But 10 percent do develop a severe enough form that threatens to cause blindness from a separation of the retina from the wall of the eye. It is this fraction that requires treatment to prevent a retinal detachment. The more premature babies are, the more likely retinopathy is to develop, making the odds much higher for two groups of the tiniest premature babies - those with an estimated gestational age of 28 weeks or less, and those with a birthweight of 3.3 pounds. Such babies have up to 35 percent risk of needing treatment to prevent blindness. The laser and freezing treatments, though usually successful in preventing blindness, involve an important trade-off.
Babies born prematurely also are at risk for vision loss from other conditions like lazy eye.
About 10 percent of the tiniest babies will become extremely nearsighted and will have to wear glasses with lenses as thick as Coke bottles for life, beginning in the first year. Infants born months prematurely have immature eyes, and the blood vessels that nourish the retina are often absent. Normally at about the fourth month of fetal life, blood vessels begin to grow from the optic nerve in an orderly fashion until they reach the outer limits of the retina. That usually occurs about the time a full-term baby is born. At best, the blood vessels will continue to grow normally, reaching the outer margins of the retina at term without requiring treatment.