The blood vessels of the retina begin to develop about 3 months into pregnancy. They complete development at the time of normal birth. The eyes may not develop properly if a baby is born very early. The vessels may stop growing or grow abnormally from the retina into the back of the eye. The vessels are fragile. They can leak and cause 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, the use of too much oxygen in treating premature babies caused vessels to grow abnormally. Better methods are now available for monitoring oxygen, so this problem is rare.
Today, the risk of developing ROP depends on the degree of prematurity. Smaller babies with more medical problems are at higher risk.
Almost all babies who are born before 30 weeks or weigh fewer than 3 pounds at birth are screened for the condition. Some 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 most premature infants has gone down greatly due to better care in the neonatal intensive care unit (NICU). However, more babies born very early are now able to survive.
Since these very premature infants are at the highest risk for ROP, the problem is being seen more often.