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Retina
Right human eye cross-sectional view. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain Courtesy NIH National Eye Institute. "NIH" redirects here For other meanings of NIH see NIH (disambiguation. The National Eye Institute (NEI is one of the US National Institutes of Health that was established in 1968. Many animals have eyes different from the human eye.
Gray's subject #225 1014
Artery central retinal artery
MeSH Retina
Dorlands/Elsevier r_10/12705919

The vertebrate retina is a light sensitive part inside the inner layer of the eye. the Peripheral organs of the Special senses the organs of Taste ( Peripheral gustatory or Arteries are Blood vessels that carry blood away from the Heart. The central retinal artery ( retinal artery) branches off the Ophthalmic artery, running inferior to the Optic nerve within its dural sheath to Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and books Elsevier, the world's largest Publisher of Medical and Scientific literature, forms part of the Reed Elsevier group Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain Two of its three types of photoreceptor cells, rods and cones, receive light and transform it into image-forming signals which are transmitted through the optic nerve to the brain. A photoreceptor, or photoreceptor cell, is a specialized type of Neuron (nerve cell found in the Eye 's Retina that is capable of Rod cells, or rods, are Photoreceptor cells in the Retina of the Eye that can function in less intense Light than can the other type Cone cells, or cones, are Photoreceptor cells in the Retina of the Eye which function best in relatively bright Light. The optic nerve, also called cranial nerve II, is the Nerve that transmits visual information from the Retina to the Brain. The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain In this respect, the retina is comparable to the film in a camera.

The third and more recently discovered category of photosensitive cells is probably not involved in image-forming vision. Photosensitive ganglion cells, or melanopsin-containing ganglion cells, are a recently discovered type of nerve cell in the Retina of the mammalian These are a small proportion, about 2% in humans, of the retina's ganglion cells, themselves photosensitive through the photopigment melanopsin, which transmit information about light through the RHT (retinohypothalamic tract) directly to the SCN (suprachiasmatic nucleus) and other brain structures. Melanopsin is a Photopigment found in specialized Photosensitive ganglion cells of the Retina that are involved in the regulation of Circadian rhythms The Retinohypothalamic tract (RHT is a photic input pathway involved in Circadian rhythms. The suprachiasmatic nucleus ( SCN) is a bilateral region of the brain located in the Hypothalamus, that is responsible for controlling endogenous Circadian rhythms Signals from these ganglion cells are used to adjust the size of the pupil, entrain the body's circadian rhythms and acutely suppress the pineal hormone melatonin, processes which in fact function in many blind people who do not have functioning rods and cones. In Chronobiology, entrainment of a Circadian system is the alignment of its own period and phase to the period and phase of an external rhythm The pineal gland (also called the pineal body, epiphysis cerebri, or epiphysis) is a small endocrine gland in the vertebrate Brain Melatonin is a naturally occurring Hormone found in most animals including humans and some other living organisms including Algae.

While rods and cones respond maximally to wavelengths around 555 nanometers (green), the light sensitive ganglion cells respond maximally to about 480nm (blue-violet). There are several different photopigments involved.

Neural signals from the rods and cones undergo complex processing by other neurons of the retina. Neurons (ˈnjuːɹɒn also known as neurones and nerve cells) are responsive cells in the Nervous system that process and transmit information The output takes the form of action potentials in retinal ganglion cells whose axons form the optic nerve. In Neurophysiology, the action potential is a self-regenerating Wave of Electrochemical activity that allows Nerve cells to carry a signal An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell The optic nerve, also called cranial nerve II, is the Nerve that transmits visual information from the Retina to the Brain. Several important features of visual perception can be traced to the retinal encoding and processing of light. In Psychology, visual perception is the ability to interpret information from Visible light reaching the Eyes The resulting Perception is also

In vertebrate embryonic development, the retina and the optic nerve originate as outgrowths of the developing brain. Embryogenesis is the process by which the Embryo is formed and develops The optic nerve, also called cranial nerve II, is the Nerve that transmits visual information from the Retina to the Brain. The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain Hence, the retina is part of the central nervous system (CNS). In Vertebrates the central nervous system ( CNS) is the part of the Nervous system which is enclosed in the Meninges. It is the only part of the CNS that can be imaged directly.

The unique structure of the blood vessels in the retina has been used for biometric identification. The blood vessels are part of the Circulatory system and function to transport Blood throughout the body A retinal scan is a Biometric technique that uses the unique patterns on a person's Retina to identify them

Contents

Anatomy of vertebrate retina

Section of retina.
Section of retina.

The vertebrate retina has ten distinct layers. [1] From innermost to outermost, they include:

  1. Inner limiting membrane - Müller cell footplates
  2. Nerve fiber layer
  3. Ganglion cell layer - Layer that contains nuclei of ganglion cells and gives rise to optic nerve fibers. The inner limiting membrane is the boundary between the Retina and the Vitreous body, formed by Astrocytes and the end feet of Müller cells The Retinal nerve fiber layer ( nerve fibre layer, stratum opticum, RNFL) is formed by the expansion of the fibers of the Optic nerve The ganglion cell layer ( ganglionic layer) consists of a single layer of large Ganglion cells except in the Macula lutea, where there are several strata
  4. Inner plexiform layer
  5. Inner nuclear layer
  6. Outer plexiform layer - In the macular region, this is known as the Fiber layer of Henle. The inner plexiform layer is made up of a dense reticulum of minute Fibrils formed by the interlacement of the Dendrites of the Ganglion cells with those The inner nuclear layer or layer of inner granules is made up of a number of closely packed cells of which there are three varieties viz The outer plexiform layer ( external plexiform layer) is a layer of neuronal synapses in the Retina of the Eye. The macula or macula lutea (from Latin macula, "spot" + lutea, "yellow" is an oval Yellow spot near the center
  7. Outer nuclear layer
  8. External limiting membrane - Layer that separates the inner segment portions of the photoreceptors from their cell nuclei. The outer nuclear layer (or layer of outer granules or external nuclear layer) like the Inner nuclear layer, contains several strata of oval nuclear bodies In the outer nuclear layer they form a network around the rod- and cone-fibrils and unite to form the external limiting membrane (or outer limiting membrane) at the bases of
  9. Photoreceptor layer - Rods / Cones
  10. Retinal pigment epithelium

Physical structure of human retina

In adult humans the entire retina is 72% of a sphere about 22 mm in diameter. The elements composing the Layer of Rods and Cones ( Jacob’s membrane) are of two kinds Rod cells and Cone cells the former being much more numerous than Rod cells, or rods, are Photoreceptor cells in the Retina of the Eye that can function in less intense Light than can the other type Cone cells, or cones, are Photoreceptor cells in the Retina of the Eye which function best in relatively bright Light. The retinal pigment epithelium ( RPE) is the Pigmented cell layer just outside the neurosensory Retina that nourishes retinal visual cells and is firmly An area of the retina is the optic disc, sometimes known as "the blind spot" because it lacks photoreceptors. The optic disc or optic nerve head is the location where Ganglion cell axons exit the Eye to form the Optic nerve. It appears as an oval white area of 3 mm². Temporal (in the direction of the temples) to this disc is the macula. The macula or macula lutea (from Latin macula, "spot" + lutea, "yellow" is an oval Yellow spot near the center At its center is the fovea, a pit that is most sensitive to light and is responsible for our sharp central vision. The fovea, also known as the fovea centralis, is a part of the Eye, located in the center of the Macula region of the Retina. Human and non-human primates possess one fovea as opposed to certain bird species such as hawks who actually are bifoviate and dogs and cats who possess no fovea but a central band known as the visual streak. A primate is a member of the biological order Primates ( Latin: "prime first rank" the group that contains Lemurs the Aye-aye Around the fovea extends the central retina for about 6 mm and then the peripheral retina. The edge of the retina is defined by the ora serrata. The ora serrata is the serrated junction between the Retina and the Ciliary body. The length from one ora to the other (or macula), the most sensitive area along the horizontal meridian is about 3. 2 mm.

Retina's simplified axial organization. The retina is a stack of several neuronal layers. Light is concentrated from the eye and passes across these layers (from left to right) to hit the photoreceptors (right layer). This elicits chemical transformation mediating a propagation of signal to the bipolar and horizontal cells (middle yellow layer). The signal is then propagated to the amacrine and ganglion cells. These neurons ultimately may produce action potentials on their axons. This spatiotemporal pattern of spikes determines the raw input from the eyes to the brain. (Modified from a drawing by Ramón y Cajal.)
Retina's simplified axial organization. The retina is a stack of several neuronal layers. Light is concentrated from the eye and passes across these layers (from left to right) to hit the photoreceptors (right layer). This elicits chemical transformation mediating a propagation of signal to the bipolar and horizontal cells (middle yellow layer). The signal is then propagated to the amacrine and ganglion cells. These neurons ultimately may produce action potentials on their axons. This spatiotemporal pattern of spikes determines the raw input from the eyes to the brain. (Modified from a drawing by Ramón y Cajal. Santiago Ramón y Cajal ( May 1 1852 &ndash October 17 1934) was a Spanish histologist, Physician, and )

In section the retina is no more than 0. 5 mm thick. It has three layers of nerve cells and two of synapses. A nerve is an enclosed cable-like bundle of peripheral Axons (the long slender projections of Neurons. Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands The optic nerve carries the ganglion cell axons to the brain and the blood vessels that open into the retina. A ganglion cell (more correctly a retinal ganglion cell or RGC) is a type of Neuron typically located near the inner surface of the Retina An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell As a byproduct of evolution, the ganglion cells lie innermost in the retina while the photoreceptive cells lie outermost. eVolution is the third Album by eLDee, it was due to be released in 2008 Because of this arrangement, light must first pass through the thickness of the retina before reaching the rods and cones. However it does not pass through the epithelium or the choroid (both of which are opaque). In biology and medicine epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body The choroid, also known as the choroidea or choroid coat, is the vascular layer of the Eye lying between the Retina and the Sclera

The white blood cells in the capillaries in front of the photoreceptors can be perceived as tiny bright moving dots when looking into blue light. Capillaries are the smallest of a body's Blood vessels measuring 5-10 μm in diameter which connect Arterioles and Venules and enable the interchange This is known as the blue field entoptic phenomenon (or Scheerer's phenomenon). The blue field Entoptic phenomenon or Scheerer's phenomenon is the appearance of tiny bright dots moving quickly along squiggly lines in the visual field especially

Between the ganglion cell layer and the rods and cones there are two layers of neuropils where synaptic contacts are made. Neuropil consists of unmyelinated neuronal processes (axonal and dendritic within the gray matter of the central nervous system The neuropil layers are the outer plexiform layer and the inner plexiform layer. The outer plexiform layer ( external plexiform layer) is a layer of neuronal synapses in the Retina of the Eye. The inner plexiform layer is made up of a dense reticulum of minute Fibrils formed by the interlacement of the Dendrites of the Ganglion cells with those In the outer the rod and cones connect to the vertically running bipolar cells and the horizontally oriented horizontal cells connect to ganglion cells.

The central retina is cone-dominated and the peripheral retina is rod-dominated. In total there are about seven million cones and a hundred million rods. At the centre of the macula is the foveal pit where the cones are smallest and in a hexagonal mosaic, the most efficient and highest density. Below the pit the other retina layers are displaced, before building up along the foveal slope until the rim of the fovea or parafovea which is the thickest portion of the retina. The macula has a yellow pigmentation from screening pigments and is known as the macula lutea.

Vertebrate and cephalopod retina differences

The vertebrate retina is inverted in the sense that the light sensing cells sit at the back side of the retina, so that light has to pass through a layer of neurons before it reaches the rods and cones. By contrast, the cephalopod retina is everted: the photoreceptors are located at the front side of the retina, with processing neurons behind them. The cephalopods ( Greek plural (kephalópoda "head-feet" are the Mollusc class Cephalopoda characterized by Because of this, cephalopods do not have a blind spot.

The cephalopod retina does not originate as an outgrowth of the brain, as the vertebrate one does. This shows that vertebrate and cephalopod eyes are not homologous but have evolved separately. In Evolutionary biology, homology has come to mean any similarity between characters that is due to their shared ancestry.

Physiology

An image is produced by the "patterned excitation" of the cones and rods in the retina. The excitation is processed by the neuronal system and various parts of the brain working in parallel to form a representation of the external environment in the brain.

The cones respond to bright light and mediate high-resolution vision and colour vision. The rods respond to dim light and mediate lower-resolution, black-and-white, night vision. It is a lack of cones sensitive to red, blue, or green light that causes individuals to have deficiencies in colour vision or various kinds of colour blindness. Color blindness, a Color vision deficiency is the inability to perceive differences between some of the Colors that others can distinguish Humans and old world monkeys have three different types of cones (trichromatic vision) while other mammals lack cones with red sensitive pigment and therefore have poorer (dichromatic) colour vision. Trichromacy is the condition of possessing three independent channels for conveying Color information derived from the three different cone types

When light falls on a receptor it sends a proportional response synaptically to bipolar cells which in turn signal the retinal ganglion cells. A bipolar cell is a type of Neuron which has two extensions Bipolar cells are specialized sensory neurons for the transmission of special senses The receptors are also 'cross-linked' by horizontal cells and amacrine cells, which modify the synaptic signal before the ganglion cells. Horizontal cells are the laterally interconnecting neurons in the outer plexiform layer of the Retina of mammalian eyes Amacrine cells are Interneurons in the Retina. Amacrine cells are responsible for 70% of input to retinal ganglion cells Rod and cone signals are intermixed and combine, although rods are mostly active in very poorly lit conditions and saturate in broad daylight, while cones function in brighter lighting because they are not sensitive enough to work at very low light levels. In Colorimetry and Color theory, colorfulness, chroma, and saturation are related but distinct concepts referring to the perceived intensity

Despite the fact that all are nerve cells, only the retinal ganglion cells and few amacrine cells create action potentials. In the photoreceptors, exposure to light hyperpolarizes the membrane in a series of graded shifts. The outer cell segment contains a photopigment. Photopigments are unstable pigments that undergo a chemical change Inside the cell the normal levels of cGMP keeps the Na+ channel open and thus in the resting state the cell is depolarised. The photon causes the retinal bound to the receptor protein to isomerise to trans-retinal. Retinal, technically called retinene1 or retinaldehyde, is a light-sensitive Retinene molecule found in the Photoreceptor cells of This article is about the chemical concept For "isomerism" of atomic nuclei see Nuclear isomer. Retinal, technically called retinene1 or retinaldehyde, is a light-sensitive Retinene molecule found in the Photoreceptor cells of This causes receptor to activate multiple G-proteins. GTP chemical structurepng|thumb|180px| Guanosine triphosphate]] G proteins short for guanine nucleotide-binding proteins, are a family of Proteins involved This in turn causes the Ga-subunit of the protein to bind and degrade cGMP inside the cell which then cannot bind to the CNG Na+ channels. Thus the cell is hyperpolarised. The amount of neurotransmitter released is reduced in bright light and increases as light levels fall. The actual photopigment is bleached away in bright light and only replaced as a chemical process, so in a transition from bright light to darkness the eye can take up to thirty minutes to reach full sensitivity (see dark adaptation). In ocular physiology adaptation is the ability of the Eye to adjust to various levels of darkness and light

In the retinal ganglion cells there are two types of response, depending on the receptive field of the cell. The receptive field of a sensory Neuron is a region of space in which the presence of a stimulus will alter the firing of that neuron The receptive fields of retinal ganglion cells comprise a central approximately circular area, where light has one effect on the firing of the cell, and an annular surround, where light has the opposite effect on the firing of the cell. In ON cells, an increment in light intensity in the centre of the receptive field causes the firing rate to increase. In OFF cells, it makes it decrease. In a linear model, this response profile is well described by a Difference of Gaussians and is the basis for edge detection algorithms. In Computer vision, Difference of Gaussians is a Grayscale image enhancement algorithm that involves the subtraction of one blurred version of an original grayscale Edge detection is a terminology in Image processing and Computer vision, particularly in the areas of feature detection and Feature extraction Beyond this simple difference ganglion cells are also differentiated by chromatic sensitivity and the type of spatial summation. Cells showing linear spatial summation are termed X cells (also called "parvocellular", "P", or "midget" ganglion cells), and those showing non-linear summation are Y cells (also called "magnocellular, "M", or "parasol" retinal ganglion cells), although the correspondence between X and Y cells (in the cat retina) and P and M cells (in the primate retina) is not as simple as it once seemed.

In the transfer of visual signals to the brain, the visual pathway, the retina is vertically divided in two, a temporal (nearer to the temple) half and a nasal (nearer to the nose) half. The visual system is the part of the Nervous system which allows organisms to see. The axons from the nasal half cross the brain at the optic chiasma to join with axons from the temporal half of the other eye before passing into the lateral geniculate body. The optic chiasm ( Greek χίασμα "crossing" from the Greek χλαζειν 'to mark with an X' after the Greek letter ' Χ ' chi) is the The lateral geniculate nucleus ( LGN) of the Thalamus is a part of the Brain, which is the primary processor of visual information received from the

Although there are more than 130 million retinal receptors, there are only approximately 1. 2 million fibres (axons) in the optic nerve; a large amount of pre-processing is performed within the retina. The fovea produces the most accurate information. Despite occupying about 0. 01% of the visual field (less than 2° of visual angle), about 10% of axons in the optic nerve are devoted to the fovea. The visual angle is the angle a viewed object subtends at the eye usually stated in degrees of arc The resolution limit of the fovea has been determined at around 10,000 points. The information capacity is estimated at 500,000 bits per second (for more information on bits, see information theory) without colour or around 600,000 bits per second including colour. Information theory is a branch of Applied mathematics and Electrical engineering involving the quantification of Information.

Spatial Encoding

On-centers and off-centers of the retina
On-centers and off-centers of the retina

The retina, unlike a camera, does not simply send a picture to the brain. The retina spatially encodes (compresses) the image to fit the limited capacity of the optic nerve. Compression is necessary because there are 100 times more Photoreceptor cells than ganglion cells as mentioned above. A photoreceptor, or photoreceptor cell, is a specialized type of Neuron (nerve cell found in the Eye 's Retina that is capable of The retina does so by "decorrelating" the incoming images in a manner to be described below. Decorrelation is a general term for any process that is used to reduce Autocorrelation within a signal or Cross-correlation within a set of signals while preserving These operations are carried out by the center surround structures as implemented by the bipolar and ganglion cells.

There are two types of center surround structures in the retina -- on-centers and off-centers. On-centers have a positively weighted center and a negatively weighted surround. Off-centers are just the opposite. Positive weighting is more commonly known as excitatory and negative weighting is more commonly known as inhibitory. Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands

These center surround structures are not physical in the sense that you cannot see them by staining samples of tissue and examining the retina's anatomy. The center surround structures are logical (i. e. , mathematically abstract) in the sense that they depend on the connection strengths between ganglion and bipolar cells. It is believed that the connection strengths between cells is caused by the number and types of ion channels embedded in the synapses between the ganglion and bipolar cells. Ion channels are pore-forming Proteins that help establish and control the small Voltage Gradient across the Plasma membrane of all living Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands Stephen Kuffler in the 1950s was the first person to begin to understand these center surround structures in the retina of cats. Stephen William Kuffler ( August 24, 1913 &ndash October 11, 1980) was an preeminent Hungarian-American Neurophysiologist. See Receptive field for figures and more information on center surround structures. The receptive field of a sensory Neuron is a region of space in which the presence of a stimulus will alter the firing of that neuron See chapter 3 of David Hubel's on-line book (listed below) for an excellent introduction. David Hunter Hubel (born February 27, 1926) was co-recipient with Torsten Wiesel of the 1981 Nobel Prize in Physiology or Medicine, for their

The center surround structures are mathematically equivalent to the edge detection algorithms used by computer programmers to extract or enhance the edges in a digital photograph. Edge detection is a terminology in Image processing and Computer vision, particularly in the areas of feature detection and Feature extraction Thus the retina performs operations on the image to enhance the edges of objects within its visual field. For example, in a picture of a dog, a cat and a car, it is the edges of these objects that contain the most information. In order for higher functions in the brain (or in a computer for that matter) to extract and classify objects such as a dog and a cat, the retina is the first step to separating out the various objects within the scene.

As an example, the following matrix is at the heart of the computer algorithm that implements edge detection. In Mathematics, a matrix (plural matrices) is a rectangular table of elements (or entries) which may be Numbers or more generally In Mathematics, Computing, Linguistics and related subjects an algorithm is a sequence of finite instructions often used for Calculation This matrix is the computer equivalent to the center surround structure. In this example, each box (element) within this matrix would be connected to one photoreceptor. The photoreceptor in the center is the current receptor being processed. The center photoreceptor is multiplied by the +1 weight factor. The surrounding photoreceptors are the "nearest neighbors" to the center and are multiplied by the -1/8 value. The sum of all nine of these elements is finally calculated. This summation is repeated for every photoreceptor in the image by shifting left to the end of a row and then down to the next line.

The total sum of this matrix is zero if all the inputs from the nine photoreceptors are the same value. The zero result indicates the image was uniform (non-changing) within this small patch. Negative or positive sums mean something was varying (changing) within this small patch of nine photoreceptors.

-1/8 -1/8 -1/8
-1/8 +1 -1/8
-1/8 -1/8 -1/8

The above matrix is only an approximation to what really happens inside the retina. First, the above example is called "balanced". The term balanced means that the sum of the negative weights is equal to the sum of the positive weights so that they cancel out perfectly. Retinal ganglion cells are almost never perfectly balanced. Second, the table is square while the center surround structures in the retina are circular. Third, neurons operate on spike trains traveling down nerve cell axons. An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell Computers operate on a single number that is essentially constant from each input pixel. In Digital imaging, a pixel ( pict ure el ement is the smallest piece of information in an image (The computer pixel is basically the equivalent of a biological photoreceptor. ) Fourth, the retina performs all these calculations in parallel while the computer operates on each pixel one at a time. There are no repeated summations and shifting as there would be in a computer. Finally, the horizontal and amacrine cells play a significant role in this process but that is not represented here. Horizontal cells are the laterally interconnecting neurons in the outer plexiform layer of the Retina of mammalian eyes Amacrine cells are Interneurons in the Retina. Amacrine cells are responsible for 70% of input to retinal ganglion cells

Here is an example of an input image and how edge detection would modify it.

Image:Edge-detection-2.jpg

Once the image is spatially encoded by the center surround structures, the signal is sent out the optical nerve (via the axons of the ganglion cells) through the optic chiasm to the LGN (lateral geniculate nucleus). The optic chiasm ( Greek χίασμα "crossing" from the Greek χλαζειν 'to mark with an X' after the Greek letter ' Χ ' chi) is the The lateral geniculate nucleus ( LGN) of the Thalamus is a part of the Brain, which is the primary processor of visual information received from the The exact function of the LGN is unknown at this time. The output of the LGN is then sent to the back of the brain. Specifically the output of the LGN "radiates" out to the V1 Primary visual cortex. The term visual cortex refers to the primary visual cortex (also known as striate cortex or


Simplified Signal Flow: Photoreceptors ==> Bipolor ==> Ganglion ==> Chiasm ==> LGN ==> V1 cortex


Diseases and disorders

Main article: List of eye diseases and disorders

There are many inherited and acquired diseases or disorders that may affect the retina. This is a partial list of human Eye diseases and disorders. The World Health Organization publishes a classification of known diseases and injuries called the Some of them include:

Diagnosis and treatment

A number of different instruments are available for the diagnosis of diseases and disorders affecting the retina. An ophthalmoscope is used to examine the retina. The ophthalmoscope (or funduscope) is an instrument used to examine the Eye. Recently, adaptive optics has been used to image individual rods and cones in the living human retina. Adaptive optics (AO is a Technology used to improve the performance of optical systems by reducing the effects of rapidly changing optical distortion

The electroretinogram is used to measure non-invasively the retina's electrical activity, which is affected by certain diseases. Electroretinography measures the electrical responses of various cell types in the Retina, including the photoreceptors ( rods and cones) The term non-invasive in Medicine has two meanings A Medical procedure which does not penetrate mechanically, nor break the Skin A relatively new technology, now becoming widely available, is optical coherence tomography (OCT). Optical coherence tomography (OCT is an optical signal acquisition and processing method allowing extremely high-quality micrometre-resolution three-dimensional images from within optical This non-invasive technique allows one to obtain a 3D volumetric or high resolution cross-sectional tomogram of the retinal fine structure with histologic-quality. In mathematics the dimension of a Space is roughly defined as the minimum number of Coordinates needed to specify every point within it Tomography is imaging by sections or sectioning A device used in tomography is called a tomograph, while the image produced is a tomogram. Histology (from the Greek = 'tissue' is the study of the microscopic anatomy of cells and tissues of Plants and

OCT scan of a retina at 800nm with an axial resolution of 3µm
OCT scan of a retina at 800nm with an axial resolution of 3µm

Treatment depends upon the nature of the disease or disorder. Transplantation of retinas has been attempted, but without much success. At MIT, The University of Southern California, and the University of New South Wales, an "artificial retina" is under development: an implant which will bypass the photoreceptors of the retina and stimulate the attached nerve cells directly, with signals from a digital camera. The University of New South Wales, also known as UNSW or colloquially as New South, is a University situated in Kensington, a suburb in

Research

George Wald, Haldan Keffer Hartline and Ragnar Granit won the 1967 Nobel Prize in Physiology or Medicine for their scientific research on the retina. George Wald ( November 18, 1906 &ndash April 12, 1997) was an American Scientist who is best known for his work with pigments Haldan Keffer Hartline ( December 22, 1903 &ndash March 17, 1983) was an American physiologist who was a cowinner (with Ragnar Arthur Granit ( October 30, 1900, Vantaa, Finland &ndash March 12, 1991, Stockholm, Sweden Year 1967 ( MCMLXVII) was a Common year starting on Sunday (link will display full calendar of the 1967 Gregorian calendar. The Nobel Prize in Physiology or Medicine (Nobelpriset i fysiologi eller medicin is awarded once a year by the Swedish Karolinska Institute.

A recent University of Pennsylvania study calculated the approximate bandwidth of human retinas is 8. The University of Pennsylvania (also known as Penn) is a private University located in Philadelphia, Pennsylvania, USA. 75 megabits per second, whereas a guinea pig retinas transfer at 875 kilobits. The Guinea pig (also commonly called the cavy after its scientific name Cavia porcellus) is a species of Rodent belonging to the family Caviidae [2]

Robert MacLaren and colleagues at University College London and Moorfields Eye Hospital in London showed in 2006 that photoreceptor cells could be transplanted successfully in the mouse retina if donor cells were at a critical developmental stage. University College London ( UCL) is a multi-faculty university institution based in the United Kingdom and a constituent college of the University of London A photoreceptor, or photoreceptor cell, is a specialized type of Neuron (nerve cell found in the Eye 's Retina that is capable of [3]

References

  1. ^ The Retinal Tunic
  2. ^ Calculating the speed of sight - being-human - 28 July 2006 - New Scientist
  3. ^ Retinal repair by transplantation of photoreceptor precursors : Abstract : Nature

See also

External links

Technology Review is a magazine published by Technology Review Inc a media company owned by the Massachusetts Institute of Technology. The University of New South Wales, also known as UNSW or colloquially as New South, is a University situated in Kensington, a suburb in The University of Würzburg is a university in Würzburg, Germany, founded in 1402 The United States National Library of Medicine ( NLM) operated by the United States federal government, is the world's largest Medical library. The University of Utah (referred to locally as ' The U' or ' the U of U') is a publicly funded Research university in Salt Lake For similarly-named academic institutions see Education in Boston MA.

Dictionary

retina

-noun

  1. (anatomy) The thin layer of cells at the back of the eyeball where light is converted into neural signals sent to the brain.
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