Our study showed a statistically significant increase in systolic and diastolic velocities with no changes in pulsatility or resistance indices in very-low-birth-weight infants from birth to 38-weeks' corrected age. The results allow defining a standard for ophthalmic artery blood flow velocities and indices during neonatal intensive care unit stays.
Lindner et al.
14 assessed ophthalmic artery blood flow velocity by Doppler ultrasound in the first week of life in 15 newborns at term and 10 preterm infants born at gestational ages between 26 and 35 weeks. They found no statistically significant difference in blood flow velocity in the ophthalmic artery between full-term newborns and preterm infants.
14 Holland et al.
15 determined the velocity of blood flow and resistance index in the central retinal artery in a small sample of 34-weeks' corrected age premature newborns undergoing evaluation for retinopathy of prematurity. Six had no retinopathy of prematurity, 9 had retinopathy of prematurity without Plus disease, and 7 had retinopathy of prematurity with Plus disease; there were no statistically significant differences in the measures among those three groups.
15 Pappacci et al.
7 studied 45 term healthy newborn infants from the first to the fifth day of life and measured ophthalmic and central retinal blood flow velocities, resistance index, and pulsatility index. They reported an increase of blood flow velocities and indices on the fifth day of life.
7 Romagnoli et al.
8 measured ophthalmic and central retinal artery blood flow velocities, resistance index, and pulsatility index on days 1, 3, 5, and 7 of life in 41 healthy term newborns. Both blood flow velocities and resistance index increased significantly from the third to seventh postnatal days in both arteries.
8 Our results are in very-low-birth-weight infants studied longitudinally from birth to hospital discharge. There are no published data in very-low-birth-weight infants followed longitudinally, and the published data do not allow comparison with our findings. Very preterm infants do not grow after an intrauterine growth curve, and when they reach the term they are smaller than normal term infants.
16 They also develop several morbidities during their hospital stays; hence, the findings at 38 postmenstrual weeks are not comparable to those of normal term infants.
Our study set a longitudinal standard for normal systolic and diastolic velocities, pulsatility, and resistance indices during hospital stays in the neonatal intensive care unit from birth to 38 weeks' postmenstrual age.
We want to stress that eye Doppler ultrasound is an innocuous, rapid, and very easy examination to perform in very-low-birth-weight infants.
17 Currently, the clinical detection of retinopathy of prematurity is limited to indirect ophthalmoscopy, a technique that requires a skilled and experienced examiner and carries the possibility of significant morbidity.
18–20 Because retinopathy of prematurity is a vascular-circulatory disease, we suggest that further studies are needed to associate changes in ophthalmic artery blood flow as an early predictor for retinopathy of prematurity. We were unable to determine an association between ophthalmic artery blood flow and severe retinopathy of prematurity because of the small number of patients with that disorder in our unit. We have a strict guideline for oxygen therapy in preterm neonates, and threshold retinopathy of prematurity disease occurs in only 2.3% of the very-low-birth-weight infants.
21
In our study we used conventional ultrasound, which is limited to assessment of vascular development, especially when the ocular blood flow may not be detectable at very low frequencies. Doppler ultrasound with high frequencies would be more useful, but its use is still limited in humans.
22,23 The mouse eye appears to be a good model to evaluate vascular development.
24 Ultrasound biomicroscopy uses higher frequencies than conventional ultrasound, providing anatomic and functional information about in vivo mouse ocular structures. Vascular development can also be assessed with high-frequency Doppler imaging, which permits detection and characterization of ocular blood flow not detectable at lower conventional Doppler frequencies.
23
We suggest that Doppler ultrasound examination of the ophthalmic artery is feasible in very-low-birth-weight infants admitted to the neonatal intensive care unit. Examination should be performed with the newborn out of feeding time and asleep and under normal systemic and cardiovascular conditions. The data collected in our population describe a typical pattern of ophthalmic artery blood flow velocity, pulsatility index, and resistance index during the neonatal period in very-low-birth-weight infants. These data should be used when one suspects vascular-circulatory disorders of the eye.
Supported in part by Conselho Nacional de Desenvolvimento Científico e Tecnológico Grants 403057/2004–3 and FIPE-HCPA.
The authors thank Mário Wagner for statistical guidance, and João Borges Fortes Filho and Humberto Lubisco Filho for assistance with the Doppler ultrasound technique.