Fig. 2

Zones of the right eye and appearance of retinal vasculature according to ROP stage. Zone I, the most posterior, is a circular zone centred on the optic nerve and with a radius twice the distance (2x) from the centre of the optic nerve to the centre of the macula (x). Zone II represents a middle zone, concentric to zone I, extending from the border of zone I to the nasal ora serrata (furthest extent of the nasal retina). Zone II is itself subdivided into a posterior zone II, two disc diameters out from the border of zone I, and anterior zone II encompassing the remaining peripheral area of zone II. Zone III is the most peripheral zone extending from the temporal border of zone II and capturing a remaining temporal crescentic area beyond zone II. ROP is likely to be more severe when located in zone I or posterior zone II. Stages 1–3 can occur in any zone of the eye. Here, they are shown in zone II for clarity