Lymphatic sinusoids exist in chick but not in rabbit choroid.

Purpose: Although it is generally thought that lymphatics do not exist in the choroid, there is mounting evidence that lymphatic-like structures do exist in primates and fowl.
Methods/results: Our comparison of the ultrastructure of chick and rabbit outer choroid indicates that major differences exist in the non-vascular areas of the choroid: notably, the chick has large lymphatic sinusoids, whereas the rabbit only has a system of large vacuoles contained within the processes of individual fibroblasts.
Conclusions: These results raise questions regarding the similarities or otherwise between species of the management of retinal metabolites, excess tissue fluid and choroidal homeostasis, especially during conditions of overload.