Ultrasound imaging velocimetry of the human vitreous

Knowledge of vitreous motion in response to saccades is a prerequisite for understanding vitreous rheology. Purpose of present paper is to introduce Ultrasound Image Velocimetry of the human eye, measure scleral and vitreous velocity fields and test the reproducibility of the proposed technique. Twelve patients with varying diagnosis underwent Ocular Dynamic Ultrasound; scleral angular velocity (VS) was measured by 2 different operators and reproducibility calculated. Squared velocity of the vitreous (E), which is representative of kinetic energy per unit mass, was computed from velocity. The time evolution of the energy of the vitreous was described by its spatial average (ES), whereas spatial distribution was described by its time average (ET). Peak and average ES, the ratio Kp of the peak of the spatially averaged kinetic energy per unit mass to the maximum squared scleral angular velocity, vitreous motion onset time (TO) and vitreous motion decay time (TD) were also defined. Inter-operator reproducibility coefficient was 0.043 and correlation between operators was significant. VS, peak and average ES, Kp ratio and TD differed among patients but not among operators. VS correlated with ES and TD. ES and TD but not VS, were significantly different in patients with Posterior Vitreous Detachment. Patients with retinal detachment showed significantly higher VS and ES. Kp was inversely correlated to age and refraction. Measures proved accurate and reproducible. E is related to VS, retinal traction and mechanical stimulation. Identified variables varied with age, refraction pathologic conditions. ► We introduce the application of Particle Image Velocimetry applied to Ocular Dynamic Ultrasound. ► We measure scleral velocity and vitreous velocity fields as generated by saccades. ► We calculated measure consistency by comparing 2 operators. ► We found a positive correlation between scleral velocity and vitreous kinetic energy. ► Vitreous kinetic energy correlated directly to age and inversely to refraction.