retina


retina
/ret"n euh, ret"neuh/, n., pl. retinas, retinae /ret"n ee'/. Anat.
the innermost coat of the posterior part of the eyeball that receives the image produced by the lens, is continuous with the optic nerve, and consists of several layers, one of which contains the rods and cones that are sensitive to light. See diag. under eye.
[1350-1400; ME ret(h)ina < ML retina, perh. equiv. to L ret- (s. of rete) net + -ina -INE1]

* * *

Layer of nerve tissue covering the back two-thirds of the eyeball.

Light focused onto the retina by the lens of the eye stimulates two types of light-sensitive cells: rods, which are sensitive to low light levels, and cones, which provide detailed vision and colour perception. Chemical changes in these cells trigger nerve impulses, which are assembled by complex connections among retinal nerves into a pattern to be carried through the optic nerve to the visual centres of the brain. Disorders affecting the retina or the macula in its centre decrease vision and can cause blindness. See also detached retina; macular degeneration.

* * *

      layer of nervous tissue that covers the inside of the back two-thirds of the eyeball, in which stimulation by light occurs, initiating the sensation of vision. The retina is actually an extension of the brain, formed embryonically from neural tissue and connected to the brain proper by the optic nerve.

      The retina is a complex transparent tissue consisting of several layers, only one of which contains light-sensitive photoreceptor cells. Light must pass through the overlying layers to reach the photoreceptor cells, which are of two types, rods (rod) and cones (cone), that are differentiated structurally by their distinctive shapes and functionally by their sensitivity to different kinds of light. Rods predominate in nocturnal animals and are most sensitive to reduced light intensities; in humans they provide night vision and aid in visual orientation. Cones are more prominent in humans and those animals that are active during the day and provide detailed vision (as for reading) and colour perception. In general, the more cones per unit area of retina, the finer the detail that can be discriminated by that area. Rods are fairly well distributed over the entire retina, but cones tend to concentrate at two sites: the fovea centralis, a pit at the rear of the retina, which contains no rods and has the densest concentration of cones in the eye, and the surrounding macula lutea, a circular patch of yellow-pigmented tissue about 5 to 6 mm (0.2 to 0.24 inch) in diameter.

      When light enters the eye, it passes through the cornea and the lens and is refracted, focusing an image onto the retina. Light-sensitive molecules in the rods and cones react to specific wavelengths of light and trigger nerve impulses. Complex interconnections (synapses) between and within retinal cell layers assemble these impulses into a coherent pattern, which in turn is carried through the optic nerve to the visual centres of the brain, where they are further organized and interpreted.

* * *


Universalium. 2010.

Look at other dictionaries:

  • Retina — Saltar a navegación, búsqueda La retina de los vertebrados es un tejido sensible a la luz situado en la superficie interior del ojo. Es similar a una tela donde se proyectan las imágenes. La luz que incide en la retina desencadena una serie de… …   Wikipedia Español

  • retina — f. anat. La más interna de las tres túnicas del globo ocular; rodea el cuerpo vítreo y continúa por la parte trasera con el nervio óptico. La túnica es sensible a la luz y está integrada por una membrana nerviosa compuesta por nueve capas… …   Diccionario médico

  • Retina — (от англ. retina  сетчатка)  название ЖК дисплея используемого в устройствах Apple отличающегося более высоким заявленным разрешением  326 ppi. Опираясь на исследования, что человеческий глаз может различить только 300 ppi,… …   Википедия

  • Retina — bezeichnet: in der Anatomie die Netzhaut im Auge eine Kamera Reihe der Firma Kodak eine Sorte des Kulturapfel (Malus domestica), siehe Retina (Apfel) ein astronomisches Objekt, siehe Retina Nebel …   Deutsch Wikipedia

  • retină — RETÍNĂ, retine, s.f. Membrană nervoasă, sensibilă la lumină, situată în fundul ochiului şi alcătuită din mai multe straturi de celule, pe care se formează imaginea vizuală. – Din fr. rétine. Trimis de LauraGellner, 08.07.2004. Sursa: DEX 98 … …   Dicționar Român

  • retina (1) — {{hw}}{{retina (1)}{{/hw}}s. f. (anat.) Membrana del fondo oculare sensibile alle stimolazioni luminose. retina (2) {{hw}}{{retina (2)}{{/hw}}s. f. 1  Dimin. di rete . 2 Reticella per trattenere i capelli …   Enciclopedia di italiano

  • retina — (n.) late 14c., from M.L. retina, probably from V.L. (tunica) *retina, lit. net like tunic, on resemblance to the network of blood vessels at the back of the eye, and ultimately from L. rete net. The V.L. phrase may be Gerard of Cremona s 12c.… …   Etymology dictionary

  • retina — rètina ž <G mn rȅtīnā> DEFINICIJA anat. unutarnja opna očne jabučice koja prima svjetlosne podražaje; mrežnica ETIMOLOGIJA srlat. retina ≃ lat. rete: mreža …   Hrvatski jezični portal

  • Retina — Ret i*na, n. [NL., from L. rete a net. Cf. {Reticule}.] (Anat.) The delicate membrane by which the back part of the globe of the eye is lined, and in which the fibers of the optic nerve terminate. See {Eye}. [1913 Webster] Note: The fibers of the …   The Collaborative International Dictionary of English

  • Retina — Retina, Netzhaut, Verband von ⇒ Lichtsinneszellen bei Wirbellosen und Wirbeltieren; Ort der Abbildung der Gegenstände aus der Umwelt im Auge. Die R. der Wirbeltiere enthält als Teil des Zwischenhirns neben den Sinneszellen verschiedene Typen von… …   Deutsch wörterbuch der biologie

  • retina — s. f. 1. A mais interior das membranas do globo ocular e em que se formam as imagens. 2. Tecido encorpado para sobretudo ou terno (também chamado ratina).   ‣ Etimologia: latim tardio *retina, do latim rete, is, rede …   Dicionário da Língua Portuguesa


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.