A rare myeloproliferative neoplasm characterized by stem-cell derived clonal over proliferation of mature myeloid lineages, such as erythrocytes, leukocytes, and megakaryocytes, with variable degrees of megakaryocyte atypia, associated with reticulin and/or collagen bone marrow fibrosis, osteosclerosis, ineffective erythropoiesis, angiogenesis, extramedullary hematopoiesis, and abnormal cytokine expression.

In wound repair, neovascularization (NV) involves the sprouting of new vessels from pre-existent vessels to repair or replace damaged vessels. In the retina, NV is a response to ischemia. The NV adheres to the inner surface of the retina and outer surface of the vitreous. NV are deficient in tight junctions and hence leak plasma into surrounding tissue including the vitreous. Plasma causes the vitreous gel to degenerate, contract, and eventually collapse which pulls on the retina. Since retinal NV is adherent to both retina and vitreous, as the vitreous contracts the NV may be sheared resulting in vitreous hemorrhage or the NV may remain intact and pull the retina with the vitreous resulting in retinal elevation referred to as traction retinal detachment.