Pediatric Rotations Retinopathy of Prematurity Retinopathy of prematurity is a neonatal complication, primarily related to exposure to elevated oxygen tension during the period in which the retina is maturing. Embryologically, the retina begins vascularization at 16 weeks gestational age, and is complete on the nasal side by 8 months, and entirely complete at term. The oxygen causes constriction of the capillaries growing in the forming retina, and results in obliteration of the capillary bed. This is followed by neovascularization of the vitreous and retinal edema.
Fibrosis then occurs and is followed by traction and detachment of the retina.
ROP is classified by stage, the number of circumferential clock hours of involved retina, and by zone. Zone I is defined as 30 degrees around the macula, zone II extends to the ora serrata nasally, and to the anatomic equator temporally, and Zone III is the small crescent of remaining temporal territory. A demarcation line between the vascularized and still avascular retina. Histologically, there is evidence of an AV shunt in this tissue. Vessels posterior to the ridge become dilatated and tortuous, engorgement of the iris, hazy vitreous.