“This study indicates that the beneficial effects of early vitamin A supplementation for preterm infants extend to the developing retina as well as the developing lung,” comment Dr. Helen Mactier, at Princess Royal Maternity in Glasgow, and colleagues.
They explain that retinaldehyde formed by oxidation of retinol is an essential component of rhodopsin in photoreceptors in the outer retina. Compared to term infants, preterm infants at term-corrected age have reduced dark-adapted retinal sensitivity, which could be due to reduced availability of retinaldehyde.
To test their hypothesis that boosting vitamin A levels might improve retinal sensitivity in preemies, the team conducted a randomized, double-blind trial involving 89 infants born at <32 weeks’ gestational age or <1501 grams birth weight.
From day 2, 42 of the infants were given additional 10,000 IU vitamin A intramuscularly 3 times weekly for at least 2 weeks or until oral feeding was established. The other 47 babies served as controls. “No infant showed signs of vitamin A toxicity,” the authors note.
The main outcome was dark-adapted retinal rod sensitivity measured by electroretinogram (ERG) at 36 week’s postmenstrual age. At that point 67 infants underwent ERG testing, 13 were not well enough to be tested, 3 were missed or consent was withdrawn, and 6 had died.
Dark-adapted retinal sensitivity was significantly better in the supplemented group than the control group, the researchers report. The mean luminance eliciting a half-maximal rod ERG response in the two groups was 0.15 vs 0.25 units, respectively.
In the supplemented group, 79% did not develop retinopathy of prematurity (ROP) compared with 68% in the control group, but the difference was not significant, the report indicates.
Discussing the results, Dr. Mactier and colleagues explain that the targeted oxygen saturation levels during the study were relatively low to reduce the incidence of ROP, but emerging evidence of an adverse effect on mortality is prompting a change in that practice.
“So it is likely that the incidence of ROP will increase as higher targeted oxygen saturation levels become widely adopted. Factors influencing retinal maturation will therefore assume even greater importance for the next generation of extremely preterm infants,” they conclude.