Ocular Blood Flow in Preterm Neonates: A Preliminary Report

Abstract

Purpose: Retinopathy of prematurity (ROP) is a vision-threatening complication occurring in pre-term neonates. The standard of care entails regular monitoring by dilated ophthalmoscopy examinations, which entail stress and potential morbidity. In this pilot study, we used plane-wave ultrasound (PWUS) to image, measure, and assess the association of blood-flow velocities in the retrobulbar vessels with ROP stages ranging from stage 0 (immature vessels without ROP) to stage 3.

Methods: Both eyes of 14 preterm neonates at risk for ROP were examined by 18 MHz PWUS. All but two subjects had a follow-up examination. PWUS was acquired for 1.5 seconds at 3000 compound B-scans/sec. Data were postprocessed to form color-flow images and spectrograms depicting flow velocity in the central retinal artery (CRA), central retinal vein (CRV), and the short posterior ciliary arteries (SPCA). Flow parameters derived from spectrograms were compared by ROP stage.

Results: ROP stage was found to correlate with flow velocities. Velocities were significantly elevated with respect to non-ROP eyes in all vessels at stage 3 and in the SPCAs at stage 2.

Conclusions: PWUS measurement of blood flow may provide a quantitative, clinically important, and easily tolerated means for detecting and assessing the risk of ROP in preterm neonates. We speculate that the observed increase in flow velocity results from elevated vascular endothelial growth factor (VEGF) in ROP eyes.

Translational relevance: PWUS offers a gentle, nonmydriatic method for monitoring neonates at risk for ROP that would complement ophthalmoscopy.

Figure 1.

Representative plane-wave color-flow directionally-encoded power Doppler image of a neonatal eye. Red coloration generally indicates arterial flow and blue venous flow. ONH, optic nerve head; R, retina; Ch, choroid; CRA, central retinal artery; CRV, central retinal vein; SPCA, short posterior ciliary artery.

Figure 2.

Directionally encoded power Doppler superimposed on grayscale structural data of neonatal posterior pole. Note venous flow (arrows) along optic nerve sheath, identified as the pial plexus.

Figure 3.

Top: Directionally encoded power Doppler image of posterior pole of neonatal eye. Red represents flow toward the probe (usually interpreted as arterial flow), whereas blue represents flow away from the probe (usually interpreted as venous flow). The color flow information is superimposed upon the grey-scale structural data that are suppressed by the SVM filter. Three regions of interest are outlined by green boxes: the CRA, CRV, and an SPCA. The yellow lines through the analysis boxes depict vessel angle with respect to the ultrasound axis and used for cosine correction (because the Doppler only detects the component of flow velocity along the acoustic beam axis). Bottom: Spectrograms of the vessels demarcated in the image above. Flow in the CRV is non-pulsatile and opposite in direction from arterial flow in the CRA and SPCA.