Robert J. Campbell MD, MSc and William G. Hodge MD, PhD, FRCSC, University of Ottawa Eye Institute, Ottawa, ON.

The differential diagnosis of the red eye involves structures ranging from the periorbita, lids and conjunctiva, to the surface sclera and episclera, to the cornea and uvea and to acute angle closure glaucoma. The history and physical examination can usually differentiate these entities from one another. The most important part of the examination is the visual acuity, which can usually distinguish the serious red eye from more benign causes.
Key words: orbital cellulites, conjunctivitis, blepharitis, keratitis, acute glaucoma, red eye.