In severe zoster keratitis many pathogenic factors are involved. In addition to viral manifestations, the cornea is often affected by anterior uveitis or secondary glaucoma. Neuroparalytic keratitis causes lowered blinking frequency and decreased tear secretion. In addition, zoster ulcerations of the upper lid margin mechanically disturb reformation of the tear film and weaken the lipid layer by necrosis of the Meibomian glands. Ointments reduce break-up time and parasympathicolytic mydriatics further decrease tear secretion. When the average time between two blinks is shorter than the tear film break-up time, a "dry eye" condition usually develops. The appropriate treatment in such cases is thorough prevention of evaporation.