Dextran-Blue 2000 was used as a marker to determine the effect of steroids on large molecule transfer through the cornea. In superficially scarified corneas topically applied steroids greatly enhanced the transfer of this chromophore through the cornea in the in vivo state, but had little effect in vitro. This implies that the steroid effect is an active process. Since herpes simplex virus is approximately the same molecular weight and configuration as the chromophore used, this study explains one aspect of how steroids may be detrimental when used in the presence of this virus.
Robbins RM, Galin MA. A Model for Steroid Effects in Herpes Keratitis. Arch Ophthalmol. 1975;93(9):828-830. doi:10.1001/archopht.1975.01010020716009