Scheme of retina of the right and left eyes showing zone borders and clock hours used to describe the location and extent of retinopathy of prematurity. Diagrammatic representation of the potential total area of the premature retina, with zone I (the most posterior) symmetrically surrounding the optic nerve head (the earliest to develop). A larger retinal area is present temporally (laterally) than nasally (medially) (zone III). Only zones I and II are present nasally. The retinal changes discussed in recommendation 4 are usually recorded on a diagram such as this.
Shown is a schedule for detecting prethreshold ROP with 99% confidence, usually well before any required treatment.
↵a This guideline should be considered tentative rather than evidence-based for infants with a gestational age of 22 to 23 weeks because of the small number of survivors in these gestational-age categories.