Clinical meaning
Retinopathy of prematurity (ROP) is a vasoproliferative disorder of the developing retina affecting premature infants. Normal retinal vascularization begins at 16 weeks gestation from the optic disc and progresses peripherally, completing at ~36-40 weeks nasally and 40 weeks temporally. In premature infants, this process is interrupted. ROP pathogenesis occurs in two phases: Phase 1 (vaso-obliterative): hyperoxia from supplemental oxygen causes vasoconstriction and cessation of normal retinal vessel growth; existing immature vessels may regress. Phase 2 (vasoproliferative): the avascular retina becomes ischemic and produces vascular endothelial growth factor (VEGF) and other angiogenic factors, stimulating abnormal neovascularization (new vessel growth). These abnormal vessels are fragile and can cause vitreous hemorrhage, retinal traction, and ultimately retinal detachment and blindness. ROP is classified by zone (I-III, with Zone I being the most posterior/severe), stage (1-5, with stage 5 being total retinal detachment), and the presence of 'plus disease' (dilated and tortuous posterior pole vessels indicating active disease — a key indicator for treatment). Screening is based on gestational age and birth weight criteria.