The human eye is an organ which reacts to light for several purposes.
As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can distinguish about 16 million colors.
In common with the eyes of other mammals, the human eye's non-image-forming photosensitive ganglion cells in the retina receive the light signals which affect adjustment of the size of the pupil, regulation and suppression of the hormone melatonin and entrainment of the body clock.
Posterior chamber of eyeball
The posterior chamber should not be confused with vitreous chamber. The posterior chamber is a narrow chink behind the peripheral part of the iris of the lens, and in front of the suspensory ligament of the lens and the ciliary processes the Posterior Chamber consists of small space directly posterior of the Iris but anterior to the lens.
Ora serrata
The ora serrata is the serrated junction between the retina and the ciliary body. This junction marks the transition from the simple non-photosensitive area of the retina to the complex, multi-layered photosensitive region. In animals in which the region does not have a serrated appearance, it is called the ora ciliaris retinae.
Ciliary muscle
The ciliary muscle is a ring of striated smooth muscle in the eye's middle layer that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humour into Schlemm's canal. The muscle has parasympathetic and sympathetic innervation.
Zonule of Zinn
The zonule of Zinn is a ring of fibrous strands connecting the ciliary body with the crystalline lens of the eye.
The zonule of Zinn is split into two layers: a thin layer, which lines the hyaloid fossa, and a thicker layer, which is a collection of zonular fibers. Together, the fibers are known as the suspensory ligament of the lens.
Schlemm's canal
Schlemm's 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 via the anterior ciliary veins.
The canal is essentially an endothelium-lined tube, resembling that of a lymphatic vessel. On the inside of the canal, nearest to the aqueous humor, it is covered by the trabecular meshwork, this region makes the greatest contribution to outflow resistance of the aqueous humor.
Named after Friedrich Schlemm (1795-1858), a German anatomist.
Pupil
The pupil is an opening located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In optical terms, the anatomical pupil is the eye's aperture and the iris is the aperture stop. The image of the pupil as seen from outside the eye is the entrance pupil, which does not exactly correspond to the location and size of the physical pupil because it is magnified by the cornea. On the inner edge lies a prominent structure, the collarette, marking the junction of the embryonic pupillary membrane covering the embryonic pupil.
Anterior chamber of eyeball
The anterior chamber is the fluid-filled space inside the eye between the iris and the cornea's innermost surface, the endothelium. Aqueous humor is the fluid that fills the anterior chamber. Hyphema and glaucoma are two main pathologies in this area. In hyphema, blood fills the anterior chamber. In glaucoma, blockage of the canal of Schlemm prevents the normal outflow of aqueous humor, resulting in accumulation of fluid, increased intraocular pressure, and eventually blindness.
One peculiar feature of the anterior chamber is dampened immune response to allogenic grafts. This is called anterior chamber associated immune deviation (ACAID), a term introduced in 1981 by Streilein et al.
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. While the cornea contributes most of the eye's focusing power, its focus is fixed. The curvature of the lens, on the other hand, can be adjusted to "tune" the focus depending upon the object's distance. Medical terms related to the cornea often start with the prefix "kerat-" from the Greek word κέρας, horn.
Iris
The iris is an anatomical structure in the eye, responsible for controlling the diameter and size of the pupils and the amount of light reaching the pupil. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel (light brown). In response to the amount of light entering the eye, muscles attached to the iris expand or contract the aperture at the center of the iris, known as the pupil. The larger the pupil, the more light can enter.
The plural form of iris, in this context, is irides.
Lens
The lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina. This adjustment of the lens is known as accommodation (see also Accommodation, below). It is similar to the focusing of a photographic camera via movement of its lenses. The lens is flatter on its anterior side.
The lens is also known as the aquula (Latin, a little stream, dim. of aqua, water) or crystalline lens. In humans, the refractive power of the lens in its natural environment is approximately 18 dioptres, roughly one-third of the eye's total power.
The lens is also known as the aquula (Latin, a little stream, dim. of aqua, water) or crystalline lens. In humans, the refractive power of the lens in its natural environment is approximately 18 dioptres, roughly one-third of the eye's total power.
Ciliary processes
The ciliary processes are formed by the inward folding of the various layers of the choroid, i.e., the choroid proper and the lamina basalis, and are received between corresponding foldings of the suspensory ligament of the lens.
Conjunctiva
The conjunctiva is a clear mucous membrane consisting of cells and underlying basement membrane that covers the sclera (white part of the eye) and lines the inside of the eyelids. It is made up of the rare non-keratinizing squamous epithelium.
Inferior oblique muscle
The Obliquus oculi inferior (inferior oblique) is a thin, narrow muscle, placed near the anterior margin of the floor of the orbit.
Inferior rectus muscle
The inferior rectus muscle is a muscle in the orbit. It depresses, adducts, and helps extorts the eye. As with most of the muscles of the orbit, it is innervated by the oculomotor nerve (Cranial Nerve III).
Medial rectus muscle
The medial rectus muscle is a muscle in the orbit. As with most of the muscles of the orbit, it is innervated by the inferior division of the oculomotor nerve (Cranial Nerve III).
This muscle shares an origin with several other extrinsic eye muscles, the anulus tendineus, or common tendon. It is the largest of the extraocular muscles and its only action is adduction of the eyeball. Its function is to bring the pupil closer to the midline of the body. It is tested clinically by asking the patient to look medially.
Retina
The vertebrate retina is a light sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses. These are sent to various visual centers of the brain through the fibers of the optic nerve.
In vertebrate embryonic development, the retina and the optic nerve originate as outgrowths of the developing brain, so the retina is considered part of the central nervous system (CNS).It is the only part of the CNS that can be visualized non-invasively.
The retina is a complex, layered structure with several layers of neurons interconnected by synapses. The only neurons that are directly sensitive to light are the photoreceptor cells. These are mainly of two types: the rods and cones. Rods function mainly in dim light and provide black-and-white vision, while cones support daytime vision and the perception of colour. A third, much rarer type of photoreceptor, the photosensitive ganglion cell, is important for reflexive responses to bright daylight.
Neural signals from the rods and cones undergo complex processing by other neurons of the retina. The output takes the form of action potentials in retinal ganglion cells whose axons form the optic nerve. Several important features of visual perception can be traced to the retinal encoding and processing of light.
Optic disc
The optic disc or optic nerve head is the location where ganglion cell axons exit the eye to form the optic nerve. There are no light sensitive rods or cones to respond to a light stimulus at this point. This causes a break in the visual field called "the blind spot" or the "physiological blind spot". The optic nerve head in a normal human eye carries from 1 to 1.2 million neurons from the eye towards the brain.
Dura mater
The dura mater or dura, is the outermost of the three layers of the meninges surrounding the brain and spinal cord. The other two meningeal layers are the pia mater and the arachnoid mater. The dura surrounds the brain and the spinal cord and is responsible for keeping in the cerebrospinal fluid. The name "dura mater" is derived from the Latin "hard mother", and is also referred to by the term "pachymeninx" (plural "pachymeninges").The dura has been described as "tough and inflexible" and "leather-like".
Central retinal artery
The central retinal artery (retinal artery) branches off the ophthalmic artery, running inferior to the optic nerve within its dural sheath to the eyeball.
Central retinal vein
The central retinal vein (retinal vein) is a short vein that runs through the optic nerve and drains blood from the capillaries of the retina into the larger veins outside the eye. The anatomy of the veins of the orbit of the eye varies between individuals, and in some the central retinal vein drains into the superior ophthalmic vein, and in some it drains directly into the cavernous sinus.
Optic nerve
The optic nerve, also called cranial nerve II, transmits visual information from the retina to the brain.
Vorticose veins
The outer layer of the choroid (lamina vasculosa) consists, in part, of the larger branches of the short ciliary arteries which run forward between the veins, before they bend inward to end in the capillaries, but is formed principally of veins, named, from their arrangement, the vorticose veins.
They converge to four or five equidistant trunks, which pierce the sclera about midway between the sclero-corneal junction and the entrance of the optic nerve.They drain uveal tract.
Tenon's capsule
The fascia bulbi (also known as the capsule of Ténon and the bulbar sheath) is a thin membrane which envelops the eyeball from the optic nerve to the limbus, separating it from the orbital fat and forming a socket in which it plays.
Its inner surface is smooth, and is separated from the outer surface of the sclera by the periscleral lymph space.This lymph space is continuous with the subdural and subarachnoid cavities, and is traversed by delicate bands of connective tissue which extend between the fascia and the sclera.
The fascia is perforated behind by the ciliary vessels and nerves, and fuses with the sheath of the optic nerve and with the sclera around the entrance of the optic nerve.In front it blends with the conjunctiva, and with it is attached to the ciliary region of the eyeball.The structure was named after Jacques-René Tenon (1724-1816), a French surgeon and pathologist.
Macula of retina
The macula or macula lutea (from Latin macula, "spot" + lutea, "yellow") is an oval-shaped highly pigmented yellow spot near the center of the retina of the human eye. It has a diameter of around 5 mm and is often histologically defined as having two or more layers of ganglion cells. Near its center is the fovea, a small pit that contains the largest concentration of cone cells in the eye and is responsible for central vision, and also contains the parafovea and perifovea.
Because the macula is yellow in colour it absorbs excess blue and ultraviolet light that enter the eye, and acts as a natural sunblock or sunglasses for this area of the retina. The yellow colour comes from its content of lutein and zeaxanthin, which are yellow xanthophyll carotenoids, derived from the diet. Zeaxanthin predominates at the macula, while lutein predominates elsewhere in the retina. There is some evidence that these carotenoids protect the pigmented region from some types of macular degeneration.
Structures in the macula are specialized for high acuity vision. Within the macula are the fovea and foveola which contain a high density of cones (photoreceptors with high acuity).
Fovea centralis in macula
The term fovea comes from the Latin, meaning pit or pitfall. As an anatomical term, there are several foveae around the body, including in the head of the femur.
Sclera
The sclera, also known as the white part of the eye, is the opaque (usually white, though certain animals, such as horses and lizards, can have black sclera), fibrous, protective, outer layer of the eye containing collagen and elastic fiber. In the development of the embryo, the sclera is derived from the neural crest. In children, it is thinner and shows some of the underlying pigment, appearing slightly blue. In the elderly, fatty deposits on the sclera can make it appear slightly yellow.
Choroid
The choroid, also known as the choroidea or choroid coat, is the vascular layer containing connective tissue, of the eye lying between the retina and the sclera. In humans its thickness is about 0.5 mm. The choroid provides oxygen and nourishment to the outer layers of the retina. Along with the ciliary body and iris, the choroid forms the uveal tract.
Superior rectus muscle
The superior rectus muscle is a muscle in the orbit. It is one of the extraocular muscles.It is innervated by the superior division of the oculomotor nerve (Cranial Nerve III).In the primary position (looking straight ahead), the superior rectus muscle's primary function is elevation, although it also contributes to intorsion and adduction.
Retina
The vertebrate retina is a light sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses. These are sent to various visual centers of the brain through the fibers of the optic nerve.
In vertebrate embryonic development, the retina and the optic nerve originate as outgrowths of the developing brain, so the retina is considered part of the central nervous system (CNS). It is the only part of the CNS that can be visualized non-invasively.
The retina is a complex, layered structure with several layers of neurons interconnected by synapses. The only neurons that are directly sensitive to light are the photoreceptor cells. These are mainly of two types: the rods and cones. Rods function mainly in dim light and provide black-and-white vision, while cones support daytime vision and the perception of colour. A third, much rarer type of photoreceptor, the photosensitive ganglion cell, is important for reflexive responses to bright daylight.
Neural signals from the rods and cones undergo complex processing by other neurons of the retina. The output takes the form of action potentials in retinal ganglion cells whose axons form the optic nerve. Several important features of visual perception can be traced to the retinal encoding and processing of light.
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