Interestingly, in optic nerve sheath compartment syndrome, a condition connected to cases of papilledema and normal tension glaucoma, the SAS of the optic nerve is no longer normally perfused with CSF.[23] Here, MECs seem to react to altered flow conditions as reflected by upregulated L‐PGDS levels,[24] an important soluble transport protein of the CSF produced by MECs. This evidence concerns the gene PTGDS and optic papillitis.