Purpose:
To investigate retinal and choroidal vascular structure and flow, vessel tortuosity, and electroretinographic (ERG) visual function in a rodent model of retinopathy of prematurity (ROP).
Methods:
Stereo line-confocal Doppler power imaging and ERG measurements were performed in adult (50-90 day old), anesthetized, Sprague-Dawley albino rats. Three control rats and three Penn et al. (1995) "50/10 model" ROP rats were studied. Imaging was performed in both eyes. In such unpigmented retinae, choroidal vessels are exceptionally difficult to image due to low contrast in conventional fundoscopy. To overcome this, a wide-field tracking line-scanning ophthalmoscope (TLSO) was used in a slow-scan Doppler power mode using blood flow itself as a contrast agent enabling large dynamic range, semi-quantitative vascular flow visualizations; the tracking function was not required. Stereo pairs were acquired to validate apparent depths of the vessels. Tortuosity of the major superficial arterioles (TA, radians/pixel) was computed for each eye.
Results:
A stereo pair for a control rat is shown. For easy interpretation, low, medium, and high frequency Doppler spectral power was binned in RGB pseudo-color planes: the superficial retinal vasculature was predominantly blue, the choroid green, and low speed perfusion regions (e.g., capillary beds) red. Very high flow, such as in vortex veins, and no-flow, such as in the horizontal meridional line, appear dark (figure). The ERG a- and b-waves and the oscillatory potentials were attenuated in the ROP rats, and TA was high vs. controls.
Conclusions:
The 3D structure and function of the vasculature is readily visualized and interpreted with the TLSO Doppler power imaging mode. Vascular changes may be related to the persistent electrophysiological functional abnormality. Larger numbers of animals and improved analysis algorithms are required for more definitive conclusions in future studies.
Keywords: retina • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • blood supply