Chapter 126

### I. DEFINITIONS

1. Retinopathy of prematurity (ROP). A disorder of the developing retinal vasculature resulting from interruption of normal progression of newly forming retinal vessels. Vasoconstriction and obliteration of the advancing capillary bed are followed in succession by neovascularization extending into the vitreous, retinal edema, retinal hemorrhages, fibrosis, and traction on, and eventual detachment of, the retina. In most cases, the process is reversed before fibrosis occurs. Advanced stages may lead to blindness.

2. Retrolental fibroplasia (RLF). As originally described, the condition was seen only in its most advanced form, after extensive fibrosis and scarring had already occurred behind the lens. It was, therefore, termed retrolental fibroplasia. It is now understood that recognizable changes occur in the developing vasculature before end-stage fibrosis occurs, making this condition a true retinopathy. Because it is found chiefly in premature infants, it is called retinopathy of prematurity.

3. Cicatricial ROP. The term cicatricial ROP refers to fibrotic disease.

### II. INCIDENCE

ROP represents ∼20% of blindness in preschool children in the United States. Of particular concern are the increasing numbers of survivors weighing <1000 g, who have the highest incidence of ROP. The U.S. National Institutes of Health (NIH) sponsored the Cryotherapy for Retinopathy of Prematurity (CRYO-ROP) study in 1986–1987, which showed that 65.8% of infants weighing <1251 g developed ROP of any stage. Two percent of infants weighing 1000–1250 g developed threshold stage III+ disease eligible for treatment, whereas 15.5% of infants weighing <750 g did so. Threshold disease occurred at a median postconceptional age of 36–37 weeks, regardless of gestational age at birth or chronologic age. A study of earlier treatment, the ETROP (Early Treatment for Retinopathy of Prematurity) study, carried out in 2002, showed little difference in the overall incidence of the disorder and time of onset from the earlier CRYO-ROP study. The International NO-ROP Group, however, published data in 2005 suggesting that severe ROP in larger infants is an emerging worldwide issue. Care and survival of these premature infants is improving, whereas specialized treatment for ROP is not yet as prevalent.

### III. PATHOPHYSIOLOGY

1. Historical perspective. RLF was first described by Terry in the 1940s and was associated with the use of oxygen in newborn infants by Patz in 1984. The first epidemic, estimated to be responsible for 30% of cases of blindness in preschool children by the end of the 1940s, occurred during a period of relatively liberal oxygen administration. After this association was recognized, oxygen use in nurseries was curtailed. Although the incidence of RLF fell, mortality rates in newborn infants increased. In the 1960s, improved oxygen monitoring techniques made possible the cautious reintroduction of oxygen into the nursery. Despite improved oxygen monitoring, however, a second epidemic of RLF (ROP) appeared in the late 1970s and is associated with the increased survival of very low birthweight infants.

2. Normal embryology of the eye. In the normally developing retina, there are no retinal vessels until about 16 weeks' gestation. Until then, oxygen diffuses from the underlying choroidal circulation. At 16 weeks, in response to a stimulus (experimental evidence suggests relative hypoxia stimulating the release of angiogenic factors as the retina thickens), cells derived from mesenchyme traveling in the nerve fiber layer emanate from the optic nerve head. These cells are the precursors of the retinal vascular system. ...

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