Objective: To study the extent of retinal vascular development and influencing factors at birth and the relation between retinal vascularization and retinopathy of prematurity (ROP).
Methods: From October, 2006 to December 2006, retinal vascularization was screened and evaluated in 84 neonates at different weeks of gestation and birth weights (BWs), had dilated fundus evaluation for zone of retinal vascularization by the 130 degrees lens of a digital fundus camera. The infants' pupils were dilated with 2.5% phenylephrine and 0.5% cyclopentolate eye drops. The study cohort was divided into subgroups depending on the weeks of gestation and birth weights. The control group consisted of healthy term infants. Maternal and neonatal factors were ascertained and analysed.
Results: Vascularization up to zone I and II was considered to be immature retina; vascularization up to zone III or beyond was considered to be mature retina. In this study, 11 of 12 infants who were born at < 30 weeks of gestation, 12 of 26 infants who were born at < 31 approximately 33 weeks of gestation, 1 of 26 babies who were born at < 34 approximately 36 weeks of gestation and none of 20 babies who were born at < 37-40 weeks of gestation had immature retina; 12 of 15 babies at < 1500 g BW, 8 of 14 infants at 1500 g < BW < 1700 g, 4 of 11 infants at 1700 g < BW < 2000 g and of 44 infants at > 2000 g BW had immature retina. Those infants who were born at > 34 weeks of gestational age and at > 2000 g BW had mature retina. Infants who were born between 31 to 34 weeks of gestation and at 1501 to 2000 g BW had variable extent of retinal vascularization at birth. Vascularization was associated with postconceptional age (F = 31.9193, P = 0.000), birth weight (F = 32.4532, P = 0.000), anemia (F = 36.9391, P = 0.000), surfactant (F = 24.000, P = 0.0000), poor nutrition (F = 4.184, P = 0.041), RDS (F = 17.6191, P = 0.000), cesarean delivery (F = 10.972, P = 0.0022) and oxygen > 48 h (F = 22.076, P = 0.0000). Vascularization was affected mainly by the postconceptional age (95% CI = 1.57-261.728, P = 0.021). At last, 15/24 infants with immature retina developed ROP while none of the infants with mature retina developed ROP (chi2 = 45.1087, P = 0.000).
Conclusion: There is considerable variability in the extent of retinal vascularization in infants who we born between 31 to 34 weeks of gestation. Modifiable maternal and fetal factors could influence extent of vascularization at birth. Immature retina is the critical factor of ROP. Gestational age is the main factor of the immature retina in premature infants.