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A human eye
A human eye

Eyes are organs that detect light. Different kinds of light-sensitive organs are found in a variety of animals. The simplest eyes do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms but can hardly be called vision. More complex eyes can distinguish shapes and colors. The visual fields of some such complex eyes largely overlap, to allow better depth perception (binocular vision), as in humans; and others are placed so as to minimize the overlap, such as in rabbits and chameleons. Look up eye in Wiktionary, the free dictionary. ... Image File history File linksMetadata Download high-resolution version (2788x1864, 652 KB) Human eye. ... Image File history File linksMetadata Download high-resolution version (2788x1864, 652 KB) Human eye. ... This article is about modern humans. ... This article is about the biological unit. ... For other uses, see Light (disambiguation). ... For other uses, see Animal (disambiguation). ... Dark redirects here. ... 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, which in this context is called zeitgeber. ... The Circadian rhythm is a name given to the internal body clock that regulates the (roughly) 24 hour cycle of biological processes in animals and plants. ... Color is an important part of the visual arts. ... Look up vision in Wiktionary, the free dictionary. ... Depth perception is the visual ability to perceive the world in three dimensions. ... Binocular vision is vision in which both eyes are used synchronously to produce a single image. ... This article is about modern humans. ... For other uses, see Rabbit (disambiguation). ... For other uses, see Chameleon (disambiguation). ...

In the human eye, light enters the pupil and is focused on the retina by the lens. Light-sensitive nerve cells called rods (for brightness) and cones (for color) react to the light. They interact with each other and send messages to the brain that indicate brightness, color, and contour. Compound eye of a dragonfly. ... Compound eye of a dragonfly. ... Compound eye of a dragonfly A compound eye is a visual organ found in arthropods such as insects and crustaceans. ... This article is about the insect. ... 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 of photoreceptor, cone cells. ... Normalized responsivity spectra of human cone cells, S, M, and L types Cone cells, or cones, are photoreceptor cells in the retina of the eye which function best in relatively bright light. ...


The first proto-eyes evolved among animals 540 million years ago. Almost all animals have eyes, or descend from animals that did.


In most vertebrates and some mollusks, the eye works by allowing light to enter it and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for color) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals. The visual signals are then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and often an iris; the relaxing or tightening of the muscles around the iris change the size of the pupil, thereby regulating the amount of light that enters the eye,[1] and reducing aberrations when there is enough light.[2] This article does not cite any references or sources. ... Classes Caudofoveata Aplacophora Polyplacophora Monoplacophora Bivalvia Scaphopoda Gastropoda Cephalopoda † Rostroconchia The mollusks or molluscs are the large and diverse phylum Mollusca, which includes a variety of familiar creatures well-known for their decorative shells or as seafood. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... Human eye cross-sectional view. ... Normalized responsivity spectra of human cone cells, S, M, and L types Cone cells, or cones, are photoreceptor cells in the retina of the eye which function best in relatively bright light. ... 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 of photoreceptor, cone cells. ... For other uses, see Brain (disambiguation). ... This article is about the anatomical structure. ... Transparent glass ball In optics, transparency is the property of allowing light to pass. ... Vitreous humour is the clear aqueous solution that fills the space between the lens and the retina of the vertebrate eyeball. ... Light from a single point of a distant object and light from a single point of a near object being brought to a focus by changing the curvature of the lens. ... In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, including humans. ... The human eye The pupil is the central transparent area (showing as black). ...


The eyes of cephalopods, fish, amphibians and snakes usually have fixed lens shapes, and focusing vision is achieved by telescoping the lens—similar to how a camera focuses.[3] Orders Subclass Nautiloidea †Plectronocerida †Ellesmerocerida †Actinocerida †Pseudorthocerida †Endocerida †Tarphycerida †Oncocerida †Discosorida Nautilida †Orthocerida †Ascocerida †Bactritida Subclass †Ammonoidea †Goniatitida †Ceratitida †Ammonitida Subclass Coleoidea †Belemnoidea †Aulacocerida †Belemnitida †Hematitida †Phragmoteuthida Neocoleoidea (most living cephalopods) ?†Boletzkyida Sepiida Sepiolida Spirulida Teuthida Octopoda Vampyromorphida The cephalopods (Greek plural (kephalópoda); head-foot) are the mollusc class... For other uses, see Fish (disambiguation). ... ‹ The template below (Citations missing) is being considered for deletion. ... For other uses, see Snake (disambiguation). ... For other uses, see Camera (disambiguation). ...


Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the details of anatomy, may give either a single pixelated image or multiple images, per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors, which are arranged hexagonally, and which can give a full 360-degree field of vision. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an image, creating multiple-image vision. With each eye viewing a different angle, a fused image from all the eyes is produced in the brain, providing very wide-angle, high-resolution images. Compound eye of a dragonfly A compound eye is a visual organ found in arthropods such as insects and crustaceans. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ... Families Mengenillidae Mengeidae Stylopidae Bohartillidae Corioxenidae Halictophagidae Callipharixenidae Elenchidae Myrmecolacidae Species in the nine families of this small (~600 species) order of insects are parasites in other insects; their hosts include bees, wasps, leafhoppers, silverfish, and cockroaches. ...

Compound eye of Antarctic krill
Compound eye of Antarctic krill

Possessing detailed hyperspectral color vision, the Mantis shrimp has been reported to have the world's most complex color vision system.[4] Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods, which have soft eyes. The number of lenses in such an eye varied, however: some trilobites had only one, and some had thousands of lenses in one eye. Download high resolution version (1574x1505, 252 KB)Antarctic krill Euphausia superba (Photo by Gerd Alberti and Uwe Kils) GFDL goto large resolution File links The following pages link to this file: Scanning electron microscope Antarctic krill User talk:Jimbo Wales Eye Compound eye Image:Krilleyekils. ... Download high resolution version (1574x1505, 252 KB)Antarctic krill Euphausia superba (Photo by Gerd Alberti and Uwe Kils) GFDL goto large resolution File links The following pages link to this file: Scanning electron microscope Antarctic krill User talk:Jimbo Wales Eye Compound eye Image:Krilleyekils. ... Binomial name Dana, 1850 Antarctic krill are eaten by penguins(Euphausia superba) is a species of krill found in the Antarctic waters of the Southern Ocean. ... The term hyperspectral is found in military and remote sensing jargon and denotes, a sensor system observing a target in very different spectral bands, by different types of sensors, e. ... Suborders, superfamilies and families [1] Suborder Archaestomatopodea Tyrannophontidae† Suborder Unipeltata Bathysquilloidea Bathysquillidae Indosquillidae Gonodactyloidea Alainosquillidae Hemisquillidae Gonodactylidae Odontodactylidae Protosquillidae Pseudosquillidae Takuidae Erythrosquilloidea Erythrosquillidae Lysiosquilloidea Coronididae Lysiosquillidae Nannosquillidae Tetrasquillidae Squilloidea Squillidae Eurysquilloidea Eurysquillidae Parasquilloidea Parasquillidae Mantis shrimp or stomatopods are marine crustaceans belonging to the order Stomatopoda, one part of the... For the robot vacuum cleaner, see Electrolux Trilobite. ... Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico. ...


In contrast to compound eyes, simple eyes are those that have a single lens. For example, jumping spiders have a large pair of simple eyes with a narrow field of view, supported by an array of other, smaller eyes for peripheral vision. Some insect larvae, like caterpillars, have a different type of simple eye (stemmata) which gives a rough image. Some of the simplest eyes, called ocelli, can be found in animals like snails, who cannot actually "see" in the normal sense. They do have photosensitive cells, but no lens and no other means of projecting an image onto these cells. They can distinguish between light and dark, but no more. This enables snails to keep out of direct sunlight. Diversity 553 genera, 5025 species Genera See List of Salticidae genera The jumping spider family (Salticidae) contains more than 500 described genera and over 5,000 species, making it the largest family of spiders with about 13% of all species (Peng , 2002). ... The field of view is the part of the observable world that is seen at any given moment. ... Peripheral vision is a part of vision that occurs outside the very center of gaze. ... A larval insect A larva (Latin; plural larvae) is a juvenile form of animal with indirect development, undergoing metamorphosis (for example, insects or amphibians). ... This article is about a form of an insect. ... Stemma (pl. ... An ocellus (plural: ocelli) is a type of photoreceptor organ in animals. ... For other uses, see Snail (disambiguation). ... Photosensitivity is the amount to which an object reacts upon receiving photons of light. ... Prism splitting light High Resolution Solar Spectrum Sunlight in the broad sense is the total spectrum of the electromagnetic radiation given off by the Sun. ...

Contents

Evolution of eyes

Main article: Evolution of the eye
Diagram of major stages in the eye's evolution
Diagram of major stages in the eye's evolution

Biologists use the theory of evolution to explain the origin and development of eyes, as well as of organs in general. Diagram of major stages in the eyes evolution. ... Image File history File links Diagram_of_eye_evolution. ... Image File history File links Diagram_of_eye_evolution. ... This article is about evolution in biology. ...


The common origin (monophyly) of all animal eyes is established by shared anatomical and genetic features of all eyes; that is, all modern eyes, varied as they are, have their origins in a proto-eye evolved some 540 million years ago.[5][6][7] The majority of the advancements in early eyes are believed to have taken only a few million years to develop, as the first predator to gain true imaging would have touched off an "arms race",[8] or rather, a phylogenetic radiation from the species with that first proto-eye, among the descendents of which, there may well have been an "arms race". Prey animals and competing predators alike would be forced to rapidly match or exceed any such capabilities to survive. Hence multiple eye types and subtypes developed in parallel. In phylogenetics, a group is monophyletic (Greek: of one race) if it consists of an inferred common ancestor and all its descendants. ...


Vision in various animals shows adaptation to environmental requirements. For example, birds of prey have much greater visual acuity than humans, and some can see ultraviolet light. The different forms of eyes in, for example, vertebrates and mollusks are often cited as examples of parallel evolution, despite their distant common ancestry. Orders Accipitriformes     Cathartidae     Pandionidae     Accipitridae     Sagittariidae Falconiformes     Falconidae A bird of prey or raptor is a bird that hunts its food, especially one that preys on mammals or other birds. ... For other uses, see Ultraviolet (disambiguation). ... This article does not cite any references or sources. ... Classes Caudofoveata Aplacophora Polyplacophora Monoplacophora Bivalvia Scaphopoda Gastropoda Cephalopoda † Rostroconchia The mollusks or molluscs are the large and diverse phylum Mollusca, which includes a variety of familiar creatures well-known for their decorative shells or as seafood. ... Bee hovering in flight In evolutionary biology, parallel evolution refers to the independent evolution of similar traits in closely related lineages of species, while convergent evolution refers to the appearance of striking similarities among lineages of organisms only very distantly related. ...


The earliest "eyes", called eyespots, were light-sensitive proteins in unicellular organisms. In multicellular organisms, simple patches of photoreceptor cells are physically similar to the receptor patches for taste and smell. Eyespots can only sense ambient brightness: they can distinguish light and dark, but not the direction of the lightsource.[9] Thus, they are sufficient for synchronization of circadian rhythms and they enable a reaction such as turning toward or away from the light source, which from under water can mean the surface, for example. They are not sufficient for image-forming. A photoreceptor, or photoreceptor cell, is a specialized type of neuron found in the eyes retina that is capable of phototransduction. ... Low-key lighting is a style of lighting for film or television. ... A circadian rhythm is a roughly-24-hour cycle in the physiological processes of living beings, including plants, animals, fungi and cyanobacteria. ...


This gradually changed as the eyespot depressed into a shallow "cup" shape, granting the ability to slightly discriminate directional brightness by using the angle at which the light hit certain cells to identify the source. The pit deepened over time, the opening diminished in size, and the number of photoreceptor cells increased, forming an effective pinhole camera that was capable of slightly distinguishing dim shapes (for example in the nautilus).[10] Principle of a pinhole camera. ... Genera Allonautilus Nautilus Nautilus (from Greek ναυτίλος, sailor) is the common name of any marine creatures of the cephalopod family Nautilidae, the sole family of the suborder Nautilina. ...


The thin overgrowth of transparent cells over the eye's aperture, originally formed to prevent damage to the eyespot, allowed the segregated contents of the eye chamber to specialize into a transparent humour that optimized color filtering, blocked harmful radiation, improved the eye's refractive index, and allowed functionality outside of water. The transparent protective cells eventually split into two layers, with circulatory fluid in between that allowed wider viewing angles and greater imaging resolution, and the thickness of the transparent layer gradually increased, in most species with the transparent crystallin protein.[11] a big (1) and a small (2) aperture For other uses, see Aperture (disambiguation). ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... In biology, a crystallin is a water-soluble structural protein in the lens of the eye, which accounts for the transparency of the structure. ...


Anatomy of the mammalian eye

1. posterior compartment 2. ora serrata 3. ciliary muscle 4. ciliary zonules 5. canal of Schlemm 6. pupil 7. anterior chamber 8. cornea 9. iris 10. lens cortex 11. lens nucleus 12. ciliary process 13. conjunctiva 14. inferior oblique muscle 15. inferior rectus muscle 16. medial rectus muscle 17. retinal arteries and veins 18. optic disc 19. dura mater 20. central retinal artery 21. central retinal vein 22. optical nerve 23. vorticose vein 24. bulbar sheath 25. macula 26. fovea 27. sclera 28. choroid 29. superior rectus muscle 30. retina

posterior compartmentora serrataciliary muscleciliary zonulescanal of Schlemmpupilanterior chambercorneairislens cortexlens nucleusciliary processconjunctivainferior oblique musculeinferior rectus musculemedial rectus muscleretinal arteries and veinsoptic discdura matercentral retinal arterycentral retinal veinoptical nervevorticose veinbulbar sheathmaculafoveasclerachoroidsuperior rectus musculeretina
  1. posterior compartment
  2. ora serrata
  3. ciliary muscle
  4. ciliary zonules
  5. canal of Schlemm
  6. pupil
  7. anterior chamber
  8. cornea
  9. iris
  10. lens cortex
  11. lens nucleus
  12. ciliary process
  13. conjunctiva
  14. inferior oblique muscule
  15. inferior rectus muscule
  16. medial rectus muscle
  17. retinal arteries and veins
  18. optic disc
  19. dura mater
  20. central retinal artery
  21. central retinal vein
  22. optical nerve
  23. vorticose vein
  24. bulbar sheath
  25. macula
  26. fovea
  27. sclera
  28. choroid
  29. superior rectus muscule
  30. retina

Image File history File links No higher resolution available. ...

Dimensions

Dimensions vary only 1-2 mm among individuals. The vertical diameter is 24 mm; the transverse being larger. At birth is it generally 16-17 mm, enlarging to 22.5-23 mm by three years of age, between then and age 13 the eye attains its mature size. It weighs 7.5 grams and its volume 6.5 millilitres.


Three layers

The structure of the mammalian eye can be divided into three main layers or tunics whose names reflect their basic functions: the fibrous tunic, the vascular tunic, and the nervous tunic.[12][13][14] Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria For the folk-rock band see The Mammals. ... The sclera and cornea form the fibrous tunic of the bulb of the eye; the sclera is opaque, and constitutes the posterior five-sixths of the tunic; the cornea is transparent, and forms the anterior sixth. ... For the Pacific island, see Wallis Island. ... Human eye cross-sectional view. ...

  • The fibrous tunic, also known as the tunica fibrosa oculi, is the outer layer of the eyeball consisting of the cornea and sclera.[15] The sclera gives the eye most of its white color. It consists of dense connective tissue filled with the protein collagen to both protect the inner components of the eye and maintain its shape.[16]
  • The vascular tunic, also known as the tunica vasculosa oculi, is the middle vascularized layer which includes the iris, ciliary body, and choroid.[15][17][18] The choroid contains blood vessels that supply the retinal cells with necessary oxygen and remove the waste products of respiration. The choroid gives the inner eye a dark color, which prevents disruptive reflections within the eye. The iris is seen rather than the cornea when looking straight in one's eye due to the latter's transparency, the pupil (central aperture of iris) is black because there is no light reflected out of the interior eye. If an ophthalmoscope is used, one can see the fundus, as well as vessels especially those crossing the optic disk - the point where the optic nerve fibers depart from the eyeball - among others [19]
  • The nervous tunic, also known as the tunica nervosa oculi, is the inner sensory which includes the retina.[15][18] The retina contains the photosensitive rod and cone cells and associated neurons. To maximise vision and light absorption, the retina is a relatively smooth (but curved) layer. It has two points at which it is different; the fovea and optic disc. The fovea is a dip in the retina directly opposite the lens, which is densely packed with cone cells. It is largely responsible for color vision in humans, and enables high acuity, such as is necessary in reading. The optic disc, sometimes referred to as the anatomical blind spot, is a point on the retina where the optic nerve pierces the retina to connect to the nerve cells on its inside. No photosensitive cells exist at this point, it is thus "blind". In addition to the rods and cones, a small proportion (about 2% in humans) of the ganglion cells in the retina are photosensitive through the pigment melanopsin. They are generally most excitable by blue light, about 470 nm. Their information is sent to the SCN (suprachiasmatic nuclei), not to the visual center, through the retinohypothalamic tract which is formed as melanopsin-sensitive axons exit the optic nerve. It is these light signals which regulate circadian rhythms in mammals and several other animals.[20] Many, but not all, totally blind individuals have their circadian rhythms adjusted daily in this way.

The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ... Schematic diagram of the human eye. ... Connective tissue is one of the four types of tissue in traditional classifications (the others being epithelial, muscle, and nervous tissue. ... Tropocollagen triple helix. ... In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, including humans. ... Schematic diagram of the human eye The ciliary body is the part of the eye containing the ciliary muscle and ciliary processes. ... The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye lying between the retina and the sclera. ... f you all The blood vessels are part of the circulatory system and function to transport blood throughout the body. ... This article is about the chemical element and its most stable form, or dioxygen. ... Cellular respiration was discovered by mad scientist Mr. ... The human eye The pupil is the central transparent area (showing as black). ... Example of eye fundus image The fundus of the eye is the interior surface of the eye, opposite the lens, and includes the retina, optic disc, macula, and posterior pole. ... Human eye cross-sectional view. ... 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 of photoreceptor, cone cells. ... Normalized responsivity spectra of human cone cells, S, M, and L types Cone cells, or cones, are photoreceptor cells in the retina of the eye which function best in relatively bright light. ... Schematic diagram of the human eye, with the fovea at the bottom. ... The optic disc or optic nerve head is the location where ganglion cell axons exit the eye to form the optic nerve. ... Color vision is the capacity of an organism or machine to distinguish objects based on the wavelengths (or frequencies) of the light they reflect or emit. ... Reading is a process of retrieving and comprehending some form of stored information or ideas. ... For other uses, see Blind spot. ... Human eye cross-sectional view. ... This article is about the anatomical structure. ... Melanopsin is a photopigment found in specialized ganglion cells of the retina that are involved in the regulation of circadian rhythms and pupillary reflex. ... The suprachiasmatic nucleus (SCN) is a region of the brain, located in the hypothalamus, that is responsible for controlling endogenous circadian rhythms. ... The Retinohypothalamic tract (RHT) is a photic input pathway involved in circadian rhythms. ...

Anterior and posterior segments

Diagram of a human eye; note that not all eyes have the same anatomy as a human eye.
Diagram of a human eye; note that not all eyes have the same anatomy as a human eye.

The mammalian eye can also be divided into two main segments: the anterior segment and the posterior segment.[21] Image File history File links Human_eye_cross-sectional_view_grayscale. ... Image File history File links Human_eye_cross-sectional_view_grayscale. ... anterior segment ... The posterior segment is the back two-thirds of the eye that includes the anterior hyaloid membrane and all structures behind it: the vitreous humor, retina, choroid, and optic nerve. ...

Eye
Human Eye Anterior Segment - Magnified view seen on examination with a slit lamp under diffuse illumination showing conjunctiva overlying the white sclera, transparent cornea, pharmacologically dilated pupil and cataract
Schematic diagram of the human eye.
Latin segmentum anterius bulbi oculi
Dorlands/Elsevier s_07/13264628

The human eye is not a plain sphere but is like two spheres combined, a smaller, sharper curved one and a larger lesser curved sphere. The former, the anterior segment is the front sixth [22] of the eye that includes the structures in front of the vitreous humour: the cornea, iris, ciliary body, and lens.[17] [23] Image File history File links Download high resolution version (1543x1120, 1933 KB) Summary Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cataract Lens (anatomy) Slit lamp Cataract surgery Anterior segment ... Image File history File links Schematic_diagram_of_the_human_eye_en. ... For other uses, see Latins and Latin (disambiguation). ... Elseviers logo. ... Vitreous humour is the clear aqueous solution that fills the space between the lens and the retina of the vertebrate eyeball. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eyes optical power [1]. Together with the lens, the cornea refracts light and, as a result, helps the eye to focus. ... In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, including humans. ... Schematic diagram of the human eye The ciliary body is the part of the eye containing the ciliary muscle and ciliary processes. ... Light from a single point of a distant object and light from a single point of a near object being brought to a focus by changing the curvature of the lens. ...


Within the anterior segment are two fluid-filled spaces:

Aqueous humor fills these spaces within the anterior segment and provides nutrients to the surrounding structures. The anterior chamber if the fluid-filled space inside the eye between the iris and the corneas innermost surface, the endothelium . ... Corneal endothelium is the inner most layer of the cornea, the corneal endothelium is actually a monolayer of squamate epithelial cells lining the anterior chamber of the eye. ... The posterior chamber is a narrow chink behind the peripheral part of the iris, and in front of the suspensory ligament of the lens and the ciliary processes. ... The aqueous humour is the clear, watery fluid that fills the complex space in the front of the eye which is bounded at the front by the cornea and at the rear by the front surface or face of the vitreous humour. ...


Some ophthalmologists specialize in the treatment and management of anterior segment disorders and diseases.[23] Ophthalmology is the branch of medicine which deals with the diseases of the eye and their treatment. ...


The posterior segment is the back five-sixths [24] of the eye that includes the anterior hyaloid membrane and all of the optical structures behind it: the vitreous humor, retina, choroid, and optic nerve.[25] The vitreous membrane (or hyaloid membrane) is a layer of collagen separating the cornea from the vitreous humour. ... Vitreous humour is the clear gel that fills the eyeball, lying between the lens and the retina in the eye. ... Human eye cross-sectional view. ... The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye lying between the retina and the sclera. ... This article is about the anatomical structure. ...


The radii of the anterior and posterior sections are 8 mm and 12 mm, respectively. The point of junction is called the limbus. Limbus may refer to: Limbus (ethnic group), an ethnic group in Asia Limbus, the border of the cornea and the sclera Limbus (band), a Swedish punk rock band Limbo, the temporary status of the souls of good persons who died but did not go to Heaven Category: ...


On the other side of the lens is the second humour, the aqueous humour, which is bounded on all sides: by the lens, ciliary body, suspensory ligaments and by the retina. It lets light through without refraction, helps maintain the shape of the eye and suspends the delicate lens. In some animals, the retina contains a reflective layer (the tapetum lucidum) which increases the amount of light each photosensitive cell perceives, allowing the animal to see better under low light conditions. Schematic diagram of the human eye. ... Light from a single point of a distant object and light from a single point of a near object being brought to a focus by changing the curvature of the lens. ... Schematic diagram of the human eye The ciliary body is the part of the eye containing the ciliary muscle and ciliary processes. ... Tapetum lucidum in a calf eye, with the retina hanging down. ...


Some ophthalmologists specialise in the treatment and management of posterior segment disorders and diseases.[26] Ophthalmology is the branch of medicine which deals with the diseases of the eye and their treatment. ...


Extraocular anatomy

Lying over the sclera and the interior of the eyelids is a transparent membrane called the conjunctiva. It helps lubricate the eye by producing mucus and tears. It also contributes to immune surveillance and helps to prevent the entrance of microbes into the eye. Image of a human eye clearly showing the blood vessels of the conjuntiva. ... Mucus cells. ... The tear system. ... A scanning electron microscope image of a single neutrophil (yellow), engulfing anthrax bacteria (orange). ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ...


In many animals, including humans, eyelids wipe the eye and prevent dehydration. They spread tears on the eyes, which contains substances which help fight bacterial infection as part of the immune system. Some aquatic animals have a second eyelid in each eye which refracts the light and helps them see clearly both above and below water. Most creatures will automatically react to a threat to its eyes (such as an object moving straight at the eye, or a bright light) by covering the eyes, and/or by turning the eyes away from the threat. Blinking the eyes is, of course, also a reflex. An eyelid is a thin fold of skin that covers and protects an eye. ... The tear system. ... Infection is also the title of an episode of the television series Babylon 5; see Infection (Babylon 5). ... A scanning electron microscope image of a single neutrophil (yellow), engulfing anthrax bacteria (orange). ... Example of a blinking eye (slow-motion) Blinking is the rapid closing and opening of the eyelid. ... For other uses, see Reflexive (disambiguation). ...


In many animals, including humans, eyelashes prevent fine particles from entering the eye. Fine particles can be bacteria, but also simple dust which can cause irritation of the eye, and lead to tears and subsequent blurred vision. An eyelash or simply lash is one of the hairs that grow at the edge of the eyelid. ...


In many species, the eyes are inset in the portion of the skull known as the orbits or eyesockets. This placement of the eyes helps to protect them from injury. In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. ...


In humans, the eyebrows redirect flowing substances (such as rainwater or sweat) away from the eye. This article does not cite any references or sources. ...


Function of the mammalian eye

The structure of the mammalian eye owes itself completely to the task of focusing light onto the retina. This light causes chemical changes in the photosensitive cells of the retina, the products of which trigger nerve impulses which travel to the brain. For other uses, see Light (disambiguation). ... Human eye cross-sectional view. ... A chemical substance is any material substance used in or obtained by a process in chemistry: A chemical compound is a substance consisting of two or more chemical elements that are chemically combined in fixed proportions. ... Photosensitivity is the amount to which an object reacts upon receiving photons of light. ... Schematic of an electrophysiological recording of an action potential showing the various phases which occur as the wave passes a point on a cell membrane. ...


Retina

The retina contains two forms of photosensitive cells important to vision—rods and cones—in addition to the photosensitive ganglion cells involved in circadian adjustment but not vision. Though structurally and metabolically similar, the functions of rods and cones are quite different. Rod cells are highly sensitive to light, allowing them to respond in dim light and dark conditions; however, they cannot detect color differences. These are the cells that allow humans and other animals to see by moonlight, or with very little available light (as in a dark room). Cone cells, conversely, need high light intensities to respond and have high visual acuity. Different cone cells respond to different wavelengths of light, which allows an organism to see color. The shift from cone vision to rod vision is why the darker conditions become, the less color objects seem to have. 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 of photoreceptor, cone cells. ... Normalized responsivity spectra of human cone cells, S, M, and L types Cone cells, or cones, are photoreceptor cells in the retina of the eye which function best in relatively bright light. ... For other uses, see Wavelength (disambiguation). ...


The differences between rods and cones are useful; apart from enabling sight in both dim and light conditions, they have further advantages. The fovea, directly behind the lens, consists of mostly densely-packed cone cells. The fovea gives humans a highly detailed central vision, allowing reading, bird watching, or any other task which primarily requires staring at things. Its requirement for high intensity light does cause problems for astronomers, as they cannot see dim stars, or other celestial objects, using central vision because the light from these is not enough to stimulate cone cells. Because cone cells are all that exist directly in the fovea, astronomers have to look at stars through the "corner of their eyes" (averted vision) where rods also exist, and where the light is sufficient to stimulate cells, allowing an individual to observe faint objects. Schematic diagram of the human eye, with the fovea at the bottom. ... Galileo is often referred to as the Father of Modern Astronomy. ... ... Averted vision is a technique for viewing faint objects which involves not looking directly at the object, but looking a little off to the side, while continuing to concentrate on the object. ...


Rods and cones are both photosensitive, but respond differently to different frequencies of light. They contain different pigmented photoreceptor proteins. Rod cells contain the protein rhodopsin and cone cells contain different proteins for each color-range. The process through which these proteins go is quite similar — upon being subjected to electromagnetic radiation of a particular wavelength and intensity, the protein breaks down into two constituent products. Rhodopsin, of rods, breaks down into opsin and retinal; iodopsin of cones breaks down into photopsin and retinal. The breakdown results in the activation of Transducin and this activates cyclic GMP Phosphodiesterase, which lowers the number of open Cyclic nucleotide-gated ion channels on the cell membrane, which leads to hyperpolarization; this hyperpolarization of the cell leads to decreased release of transmitter molecules at the synapse. A photoreceptor, or photoreceptor cell, is a specialized type of neuron found in the eyes retina that is capable of phototransduction. ... A representation of the 3D structure of myoglobin showing coloured alpha helices. ... A rhodopsin molecule (yellow) with bound retinal (orange), embedded in a cell membrane (lipids shown as green, head groups as red/blue). ... This box:      Electromagnetic (EM) radiation is a self-propagating wave in space with electric and magnetic components. ... A rhodopsin molecule in the cell membrane. ... Retinal, technically called retinene1 or retinaldehyde, is a light-sensitive retinene molecule found in the photoreceptor cells of the retina. ... This article or section does not cite its references or sources. ... Transducin is the name given to the G-protein alpha-subunits that are naturally expressed in vertebrate retina rods and cones. ... A Cyclic nucleotide-gated ion channel is any ion channel that opens in the presence of cyclic nucleotides. ... Look up cell membrane in Wiktionary, the free dictionary. ... In biology, hyperpolarization is any change in a cells membrane potential that makes it more polarized. ... Chemical structure of D-aspartic acid, a common amino acid neurotransmitter. ... Illustration of the major elements in a prototypical synapse. ...


Differences between the rhodopsin and the iodopsins is the reason why cones and rods enable organisms to see in dark and light conditions — each of the photoreceptor proteins requires a different light intensity to break down into the constituent products. Further, synaptic convergence means that several rod cells are connected to a single bipolar cell, which then connects to a single ganglion cell by which information is relayed to the visual cortex. This convergence is in direct contrast to the situation with cones, where each cone cell is connected to a single bipolar cell. This divergence results in the high visual acuity, or the high ability to distinguish detail, of cone cells compared to rods. If a ray of light were to reach just one rod cell, the cell's response may not be enough to hyperpolarize the connected bipolar cell. But because several "converge" onto a bipolar cell, enough transmitter molecules reach the synapses of the bipolar cell to hyperpolarize it. As a part of the retina, the bipolar cell exists between photoreceptors (rod cells and cone cells) and ganglion cells. ... A ganglion cell (or sometimes called a gangliocyte) is a type of neuron located in the retina that receives visual information from photoreceptors via various intermediate cells such as bipolar cells, amacrine cells, and horizontal cells. ... Brodmann area 17 (primary visual cortex) is shown in red in this image which also shows area 18 (orange) and 19 (yellow) The visual cortex refers to the primary visual cortex (also known as striate cortex or V1) and extrastriate visual cortical areas such as V2, V3, V4, and V5. ... Chemical structure of D-aspartic acid, a common amino acid neurotransmitter. ... Illustration of the major elements in a prototypical synapse. ...


Furthermore, color is distinguishable due to the different iodopsins of cone cells; there are three different kinds, in normal human vision, which is why we need three different primary colors to make a color space. Normalised absorption spectra of the three human photopsins and of human rhodopsin (dashed). ... Normalized responsivity spectra of human cone cells, S, M, and L types Cone cells, or cones, are photoreceptor cells in the retina of the eye which function best in relatively bright light. ... This article is about colors. ... A comparison of different color spaces. ...


A small percentage of the ganglion cells in the retina contain melanopsin and, thus, are themselves photosensitive. The light information from these cells is not involved in vision and it reaches the brain not via the optic nerve but via the retinohypothalamic tract, the RHT. By way of this light information, the body clock's inherent approximate 24-hour cycling is adjusted daily to nature's light/dark cycle. Melanopsin is a photopigment found in specialized ganglion cells of the retina that are involved in the regulation of circadian rhythms and pupillary reflex. ... The Retinohypothalamic tract (RHT) is a photic input pathway involved in circadian rhythms. ... The Circadian rhythm is a name given to the internal body clock that regulates the (roughly) 24 hour cycle of biological processes in animals and plants. ...


Accommodation

Light from a single point of a distant object and light from a single point of a near object being brought to a focus on the retina
Light from a single point of a distant object and light from a single point of a near object being brought to a focus on the retina
Main article: Accommodation (eye)

The purpose of the optics of the mammalian eye is to bring a clear image of the visual world onto the retina. Because of limited depth of field of the mammalian eye, an object at one distance from the eye might project a clear image, while an object either closer to or further from the eye will not. To make images clear for objects at different distances from the eye, its optical power needs to be changed. This is accomplished mainly by changing the curvature of the lens. For distant objects, the lens needs to be made flatter, for near objects the lens needs to be made thicker and more rounded. Image File history File links Focus_in_an_eye. ... Image File history File links Focus_in_an_eye. ... Light from a single point of a distant object and light from a single point of a near object being brought to a focus by changing the curvature of the lens. ... In optics, particularly film and photography, the depth of field (DOF) is the distance in front of and beyond the subject that appears to be in focus. ...


Water in the eye can alter the optical properties of the eye and blur vision. It can also wash away the tear fluid—along with it the protective lipid layer—and can alter corneal physiology, due to osmotic differences between tear fluid and freshwater. Osmotic effects are made apparent when swimming in freshwater pools, becase the osmotic gradient draws water from the pool into the corneal tissue (the pool water is hypotonic), causing edema, and subsequently leaving the swimmer with "cloudy" or "misty" vision for a short period thereafter. The edema can be reversed by irrigating the eye with hypertonic saline which osmotically draws the excess water out of the eye. Osmosis is the spontaneous net movement of water across a semipermeable membrane from a region of low solute concentration to a solution with a high solute concentration, down a solute concentration gradient. ... Tonicity is a measure of effective osmolarity or effective osmolality. ... This page is about the condition called edema. ... Tonicity is a measure of effective osmolarity or effective osmolality. ... Saline may refer to: Salinity Saline (medicine) Saline, Michigan Saline, Scotland - a village in the burgh of Fife, Scotland. ...


Color

The use of color in machines is a critical design consideration. The red, green, and blue color wave lengths have different focal lengths as they pass through the eye lens and without proper consideration the eye is unable to focus on the image. Blue has the largest shift in focal length from green and red. That is why it should never be used in situations of prolonged display use or when information must be quickly accessed. Essentially introducing blue causes the eye to loose focus in the presence of all other colors. This was learned by the Air Traffic Control community in the 1970's with the Federal Aviation Administration (FAA) and MITRE involved in detailed studies (MTR-7728 or DOT-FA-78WA-4075). Introducing blue into the display mix also has the potential of inducing myopia (Near-sightedness) into the population. The concern from the FAA was both system effectiveness as the air traffic controllers interacted with the system via their air traffic control consoles and air traffic controller eye health. There are also related stress studies and the impact of color on stress and its effects on controller maximum workload levels.


To preserve night vision red has long been used as the source of light in machines. The automobile brake light is a classic example. If other colors are introduced into the mix there is a loss of night vision leading to serious safety issues. The use of red, white, and blue in a night setting has the effect of destroying night vision (white) and preventing the eyes ability to focus (blue).


Acuity

A hawk's eye
A hawk's eye

Visual acuity is often measured in cycles per degree (CPD), which measures an angular resolution, or how much an eye can differentiate one object from another in terms of visual angles. Resolution in CPD can be measured by bar charts of different numbers of white–black stripe cycles. For example, if each pattern is 1.75 cm wide and is placed at 1 m distance from the eye, it will subtend an angle of 1 degree, so the number of white–black bar pairs on the pattern will be a measure of the cycles per degree of that pattern. The highest such number that the eye can resolve as stripes, or distinguish from a gray block, is then the measurement of visual acuity of the eye. From http://www. ... From http://www. ... Binomial name (Gmelin, 1788) Synonyms Buteo borealis Buteo broealis (lapsus) The Red-tailed Hawk (Buteo jamaicensis) is a medium-sized bird of prey, one of three species colloquially known in the United States as the chickenhawk. ... This article describes the unit of angle. ... Angular resolution describes the resolving power of any optical device such as a telescope, a microscope, a camera, or an eye. ...


For a human eye with excellent acuity, the maximum theoretical resolution would be 50 CPD[27] (1.2 minute of arc per line pair, or a 0.35 mm line pair, at 1 m). However, the eye can only resolve a contrast of 5%. Taking this into account, the eye can resolve a maximum resolution of 37 CPD, or 1.6 minute of arc per line pair (0.47 mm line pair, at 1 m).[28] A rat can resolve only about 1 to 2 CPD.[29] A horse has higher acuity through most of the visual field of its eyes than a human has, but does not match the high acuity of the human eye's central fovea region.


Equivalent resolution

A maximum resolution of the human eye in good light of 1.6 minute of arc per line pair will correspond to 1.25 lines per minute of arc. Assuming two pixels per line pair (one pixel per line) and a square field of 120 degrees, this would be equivalent to approximately 120×60×1.25 = 9000 pixels in each of the X and Y dimensions, or about 81 megapixels.[citation needed] A pixel (a contraction of picture element) is one of the many tiny dots that make up the representation of a picture in a computers memory. ...


However, the human eye itself has only a small spot of sharp vision in the middle of the retina, the fovea centralis, the rest of the field of view being progressively lower resolution as it gets further from the fovea. The angle of the sharp vision being just a few degrees in the middle of the view, the sharp area thus barely achieves even a single megapixel resolution. The experience of wide sharp human vision is in fact based on turning the eyes towards the current point of interest in the field of view, the brain thus perceiving an observation of a wide sharp field of view. Schematic diagram of the human eye, with the fovea at the bottom. ...


The narrow beam of sharp vision is easy to test by putting a fingertip on a newspaper and trying to read the text while staring at the fingertip — it is very difficult to read text that's just a few centimeters away from the fingertip.


Spectral response

Human eyes respond to light with wavelength in the range of approximately 400 to 700 nm. Other animals have other ranges, with many such as birds including a significant ultraviolet (shorter than 400 nm) response. For other uses, see Ultraviolet (disambiguation). ...


Dynamic range

The retina has a static contrast ratio of around 100:1 (about 6 1/2 stops). As soon as the eye moves (saccades) it re-adjusts its exposure both chemically and by adjusting the iris. Initial dark adaptation takes place in approximately four seconds[citation needed] of profound, uninterrupted darkness; full adaptation through adjustments in retinal chemistry (the Purkinje effect) are mostly complete in thirty minutes[citation needed]. Hence, a dynamic contrast ratio of about 1,000,000:1 (about 20 stops) is possible. The process is nonlinear and multifaceted, so an interruption by light nearly starts the adaptation process over again. Full adaptation is dependent on good blood flow; thus dark adaptation may be hampered by poor circulation, and vasoconstrictors like alcohol or tobacco. The contrast ratio is a measure of a display system, defined as the ratio of the luminosity of the brightest color (white) to that of the darkest color (black) that the system is capable of producing. ... A 35mm lens set to f/11, as indicated by the white dot above the f-stop scale on the aperture ring In photography the f-number (focal ratio) expresses the diameter of the diaphragm aperture in terms of the effective focal length of the lens. ... A saccade is a fast movement of an eye, head, or other part of an animals body or of a device. ... The Purkinje effect (sometimes called the Purkinje shift, or dark adaptation) is the tendency for the peak sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels. ... The contrast ratio is a measure of a display system, defined as the ratio of the luminosity of the brightest color (white) to that of the darkest color (black) that the system is capable of producing. ... A 35mm lens set to f/11, as indicated by the white dot above the f-stop scale on the aperture ring In photography the f-number (focal ratio) expresses the diameter of the diaphragm aperture in terms of the effective focal length of the lens. ...


Eye movement

MRI scan of human eye
Main article: Eye movements

The visual system in the brain is too slow to process information if the images are slipping across the retina at more than a few degrees per second.[30] Thus, for humans to be able to see while moving, the brain must compensate for the motion of the head by turning the eyes. Another complication for vision in frontal-eyed animals is the development of a small area of the retina with a very high visual acuity. This area is called the fovea, and covers about 2 degrees of visual angle in people. To get a clear view of the world, the brain must turn the eyes so that the image of the object of regard falls on the fovea. Eye movements are thus very important for visual perception, and any failure to make them correctly can lead to serious visual disabilities. Image File history File links MRI_of_human_eye. ... Image File history File links MRI_of_human_eye. ... Eye movements are the voluntary or involuntary movements of the eye. ...


Having two eyes is an added complication, because the brain must point both of them accurately enough that the object of regard falls on corresponding points of the two retinas; otherwise, double vision would occur. The movements of different body parts are controlled by striated muscles acting around joints. The movements of the eye are no exception, but they have special advantages not shared by skeletal muscles and joints, and so are considerably different.


Extraocular muscles

Main article: Extraocular muscles

Each eye has six muscles that control its movements: the lateral rectus, the medial rectus, the inferior rectus, the superior rectus, the inferior oblique, and the superior oblique. When the muscles exert different tensions, a torque is exerted on the globe that causes it to turn, in almost pure rotation, with only about one millimeter of translation.[31] Thus, the eye can be considered as undergoing rotations about a single point in the center of the eye. Once the human eye sustains damage to the optic nerve, the impulses will not be taken to the brain. Eye transplants can happen but the person receiving the transplant will not be able to see. As for the optic nerve, once it is damaged it cannot be fixed. The extraocular muscles are the six muscles that control the movements of the eye. ... For other uses of Muscles, see Muscles (disambiguation). ... The lateral rectus muscle is a muscle in the orbit that abducts the eyeball (makes it move outwards). ... The medial rectus muscle is a muscle in the orbit that adducts the eyeball (makes it move inwards). ... The inferior rectus muscle is a muscle in the orbit that depresses, adducts, and rotates the eye laterally. ... The superior rectus muscle is a muscle in the orbit that elevates, adducts, and rotates the eye medially. ... The inferior oblique muscle is a muscle in the orbit that adducts (medially rotates) and elevates the eyeball. ... The superior oblique muscle is a muscle in the orbit that causes the eye to look downwards when it is already directed medially (looking towards the nose). ...


Rapid eye movement

Main article: Rapid eye movement sleep

Rapid eye movement, or REM for short, typically refers to the stage during sleep during which the most vivid dreams occur. During this stage, the eyes move rapidly. It is not in itself a unique form of eye movement. Rapid eye movement (REM) sleep is the normal stage of sleep characterized by rapid movements of the eyes. ... For other uses, see Sleep (disambiguation). ...


Saccades

Main article: Saccade

Saccades are quick, simultaneous movements of both eyes in the same direction controlled by the frontal lobe of the brain. A saccade is a fast movement of an eye, head, or other part of an animals body or of a device. ...


Microsaccades

Main article: Microsaccade

Even when looking intently at a single spot, the eyes drift around. This ensures that individual photosensitive cells are continually stimulated in different degrees. Without changing input, these cells would otherwise stop generating output. Microsaccades move the eye no more than a total of 0.2° in adult humans. Microsaccades are a kind of fixational eye movement. ...


Vestibulo-ocular reflex

Main article: Vestibulo-ocular reflex

The vestibulo-ocular reflex is a reflex eye movement that stabilizes images on the retina during head movement by producing an eye movement in the direction opposite to head movement, thus preserving the image on the center of the visual field. For example, when the head moves to the right, the eyes move to the left, and vice versa. Figure 3 Three-neuron arc, during a head movement to the right. ... Figure 3 Three-neuron arc, during a head movement to the right. ... For other uses of A, see A (disambiguation). ... For other uses, see Reflexive (disambiguation). ... An eye is an organ that detects light. ... Human eye cross-sectional view. ...


Smooth pursuit movement

Main article: Pursuit movement

The eyes can also follow a moving object around. This tracking is less accurate than the vestibulo-ocular reflex, as it requires the brain to process incoming visual information and supply feedback. Following an object moving at constant speed is relatively easy, though the eyes will often make saccadic jerks to keep up. The smooth pursuit movement can move the eye at up to 100°/s in adult humans. Pursuit movement is the ability of the eyes to smoothly follow a moving object. ... For other uses, see Feedback (disambiguation). ...


It is more difficult to visually estimate speed in low light conditions or while moving, unless there is another point of reference for determining speed.


Optokinetic reflex

The optokinetic reflex is a combination of a saccade and smooth pursuit movement. When, for example, looking out of the window in a moving train, the eyes can focus on a 'moving' train for a short moment (through smooth pursuit), until the train moves out of the field of vision. At this point, the optokinetic reflex kicks in, and moves the eye back to the point where it first saw the train (through a saccade).


Vergence movement

Main article: Vergence
The two eyes converge to point to the same object.
The two eyes converge to point to the same object.

When a creature with binocular vision looks at an object, the eyes must rotate around a vertical axis so that the projection of the image is in the centre of the retina in both eyes. To look at an object closer by, the eyes rotate 'towards each other' (convergence), while for an object farther away they rotate 'away from each other' (divergence). Exaggerated convergence is called cross eyed viewing (focusing on the nose for example) . When looking into the distance, or when 'staring into nothingness', the eyes neither converge nor diverge. A vergence is the simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision ^ . The two eyes converge to point to the same object When a creature with binocular vision looks at an object, the eyes must rotate around a vertical axis so that the... Image:Stereogram Tut Eye Convergence. ... Image:Stereogram Tut Eye Convergence. ... In ophthalmology, convergence is the simultaneous inward movement of both eyes toward each other, usually in an effort to maintain single binocular vision when viewing an object ^ . It is a type of vergence eye movement. ... In ophthalmology, divergence is the simultaneous outward movement of both eyes away each other, usually in an effort to maintain single binocular vision when viewing an object. ...


Vergence movements are closely connected to accommodation of the eye. Under normal conditions, changing the focus of the eyes to look at an object at a different distance will automatically cause vergence and accommodation.


Diseases, disorders, and age-related changes

The stye is a common irritating inflammation of the eyelid.
The stye is a common irritating inflammation of the eyelid.

There are many diseases, disorders, and age-related changes that may affect the eyes and surrounding structures. This is a partial list of human eye diseases and disorders. ... This is a list of systemic diseases with ocular manifestations. ... Image File history File linksMetadata Download high resolution version (984x723, 139 KB) Summary Description de: Gerstenkorn nach ca. ... Image File history File linksMetadata Download high resolution version (984x723, 139 KB) Summary Description de: Gerstenkorn nach ca. ... A stye (IPA: ) or hordeolum () is an infection of the sebaceous glands at the base of the eyelashes. ...


As the eye ages certain changes occur that can be attributed solely to the aging process. Most of these anatomic and physiologic processes follow a gradual decline. With aging, the quality of vision worsens due to reasons independent of aging eye diseases. While there are many changes of significance in the nondiseased eye, the most functionally important changes seem to be a reduction in pupil size and the loss of accommodation or focusing capability (presbyopia). The area of the pupil governs the amount of light that can reach the retina. The extent to which the pupil dilates also decreases with age. Because of the smaller pupil size, older eyes receive much less light at the retina. In comparison to younger people, it is as though older persons wear medium-density sunglasses in bright light and extremely dark glasses in dim light. Therefore, for any detailed visually guided tasks on which performance varies with illumination, older persons require extra lighting. Certain ocular diseases can come from sexually transmitted diseases such as herpes and genital warts. If contact between eye and area of infection occurs, the STD will be transmitted to the eye.[32] Presbyopia (Greek word presbyteros (πρεσβύτερος), meaning elder) is the eyes diminished ability to focus that occurs with aging. ...


With aging a prominent white ring develops in the periphery of the cornea- called arcus senilis. Aging causes laxity and downward shift of eyelid tissues and atrophy of the orbital fat. These changes contribute to the etiology of several eyelid disorders such as ectropion, entropion, dermatochalasis, and ptosis. The vitreous gel undergoes liquefaction (posterior vitreous detachment or PVD) and its opacities—visible as floaters—gradually increase in number. Ectropion is a condition of loose eyelids. ... Entropion is a medical condition in which the eyelids fold inward. ... Dermatochalasis is defined as excess of skin in the upper eyelid. ... In ophthalmology, ptosis is an abnormally low position (drooping) of the upper eyelid which may grow more or less severe during the day. ... A posterior vitreous detachment (PVD) is an ocular condition in which there is a separation of the vitreous humor from the retina. ... For other uses, see Floater (disambiguation). ...


Various eye care professionals, including ophthalmologists, optometrists, and opticians, are involved in the treatment and management of ocular and vision disorders. A Snellen chart is one type of eye chart used to measure visual acuity. At the conclusion of an eye examination, an eye doctor may provide the patient with an eyeglass prescription for corrective lenses. Some disorders of the eyes for which corrective lenses are prescribed include myopia (near-sightedness) which affects one-third of the population, hyperopia (far-sightedness) which affects one quarter of the population, and presbyopia, a loss of focusing range due to aging. An eye care professional is an individual who provides a service related to the eyes or vision. ... Ophthalmology is the branch of medicine which deals with the diseases of the eye and their treatment. ... Optometrists are primary care practitioners for vision and ocular health concerns. ... An optician is an eye care professional who provides corrective lenses based on a refraction prescription supplied by a ophthalmologist or optometrist. ... Traditional Snellen chart. ... Traditional Snellen chart. ... Traditional Snellen chart used for visual acuity testing. ... Traditional Snellen chart used for visual acuity testing. ... Using a phoropter to determine a prescription for eyeglasses An eyeglass prescription is a written order by an ophthalmologist or an optometrist to an optician for eyeglasses. ... A bifocal corrective eyeglasses lens A corrective lens is a lens worn on or before the eye, used to treat myopia, hyperopia, astigmatism, and presbyopia. ... For other uses, see Myopia (disambiguation). ... Hyperopia, also known as hypermetropia or colloquially as farsightedness or longsightedness, is a defect of vision caused by an imperfection in the eye (often when the eyeball is too short or when the lens cannot become round enough), causing inability to focus on near objects, and in extreme cases causing... Presbyopia (Greek word presbyteros (πρεσβύτερος), meaning elder) is the eyes diminished ability to focus that occurs with aging. ...


Eye injury/safety

An example of eye trauma.
An example of eye trauma.

Accidents involving common household products cause 125,000 eye injuries each year in the U.S.[33] More than 40,000 people a year suffer eye injuries while playing sports.[33] Sports-related eye injuries occur most frequently in baseball, basketball and racquet sports.[33]


Occupational eye injury

Each day about 2000 U.S. workers have a job-related eye injury that requires medical treatment.[34] About one third of the injuries are treated in hospital emergency departments and more than 100 of these injuries result in one or more days of lost work.[34] The majority of these injuries result from small particles or objects striking or abrading the eye. Examples include metal slivers, wood chips, dust, and cement chips that are ejected by tools, wind blown, or fall from above a worker. Some of these objects, such as nails, staples, or slivers of wood or metal penetrate the eyeball and result in a permanent loss of vision. Large objects may also strike the eye/face causing blunt force trauma to the eyeball or eye socket. Chemical burns to one or both eyes from splashes of industrial chemicals or cleaning products are common. Thermal burns to the eye occur as well. Among welders, their assistants, and nearby workers, UV radiation burns (welder’s flash) routinely damage workers’ eyes and surrounding tissue. A welder is a tradesman who specialises in welding materials together. ... Arc eye, also known as arc flash, welders flash, corneal flash burns, or flash burns, is a painful ocular condition sometimes experienced by welders who have failed to use adequate eye protection. ...


In addition to common eye injuries, health care workers, laboratory staff, janitorial workers, animal handlers, and other workers may be at risk of acquiring infectious diseases via ocular exposure.[34] In medicine, infectious disease or communicable disease is disease caused by a biological agent (e. ...


Cuisine

In some countries, stuffed cow's eyes are considered a delicacy. They are made by first removing the vitreous humor, lens, cornea, and iris, then are usually boiled. Cow eyes are often stuffed with varieties of coleslaw, beef, and even cream cheese. For general information about the genus, including other species of cattle, see Bos. ... This is a List of delicacies. ... A bowl of coleslaw Coleslaw (or cole slaw) is a salad consisting primarily and minimally of shredded, raw, white cabbage, although it often also includes shredded carrots. ... For other uses, see Beef (disambiguation). ... Country of origin United States Region, town Chester, New York Source of milk Cow Pasteurised Texture Soft Aging time none Certification Cream cheese is a sweet, soft, mild-tasting, white cheese that contains at least 33% milkfat (as marketed) with a moisture content of not more than 55%, and a...


Seal eyes are eaten by the Inuit, providing a source of zinc in their diet.[35] For other uses, see Inuit (disambiguation). ... General Name, symbol, number zinc, Zn, 30 Chemical series transition metals Group, period, block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ...


A delicacy in western Norwegian cuisine is the singed head of a sheep or lamb (smalahovud), where the eyes are also eaten. Smalahove (or smalehovud) is a Norwegian traditional dish, usually eaten around and before Christmas time, made from a sheeps head. ...


See also

This article is about the branch of medicine. ... Traditional Snellen chart used for visual acuity testing. ... It has been suggested that this article or section be merged with Gaze aversion. ... Eyespots on a peafowl. ... The science of infant vision gives a verifiable basis for some practices of pediatric ophthalmology and gathers measurements intended to describe, monitor and predict: development of retinal photoreceptor cells infant sensitivity to detail, color, contrast, and movement binocularity eye movements refraction cognitive processing By establishing a timeline of visual perception... There are very few or no other articles that link to this one. ... The annulus of Zinn, also known as the annular tendon or common tendinous ring, is a ring of fibrous tissue surrounding the optic nerve at its entrance at the apex of the orbit. ... Image of a human eye clearly showing the blood vessels of the conjuntiva. ... Human eye cross-sectional view. ... Many species of land animals have a nictitating membrane, which can move across the eyeball to give the sensitive eye structures additional protection in particular circumstances. ... Schlemms canal, also known as canal of Schlemm or the scleral venous sinus, is a circular channel in the eye that collects aqueous humor from the anterior chamber and delivers it into the bloodstream. ... This is an area of tissue located around the base of the cornea, near the ciliary body, and is responsible for draining the aqueous humour from the eye via the anterior chamber (the chamber on the front of the eye covered by the cornea). ...

References

  1. ^ Nairne, James (2005). Psychology. Belmont: Wadsworth Publishing. ISBN 049503150x. 
  2. ^ Vicki Bruce, Patrick R. Green, and Mark A. Georgeson (1996). Visual Perception: Physiology, Psychology and Ecology. Psychology Press, p.20. ISBN 0863774504. 
  3. ^ BioMedia Associates Educational Biology Site: What animal has a more sophisticated eye, Octopus or Insect?
  4. ^ Who You Callin' "Shrimp"? - National Wildlife Magazine
  5. ^ Halder, G., Callaerts, P. and Gehring, W.J. (1995). "New perspectives on eye evolution." Curr. Opin. Genet. Dev. 5 (pp. 602–609).
  6. ^ Halder, G., Callaerts, P. and Gehring, W.J. (1995). "Induction of ectopic eyes by targeted expression of the eyeless gene in Drosophila". Science 267 (pp. 1788–1792).
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2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 38th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 296th day of the year (297th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 296th day of the year (297th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... Eric Richard Kandel (born November 7, 1929) is a psychiatrist, a neuroscientist and professor of biochemistry and biophysics at Columbia University. ... Principles of Nerual Science cover First published in 1981, Principles of Neural Science is a neuroscience textbook edited by Eric R. Kandel, James Schwartz, and Thomas Jessell. ...

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Refraction error, also known as refractive error, is an error in the focusing of light by the eye and a frequent reason for reduced visual acuity. ... Hyperopia, also known as hypermetropia or colloquially as farsightedness or longsightedness, is a defect of vision caused by an imperfection in the eye (often when the eyeball is too short or when the lens cannot become round enough), causing inability to focus on near objects, and in extreme cases causing... For other uses, see Myopia (disambiguation). ... Astigmatism is an affliction of the eye, where vision is blurred by an irregularly shaped cornea. ... Anisometropia is a condition in which the lenses of the two eyes have different focal lengths; that is, are in different states of myopia (nearsightedness) and hyperopia (farsightedness). ... The following text is a summary of Optical Diagnostics aniseikonia information webpage. ... Presbyopia (Greek word presbyteros (πρεσβύτερος), meaning elder) is the eyes diminished ability to focus that occurs with aging. ... This article is about the visual condition. ... Amblyopia, or lazy eye, is a disorder of the eye. ... Lebers congenital amaurosis is a rare inherited eye disease that appears at birth or in the first few months of life, typically characterized by nystagmus, sluggish or no pupillary responses, and severe vision loss or blindness. ... ... Hemeralopia is the exact opposite of Nyctalopia (Night Blindness). ... Photophobia (also light sensitivity) or fear of light, is a symptom of excessive sensitivity to light and the aversion to sunlight or well-lit places. ... Scintillating scotoma is the most common visual aura preceding migraine and was first described by 19th century physician Hubert Airy (1838–1903). ... Diplopia, commonly known as double vision, is the perception of two images from a single object. ... The word scotoma is derived from the Greek word for darkness. ... An anopsia (or anopia) is a defect in the visual field. ... Paris as seen with full visual fields Binasal hemianopia is the medical description of a type of partial blindness that is associated with certain lesions of the eye, and of the central nervous system, such as congenital hydrocephalus. ... Paris as seen with full visual fields Paris as seen with bitemporal hemianopsia Bitemporal hemianopsia is the medical description of a type of partial blindness that is associated with lesions of the optic chiasm, the area where the optic nerves from the right and left eyes cross near the pituitary... Homonymous hemianopsia is a medical term for a type of partial blindness resulting in a loss of vision in the same visual field of both eyes. ... Quadrantanopia (or quadrant anopia, as two words) refers to an anopia affecting a quarter of the field of vision. ... Color blindness in humans is the inability to perceive differences between some or all colors that other people can distinguish. ... Achromatopsia is the inability to see color. ... Nyctalopia (Greek for night blindness) is a condition making it difficult or impossible to see in relatively low light. ... This article is about the visual condition. ... Low vision is alternatively a general term used to describe lowered visual acuity, and a specific legal term in Canada and the United States used to designate someone with vision of 20/70 or less in the better eye with correction. ... The human eye The pupil is the central transparent area (showing as black). ... Anisocoria is a condition characterized by an unequal size of the pupils. ... Argyll Robertson pupils (“AR pupils”) are bilateral small pupils that constrict when the patient focuses on a near object (they “accommodate” with near vision), but do not constrict when exposed to bright light (they do not “react” to light). ... The pupil dilates instead of constricting when the light moves from the good eye to the bad eye. ... Marcus Gunn Phenomenon (a. ... Adie syndrome, also Adies syndrome, is caused by damage to the postganglionic fibers of the parasympathetic innervation of the eye and characterized by a tonically dilated pupil. ... An infection is the detrimental colonization of a host organism by a foreign species. ... Binomial name Onchocerca volvulus Bickel 1982 Onchocerciasis (pronounced ) or river blindness is the worlds second leading infectious cause of blindness. ... Nystagmus is involuntary eye movement that can be part of the vestibulo-ocular reflex (VOR), with the eyes moving first in the direction of the lesioned side (slow phase) followed by a quick correction (fast phase) to the opposite side or away from the lesioned side. ... Miosis should not be confused with meiosis, the cellular division process involved in sexual reproduction. ... Mydriasis is an excessive dilation of the pupil due to disease or drugs. ... Ocular hypertension (OHT) is intraocular pressure higher than normal in the absence of optic nerve damage or visual field loss . Current consensus in ophthalmology defines normal introcular pressure (IOP) as that between 10 mmHg and 21 mmHg . Elevated IOP is the most important risk factor for glaucoma, so those with... For other uses, see Floater (disambiguation). ... Leber’s hereditary optic neuropathy (LHON) or Leber optic atrophy is a mitochondrially inherited (mother to all offspring) form of acute or subacute loss of central vision that may lead to degeneration of retinal ganglion cells (RGCs) and their axons; this affects predominantly young adult males. ... In medicine, red eye is a non-specific term to describe an eye that appears red due to illness, injury, or some other condition. ... A fungal keratitis is an inflammation of the eyes cornea (called keratitis) that results from infection by a fungal organism. ... Xerophthalmia (Greek for dry eyes) is a medical condition in which the eye doesnt produce tears. ... Aniridia is a rare congenital condition characterized by the underdevelopment of the eyes iris. ...


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Eye (170 words)
Eye is the official journal of The Royal College of Ophthalmologists.
Authors are recommended to read Eye's editorial "Publishing in Eye: The current status" (Eye 2007; 21: 1) and Instructions to Authors before submitting a manuscript for publication in the journal.
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The allergen causes certain cells in the eye (called mast cells) to release histamine and other substances or chemicals that cause blood vessels in the eyes to swell, and the eyes to become itchy, red and watery.
Eye allergies can be extremely annoying and uncomfortable, and they may disrupt your day-to-day activities, but they cannot harm your eyes.
Prescription eye drops provide both short- and long-term targeted relief of eye allergy symptoms, and they can be used to manage eye allergy symptoms in conjunction with an oral antihistamine that might be taken to manage nasal allergy symptoms.
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