Table.

International Classification of Retinopathy of Prematurity^a

Location of Disease	Description
Zone I	A circle centered on the optic disc with radius twice the distance from the optic disc to the fovea
Zone II	The region within a circle centered on the optic disc with radius from the optic disc to the nasal ora serrata, excluding the area within zone I
Zone II	The temporal crescent outside of zone II
Staging
Stage 1	A demarcation line that separates the vascular from avascular retina
Stage 2	A ridge separates the vascular from avascular retina
Stage 3	Extraretinal fibrovascular proliferation
Stage 4a	Partial retinal detachment not involving the fovea
Stage 4b	Partial retinal detachment involving the fovea
Stage 5	Total retinal detachment

^aData from International Committee for the Classification of Retinopathy of Prematurity.³²