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Retinopathy of prematurity (ROP) is a disorder that affects the developing retinal blood vessels of premature infants. It the leading cause of acquired childhood blindness in the United States. The disease was first recognized in the 1940s1 and was initially thought to be due to the normal primitive vascular system in the vitreous cavity persisting in an abnormal fibrotic state.2 By 1952, ROP became recognized as an acquired disease,3 and in 1955, the role of excessive supplementary oxygen for premature infants was proven to be a significant causative factor.4 Despite many improvements in neonatal care practices, ROP continues into the 21st century as a major complication of premature birth.

In the data of the CRYO-ROP study, black infants demonstrated 65% lower odds of reaching severe ROP in need of treatment.5 The reason for this is unclear,6 but genetic influences are a possibility. In addition, there are relatively rare genetic disorders of the eye with similarities to ROP, including familial exudative vitreoretinopathy (FEVR), Norrie disease, and incontinentia pigmenti. The main pediatric retinal vascular diseases to distinguish from ROP are considerably more rare than ROP. Premature infants at risk for ROP undergo routine ophthalmologic examination, so, in general, the ability to observe the classical appearance and development of ROP allows a firm diagnosis. Polymorphisms of the X-linked recessive gene, which when mutated is associated with Norrie disease, have been suggested as a predisposing factor for ROP; however, this has not been replicated by all investigators. Thus, although ROP is generally considered to be nonhereditary, genetic factors are possible.

The development of ROP usually correlates with the overall extent of medical illnesses and complications associated with prematurity, such as patent ductus arteriosus, bronchopulmonary dysplasia, acidosis, anemia, blood transfusion, infection, necrotizing enterocolitis, and intracranial hemorrhage. Medical risk factors are dominated by the fact that the incidence and severity of ROP increase inversely with birth weight and gestational age.7 Full-term infants rarely, if ever, develop significant ROP. During the past several decades, the main epidemiological change observed in the United States has been a lower incidence/severity of ROP among higher-gestational-age premature infants. However, at the same time, an increased survival rate for less mature infants has produced a new, less-mature population at risk.

In the United States, problematic ROP appears essentially to be limited to infants with birth weights less than 1500 g. As of the early part of this millennium, the average birth weight for US infants requiring treatment for ROP is about 800 g.8 ROP occurs in about two thirds of infants born weighing 1250 g or less.7,9 In that same group, about 10% require treatment.

In utero, the normally developing human retinal vasculature proceeds centrifugally outward from the optic nerve head, reaching the ora serrata on the nasal side of the eye by about the full gestational term of 38 to 40 weeks. The vessels reach ...

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