A human eye

Eyes are organs of vision that detect light. Different kinds of light-sensitive organs are found in a variety of organisms. The simplest eyes do nothing but detect whether the surroundings are light or dark, while 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. ... In psychology, visual perception is the ability to interpret visible light information reaching the eyes which is then made available for planning and action. ... This article does not cite any references or sources. ... “Life on Earth” redirects here. ... Darkness is the absence of light. ... Color is an important part of the visual arts. ... 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. ... Genera Pentalagus Bunolagus Nesolagus Romerolagus Brachylagus Sylvilagus Oryctolagus Poelagus Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world. ... For other uses, see Chameleon (disambiguation). ...

The compound eyes of a dragonfly.

Compound eye of a dragonfly. ... Compound eye of a dragonfly. ... Compound eye of a dragonfly Compound eye of Antarctic krill as imaged by an electron microscope A compound eye is a visual organ found in certain arthropods such as insects and crustaceans. ... This article is about the insect. ...

Varieties

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, where the light is detected and converted into electrical signals. These 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 which regulates the intensity of the light that enters the eye. 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. 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. ... 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. ... 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 mollusk class... For other uses, see Fish (disambiguation). ... For other uses, see Amphibian (disambiguation). ... For other uses, see Snake (disambiguation). ... This article is about the photographing device. ...

Compound eyes are found among the arthropods and are composed of many simple facets which give a pixelated image (not multiple images, as is often believed). 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 composed of a few facets each, with a retina capable of creating an image, which does provide 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 Compound eye of Antarctic krill as imaged by an electron microscope A compound eye is a visual organ found in certain 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

Possessing detailed hyperspectral color vision, the Mantis shrimp has been reported to have the world's most complex color vision system.^[1] 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 Euphausia superba Dana, 1850 The Antarctic krill (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. ... Superfamilies and families Bathysquillidoidea Bathysquillidae Indosquillidae Erythrosquilloidea Erythrosquillidae Gonodactyloidea Alainosquillidae Eurysquillidae Gonodactylidae Hemisquillidae Odontodactylidae Protosquillidae Pseudosquillidae Takuidae Lysiosquilloidea Coronididae Heterosquillidae Lysiosquillidae Nannosquillidae Tetrasquillidae Squilloidea Harpiosquillidae Squillidae incertae sedis Parasquillidae Sculdidae Mantis shrimp or stomatopods are marine crustaceans belonging to the order Stomatopoda, one part of the class Malacostraca, the largest... Orders Agnostida Nectaspida Redlichiida Corynexochida Lichida Phacopida Subclass: Librostoma Proetida Asaphida Harpetida Ptychopariida For the robot vacuum cleaner, see Electrolux Trilobite. ... Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico. ...

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. Jumping spiders have simple eyes that are so large, supported by an array of other, smaller eyes, that they can get enough visual input to hunt and pounce on their prey. Some insect larvae, like caterpillars, have a different type of simple eye (stemmata) which gives a rough image. An ocellus (plural: ocelli) is a type of photoreceptor organ in animals. ... This article is about the animal. ... 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. ... 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. ...

Evolution of eyes

Main article: Evolution of the eye

Diagram of major stages in the eye's evolution

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.^[2][3][4] 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",^[5] 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. 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. ... In phylogenetics, a group is monophyletic (Greek: of one race) if it consists of an inferred common ancestor and all its descendants. ...

Eyes in various animals show adaptation to their 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 simple patches of photoreceptor cells, physically similar to the receptor patches for taste and smell. These eyespots could only sense ambient brightness: they could distinguish light and dark, but not the direction of the lightsource.^[6] 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.^[7] A photoreceptor, or photoreceptor cell, is a specialized type of neuron found in the eyes retina that is capable of phototransduction. ... Principle of a pinhole camera. ...

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.^[8] 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. ...

The gap between tissue layers naturally formed a biconvex shape, an ideal structure for a normal refractive index. Independently, a transparent layer and a nontransparent layer split forward from the lens: the cornea and iris. Separation of the forward layer again forms a humour, the aqueous humour. This increases refractive power and again eases circulatory problems. Formation of a nontransparent ring allows more blood vessels, more circulation, and larger eye sizes.^[8] 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. ...

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. conjuntiva
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 sheat
25. macula
26. fovea
27. sclera
28. choroid
29. superior rectus muscule
30. retina

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

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.^[9][10][11] Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the presence of sweat glands, including those that produce milk, and by the presence of: hair, three middle ear bones used in hearing, and a neocortex... 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.^[12] 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.^[13]
• The vascular tunic, also known as the tunica vasculosa oculi, is the middle vascularized layer which includes the iris, ciliary body, and choroid.^[12][14][15] 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 nervous tunic, also known as the tunica nervosa oculi, is the inner sensory which includes the retina.^[12][15] 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 does have 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 whatsoever exist at this point, it is thus "blind". Squids and Octupi don't have this blind spot, however.

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. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... Cellular respiration was discovered by mad scientist Mr. ... 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. ... Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina of the eye which only function in relatively bright light. ... The fovea, a part of the eye, is a spot located in the center of the macula. ... 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. ...

Anterior and posterior segments

The mammalian eye can also be divided into two main segments: the anterior segment and the posterior segment.^[16] 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. ...

Anterior segment

The anterior segment is the front third of the eye that includes the structures in front of the vitreous humour: the cornea, iris, ciliary body, and lens.^[14][17] Within the anterior segment are two fluid-filled spaces: the anterior chamber and the posterior chamber. The anterior chamber is the space between the posterior surface of the cornea (i.e. the corneal endothelium) and the iris, whereas the posterior chamber is between the iris and the front face of the vitreous.^[14] 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. ... The anterior chamber if the fluid-filled space inside the eye between the iris and the corneas innermost surface, the endothelium . ... 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. ... 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 cornea and lens help to converge light rays to focus onto the retina. The lens, behind the iris, is a convex, springy disk which focuses light, through the second humour, onto the retina. It is attached to the ciliary body via a ring of suspensory ligaments known as the Zonule of Zinn. To clearly see an object far away, the ciliary muscle is relaxed, which stretches the fibers connecting it with the lens, flattening the lens. When the ciliary muscle contracts, the tension of the fibers decrease (imagine that the distance between the tip of a triangle to its base, is less than the tip of the triangle to the other two tips.) which lets the lens bounce back a more convex and round shape. Humans gradually lose this flexibility with age, resulting in the inability to focus on nearby objects, which is known as presbyopia. There are other refraction errors arising from the shape of the cornea and lens, and from the length of the eyeball. These include myopia, hyperopia, and astigmatism. The iris, between the lens and the first humour, is a pigmented ring of fibrovascular tissue and muscle fibres. Light must first pass though the centre of the iris, the pupil. The size of the pupil is actively adjusted by the circular and radial muscles to maintain a relatively constant level of light entering the eye. Too much light being let in could damage the retina; too little light makes sight difficult. Converge denotes Converge PL a programming language developed by Laurence Tratt Converge, a metalcore band from Massachusetts For the mathematical meaning of this term see Convergence. ... Human eye cross-sectional view. ... Schematic diagram of the human eye The ciliary body is the part of the eye containing the ciliary muscle and ciliary processes. ... The zonula ciliaris splits into two layers, one of which is thin and lines the hyaloid fossa; the other is named the suspensory ligament of the lens: it is thicker, and passes over the ciliary body to be attached to the capsule of the lens a short distance in front... The zonule of Zinn is a ring of fibrous strands connecting the ciliary body with the crystalline lens of the eye. ... The ciliary muscle is a smooth muscle that affects zonular fibers in the eye (fibers that suspend the lens in position during accommodation), enabling changes in lens shape for light focusing. ... Presbyopia (Greek word presbyteros (πρεσβύτερος), meaning elder) is the eyes diminished ability to focus that occurs with aging. ... Refraction error is an error in the focussing of light by the human eye. ... Normal vision. ... 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... Astigmatism is an affliction of the eye, where vision is blurred by an irregularly shaped cornea. ... The human eye The pupil is the central transparent area (showing as black). ...

All of the individual components through which light travels within the eye before reaching the retina are transparent, minimising dimming of the light. Light enters the eye from an external medium such as air or water, passes through the cornea, and into the first of two humours, the aqueous humour. Most of the light refraction occurs at the cornea which has a fixed curvature. The first humour is a clear mass which connects the cornea with the lens of the eye, helps maintain the convex shape of the cornea (necessary to the convergence of light at the lens) and provides the corneal endothelium with nutrients. Schematic diagram of the human eye. ... In the absence of a more specific context, convergence denotes the approach toward a definite value, as time goes on; or to a definite point, a common view or opinion, or toward a fixed or equilibrium state. ... 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. ...

Posterior segment

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

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.^[18] On the other side of the lens is the second humour, the vitreous 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. Image File history File links Human_eye_cross-sectional_view_grayscale. ... Image File history File links Human_eye_cross-sectional_view_grayscale. ... 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. ... 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. ... 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. ...

Light from a single point of a distant object and light from a single point of a near object being brought to a focus

Image File history File links Focus_in_an_eye. ... Image File history File links Focus_in_an_eye. ...

Extraocular anatomy

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. Water in the eye can alter the refractive 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. This is made apparent when swimming in freshwater pools, as the osmotic gradient draws "pool water" 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. It can be reversed by irrigating the eye with hypertonic saline which osmotically draws the excess water out of the eye. This article does not cite any references or sources. ... Osmosis is the net movement of water across a partially permeable membrane from a region of high solvent potential to an area of low solvent potential, up a solute concentration gradient. ... This article does not cite any references or sources. ... This page is about the condition called edema. ... This article does not cite any references or sources. ... Saline may refer to: Salinity Saline (medicine) Saline, Michigan Saline, Scotland - a village in the burgh of Fife, Scotland. ...

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 and muscle 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. ... This article is about biological reflex. ...

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. ...

Other articles regarding eye anatomy

Annulus of Zinn, Conjunctiva, Macula, Nictitating membrane, Schlemm's canal, Trabecular meshwork. 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. ... The conjunctiva is a membrane that covers the sclera (white part of the eye) and lines the inside of the eyelids. ... 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). ...

Cytology

This image clearly shows the pupil and iris of the human 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. Image File history File linksMetadata Size of this preview: 480 × 600 pixelsFull resolution (600 × 750 pixel, file size: 49 KB, MIME type: image/jpeg) By Matthew Dingemans (Self) http://flickr. ... Image File history File linksMetadata Size of this preview: 480 × 600 pixelsFull resolution (600 × 750 pixel, file size: 49 KB, MIME type: image/jpeg) By Matthew Dingemans (Self) http://flickr. ... The human eye The pupil is the central transparent area (showing as black). ... In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, including humans. ... This article does not cite any references or sources. ... 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. ...

The retina contains two forms of photosensitive cells important to vision—rods and cones. Though structurally and metabolically similar, their function is quite different. Rod cells are highly sensitive to light allowing them to respond in dim light and dark conditions, however, they cannot detect color. These are the cells which allow humans and other animals to see by moonlight, or with very little available light (as in a dark room). This is why the darker conditions become, the less color objects seem to have. 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. 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. ... Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina of the eye which only function in relatively bright light. ... The wavelength is the distance between repeating units of a wave pattern. ...

The differences are useful; apart from enabling sight in both dim and light conditions, humans have given them further application. The fovea, directly behind the lens, consists of mostly densely-packed cone cells. This gives humans a highly detailed central vision, allowing reading, bird watching, or any other task which primarily requires looking at things. Its requirement for high intensity light does cause problems for astronomers, as they cannot see dim stars, or other 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 the individual to observe distant stars. An astronomer or astrophysicist is a person whose area of interest is astronomy or astrophysics. ... 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 both 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 opsin in both opens ion channels on the cell membrane which leads to hyperpolarization, this hyperpolarization of the cell leads to a 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). ... Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... 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. ... Ion channels are pore-forming proteins that help to establish and control the small voltage gradient that exists across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient. ... 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. ...

This 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 is in direct contrast to the situation with cones, where each cone cell is connected to a single bipolar cell. This results in the high visual acuity, or the high ability to distinguish between detail, of cone cells and not rods. If a ray of light were to reach just one rod cell this may not be enough to hyperpolarize the connected bipolar cell. But because several "converge" onto a bipolar cell, enough transmitter molecules reach the synapse 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 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). ... Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina of the eye which only function in relatively bright light. ... This article is about colors. ... A comparison of different color spaces. ...

Acuity

Closeup of a hawk's eye

Main article: Visual acuity

Visual acuity can be measured with several different metrics. From http://www. ... From http://www. ... Binomial name (Gmelin, 1788) 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. ... Traditional Snellen chart used for visual acuity testing. ...

Cycles per degree (CPD) measures how much an eye can differentiate one object from another in terms of degree angles. It is essentially no different from angular resolution. To measure CPD, first draw a series of black and white lines of equal width on a grid (similar to a bar code). Next, place the observer at a distance such that the sides of the grid appear one degree apart. If the grid is 1 meter away, then the grid should be about 8.7 millimeters wide. Finally, increase the number of lines and decrease the width of each line until the grid appears as a solid grey block. In one degree, a human would not be able to distinguish more than about 12 lines without the lines blurring together. So a human can resolve distances of about 0.93 millimeters at a distance of one meter. A horse can resolve about 17 CPD (0.66 mm at 1 m) and a rat can resolve about 1 CPD (8.7 mm at 1 m). 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. ...

A diopter is the unit of measure of optical power. A dioptre (also diopter) is a unit of curvature equal to one per metre; that is, inverse metres, or 1/(metres). ... Optical power or dioptric power or refractive power is the degree to which a lens or mirror converges or diverges light. ...

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 of profound, uninterrupted darkness; full adaptation through adjustments in retinal chemistry (the Purkinje effect) are mostly complete in thirty minutes. 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. ...

Equivalent resolution

The maximum resolution of the human eye in good light is approximately 1.6 minute of arc per line pair, or 1.25 line per minute of arc.^[19] 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. 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.

Eye movement

MRI scan of human eye

Main article: Eye movements

The visual system in the brain is too slow to process that information if the images are slipping across the retina at more than a few degrees per second (Westheimer and McKee, 1954). 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. This is an almost pure rotation, with only about one millimeter of translation.^[20] 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. ... A top-down view of skeletal muscle Muscle (from Latin musculus little mouse [1]) is contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. ... 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. ... This article is about biological reflex. ... 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 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. ... It has been suggested that this article or section be merged with Feedback loop. ...

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' tree for a short moment (through smooth pursuit), until the tree 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 tree (through a saccade).

Vergence movement

Main article: Vergence

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.

Accommodation

Main article: Accommodation (eye)

To see clearly, the lens will be pulled flatter or allowed to regain its thicker form. 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. ...

Diseases, disorders, and age-related changes

Main articles: List of eye diseases and disorders and List of systemic diseases with ocular manifestations

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 or hordeolum is an infection of the sebaceous glands at the base of the eyelashes[1]. While they produce no lasting damage, they can be quite painful. ...

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.^[21] 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 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 individual who makes and adjusts optical aids. ... 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. ...

Cuisine

In many countries^{[citation needed]}, 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 soft, mild-tasting, white cheese that contains at least 33% milkfat (as marketed) with a moisture content of not more than 55%, and a pH...

Seal eyes are eaten by the Inuit, providing a source of zinc in their diet.^[22] 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. ...

See also

• Eye exam
• Eye contact
• Infant vision

Traditional Snellen chart used for visual acuity testing. ... It has been suggested that this article or section be merged with Gaze aversion. ... 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...

References

• Anatomy. History of Ophthalmology. Retrieved on 23 April 2005.
• Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science, 4th ed. McGraw-Hill, New York (2000). ISBN 0-8385-7701-6

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. ...

External links

Wikimedia Commons has media related to:

Eyes

• DJO | Digital Journal of Ophthalmology
• Glossary of Eye Conditions
• Evolution of the Eye
• Diagram of the eye
• Webvision. The organisation of the retina and visual system.
• VisionSimulations.com | Images and vision simulators of various diseases and conditions of the eye
• Eyes and computers.
• Eyeatlas online (ophthalmological images) by Umberto Benelli, MD, PhD
• ClarkVision's estimation of the resolution of the eye
• Video: Vision and How Our Eyes Work
• Summary of eye diseases and disorders
• Your Baby's Eyes.

v • d • e Human anatomical features

HEAD: Skull - Forehead – Eye – Ear – Nose – Mouth – Tongue – Teeth – Jaw – Face – Cheek – Chin NECK: Throat - Larynx – Adam's apple Image File history File links Commons-logo. ... This article or section may be confusing for some readers, and should be edited to be clearer or more simplified. ... The visual system is the part of the nervous system which allows organisms to see. ... 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. ... The conjunctiva is a membrane that covers the sclera (white part of the eye) and lines the inside of the eyelids. ... Schematic diagram of the human eye. ... 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). ... The corneal limbus is the border of the cornea and the sclera. ... 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. ... The corneal epithelium (epithelium corneæ anterior layer) covers the front of the cornea and consists of several layers of cells. ... The Bowmans membrane is a smooth layer in the eye. ... The substantia propria (or stroma of cornea) is fibrous, tough, unyielding, and perfectly transparent. ... Descemets membrane is the basement membrane that lies between the corneal proper substance, also called stroma, and the endothelial layer of the cornea. ... 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. ... For the Pacific island, see Wallis Island. ... 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 ciliary processes are formed by the inward folding of the various layers of the choroid, i. ... The choriocapillaris is a layer of capillaries that is immediately adjacent to Bruchs membrane in the choroid. ... Bruchs membrane is the innermost layer of the choroid. ... In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, including humans. ... The stroma of the iris consists of fibers and cells. ... The human eye The pupil is the central transparent area (showing as black). ... Schematic diagram of the human eye The ciliary body is the part of the eye containing the ciliary muscle and ciliary processes. ... Human eye cross-sectional view. ... Human eye cross-sectional view. ... The fovea, a part of the eye, is a spot located in the center of the macula. ... The optic disc or optic nerve head is the location where ganglion cell axons exit the eye to form the optic nerve. ... anterior segment ... The anterior chamber if the fluid-filled space inside the eye between the iris and the corneas innermost surface, the endothelium . ... Schematic diagram of the human 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. ... 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. ... 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. ... Vitreous humour is the clear aqueous solution that fills the space between the lens and the retina of the vertebrate eyeball. ... It has been suggested that this article or section be merged with Zonule of Zinn. ... The zonule of Zinn is a ring of fibrous strands connecting the ciliary body with the crystalline lens of the eye. ... This article or section may be confusing for some readers, and should be edited to be clearer or more simplified. ... The visual system is the part of the nervous system which allows organisms to see. ... This article is about the anatomical structure. ... Visual pathway with optic chiasm circled The optic chiasm (from the Greek χλαζειν to mark with an X, after the letter Χ chi) is the part of the brain where the optic nerves partially cross, those parts of the right eye which see things on the right side being connected to the... The optic tract is a part of the visual system in the brain. ... Grays FIG. 719– Hind- and mid-brains; postero-lateral view. ... The geniculo-calcerine tract (known as the optic radiation) is a collection of axons carrying visual information from the lateral geniculate nucleus of the thalamus to the primary visual cortex (also called striate cortex). ... 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. ... Blobs are sections of the visual cortex where groups of neurons which are sensitive to color assemble in cylindrical shapes. ... List of bones of the human skeleton Human anatomy is primarily the scientific study of the morphology of the adult human body. ... For other uses of the word head, see head (disambiguation). ... This article or section does not adequately cite its references or sources. ... In human anatomy, the forehead or brow is the bony part of the head above the eyes. ... For other uses, see Ear (disambiguation). ... The visible part of the human nose is the protruding part of the face that bears the nostrils. ... Sagittal section of nose mouth, pharynx, and larynx. ... This article includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... A humans visible teeth. ... The mandible (from Latin mandibÅ­la, jawbone) or inferior maxillary bone is, together with the maxilla, the largest and strongest bone of the face. ... For other uses, see Face (disambiguation). ... Look up Cheek in Wiktionary, the free dictionary The Cheeks are the fleshy area of the face below the eyes and between the nose and the left or right ear, the skin being suspended by the chin and the yaws. ... Look up Chin in Wiktionary, the free dictionary. ... Image File history File links Human body features (external) Created by Vsion. ... A human neck. ... This article does not cite any references or sources. ... The larynx (plural larynges), colloquially known as the voicebox, is an organ in the neck of mammals involved in protection of the trachea and sound production. ... For other uses, see Adams apple (disambiguation). ... TORSO: Shoulders – Spine – Breast – Chest – Ribcage – Abdomen – Navel The human torso Torso is an anatomical term for the greater part of the human body without the head and limbs. ... This article is about the body part. ... The vertebral column seen from the side Different regions (curvatures) of the vertebral column The vertebral column (backbone or spine) is a column of vertebrae situated in the dorsal aspect of the abdomen. ... For other uses, see Breast (disambiguation). ... Male Chest The chest is a part of the anatomy of humans and various other animals. ... The human rib cage. ... The human abdomen (from the Latin word meaning belly) is the part of the body between the pelvis and the thorax. ... This article does not cite any references or sources. ... Sex organs (Clitoris/Vagina/Ovary/Uterus/Penis/Scrotum/Testicle) – Hip – Anus – Buttocks LIMBS: Arm – Elbow – Forearm – Wrist – Hand – Finger (Thumb/Index/Middle/Ring/Little) – Leg – Lap – Thigh – Knee – Calf – Heel – Ankle – Foot – Toe (Hallux) Genitalia masculina externa A sex organ, or primary sexual characteristic, as narrowly defined, is any of those anatomical parts of the body which are involved in sexual reproduction and constitute the reproductive system in a complex organism; namely: Male: testicles, penis, prepuce, scrotum, prostate, seminal vesicles, epididymis, Cowpers glands... The clitoris is a sexual organ that is present in biologically female mammals. ... The vagina, (from Latin, literally sheath or scabbard ) is the tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. ... // For ovary as part of plants see ovary (plants) An ovary is an egg-producing reproductive organ found in female organisms. ... This article is about female reproductive anatomy. ... The penis (plural penises, penes) is an external male sexual organ. ... In some male mammals, the scrotum is a protuberance of skin and muscle containing the testicles. ... Look up testes in Wiktionary, the free dictionary. ... In anatomy, the hip is the bony projection of the femur which is known as the greater trochanter, and the overlying muscle and fat. ... Female Human Anatomy Male Human Anatomy This article is about the bodily orifice. ... Bottom commonly refers to the human buttocks but also has other uses. ... A limb (from the Old English lim) is a jointed, or prehensile (as octopus tentacles or new world monkey tails), appendage of the human or animal body; a large or main branch of a tree; a representative, branch or member of a group or organization. ... Look up ARM in Wiktionary, the free dictionary. ... This article is about the joint in the arm. ... // The Human Forearm The forearm is the structure on the upper limb, between the elbow and the wrist. ... In human anatomy, the wrist is the flexible and narrower connection between the forearm and the palm. ... For other uses, see Hand (disambiguation). ... This article does not cite any references or sources. ... The thumb is one of the five fingers. ... The Index finger The index finger, pointer finger or forefinger is the second digit of a human hand, located between the thumb and the middle finger. ... This article is about the vulgar gesture. ... The ring finger on this hand is extended. ... The little finger, often called the pinky in American English and pinkie in Scottish English (from the Dutch word pink, meaning little finger), is the most ulnar and usually smallest finger of the human hand, opposite the thumb, next to the ring finger. ... In common usage, a human leg is the lower limb of the body, extending from the hip to the ankle, and including the thigh, the knee, and the cnemis. ... Manuel Márquez de León International Airport (IATA: LAP, ICAO: MMLP) is an international airport located at La Paz, Baja California Sur, Mexico. ... In humans the thigh is the area between the pelvis and buttocks and the knee. ... For other uses, see Knee (disambiguation). ... The calf or gastrosoleus is a pair of muscles—the gastrocnemius and soleus—at the back of the lower human leg. ... For other uses, see Heel (disambiguation). ... For a review of anatomical terms, see Anatomical position and Anatomical terms of location. ... For other uses, see Foot (disambiguation). ... Toes on foot. ... Toes on foot. ... SKIN: Hair