Noninvasive visualization of blood flow in the choriocapillaris of the rat

The rat has been used to generate models of various eye diseases. However, methods to study the choriocapillaris noninvasively have been inadequate in this species. Laser-targeted angiography was applied to generate local, repetitive angiograms of the choriocapillaris in the rat and to assess the similarity between the choriocapillaris of the rat and that of the subhuman primate.

Carboxyfluorescein was encapsulated in heat-sensitive liposomes and injected intravenously in rats. The liposome contents were then released locally in the choroid by the application of a short, noncoagulating heat pulse provided by an argon laser. Videoangiograms of the downstream spread of the bolus of dye were generated with excitation illumination provided by another output from the argon laser.

Laser-targeted angiography demonstrated that the bolus of dye perfused the choriocapillaris. Clusters of choriocapillaris lobules were observed and appeared similar to those described in the primate. Dynamic filling and emptying patterns also were similar to those of the primate. Lobules were filled by a central arteriole and drained by a venous annulus.

This study demonstrates the feasibility of noninvasively studying the choriocapillaris of the living rat using the technique of laser-targeted angiography. It demonstrates as well the similarity between the rat and the primate choriocapillaris, thus indicating that the rat is an acceptable and convenient model for the study of physiological and pathologic changes in the choroidal vasculature.