Table 1.

Definitions of ROP Severity Categories for STOP-ROP

Threshold ROP*
 Zone IIPresence of posterior pole dilation/tortuosity in at least 2 posterior pole quadrants (plus disease), and stage 3 ROP for at least 5 contiguous clock h or 8 composite clock h
 Zone IROP (any stage) with posterior pole dilation/tortuosity in at least 2 posterior pole quadrants (plus disease), or stage 3 ROP, with or without plus disease
Beyond thresholdStage 4 ROP, stage 5 ROP, or massive vitreal hemorrhage obscuring the view of the fundus
Prethreshold ROP
 Zone IIAny number of clock hours of stage 3 ROP, less than threshold severity, or any stage 2 ROP with at least 2 quadrants of posterior pole dilation/tortuosity disease (plus disease)
 Zone IAny ROP less than threshold severity
  • Stages and zones based on the international classification of ROP.24

  • * The definition of threshold ROP differs somewhat from that used in the CRYO-ROP study4 in 2 ways: 1) In the CRYO-ROP study, “plus disease” was a global assessment of the posterior pole and was not determined according to number of quadrants involved, and 2) in the CRYO-ROP study, the definition of threshold was the same for both zone I and zone II and is the same as stated for zone II above (except for the number of quadrants of posterior pole dilation/tortuosity, as described in note 1). In STOP-ROP, a less stringent definition of threshold in zone I was used to accommodate the clinical judgment of a majority of the participating ophthalmologists that earlier treatment was needed to improve the poor outcomes of zone I threshold ROP.