Background: Cysts of the iris are uncommon and most of them occur secondarily after surgery or penetrating injury. The minority of the iris cysts is primary without a reasonable cause. They are classified into the more common pigment epithelial cysts and the rare cysts of iris stroma ("intrastromal cysts"). These intrastromal iris cysts are generally diagnosed in children and often cause symptoms such as a decrease of visual acuity because of ingrowth into the optical axis. A diagnosis of stromal cysts in adults is very rare. Most of these patients remain without any symptoms and do not need treatment. The cellular origin is so far unknown. Mesoderm, neuroectoderm and surface ectoderm have been discussed in this context.
Case reports: Two patients with primary intrastromal iris cysts are presented, a 5-year-old boy and a 65-year-old woman. In both cases, the cyst affected the optical axis and was removed by sector iridectomy. In histological and electron-microscopic examinations both cysts presented a typical epithelial structure. Immunohistochemical examination revealed positivity for epithelial markers and negativity for mesenchymal and neuroectodermal markers.
Conclusion: Primary intrastromal iris cysts can occur in advanced age and may cause symptoms due to progressive growth. The cellular origin of primary intrastromal iris cysts is controversially discussed in the literature. On electron microscopy and immunohistochemistry, the iris cysts presented here showed characteristic features of surface ectodermal origin.