Role of Circulatory Hypoxia in the Development of Retinopathy of Prematurity

Abstract

Purpose: to study the pathogenesis of retinopathy of prematurity.Patients and methods.642 preterm infants born before 30 weeks gestation with the weight less 1500 grams were examined. The study included: indirect ophthalmoscopy; digital retinoscopy; calibrometry of retinal vessels; dopplerography; analysis of partial pressure of oxygen and carbon dioxide in the capillary blood. Results. The first phase of retinopathy of prematurity (ROP) occurred due to the immaturity of the mechanisms of autoregulation of the blood flow and the inadequate reaction of immature retinal vessels to oxygen. It was established: the less gestational age of a child, so there are less mechanisms of autoregulation of hemodynamics. The perverse reaction of autoregulation leads to pronounced arteriospasm, increasing the zone of hypoxia, and triggering pathological angiogenesis. In morphologically immature children, arteriospasm of retina vessels is more often detected, and narrowing degree of vessels is higher. Arteriospasm is defined in 82 % of children born at the age of gestation from 25 to 27 weeks, in 67 % — at a period from 28 to 29 weeks, in 54 % — from 30 to 32 weeks. In children with ROP in the preclinical period of the disease, retinal angiospasm is noted at values of pO2 in capillary blood less then 40 mm Hg or exceeding the upper limit of the norm values of pCO2 (the norm values of pO2 are 40–60 mmHg, pCO2 are 35–45 mm Hg). Autoregulation of blood flow is immature and inadequate. In the group before 30 weeks of post-conceptual gestational age without development of ROP, a spastic reaction of retinal arteries was revealed at the background of subnormal pO2 values in capillary blood. Biochemical autoregulation of blood flow is still immature. But from the 30 week of post-conceptual gestational age arteriospasm of retina is formed at values of pO2 of 45 mm Hg or higher (p < 0.05). The normal caliber of retinal arteries in children without development of ROP is revealed at the background of mean values of pO2 below 45 mm Hg and values of pCO2 below 42 mm Hg before 30 weeks of post-conceptual gestational age, and above 45 mm Hg from the 30th week of post-conceptual gestational age. In children without ROP from 30 weeks of gestational age biochemical autoregulation of blood flow functions. It is important the degree of an angiospasm for the development of ROP. Dopplerographic critical index of blood flow disturbance in the ophthalmic and anterior cerebral arteries has been established — the index of resistance (IR) exceeding 0.8. It is a precursor of the development of ROP and pathological angiogenesis. In the group of children with ROP, the IR of the anterior cerebral artery is 0.84 ± 0.02 (in av.). The IR of the ocular artery was 0.83 ± 0.03. In higher index (up to 0.9–1), the process in the eye was more active.