Features

Retinopathy of prematurity (ROP) is a vasoproliferative disorder of premature infants. The retina begins to develop at age 16 weeks in utero and typically completes development from the optic nerve to the nasal and temporal ora serrata by 36 and 40 weeks of gestational age (GA), respectively. There are 13 million premature births worldwide annually, leading to 150,000 new cases of infant blindness per year. The survival of premature infants is continually increasing as developed and undeveloped countries improve premature infants’ chance of survival.

First reported in 1942, as retrolental fibroplasia (RLF) in an infant weighing less than 3 pounds at birth, ROP and associated neovascularization is thought to occur from an initial ischemic insult followed by reactive proliferation of blood vessels. The causal relationship with oxygen has been demonstrated through the first phase which is characterized by retinovascular growth attenuation and vascular obliteration during hyperoxia (at this point hyperoxic and ischemic) which results in the second phase of vasoproliferation from the same ischemic areas that were hypoxic and ischemic. A key stimulator of vasoproliferation, vascular endothelial growth factor (VEGF), is induced by hypoxia-inducible factor (HIF), a transcription factor that is suppressed by hyperoxia of phase 1. The fetus is normally subject to “normoxic hypoxia,” a state in which oxygen concentrations rarely reach 20 mm Hg oxygen, in contrast to an adult who has 50% higher oxygen concentrations in arterioles. For example, oxygen saturation in utero may be closer to 80 to 85% in comparison to ex utero saturations of 91 to 95% in at-risk neonates receiving oxygen supplementation. In addition, fetal hemoglobin is designed to deliver oxygen in low oxygen tensions unlike the saturations seen after birth.

100.1.1 Common Symptoms

Infants are asymptomatic and must be screened; children whose ROP has subsided are at greater risk of developing myopia, strabismus, and amblyopia.

100.1.2 Exam Findings

A critical clinical sign of active ROP is plus disease, first defined as venous engorgement at the disc, but vascular tortuosity can be seen posterior to the ridge, in midperipheral retina and can affect tortuosity and engorgement of arterioles as well. Aggressive posterior retinopathy of prematurity (AP-ROP), a relatively new term, is recognized in children who have very active early disease (typically in corrected GA [CGA] of 34 weeks or less). This is primarily zone 1 disease with massive PLUS and quite often flat neovascularization. It is not unusual for AP-ROP to be accompanied by dilated iris vessels in a circular pattern, the pupillary margin simulating neovascularization of the iris.

ROP is described by zone and by stage. Zone 1 is described as vascularized retina that has the peripheral circumference less than or equal to a diameter twice the radius of the disc to the fovea, whereas zone 2 is described as having a circumference anterior to zone 1 and nearly adjacent to the nasal ora serrata. Zone 3 is the temporal crescent anterior to zone 2 temporally (▶ Fig. 100.1). Practically, this means that if the disc and the edge of vascularized retina can be seen with a single image using a 28D lens anywhere, the infant is zone 1. If scleral depression nasally shows any avascular retina outside of zone 1, the infant is zone 2. Analogously, if the retina is avascular temporally but vascularized nasally, the infant is zone 3. Concerning staging, stage 0 is immature normally developing retina; stage 1 is a sharp border between vascular and avascular tissue, with or without a flat white demarcation line; stage 2 is where the demarcation line is elevated; stage 3 is neovascularization on the ridge, accompanied or not by a fibrovascular membrane; stage 4a is retinal detachment sparing the fovea, 4b with fovea involved; and stage 5 is total retinal detachment (▶ Fig. 100.2).

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