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Retinal pigment epithelium
Gray881.png
Section of retina. (Pigmented layer labeled at bottom right.)
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Plan of retinal neurons. (Pigmented layer labeled at bottom right.)
Latin stratum pigmentosa retinae, p. pigmentosa retinae
Gray's subject #225 1016

The pigmented layer of retina or retinal pigment epithelium (RPE) is the pigmented cell layer just outside the neurosensory retina that nourishes retinal visual cells, and is firmly attached to the underlying choroid and overlying retinal visual cells.[1][2]

Contents

History

Choroid dissected from a calf's eye, showing black RPE and iridescent blue tapetum lucidum

The RPE was known in the 18th and 19th centuries as the pigmentum nigrum, referring to the observation that the RPE is dark (black in many animals, brown in humans); and as the tapetum nigrum, referring to the observation that in animals with a tapetum lucidum, in the region of the tapetum lucidum the RPE is not pigmented.[3]

Anatomy

The RPE is composed of a single layer of hexagonal cells that are densely packed with pigment granules.[1]

The retina ends at the ora serrata, where the ciliary body begins, and the RPE continues as over the ciliary body, and further, to become the posterior surface of the iris, which generate the cells that compose the dilator muscle of the iris. The other layer, the rod and cone layer (neuroepithelium), continues as a second layer that passes over the ciliary body. Together, the layers are an embryological equivalent of the layer which are together called the ciliary epithelium. The retina's front continuation, the posterior iris epithelium, obtains pigment as it enter the iris area.[4]


When viewed from the outer surface, these cells are smooth and hexagonal in shape. When seen in section, each cell consists of an outer non-pigmented part containing a large oval nucleus and an inner pigmented portion which extends as a series of straight thread-like processes between the rods, this being especially the case when the eye is exposed to light.

Function

The retinal pigment epithelium is involved in the phagocytosis of the outer segment of photoreceptor cells and it is also involved in the vitamin A cycle where it isomerizes all trans retinol to 11-cis retinal.

The retinal pigment epithelium also serves as the limiting transport factor that maintains the retinal environment by supplying small molecules such as amino acid, ascorbic acid and D-glucose while remaining a tight barrier to choroidal blood borne substances. Homeostasis of the ionic environment is maintained by a delicate transport exchange system.

Pathology

In the eyes of albinos, the cells of this layer contain no pigment. Dysfunction of the RPE is found in Age-Related Macular Degeneration and Retinitis Pigmentosa.

References

  1. ^ a b Cassin, B. and Solomon, S. (2001). Dictionary of eye terminology. Gainesville, Fla: Triad Pub. Co. ISBN 0-937404-63-2.  
  2. ^ Boyer MM, Poulsen GL, Nork TM. "Relative contributions of the neurosensory retina and retinal pigment epithelium to macular hypofluorescence." Arch Ophthalmol. 2000 Jan;118(1):27-31. PMID 10636410.
  3. ^ Coscas, Gabriel and Felice Cardillo Piccolino (1998). Retinal Pigment Epithelium and Macular Diseases. Springer. ISBN 0792351444.  
  4. ^ "eye, human."Encyclopædia Britannica from Encyclopædia Britannica 2006 Ultimate Reference Suite DVD 2009

See also

External links

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.

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