The blood vessels of the retina begin to develop 3 months after conception and complete their development at the time of normal birth. If an infant is born very prematurely, eye development can be disrupted. The vessels may stop growing or grow abnormally from the retina into the normally clear gel that fills the back of the eye. The vessels are fragile and can leak, causing bleeding in the eye.
Scar tissue may develop and pull the retina loose from the inner surface of the eye. In severe cases, this can result in vision loss.
In the past, routine use of excess oxygen to treat premature babies stimulated abnormal vessel growth. Currently, oxygen can be easily and accurately monitored, so this problem is rare.
Today, the risk of developing ROP depends on the degree of prematurity. Generally, the smallest and sickest premature babies have the highest risk.
Typically all babies younger than 30 weeks gestation or weighing fewer than 3 pounds at birth are screened for the condition. Certain high-risk babies who weigh 3 - 4.5 pounds or who are born after 30 weeks should also be screened.
In addition to prematurity, other risks factors may include:
- Brief stop in breathing (apnea)
- Heart disease
- High carbon dioxide (CO2) in the blood
- Low blood acidity (pH)
- Low blood oxygen
- Respiratory distress
- Slow heart rate (bradycardia)
The rate of ROP in moderately premature infants has decreased dramatically with better care in the neonatal intensive care unit. Ironically, however, this has led to high rates of survival of very premature infants who would have had little chance of survival in the past.
Since these very premature infants are at the highest risk of developing ROP, the condition may actually be becoming more common again.