FOR many decades the most generally accepted explanation of the cause of anisocoria has borne the name of the man who first described the unilateral dilated, fixed pupil, Sir Jonathan Hutchinson. He described the sign by stating that if disorganization of any portion of the oculomotor nerve occurs up to the ciliary ganglion paralytic anisocoria will result.1
Since 1778 the Hutchinson pupil has repeatedly been mentioned in the literature.2 Subsequent authors, either directly or indirectly, have been more explicit in describing the mechanism which resulted in a dilated, fixed pupil. Meyer3 ascribed the pressure on the oculomotor nerve to herniation of the uncus into the incisura angularis. Similarly, Jefferson4 described a pressure cone formed by uncal herniation on the crus cerebri, with resulting impingement on the oculomotor nerve. Macewen's5 data substantiated the pressure theory by showing that there was a direct proportion between the degree