Contributor: Gordon K. Klintworth
Edema of the cornea is a manifestation of corneal inflammation (as in herpes keratitis [keratitis - herpetic] or diseases of the corneal endothelium. The edema may involve primarily the corneal epithelium or the corneal stroma. Contact lens wear can lead corneal stromal edema primarily because of hypoxia. Edema of the corneal epithelium effects the diffraction of light and leads to colored haloes that are typically observed around street lights, the moon, and automoble headlights. Stromal edema causes corneal opacification and swelling. The thickened cornea can be measured by pachometry. When the corneal endothelium is defective of absence an important physiologic mechanism for counteracting the osmotic forces that hydrate the cornea is lost  and the cornea becomes edematous. This occurs with various types of congenital hereditary endothelial dystrophy, bullous keratopathy [keratopathy - bullous], pseudophakic bullous keratopathy [keratopathy - pseudophakic bullous], aphakic bullous keratopathy [keratopathy - aphakic bullous], Fuchs corneal dystrophy, and posterior polymorphous corneal dystrophy. Several factors contribute to corneal edema that follows cataract surgery (a prior deficiency of the corneal endothelium such as alow endothelial cell count, excessive postoperative inflammation, detachment of  Descemet membrane, trauma to the corneal endothelium,.and a prolonged postoperaive elevation in intraocular pressure, toxic anterior segment syndrome). Corneal edema associated with inflammation often becomes accompanied by corneal neovascularization [neovascularization - cornea], whereas this association is not a feature of the corneal edema that follows corneal endothelial decompensation.