucoma. Anesthesia for vitrectomy Options for anesthesia for vitrectomy are general anaesthesia, local anesthesia, topical anesthesia and intracameral lidocaine irrigation. Each anesthesia techn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vitreous Humour
The vitreous body (''vitreous'' meaning "glass-like"; , ) is the clear gel that fills the space between the lens and the retina of the eyeball (the vitreous chamber) in humans and other vertebrates. It is often referred to as the vitreous humor (also spelled humour, from Latin meaning liquid) or simply "the vitreous". Vitreous fluid or "liquid vitreous" is the liquid component of the vitreous gel, found after a vitreous detachment. It is not to be confused with the aqueous humor, the other fluid in the eye that is found between the cornea and lens. Structure The vitreous humor is a transparent, colorless, gelatinous mass that fills the space in the eye between the lens and the retina. It is surrounded by a layer of collagen called the vitreous membrane (or hyaloid membrane or vitreous cortex) separating it from the rest of the eye. It makes up four-fifths of the volume of the eyeball. The vitreous humour is fluid-like near the centre, and gel-like near the edges. The vitreous h ... [...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 that affected individuals see persistent flickering white, black, transparent, or coloured dots across the whole visual field. Other common symptoms are palinopsia, enhanced entoptic phenomena, photophobia, and headaches. The condition is typically always present and has no known cure, as viable treatments are still under research. Migraine and tinnitus are common comorbidities and are both associated with a more severe presentation of the syndrome. The cause of the syndrome is unclear. The underlying mechanism is believed to involve excessive excitability of neurons in the right lingual gyrus and left anterior lobe of cerebellum. Another hypothesis proposes that visual snow syndrome could be a type of thalamocortical dysrhythmia and may involve the thalamic reticular nucleus (TRN). A failure of inhibitory action from the TRN to the thalamus may be the underlying cause for inabilit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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] |
Computer Graphics
Computer graphics deals with generating images with the aid of computers. Today, computer graphics is a core technology in digital photography, film, video games, cell phone and computer displays, and many specialized applications. A great deal of specialized hardware and software has been developed, with the displays of most devices being driven by computer graphics hardware. It is a vast and recently developed area of computer science. The phrase was coined in 1960 by computer graphics researchers Verne Hudson and William Fetter of Boeing. It is often abbreviated as CG, or typically in the context of film as computer generated imagery (CGI). The non-artistic aspects of computer graphics are the subject of computer science research. Some topics in computer graphics include user interface design, sprite graphics, rendering, ray tracing, geometry processing, computer animation, vector graphics, 3D modeling, shaders, GPU design, implicit surfaces, visualization, scientific c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Noise (video)
Noise, commonly known as static, white noise, static noise, or snow, in analog video and television, is a random dot pixel pattern of static displayed when no transmission signal is obtained by the antenna receiver of television sets and other display devices. Description The random pixel pattern is superimposed on the picture or the television screen, being visible as a random flicker of "dots", "snow" or "fuzzy zig-zags" in some television sets, is the result of electronic noise and radiated electromagnetic noise accidentally picked up by the antenna like air or cable. This effect is most commonly seen with analog TV sets, blank VHS tapes, or other display devices. There are many sources of electromagnetic noise which cause the characteristic display patterns of static. Atmospheric sources of noise are the most ubiquitous, and include electromagnetic signals prompted by cosmic microwave background radiation In Big Bang cosmology the cosmic microwave background (CMB, CMB ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visual Field
The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a point. The equivalent concept for optical instruments and image sensors is the field of view (FOV). In optometry, ophthalmology, and neurology, a visual field test is used to determine whether the visual field is affected by diseases that cause local scotoma or a more extensive loss of vision or a reduction in sensitivity (increase in threshold). Normal limits The normal (monocular) human visual field extends to approximately 60 degrees nasally (toward the nose, or inward) from the vertical meridian in each eye, to 107 degrees temporally (away from the nose, or outwards) from the vertical meridian, and approximately 70 degrees above and 80 below the horizontal meridian. The binocular visual field is the superimposition of the two monocular ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Illusion
Within visual perception, an optical illusion (also called a visual illusion) is an illusion caused by the visual system and characterized by a visual perception, percept that arguably appears to differ from reality. Illusions come in a wide variety; their categorization is difficult because the underlying cause is often not clear but a classification proposed by Richard Gregory is useful as an orientation. According to that, there are three main classes: physical, physiological, and cognitive illusions, and in each class there are four kinds: Ambiguities, distortions, paradoxes, and fictions. A classical example for a physical distortion would be the apparent bending of a stick half immerged in water; an example for a physiological paradox is the motion aftereffect (where, despite movement, position remains unchanged). An example for a physiological fiction is an afterimage. Three typical cognitive distortions are the Ponzo illusion, Ponzo, Poggendorff illusion, Poggendorff, an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Palinopsia
Palinopsia (Greek: ''palin'' for "again" and ''opsia'' for "seeing") is the persistent recurrence of a visual image after the stimulus has been removed. Palinopsia is not a diagnosis; it is a diverse group of pathological visual symptoms with a wide variety of causes. Visual perseveration is synonymous with palinopsia. In 2014, Gersztenkorn and Lee comprehensively reviewed all cases of palinopsia in the literature and subdivided it into two clinically relevant groups: illusory palinopsia and hallucinatory palinopsia. Hallucinatory palinopsia, usually due to seizures or posterior cortical lesions, describes afterimages that are formed, long-lasting, and high resolution. Illusory palinopsia, usually due to migraines, head trauma, prescription drugs, visual snow or hallucinogen persisting perception disorder (HPPD), describes afterimages that are affected by ambient light and motion and are unformed, indistinct, or low resolution. Presentation People with palinopsia frequently repor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception. The retina serves a function which is in many ways analogous to that of the film or image sensor in a camera. The neural retina consists of several layers of neurons interconnected by synapses and is supported by an outer layer of pigmented epithelial cells. The primary light-sensing cells in the retina are the photoreceptor cells, which are of two types: rods and cones. Rods function mainly in dim light and provide monochromatic vision. Cones function in well-lit conditions and are responsible for the perception of colour through the use of a range of opsins, as well as high-acuity vision used for task ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
