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Congenital Stationary Night Blindness
Congenital stationary night blindness (CSNB) is a rare non-progressive retinal disorder. People with CSNB often have difficulty adapting to low light situations due to impaired photoreceptor transmission. These patients may also have reduced visual acuity, myopia, nystagmus, fundus abnormalities, and strabismus. CSNB has two forms -- complete, also known as type-1 (CSNB1), and incomplete, also known as type-2 (CSNB2), which are distinguished by the involvement of different retinal pathways. In CSNB1, downstream neurons called bipolar cells are unable to detect neurotransmission from photoreceptor cells. CSNB1 can be caused by mutations in various genes involved in neurotransmitter detection, including ''NYX''. In CSNB2, the photoreceptors themselves have impaired neurotransmission function; this is caused primarily by mutations in the gene '' CACNA1F'', which encodes a voltage-gated calcium channel important for neurotransmitter release. CSNB has been identified in horses and do ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Outer Nuclear Layer
The outer nuclear layer (or layer of outer granules or external nuclear layer), is one of the layers of the vertebrate retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ..., the light-detecting portion of the eye. Like the inner nuclear layer, the outer nuclear layer contains several strata of oval nuclear bodies; they are of two kinds, viz.: rod and cone granules, so named on account of their being respectively connected with the rods and cones of the next layer. Rod granules The spherical rod granules are much more numerous, and are placed at different levels throughout the layer. Their nuclei present a peculiar cross-striped appearance, and prolonged from either extremity of each cell is a fine process; the outer process is continuous with a single rod of the layer of rods a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Leopard Complex
The leopard complex is a group of genetically related Equine coat color, coat patterns in horses. These patterns range from progressive increases in interspersed white hair similar to Gray (horse), graying or Roan (horse), roan to distinctive, Dalmatian (dog), Dalmatian-like leopard (pattern), leopard spots on a white coat. Secondary characteristics associated with the leopard complex include a white sclera around the eye, striped horse hoof, hooves and mottling, mottled skin. The leopard complex gene is also linked to abnormalities in the eyes and vision. These patterns are most closely identified with the Appaloosa and Knabstrupper breeds, though its presence in breeds from Asia to western Europe has indicated that it is due to a very ancient mutation. Leopard complex patterns Coat patterns in the leopard complex range from being hardly distinguishable from an unaffected coat, to nearly pure white. Unlike most other Pinto horse, spotting patterns, the spotting and especially th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nyctalopia
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 hemeralo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schiff Base
In organic chemistry, a Schiff base (named after Hugo Schiff) is a compound with the general structure ( = alkyl or aryl, but not hydrogen). They can be considered a sub-class of imines, being either secondary ketimines or secondary aldimines depending on their structure. Anil refers to a common subset of Schiff bases: imines derived from anilines. The term can be synonymous with azomethine which refers specifically to secondary aldimines (i.e. where R' ≠ H). Synthesis Schiff bases can be synthesized from an aliphatic or aromatic amine and a carbonyl compound by nucleophilic addition forming a hemiaminal, followed by a dehydration to generate an imine. In a typical reaction, 4,4'-oxydianiline reacts with ''o''- vanillin: Schiff bases can also be synthesized via the Aza-Wittig reaction. Biochemistry Schiff bases have been investigated in relation to a wide range of contexts, including antimicrobial, antiviral and anticancer activity. They have also been con ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transmembrane Helix
A transmembrane domain (TMD, TM domain) is a membrane-spanning protein domain. TMDs may consist of one or several alpha-helices or a transmembrane beta barrel. Because the interior of the lipid bilayer is hydrophobic, the amino acid residues in TMDs are often hydrophobic, although proteins such as membrane pumps and ion channels can contain polar residues. TMDs vary greatly in size and hydrophobicity; they may adopt organelle-specific properties. Functions of transmembrane domains Transmembrane domains are known to perform a variety of functions. These include: * Anchoring transmembrane proteins to the membrane. *Facilitating molecular transport of molecules such as ions and proteins across biological membranes; usually hydrophilic residues and binding sites in the TMDs help in this process. *Signal transduction across the membrane; many transmembrane proteins, such as G protein-coupled receptors, receive extracellular signals. TMDs then propagate those signals across the mem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhodopsin
Rhodopsin, also known as visual purple, is a protein encoded by the ''RHO'' gene and a G-protein-coupled receptor (GPCR). It is a light-sensitive receptor protein that triggers visual phototransduction in rod cells. Rhodopsin mediates dim light vision and thus is extremely sensitive to light. When rhodopsin is exposed to light, it immediately photobleaches. In humans, it is fully regenerated in about 30 minutes, after which the rods are more sensitive. Defects in the rhodopsin gene cause eye diseases such as retinitis pigmentosa and congenital stationary night blindness. History Rhodopsin was discovered by Franz Christian Boll in 1876. The name rhodopsin derives from Ancient Greek () for "rose", due to its pinkish color, and () for "sight". It was coined in 1878 by the German physiologist Wilhelm Friedrich Kühne (1837–1900). When George Wald discovered that rhodopsin is a holoprotein, consisting of retinal and an apoprotein, he called it opsin, which tod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visual Phototransduction
Visual phototransduction is the sensory transduction process of the visual system by which light is detected by photoreceptor cells ( rods and cones) in the vertebrate retina. A photon is absorbed by a retinal chromophore (each bound to an opsin), which initiates a signal cascade through several intermediate cells, then through the retinal ganglion cells (RGCs) comprising the optic nerve. Overview Light enters the eye, passes through the optical media, then the inner neural layers of the retina before finally reaching the photoreceptor cells in the outer layer of the retina. The light may be absorbed by a chromophore bound to an opsin, which photoisomerizes the chromophore, initiating both the visual cycle, which "resets" the chromophore, and the phototransduction cascade, which transmits the visual signal to the brain. The cascade begins with graded polarisation (an analog signal) of the excited photoreceptor cell, as its membrane potential increases from a resting po ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electroretinogram
Electroretinography measures the electrical responses of various cell types in the retina, including the photoreceptors ( rods and cones), inner retinal cells ( bipolar and amacrine cells), and the ganglion cells. Electrodes are placed on the surface of the cornea (DTL silver/nylon fiber string or ERG jet) or on the skin beneath the eye (sensor strips) to measure retinal responses. Retinal pigment epithelium (RPE) responses are measured with an EOG test with skin-contact electrodes placed near the canthi. During a recording, the patient's eyes are exposed to standardized stimuli and the resulting signal is displayed showing the time course of the signal's amplitude (voltage). Signals are very small, and typically are measured in microvolts or nanovolts. The ERG is composed of electrical potentials contributed by different cell types within the retina, and the stimulus conditions (flash or pattern stimulus, whether a background light is present, and the colors of the stimulus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retinal Bipolar Cell
As a part of the retina, bipolar cells exist between photoreceptors (rod cells and cone cells) and ganglion cells. They act, directly or indirectly, to transmit signals from the photoreceptors to the ganglion cells. Structure Bipolar cells are so-named as they have a central body from which two sets of processes arise. They can synapse with either rods or cones (rod/cone mixed input BCs have been found in teleost fish but not mammals), and they also accept synapses from horizontal cells. The bipolar cells then transmit the signals from the photoreceptors or the horizontal cells, and pass it on to the ganglion cells directly or indirectly (via amacrine cells). Unlike most neurons, bipolar cells communicate via graded potentials, rather than action potentials. Function Bipolar cells receive synaptic input from either rods or cones, or both rods and cones, though they are generally designated rod bipolar or cone bipolar cells. There are roughly 10 distinct forms of cone bipolar c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cone Cell
Cone cells or cones are photoreceptor cells in the retina of the vertebrate eye. Cones are active in daylight conditions and enable photopic vision, as opposed to rod cells, which are active in dim light and enable scotopic vision. Most vertebrates (including humans) have several classes of cones, each sensitive to a different part of the visible spectrum of light. The comparison of the responses of different cone cell classes enables color vision. There are about six to seven million cones in a human eye (vs ~92 million rods), with the highest concentration occurring towards the macula and most densely packed in the fovea centralis, a diameter rod-free area with very thin, densely packed cones. Conversely, like rods, they are absent from the optic disc, contributing to the blind spot. Cones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of color. They are also able to perceive finer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rod Cell
Rod cells are photoreceptor cells in the retina of the eye that can function in lower light better than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in peripheral vision. On average, there are approximately 92 million rod cells (vs ~4.6 million cones) in the human retina. Rod cells are more sensitive than cone cells and are almost entirely responsible for night vision. However, rods have little role in color vision, which is the main reason why colors are much less apparent in dim light. Structure Rods are a little longer and leaner than cones but have the same basic structure. Opsin-containing disks lie at the end of the cell adjacent to the retinal pigment epithelium, which in turn is attached to the inside of the eye. The stacked-disc structure of the detector portion of the cell allows for very high efficiency. Rods are much more common than cones, with about 120 million rod cells ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hyperopia
Far-sightedness, also known as long-sightedness, hypermetropia, and hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blur is due to incoming light being focused behind, instead of on, the retina due to insufficient accommodation by the lens. Minor hypermetropia in young patients is usually corrected by their accommodation, without any defects in vision. But, due to this accommodative effort for distant vision, people may complain of eye strain during prolonged reading. If the hypermetropia is high, there will be defective vision for both distance and near. People may also experience accommodative dysfunction, binocular dysfunction, amblyopia, and strabismus. Newborns are almost invariably hypermetropic, but it gradually decreases as the newborn gets older. There are many causes for this condition. It may occur when the axial length of eyeball is too short or if the lens or cornea is flatter than normal. Cha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
