2.1. Pathogenesis of ROP

Vasculogenesis and angiogenesis are two distinct terms that need to be explained. In the vasculogenesis process, the origin of blood vessels is represented by the endothelial progenitor cells that coalesce and form lumen and vasculogenic networks. In the angiogenesis process, the new vessels form from the existing ones by vascular sprouting [2].

ROP is a biphasic disease directly related to the saturation of oxygen, which is administered in order to maintain the prematurely born vital functions. Phase 1 (between 22 and 30 weeks PCA) is characterized by relative hyperoxia and decreased vascular endothelial growth factors (VEGF) levels. The consequence of this situation is delayed vessel formation. Phase 2 (between 31 and 44 weeks PCA) is defined by relative hypoxia and increased VEGF levels, having as consequence uncontrolled vessel growth.

The cause of ROP is the non-development of retinal vessels with subsequent retinal ischemia and new vessel proliferation [2].
