Retinopathy of prematurity, or ROP, is a disease affecting the eyes of babies born prematurely. It occurs when the blood vessels in the retina, the light-sensitive layer at the back of the eye, do not develop correctly. In a full-term pregnancy, these vessels have time to grow from the center of the retina to the edges in a normal pattern. When a baby is born too early, this process is interrupted.
Gestational Age and Birth Weight
The two most significant factors that increase the likelihood of an infant developing ROP are a low gestational age (being born too early) and a low birth weight. The development of retinal blood vessels is a process that completes in the final weeks of a typical pregnancy. A premature birth halts this delicate growth process, leaving the peripheral retina without a sufficient blood supply. This lack of blood vessels creates a vulnerable state where abnormal vessel growth can later occur.
Medical guidelines often identify infants born at or before 30 weeks of gestation or those with a birth weight of 1,500 grams (about 3.3 pounds) or less as being at high risk for ROP. Some screening criteria may extend to infants born up to 32 weeks or weighing up to 1500 grams, especially if they have other health complications. These thresholds are used by medical teams to determine which infants require routine screening for the condition.
The risk of ROP increases as birth weight and gestational age decrease. For instance, extremely low birth weight infants, those weighing less than 1,000 grams (about 2.2 pounds), face the highest probability of both developing ROP and requiring treatment for it.
Oxygen Therapy and Respiratory Complications
Many premature infants require supplemental oxygen to survive because their lungs are not fully developed, a condition known as respiratory distress syndrome. While this oxygen is life-saving, it plays a complex role in the development of ROP. Both excessively high and fluctuating oxygen levels in the blood can disrupt the normal formation of retinal blood vessels.
Initially, high concentrations of supplemental oxygen can cause the developing blood vessels in the retina to constrict or even stop growing altogether. This pause in development, known as the first phase of ROP, leaves the edges of the retina without the circulation they need. As the infant matures and is gradually weaned off high levels of oxygen support, the oxygen-starved retina sends out signals to grow new vessels. This can lead to a rapid, disorganized, and excessive growth of fragile, abnormal vessels, which characterizes the second phase of the disease.
The need for mechanical ventilation is another factor that elevates the risk. Infants on ventilators often have more severe respiratory problems, making it challenging for medical teams to maintain stable blood oxygen levels. These fluctuations between high and low oxygen saturation can be particularly damaging to the delicate retinal vasculature. Neonatal intensive care unit (NICU) staff carefully monitor oxygen levels to provide enough for organ survival while minimizing the risk to the eyes.
Concurrent Health Conditions in Premature Infants
Beyond prematurity and oxygen exposure, other medical issues common in premature infants contribute to ROP risk. Systemic infections, often referred to as neonatal sepsis, can cause widespread inflammation. This response can interfere with developmental processes, including the orderly growth of blood vessels in the retina.
Anemia, a low red blood cell count, and the blood transfusions used to treat it are also associated with ROP. Anemia reduces the blood’s oxygen-carrying capacity, affecting the developing retina. Furthermore, blood transfusions can introduce fluctuations in blood volume and oxygen delivery, adding instability for the vulnerable retinal vessels.
Poor nutrition and slow weight gain present additional challenges, as adequate growth is necessary to support the body’s developmental tasks. When an infant struggles to gain weight, it can hinder the proper formation of tissues like the retinal vasculature. The presence of an intraventricular hemorrhage (IVH), or bleeding in the brain, is another indicator of an infant’s overall instability and is correlated with a higher risk for ROP.
The Importance of ROP Screening
Because the risk factors for ROP are well-established, standardized screening protocols are a routine part of care for at-risk infants in the NICU. These screenings are designed to detect the condition early, long before it can cause permanent vision problems. The goal is to identify any abnormal vessel growth and determine its severity.
The screening itself involves an examination by a pediatric ophthalmologist, a doctor specializing in children’s eye conditions. The examination is typically performed at the infant’s bedside in the NICU. The ophthalmologist uses special instruments and eye drops that dilate the pupils to get a clear view of the retina at the back of the eye.
The timing of the first screening is based on the infant’s gestational age at birth and their chronological age. Typically, the first exam occurs between four and six weeks after birth. Following the initial screening, follow-up exams are scheduled at regular intervals to monitor the progression of the blood vessels until the retina is fully mature or until the ROP resolves. This monitoring allows for timely intervention if severe disease develops, significantly improving the chances of a positive outcome.