Horner's syndrome. Criteria for oculosympathetic denervation.

The darkness reflex of the pupil was examined by taking photographs under standard bright lighting conditions, and after 5 and 10 s of uninterrupted darkness. The study involved 40 control subjects and 12 patients with a presumed Horner's syndrome. No control subject showed a dilatation lag (compared with the other eye) of 0.5 mm or more in the first 5 s of darkness. This criterion allows exclusion of a fortuitous combination of "physiological anisocoria" and "physiological ptosis".