Pathophysiology :

ROP is caused by the abnormal vascular development of the retina in pre-terms. The normal vascular development in human fetal retina 16 includes the process of Vasculogenesis and Angiogenesis.

Vasculogenesis :

Migration of large numbers of spindle-shaped mesenchymal precursor cells from the optic disc (completed by 15 weeks of gestation). These cells proliferate and differentiate to produce cords of endothelial cells that forms an immature vascular tree in the inner retinal layer centered on the optic disc. This is followed by Angiogenesis.

Angiogenesis :

The above mentioned immature vascular plexus become denser and gets extended peripherally. The vascular plexus matures by remodeling. The outer plexus starts forming around the incipient fovea between 25 and 26 weeks of gestation. The mature vessels then reach nasal retina followed by temporal retina at term.

Pathological development of vessels in ROP17-20

The vasculature in preterm child is immature. The child receives oxygen supplementation. Free Radicals are produced in the retina causing injury to the developing vascular plexus. This is associated with vasoconstriction and ischemia to the Retinal Pigment Epithelium (RPE). The RPE releases vascular endothelial growth factor (VEGF). This causes proliferative vitreo-retinopathy called ROP. At 16 weeks vasculogenesis begins at the optic disc, nasal ora is reached first followed the temporal ora that vascularise by 42 - 44 weeks.