Retinopathy of prematurity (ROP) is a disease of the eye affecting prematurely born babies, where the blood vessels of the retina do not develop normally. It primarily affects premature babies who receive neonatal intensive care, especially when supplemental oxygen therapy is used to support breathing. The manifestations of ROP span a spectrum: incomplete development of retinal blood vessels; development of pathological (harmful) retinal blood vessels (which leak and bleed); retinal fibrosis (scarring); and finally retinal detachment. The outcomes of ROP ranges from spontaneous resolution to blindness.
Epidemiology The prevalence of ROP is evolving and varies, from 5 to 8% in developed countries with adequate neonatological facilities, to up to 30% in middle-income developing countries. The increasing prevalence is thought to be due to increased survival of premature infants. There is increasing evidence that ROP and blindness due to ROP are now public health problems in the middle income countries of Latin America, Eastern Europe and the more advanced economies in Southeast Asia and the Middle East region. In these countries ROP is often the most common cause of blindness in children. ROP is highly likely to become an increasing problem in India, China and other countries in Asia as these countries expand the provision of services for premature infants. There is also evidence that the population of premature infants at risk of severe ROP varies depending on the level of neonatal intensive care being provided. In countries with high development indices and very low neonatal mortality rates (e.g. North America, Western Europe), severe ROP is generally limited to extremely preterm infants i.e. those weighing less than 1 kg (2.2 lbs) at birth. At the other end of the development spectrum, countries with very low development indices and very high neonatal mortality rates (e.g. much of subSaharan Africa) ROP is rare as most premature babies do not have access to neonatal intensive care and so do not survive. Countries with moderate development indices are improving access to neonatal intensive care, and in these settings bigger, more mature babies are also at risk of severe ROP as neonatal care may be suboptimal. These findings have two main implications: firstly, much can be done in countries with moderate development indices to improve neonatal care, to reduce the risk of severe ROP in bigger babies and increase survival of extremely preterm infants, and secondly, in these settings bigger more mature babies need to be included in ROP programs and examined regularly so as to detect those babies developing ROP requiring treatment. In 2012, the World Health Organization published data on rates of preterm birth and the number of premature babies born in different regions of the world. This report contained three main findings:
Premature birth has many different causes, and prevention is challenging, Prematurity is the most common cause of neonatal death in many countries, totaling as many as 1 million infants annually due to complications of preterm birth, and the number of preterm births is currently estimated to be 15 million, and increasing.
Pathophysiology
Retinal vascular development begins prior to 16 weeks gestation, growing from the optic nerve toward the ora serrata, and completing by term. This process is influenced by systemic oxygen levels and is regulated in part by vascular endothelial growth factor (VEGF). Normal angiogenesis occurs as part of a carefully regulated sequential physiological hypoxia, which increases metabolic demand at the leading edge of developing vessels. Astrocytes at this hypoxic leading edge secrete VEGF to promote vascularization and ensure normal retinal development. ROP is hypothesized to occur in two phases. First, premature infants with their incompletely vascularized retinas are exposed to elevated oxygen levels compared to the intrauterine environment; this increased oxygen tension leads to vasospasm and inhibition of angiogenesis. Second, once oxygen is reduced, the ischemic retina secretes excess VEGF, leading to abnormal, disordered angiogenesis and ultimately the pathological neovascularization that is characteristic of ROP. These abnormal blood vessels may grow up from the plane of the retina and bleed inside the eye. When the blood and abnormal vessels are reabsorbed, it may give rise to multiple band-like membranes which can pull up the retina, causing detachment of the retina and eventually blindness. In addition, poor early weight gain and low birth weight are major contributors. This leads to low IGF-1, which affects the VEGF pathway in an oxygen-independent manner. IGF-1 and VEGF work synergistically in vascular signaling. Genetic factors may also influence ROP severity. The disease has features similar to Familial Exudative Vitreoretinopathy (FEVR), another genetic condition. Mutations in Norrin have been found in up to 2% of patients with ROP.
Diagnosis The classification of ROP has been defined by the International Classification of Retinopathy of Prematurity (ICROP). There are four components in describing a child with ROP: zone, stage, plus, and clock hours. Zone identifies location of disease, stage and plus describe severity of disease, and clock hours involved describes the circumferential extent of disease. The circumferential extent of the disease is described in segments as if the top of the eye were 12 on the face of an analog clock, e.g. stage 1 from 4:00 to 7:00.
Zones
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