Polycythemia vera (PV) is an acquired myeloproliferative disorder characterized by an elevated absolute red blood cell mass caused by uncontrolled red blood cell production, frequently associated with uncontrolled white blood cell and platelet production.

A type of incomitant strabismus in which both elevator muscles (i.e., the inferior oblique and superior rectus muscles) of the same eye are weak leading to restricted elevation and hypotropia.