Iron, Transferrin and Retinopathy of Prematurity (ROP): Towards New Pathophysiological Mechanisms.

The incidence of ROP, the main cause of vision impairment in children, is increasing parallel to the recent changes in practices targeting higher oxygen saturation in preterm babies in many countries following the publication of five trials that showed higher rates of death with lower oxygen saturations. The main risk factor for ROP development is oxygen excess. Oxygen contributes to the formation of reactive oxygen species and to lipid peroxidation which leads to vasoconstriction, vascular cytotoxicity, and arrest of vascular development causing ischemia of retinal neurons, thereby promoting the development of ROP.

90% of extremely low birth weight infants need red blood cell transfusions (RBCT) due to their immature erythropoiesis, frequent blood sampling and small circulating blood volume. RBCT are a major source of iron overload and ferritin plasma levels may remain elevated for several weeks after transfusions. It has been shown that blood transfusion is a risk factor of ROP in preterm infants. However, whether this relationship is mediated by an increased iron load remains controversial.

Only two studies, conducted before the 2000s, identified plasma iron overload as a risk factor for ROP. These studies with a limited number of patients, showed contradictory results, failing to draw a conclusion.

Excess iron worsens oxidative stress. Iron catalyzes the Fenton reaction which leads to the formation of reactive oxygen species. In addition a transferrin deficiency (the main iron chelator) has been suggested in premature infants. The oxidative stress observed in ROP could therefore be the consequence not only of oxygen therapy but also of iron overload.

The main objective of this study is to determine whether increased transferrin saturation in plasma (that reflects iron overload and/or low transferrin) is an independent risk factor for ROP development and severity.