Epibulbar osseous choristomas with scleral involvement.

Epibulbar osseous choristomas are rare congenital collections of mature compact bone most often located in the superotemporal fornix. Most cases are not recognized preoperatively, as the lesion is usually felt to represent a dermatolipoma or epibulbar dermoid. Although most previous reports have described a loose attachment to the surrounding orbital structures, we report two cases in which intimate scleral incorporation was present. In one case, preoperative computerized tomography and echography allowed the diagnosis and probable scleral involvement to be considered preoperatively, and surgery was deferred. The embryogenesis of these lesions is uncertain, although they seem to correlate with the scleral ossicles seen in avian anatomy, and may represent abnormal activation of embryonic pluripotential mesenchymal cells.