In ROP, premature birth delays the normal process or retinal vascularization and other factors play a role including oxygen-induced vascular injury. Risk factors can include high oxygen at birth, fluctuations in oxygenation, poor postnatal growth, nutrition, and possible oxidative stress. In developed countries, extreme prematurity related to low birth weight and young gestational age is highly associated with ROP. In countries lacking resources, ROP can occur in larger and older infants. The role of oxygen in the causation of ROP is complex. Studies have shown that keeping the oxygen saturation at a lower level from birth can reduce the rate of advanced ROP, but some have found increased mortality. [26]