Retinopathy of prematurity (ROP) is a disorder affecting low birthweight, preterm neonates. In the preterm eye, the retina is not fully developed and neovascularization may occur at the margin between the developed vascular retina and undeveloped avascular retina. Without timely treatment by laser or intravitreal anti-vascular endothelial growth factor (VEGF) therapy, this can lead to tractional retinal detachment and blindness. Visualization of the retina in regular examinations by indirect ophthalmoscopy is hence the current standard of care, but the exams are stressful and interpretation of images is subjective.

The upregulation of VEGF in ROP would suggest an increase in ocular blood flow. In this report, we evaluate the potential of ultrafast plane-wave Doppler ultrasound (PWU) to detect increased flow velocities in the orbital vessels supplying the eye in a gentle exam with objective findings.

We imaged both eyes of 50 low-birthweight preterm neonates using 18 MHz PWU. Flow velocity in the central retinal artery (CRA) and vein (CRV), and the short posterior ciliary arteries were determined and values at each ROP Stage compared.

We found significantly increased velocities in the CRA and CRV in Stage 3 ROP eyes, where intervention would be considered. We compared multivariate models for identifying Stage 3 eyes comprised solely of clinical factors, solely of Doppler parameters, and clinical plus Doppler parameters. The respective models provided areas under their respective ROC curves of 0.760, 0.812, and 0.904. 

PWU Doppler represents a gentle, objective means for identifying neonates at risk for ROP that could complement ophthalmoscopy.

Neonate subjects were inpatients in the neonatal intensive care unit (NICU).

Inclusion criteria: Neonates with a birth weight of ≤1500g or a gestational age of ≤30 weeks.

Exclusion criteria: Presence of other congenital ophthalmic disease or cardiovascular disease; prior treatment with laser or intravitreal anti-VEGF agents.

A total of 50 low-birthweight, preterm neonates (100 eyes) were examined. 30 had follow-up exams approximately 2 weeks after their initial exam.

ROP Stage, Zone, and presence of plus disease in each eye were determined by an experienced retinal specialist by indirect ophthalmoscopic examination as defined by the International Committee for the Classification of Retinopathy of Prematurity while masked to the PWU results.

We performed PWU using a Vantage-128 (Verasonics, Inc., Kirkland, WA)  research ultrasound system with a Verasonics L22-14vXLF linear array probe. The probe had an 18-MHz center frequency, 128 piezoelectric elements, a 12.8 mm aperture, and an elevation focal length of approximately 18 mm.

Scanning was performed at cribside in the NICU with the assistance of neonatal ophthalmic nurses. Exams were performed by a single person experienced in the performance of clinical ophthalmic ultrasonography. During the exam, the probe was placed in a viral barrier sheath (Sheathes3D; Sheathing Technologies, Inc., Morgan Hill, CA) filled with a cm of water, and coupled to the upper eyelid with GenTeal (Alcon Laboratories, Inc., Fort Worth, TX) gel with minimal pressure. Scans were performed in a horizontal plane encompassing the optic nerve. B-mode color-flow images were displayed in real time. Once the optic nerve and posterior vasculature were satisfactorily displayed, the system was triggered to acquire PWU compound data from six angled transmits over ±9 degrees. Data were acquired continuously for 1.5 seconds at 3,000 compound scans per second, and the stack of 4,500 phase-resolved images stored for post-processing. We acquired three scans of each eye, repeating scans as necessary if degraded by eye or head movement. Examination of both eyes would typically take about 15 minutes.

Acoustic intensity was compliant with FDA guidelines for ophthalmic diagnostic ultrasound standards.

Doppler analysis was performed as follows: A singular value decomposition filter and a 10 Hz high-pass filter was applied to the data to suppress stationary or slowly moving structures, leaving only blood flow. This information was then used to produce a color flow image from which the CRA, CRV and short posterior ciliary arteries (SPCAs) were identified. We then sampled each vessel to produce spectrograms depicting flow pulsatile flow velocity over the 1.5 seconds of each scan. From this, after correcting for vessel angle with respect to the acoustic axis, we measured peak systolic velocity (PSV), end diastolic velocity (EDV) and mean velocity (MV), and computed the pulsatile index, PI = (PSV – EDV)/VM and resistive index, RI = (PSV- EDV)/PSV.

Statistical analysis was performed using IBM SPSS Version 29 (IBM Corp., Armonk, NY).

ANOVA, with post-hoc Dunnett’s test, was used to compare Doppler parameters between ROP Stages for each vessel. Because each eye was classified and imaged separately, we treated each eye as a separate case. However, recognizing that eyes of a given subject tend to be correlated, we additionally performed the analysis separately for right and left eyes.

ANOVA was also performed to evaluate the presence of preplus disease and Zone on flow.

Stepwise linear discriminant analysis was used to produce multivariate classification models to distinguish Stage 3 with respect to Stages 0-2. A priori probabilities for group membership were set equal. Classification accuracy was assessed and validated by a leave-one-out procedure. Receiver operator characteristic (ROC) analysis was performed to evaluate the effectiveness of classification functions.

We first produced a stepwise clinical model by entering sex, blood pressure (systolic, diastolic, mean, pulse pressure), GA and BW into the analysis (Model 1). Next, we produced a model using stepwise variable selection of all Doppler parameters (Model 2). Lastly, we produced a stepwise model simultaneously considering both clinical and Doppler parameters (Model 3).