Prethreshold (ET-ROP) : 병변의 범위와 stage보다 plus 유무에 따라 치료 시점 결정 Type 1 (high risk prethreshold ROP) → 바로 laser Tx Zone Ⅰ, any ROP with plus disease Zone Ⅰ, stage 3 ROP without plus disease Zone Ⅱ, stage 2 or 3 with plus disease Type 2 (low risk prethreshold ROP) → 추적관찰 (1주 이내 간격) Zone Ⅰ, stage 1 or 2 ROP without plus disease Zone Ⅱ, stage 3 ROP without plus disease