Corneal ulcers due to Pseudomonas aeruginosa are usually central and extremely destructive. In the majority of instances the course of an untreated Pseudomonas ulcer is one of widespread corneal suppuration, necrosis, and perforation within a few days. Treatment of these ulcers has not often resulted in useful vision. It is well to remember, however, that P. aeruginosa is in some instances a saprophyte which possesses little or no virulence in the eye or in other parts of the body. This has been demonstrated by the experimental production in animals of Pseudomonas corneal ulcers which have a relatively benign course even when untreated. Fulminating corneal ulcers, however, can be produced experimentally by the use of virulent strains. This variation in degree of virulence must be kept in mind when the success of various forms of therapy is being evaluated.
Prior to the advent of polymyxin, it was assumed that the poor