Iris pigment epithelium


The iris pigment epithelium (IPE) is a two-cell thick layer of cuboidal cells lying behind the iris. Both layers are jet black due to the numerous large melanosomes which pack the cytoplasm of each cell. Towards the central axis, the IPE terminates at the pupillary margin. Peripherally, the IPE is continuous with the ciliary epithelium, also double-layered but pigmented in only one layer. The ciliary epithelium is continuous in its turn with the multilayered retina, which has an outermost pigmented layer, the retinal pigment epithelium (RPE). Despite their very different functions and histological appearances, these regions have a common origin from the two layers of the embryological optic cup, which is derived from the neural crest. The melanosomes of the IPE are distinctive, being larger, blacker and rounder than those in the ciliary epithelium or RPE.


All of these pigmented layers, including the IPE, help to optimise visual contrast by reducing internal reflected light, just as the black paint does inside a camera. The RPE and ciliary epithelium also have well-understood metabolic roles. No analogous functions for the IPE are known so far, but its intimate contact with the aqueous humour and with the iris stroma make it likely that significant metabolic functions will be found. It can be stimulated in vivo to adopt some of the functions of the RPE, including the abilities to metabolise retinol and to engulf photoreceptor outer segments. This has led to interest in the IPE as a tissue which is much more accessible than RPE, and which, perhaps, can be substituted for RPE cells in research on outer retinal diseases.


The IPE is affected by glaucoma, diabetes, and iris inflammations and atrophies of various kinds, generally responding by showing patchy thinning and depigmentation. In complete ocular albinism it is nonpigmented and translucent, which contributes to the photophobia of that condition. However, diseases specific to the IPE itself are almost non-existent, and it seems to be a highly differentiated, stable cell type that almost never gives rise to malignancies, unlike the melanocytes of the iris stroma. Reports of adenomas and adenocarcinomas of the IPE exist, but some of these are debatable.

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Iris (anatomy) — Iris The iris is the blue area. The other structures visible are the pupil center and the white sclera surrounding the iris. The overlying cornea is pictured, but not visible, as it is transparent …   Wikipedia

  • Iris dilator muscle — Iris, front view. (Muscle visible but not labeled.) …   Wikipedia

  • Iris sphincter muscle — Iris, front view. (Muscle visible but not labeled.) …   Wikipedia

  • Epithelium — The outside layer of cells that covers all the free, open surfaces of the body including the skin, and mucous membranes that communicate with the outside of the body. By contrast the endothelium is the layer of cells lining the closed internal… …   Medical dictionary

  • epithelium pigmentosum iridis — [TA] pigmented epithelium of iris: the anterior epithelium of the iris, situated just posterior to the stroma, that contains pigment cells …   Medical dictionary

  • pigment seam — the portion of the pigmented epithelium of the iris which bends forward around the pupillary border …   Medical dictionary

  • Corneal epithelium — Vertical section of human cornea from near the margin. (Waldeyer.) Magnified. 1. Epithelium. 2. Anterior elastic lamina. 3. substantia propria. 4. Posterior elastic lamina. 5. Endothelium of the anterior chamber. a. Oblique fibers …   Wikipedia

  • ectropión congénito del epitelio pigmentario del iris — Eng. Congenital ectropion of the pigment epithelium of the iris Anomalía rara, generalmente unilateral, caracterizada por la presencia de epitelio pigmentario del iris en toda o parte de la cara anterior del borde pupilar …   Diccionario de oftalmología

  • Eye color — is a polygenic trait and is determined by the amount and type of pigments in the eye s iris.Wielgus AR, Sarna T. Melanin in human irides of different color and age of donors. Pigment Cell Res. 2005 Dec; 18(6):454 64. PMID 16280011.] Prota G, Hu… …   Wikipedia

  • Uvea — Infobox Anatomy Name = PAGENAME Latin = tunica vasculosa bulbi GraySubject = GrayPage = Caption = Horizontal section of the eyeball. (Iris labeled at top, ciliary body labeled at upper right, and choroid labeled at center right.) Caption2 =… …   Wikipedia

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.