COL4A1 and snowflake vitreoretinal degeneration: In this study, we systematically evaluated four mouse models of SVD (hypertensive BPH mice, Col4a1 mutants, Notch3 mutants and mice lacking the HtrA serine protease Htra1−/−) for the infiltration of peripheral immune cells after postmortem MRI of the brain and for the activation of resident immune cell populations and blood–brain barrier (BBB) integrity.