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Encyclopedia > Lens (anatomy)
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.
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 lens or crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to focus on the retina. Redrawing of Image:Focus in an eye. ... This article needs to be cleaned up to conform to a higher standard of quality. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber and provides most of an eyes optical power [1]. Together with the lens, the cornea refracts light and consequently helps the eye to focus. ... This article refers to refraction in waves. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength. ... Look up focus in Wiktionary, the free dictionary. ... Human eye cross-sectional view. ...


In humans, the refractive power of the lens in its natural environment is approximately 15 dioptres, roughly one-fourth of the eye's total power. Optical power or dioptric power or refractive power is the degree to which a lens or mirror converges or diverges light. ... A dioptre (also diopter) is a unit of curvature equal to one per metre; that is, inverse metres, or 1/(metres). ...


The lens is flexible and its curvature is controlled by ciliary muscles. By changing the curvature of the lens, one can focus the eye on objects at different distances from it. This process is called accommodation. The ciliary muscle is a muscle that affects zonules in the eye (fibers that suspend the lens in position during accommodation), enabling changes in lens shape for light focusing. ... The Accommodation Reflex is a reflex action of the eye, in response to focusing on a near object, then looking at distant object (and vice versa). ...


The lens is made of transparent proteins called crystallins. It is about 5 mm thick and has a diameter of about 9 mm for an adult human (though these figures can vary). The proteins are arranged in approximately 20,000 thin concentric layers, with a refractive index (for visible wavelengths) varying from approximately 1.406 in the central layers down to 1.386 in less dense cortex of the lens[1]. This index gradient enhances the optical power of the lens. The lens is included into the capsular bag, maintained by the zonules of Zinn. 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 refractive index of a material is the factor by which the phase velocity of electromagnetic radiation is slowed relative to vacuum. ... A gradient-index lens with a parabolic variation of refractive index (n) with radial distance (x). ... Optical power or dioptric power or refractive power is the degree to which a lens or mirror converges or diverges light. ...


During the fetal stage, the development of the lens is aided by the hyaloid artery. In adults, the lens depends entirely upon the aqueous and vitreous humors for nourishment. Fetus at eight weeks Foetus redirects here. ... The hyaloid artery is a branch of the ophthalmic artery, which is itself a branch of the carotid artery. ... 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. ... Vitreous humour is the clear gel that fills the eyeball, lying between the lens and the retina in the eye. ... Nutrition is interpreted as the study of the organic process by which an organism assimilates and uses food and liquids for normal functioning, growth and maintenance and to maintain the balance between health and disease. ...


Diseases

  • A cataract is an opacification of the normally transparent crystalline lens that leads to blurred vision.

For the band with this name, see Cataract (band). ...

References

  1. ^  Hecht, Eugene. Optics, 2nd ed. (1990), p178. Addison Wesley. ISBN 0-201-11609-X.

See also


Aphakia is the absence of the lens of the eye, due to surgical removal, perforating wound or ulcer, or congenital anomaly; causes a loss of accommodation, hyperopia, and a deep anterior chamber. ... This article needs to be cleaned up to conform to a higher standard of quality. ... This article needs to be cleaned up to conform to a higher standard of quality. ... The human iris The iris is the grey-brown area. ... A lens. ... The lens capsule is a component of the eye. ... Phacoemulsification refers to modern cataract surgery in which the human lens is emulsified with an ultrasonic handpiece which employs irrigation of balanced salt solution for aspiration of lens material as well as cooling the handpiece. ... Presbyopia is the eyes diminished power of accommodation that occurs with aging. ... Visual perception is one of the senses, consisting of the ability to detect light and interpret (see) it as the perception known as sight or naked eye vision. ...

Sensory system - Visual system - Eye
Anterior chamber - Aqueous humour - Blind spot - Choroid - Ciliary body - Conjunctiva - Cornea - Iris - Lens - Macula - Optic disc - Optic fovea - Posterior chamber - Pupil - Retina - Schlemm's canal - Sclera - Tapetum lucidum - Trabecular meshwork - Vitreous humour


(See also sense) A sensory system is a part of the nervous system that consists of sensory receptors, neural pathways, and those parts of the brain responsible for processing the information. ... The visual system is what allows us to see. ... This article needs to be cleaned up to conform to a higher standard of quality. ... The anterior chamber if the fluid-filled space inside the eye between the iris and the corneas innermost surface, the endothelium . ... 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. ... In anatomy, ones blind spot is the region of the retina where the optic nerve and blood vessels pass through to connect to the back of the eye. ... The choroid is a collection of blood vessels in the rear of the eye that oxygenate the retina; it is located beneath the sclera. ... There are two sets of ciliary muscles in the eye. ... The conjunctiva is a membrane that covers the sclera (white part of the eye) and lines the inside of the eyelids. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber and provides most of an eyes optical power [1]. Together with the lens, the cornea refracts light and consequently helps the eye to focus. ... The human iris The iris is the grey-brown area. ... Human eye cross-sectional view. ... The optic disc or optic nerve head is the point in the eye where the optic nerve fibres enters the retina; it is not sensitive to light. ... The fovea, a part of the eye, is a spot located in the center of the macula. ... The human eye The pupil is the central transparent area (showing as black). ... Human eye cross-sectional view. ... Schlemms canal, also known as canal of Schlemm, is a circular channel in the eye that collects aqueous humor from the anterior chamber and delivers it into the bloodstream . ... The sclera is the white outer coating of the eye. ... tapetum lucidum in a calf eye, with the retina hanging down The tapetum lucidum (Latin: bright carpet) is a reflecting layer immediately behind, and sometimes within, the retina of the eye of many vertebrates (though not humans); it serves to reflect light back to the retina, increasing the quantity of... 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). ... Vitreous humour is the clear aqueous solution that fills the space between the lens and the retina of the vertebrate eyeball. ...

Sensory system - Visual system

Eye - Optic nerve - Optic chiasm - Optic tract - Lateral geniculate nucleus - Optic radiations - Visual cortex (See also sense) A sensory system is a part of the nervous system that consists of sensory receptors, neural pathways, and those parts of the brain responsible for processing the information. ... The visual system is what allows us to see. ... This article needs to be cleaned up to conform to a higher standard of quality. ... The optic nerve is the nerve that transmits visual information from the retina to the brain. ... 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. ... The lateral geniculate nucleus (LGN) of the thalamus is a part of the brain, which is the primary processor of visual information, received from the retina, in the CNS. Schematic diagram of the primate lateral geniculate nucleus. ... Right superior quadrantanopia. ... The visual cortex is the general term applied to both the primary visual cortex (also known as striate cortex or V1) and upstream visual cortical areas also known as extrastriate cortical areas (V2, V3, V4, V5). ...


  Results from FactBites:
 
Lens Anatomy and Types of Cataracts (506 words)
The anterior side of the lens is the side exposed to the outside of the eye and the posterior side of the lens is the side inside the eyeball.
When describing the anatomy of the lens, the terms "primary lens fibers" and "secondary lens fibers" are not normally used.
The layer of cells that covers the anterior surface of the lens would then be said to be located along the anterior surface of the lens cortex.
The Crystalline Lens (3008 words)
The crystalline lens is composed of 4 layers, from the surface to the center:
This adjustment in lens shape, to focus at various distances, is referred to as “accommodation” or the “accommodative process” and is associated with a concurrent constriction (decrease in size) of the pupil.
Through this opening, the lens nucleus is removed, either as a whole or by dissolving it into tiny pieces and vacuuming out the pieces, a procedure called “phacoemulsification.” Next, the lens cortex also is sucked out, leaving the lens capsule in place, and into the lens capsule is inserted the artificial lens implant.
  More results at FactBites »

 
 

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