Iris pigment epithelium (IPE) cysts can be divided anatomically into central, midzonal, peripheral, and dislodged types (1,2).

Central (Pupillary) Cysts. Pupillary cysts can be solitary or multiple. The solitary type is nonfamilial and appears as a round, dark-brown lesion at the pupillary border. The multiple variant is usually sporadic but can be autosomal dominant. It is usually bilateral and is characterized by variable-sized, dark-brown lesions that may encircle the pupil. They often spontaneously collapse and then re-form, producing irregular, wrinkled lesions known as iris flocculi. Even when extensive, they rarely cause visual impairment, and most remain relatively stable throughout the patient’s life (1, 2, 3, 4, 5, 6, 7). Although there are usually no systemic associations, one family had iris flocculi and dissecting aortic aneurysm (5).

Midzonal (Retroiridic) Cysts. The midzonal cyst is usually discovered on routine slit lamp biomicroscopy as a round or fusiform, smooth, dark-brown lesion at the pupillary margin. It can be unilateral or bilateral, solitary or multiple. With pupillary dilation, it becomes more elongated, and its central border sometimes rolls anteriorly over the papillary margin, findings that help to differentiate it from a ciliary body melanoma. Like a melanoma, it blocks the transmission of light.

Iridociliary (Peripheral) Cysts. The more common peripheral cyst is usually unilateral and more common in young women. It presents as an asymptomatic, localized, anterior bulge of the iris stroma, usually on the temporal side, that is noted coincidentally on slit lamp biomicroscopy. With the pupil widely dilated, the cyst can sometimes be visualized with slit lamp biomicroscopy and gonioscopy, and it tends to transmit light because it is partially covered by nonpigmented ciliary epithelium. More often, however, ultrasound biomicroscopy (UBM) is necessary to better demonstrate the lesion. In contrast, a tumor shows a solid pattern, and a cavitary melanoma would appear cystic but would have a thicker wall.

Dislodged Iris Pigment Epithelium Cysts. Any IPE cyst can become dislodged and float freely in the vitreous or anterior chamber (9,16). Free-floating cysts can eventually become fixed in the anterior chamber angle. Unlike melanoma in the angle, a fixed cyst has sharp abrupt borders rather than gradual sessile borders. UBM is an excellent method for the recognition of all types of iris cysts.