RETINOPATHY OF PREMATURITY

Retinopathy of prematurity occurs only in the incompletely vascularized retina of the premature infant. The incidence of any acute retinopathy in infants under 1250 g is 66%, whereas only 6% have retinopathy severe enough to warrant intervention. The incidence is highest in babies of the lowest gestational age. The condition appears to be triggered by an initial injury to the developing retinal vessels. Hypoxia, shock, asphyxia, vitamin E deficiency, and light exposure have been associated with this initial injury. After the initial injury, normal vessel development may follow or abnormal vascularization may occur with ridge formation on the retina. The process can still regress at this point or may continue, with growth of fibrovascular tissue into the vitreous associated with inflammation, scarring, and retinal folds or detachment. The disease is graded by stages of abnormal vascular development and retinal detachment (I–V), by the zone of the eye involved (1–3, with zone 1 the posterior region around the macula), and by the amount of the retina involved, in “clock hours” (eg, a detachment in the upper, outer quadrant of the left eye would be defined as affecting the left retina from 12 to 3 o’clock).
Initial eye examination should be performed at 6 weeks of age in infants with a birth weight under 1500 g or in those born at less than 28 weeks’ gestation, as well as in infants over 1500 g with an unstable clinical course. Follow-up is done at 2- to 4-week intervals until the retina is fully vascularized. Infants with zone 1 disease need to be followed at 1- to 2-week intervals. Infants with threshold disease (stage III, zone 1 or 2, in five or more continuous clock hours, with inflammatory changes of “plus” disease) are candidates for laser therapy. Although this treatment does not always prevent retinal detachment, it reduces the incidence of poor outcomes based on visual acuity and anatomic outcomes.