Iris pigment epithelium

The iris pigment epithelium (IPE) is a one cell thick layer of cuboidal cells lying behind the iris. The epithelial cells are highly pigmented 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 inner, non-pigmented layer of the ciliary epithelium. The iris dilator muscle is strictly attached to the anterior side of the iris pigmented epithelium and represents the anterior continuation of the pigmented ciliary epithelium. The ciliary epithelia represent the anterior continuation of the multilayered retina, whose retinal pigmented epithelium (RPE) corresponds to the pigmented ciliary epithelium, while the multilayered sensory retina fades into the non-pigmented ciliary epithelium. Despite their very different functions and histological appearances, these regions have a common origin from the two layers of the embryological optic cup. The melanosomes of the IPE are distinctive, being larger, blacker and rounder than those in the ciliary epithelium or RPE.[1]

Main article: iris (anatomy)

Pathology

The IPE is affected by glaucoma, diabetes, and iris inflammations and atrophies of various kinds, generally responding by showing patchy thinning and depigmentation. In albinism, it is fully or partially 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.

gollark: No, I like that one.
gollark: The problems I have with our system are more about issues we ended up with than the entire general concept of markets.
gollark: You could complain that this is due to indoctrination of some sort by... someone, and maybe this is true (EDIT: but you could probably just change that and it would be easier than reworking the entire economy). But you can quite easily see examples of people just not actually caring about hardships far away, and I think this is a thing throughout history.
gollark: What I'm saying is that, despite some problems, our market system is pretty effective at making the things people involved in it want. And most people do not *actually* want to help people elsewhere much if it comes at cost to them.
gollark: Yep!

References
  1. Ross M, Pawlina W. Histology. 5th ed. Baltimore, MD: Lippincott Wiliams & Wilkins; 2006.
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