Ophthalmic manifestations of systemic diseases--part 1: phakomatoses, hematologic malignancies, metastases, and histiocytosis.

The orbit can be secondarily involved in various systemic conditions. The ophthalmic involvement is often the first clue to the presence of an underlying systemic condition. The ophthalmic involvement in systemic diseases can be either ocular or extraocular. The extent of involvement can be well delineated by imaging modalities like computed tomography and magnetic resonance imaging. In the first part of the article, we provide an overview of systemic diseases affecting the orbit, briefly discuss the modalities for orbital imaging, and discuss the imaging appearances of ophthalmic involvement in (1) phakomatoses, (2) hematologic malignancies, (3) metastases, and (4) histiocytosis. At the end of the 2-part article, we discuss a pattern-based approach and differential diagnosis of orbital lesions in systemic diseases.