Retinopathy of prematurity is an eye condition affecting babies born too early, where blood vessels in the retina grow abnormally and can threaten vision if left untreated.

Understanding Retinopathy of Prematurity

Retinopathy of prematurity, often shortened to ROP, is a serious eye problem that can affect babies who are born prematurely or with very low birth weight. This condition involves abnormal growth of blood vessels in the retina, which is the light-sensitive layer of tissue at the back of the eye that allows us to see. The retina works like the film in a camera, capturing images and sending them through the optic nerve to the brain for interpretation.^[1]

When a baby is born too early, the normal development of blood vessels in the retina can be interrupted. These vessels typically begin forming around the fourth month of pregnancy and continue developing until shortly before birth. In premature infants, this process is incomplete, and when it resumes after birth, the blood vessels may grow in disorganized, abnormal patterns rather than following their normal course.^[2]

The good news is that most cases of ROP are mild and resolve on their own without causing any lasting harm to the baby’s vision. However, in more severe cases, these abnormal blood vessels can leak or bleed, leading to scarring of the retina. As the scar tissue contracts, it can pull the retina away from the back of the eye, a condition called retinal detachment, which can result in vision loss or even blindness if not treated promptly.^[3]

How Common Is This Condition?

Retinopathy of prematurity affects a significant number of premature babies in the United States each year. Approximately 14,000 to 16,000 infants develop some degree of ROP annually. The vast majority of these cases—about 90 percent—are mild and do not require treatment, with the condition resolving naturally as the baby grows.^[2]

About half of all premature babies born in the United States, estimated at around 28,000 per year, have some degree of retinopathy of prematurity. Among those who develop the condition, only about 1,100 to 1,500 infants have severe enough disease to require medical intervention. Despite modern treatments, ROP still causes legal blindness in approximately 400 to 600 infants each year in the United States.^[6]

The condition has become more commonly diagnosed in recent decades, not because it’s spreading, but because medical advances allow doctors to save more premature babies than ever before. These tiny fighters survive their earliest challenges, but their incomplete eye development means they need careful monitoring for ROP during their first weeks and months of life.^[5]

What Causes Retinopathy of Prematurity?

The root cause of retinopathy of prematurity lies in the disruption of normal blood vessel development in the retina. During a healthy pregnancy, blood vessels begin growing from the center of the retina outward, starting around 16 weeks of pregnancy. This process continues throughout pregnancy and isn’t fully complete until near the baby’s due date. When a baby is born prematurely, this growth process is interrupted at a critical stage.^[3]

After premature birth, the blood vessels in the retina actually stop growing for a period of time. During this pause, the retina begins increasing production of growth factors to help the vessels continue developing. Sometimes, however, the retina produces too much of these growth factors, which leads to blood vessels growing abnormally and randomly instead of following their normal pattern across the retina.^[5]

The new vessels that form are fragile and poorly constructed. They can leak fluid or bleed into the eye, causing swelling of the retina. If too much abnormal tissue develops, it begins to pull on the retina, which can eventually detach it from the wall of the eye. This detachment is what ultimately threatens vision.^[10]

Risk Factors for Developing ROP

The two most important risk factors for developing retinopathy of prematurity are how early a baby is born and how much they weigh at birth. Babies born before 31 weeks of pregnancy are at highest risk, with those born before 30 weeks being especially vulnerable. Similarly, babies weighing less than about 3 pounds (approximately 1,500 grams) at birth face significantly increased risk of developing ROP.^[1]

The earlier the birth and the lower the birth weight, the higher the risk becomes. This is because babies born very early have had less time in the womb for their retinal blood vessels to develop normally, leaving more of the retina incompletely vascularized at birth.^[2]

Beyond prematurity and low birth weight, several other medical conditions common in premature babies increase the likelihood of developing ROP. Breathing problems, particularly respiratory distress syndrome, are strongly associated with ROP, especially when babies require extended oxygen therapy. Other risk factors include infections, anemia (low red blood cell count), poor weight gain after birth, blood transfusions, bleeding in the brain (intracranial hemorrhage), and various heart, lung, or brain problems that premature babies may experience.^[6]

Male babies appear to be at slightly higher risk than females. Additionally, babies who weren’t able to grow properly in the womb before birth face increased risk of developing retinopathy of prematurity.^[9]

Signs and Symptoms

One of the most challenging aspects of retinopathy of prematurity is that there are no visible signs that parents can observe in their baby during the early stages of the disease. The condition develops silently inside the eye, without causing pain or any outward changes in the baby’s appearance. This is why screening examinations by eye specialists are so critical for at-risk infants.^[1]

The baby won’t cry from discomfort or show any behavioral changes that might alert parents to a problem. Even as the condition progresses, there are typically no symptoms that parents can detect on their own. This makes scheduled eye examinations the only reliable way to identify ROP and monitor whether it’s worsening.^[9]

If ROP progresses to advanced stages and causes damage to the retina, parents may eventually notice certain signs as their child grows. The baby’s eyes might wander, shake, or make unusual movements. They may not follow objects with their eyes as expected for their age. In some cases, the pupils may appear white rather than dark. The child might also have trouble recognizing faces, which becomes more apparent as they get older.^[1]

Children who had ROP as babies are more likely to develop other eye problems later in childhood and beyond. These can include retinal detachment occurring later in life, nearsightedness (difficulty seeing distant objects), amblyopia or lazy eye (reduced vision in one eye), and crossed eyes or strabismus (eyes that don’t align properly). Regular eye examinations throughout childhood are essential for children who had ROP to catch and treat these problems early.^[8]

Prevention and Screening

While retinopathy of prematurity cannot always be prevented, early detection through screening gives babies the best chance of preserving their vision. All babies born before 31 weeks of pregnancy or weighing less than approximately 3.3 pounds at birth should receive eye examinations to screen for ROP. Some babies with other risk factors may also be screened even if they don’t meet these criteria, based on their neonatologist’s judgment.^[6]

The screening examination is performed by an ophthalmologist, a medical doctor who specializes in eye care and is skilled in examining infant eyes. Before the exam, eye drops are placed in the baby’s eyes to dilate (widen) the pupils, allowing the doctor to see inside to the back of the eye where the retina is located. The doctor may use a special tool called a speculum to gently hold the baby’s eyes open during the examination.^[6]

Babies often cry during these examinations, which can be distressing for parents to witness. However, the procedure itself isn’t painful, and the temporary discomfort is far outweighed by the importance of detecting ROP early. The examination allows doctors to see whether abnormal blood vessels are forming and whether treatment might be needed.^[9]

Follow-up examinations are scheduled based on what the doctor finds during each visit. It’s absolutely critical that parents keep all scheduled appointments, as ROP can worsen quickly, and the window for effective treatment can be narrow. Missing appointments could mean missing the opportunity to prevent vision loss.^[1]

How Retinopathy of Prematurity Progresses

Doctors classify retinopathy of prematurity using a system of stages and zones that describe how severe the disease is and where in the retina it’s occurring. Understanding these classifications helps medical teams make decisions about treatment and helps parents understand what their baby is facing.

The retina is divided into three zones based on how far from the center of the retina the disease occurs. Zone 1 is the innermost area at the center of the retina, Zone 2 is the middle area surrounding the center, and Zone 3 is the outer edge. Disease in Zone 1 is generally more serious because it affects the most critical part of the retina used for detailed central vision.^[6]

There are five stages of ROP, ranging from Stage 1 (mild) to Stage 5 (severe). In Stages 1 and 2, doctors observe a line or ridge developing on the retina where normal and abnormal growth meet. Most babies in these early stages get better on their own without treatment and go on to have healthy vision. Doctors watch these babies carefully with regular examinations to make sure the condition doesn’t worsen.^[1]

Stage 3 is when fragile new blood vessels begin growing abnormally on the retina. Some babies at this stage still recover without treatment, but others need intervention to stop the abnormal vessels from damaging the retina and causing detachment. This is typically when doctors begin treatment if the disease appears to be progressing.^[6]

In Stage 4, the retina has started to detach partially from its normal position. Stage 5 is the most severe, with complete retinal detachment. Both of these advanced stages are very serious and usually require surgery. Even with treatment, babies at these stages may experience significant vision loss or blindness, which is why early detection and treatment at Stage 3 is so important.^[8]

Doctors also look for something called “plus disease,” which means the blood vessels in the retina have become thick, twisted, and wavy. The presence of plus disease indicates more severe ROP that is more likely to progress and require treatment.^[6]

Changes in Normal Body Function

To understand what goes wrong in retinopathy of prematurity, it helps to know how retinal blood vessels normally develop. During healthy fetal development, blood vessels grow from the center of the retina outward in an orderly pattern, guided by low oxygen levels in the developing tissue. These vessels stay within the plane of the retina, providing oxygen and nutrients to support the retinal cells that will eventually enable vision.^[4]

When a baby is born prematurely, this carefully orchestrated process is disrupted. The incomplete blood vessel network stops growing temporarily. The retina, sensing it needs more oxygen and nutrients, begins producing growth factors—chemical signals that normally direct blood vessel formation. In some premature babies, the retina overproduces these growth factors in response to the disrupted development.^[10]

This overproduction leads to abnormal blood vessel growth, with vessels growing in disorganized patterns and sometimes growing up from the retina into the gel-like vitreous humor that fills the eye, rather than staying flat within the retinal tissue where they belong. These abnormal vessels have weak, leaky walls that allow fluid and blood to seep out, causing swelling and bleeding in the retina.^[4]

Along with the abnormal blood vessels, fibrous scar tissue develops. This fibrovascular tissue is a combination of disorganized blood vessels and scar material. As the scar tissue matures, it contracts and shrinks. Because it’s attached to the retina, this contraction creates tension that can pull the retina away from the supportive layers underneath it. Once the retina detaches, the light-sensitive cells can no longer function properly, resulting in vision loss in that area.^[4]

The key problem in ROP is this fibrovascular proliferation—the abnormal growth of blood vessels combined with scar tissue formation. While this process sometimes regresses on its own as the baby matures, it frequently progresses, especially in the smallest and most premature infants. Multiple factors influence whether the disease will spontaneously improve or worsen, including the baby’s overall health, birth weight, how early the baby was born, and the specific stage and location of ROP when first diagnosed.^[4]