The iris pigment epithelium (IPE) is a one cell thick layer of cuboidal cells lying behind the

iris Iris most often refers to: *Iris (anatomy), part of the eye *Iris (mythology), a Greek goddess * ''Iris'' (plant), a genus of flowering plants * Iris (color), an ambiguous color term Iris or IRIS may also refer to: Arts and media Fictional ent ...

. The epithelial cells are highly pigmented due to the numerous large

melanosome A melanosome is an organelle found in animal cells and is the site for synthesis, storage and transport of melanin, the most common light-absorbing pigment found in the animal kingdom. Melanosomes are responsible for color and photoprotection i ...

s 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 The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then p ...

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

Pathology

The IPE is affected by

glaucoma Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...

diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level (hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...

, 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.

References

{{Reflist Human iris