context: The smaller a baby is at birth, the greater his chance of having retinopathy of prematurity ( ROP), an eye disorder that can lead to vision loss. But most babies who are born with it get better over time. Many don't need treatment at all. ROP tends to affect premature babies who weigh less than 2 ¾ pounds and are born before the 31st week of pregnancy. ( A full-term pregnancy lasts 38-42 weeks.) In babies with ROP, abnormal blood vessels grow on the retina of each eye. The retina is the layer of tissue that lines the back of the eye and makes it possible to see. Over time, these blood vessels and the associated scar tissue can cause serious vision problems, such as: Damage to the retina and detachment (the retina is moved from its normal place) that leads to permanent and severe loss of vision Crossed eyes (strabismus) Increased eye pressure (glaucoma) " Lazy eye" (amblyopia) Nearsightedness (myopia) Of the 14,000 babies in the U. S. born with ROP each year, 400 to 600 will become legally blind. Only an ophthalmologist can tell if your baby has ROP. All infants who are at risk for it should be screened shortly after birth and again once they go home from the hospital. Sometimes, ROP isn't spotted until a baby is 4 to 6 weeks old. A baby's eyes begin to develop around the 16th week of pregnancy. If she's born very early, this process is cut short. The blood vessels in her eyes don't have enough time to develop as they should. Instead, they grow where they're not supposed to. Or they can be so fragile that they bleed or leak. An eye doctor will put drops in your infant's eyes to make his pupils larger. This helps the doctor see all the parts of the eye better. It doesn't hurt. If your baby has ROP, the doctor will see where it is in the eye, how severe it is, and what the blood vessels in the eyes look like. Stage 1 is the mildest form of ROP. Babies at this stage or stage 2 often don't need any treatment and will have normal vision. Babies with stage 3 have more blood vessels that are abnormal. These may be large or twisted, which means the retina could start to come loose. At stage 4, the retina is starting to move from its normal place. And at stage 5, the retina has come off, and severe vision problems or even blindness is likely. For many babies, ROP often gets better on its own. But if it's severe and the risk of a detached retina is high, your child's doctor will want to start treatment. About 10% of babies screened for ROP will need to be treated. This can involve: Laser surgery. Small laser beams are used to treat the sides of the retina. This stops the growth of abnormal blood vessels. It takes 30-45 minutes per eye. This is the most common way ROP is treated, and it's been done safely for many years. But your baby may lose some or all of her peripheral (side) vision. Cryotherapy. Instead of burning away the scars, freezing cold temperatures are used to stop more blood vessels from spreading on the retina. This is an older form of ROP treatment. It also causes a loss of side vision. Injection. A newer way to treat ROP is to put an anti-cancer drug into each eye. Bevacizumab ( Avastin) blocks new growth of blood vessels in tumors, and it can do the same in eyes. This treatment is promising, but more research is needed to make sure there aren't long-term side effects. It's also unclear whether the ROP may come back over time. If the retina is detached, your child's doctor may need to do a more complex surgery: Scleral buckling. A small, stretchy band is placed around the white of the eye, causing it to compress slightly. This allows the torn retina to move closer to the outer wall of the eye where it belongs. Vitrectomy. During this surgery, the clear gel (vitreous) in the center of the eye is removed and replaced with saline solution. Then, the scar tissue that's pulling the retina out of place is removed. Surgery often stops the disease from getting worse and prevents vision loss. But as many as 25% of all babies who have surgery for ROP do lose some or all of their vision. Because all children with ROP are at higher risk of eye problems later in life, your child should follow up with his eye doctor every year until he's an adult.