Evaluation of a simple photographic technique to detect pupillary dilation lag due to Horner's syndrome

Abstract

Objective: Properly timed photographs of the pupils is one technique to demonstrate delayed pupillary dilation, called dilation lag, that is present in patients with unilateral Horner's syndrome. We utilized this technique to evaluate the amount of dilation lag that could distinguish Horner's syndrome. Methods: Fifty-six patients with Horner's syndrome and 39 normal subjects (with physiologic anisocoria ranging from 0.0 to 0.5 mm) had Polaroid photographs taken of both pupils simultaneously under three conditions: at baseline (room light), after five seconds of darkness, and after 15 seconds of darkness. For this study, pupillary dilation lag was operationally defined as the difference in anisocoria between five seconds and 15 seconds of darkness. Results: The median dilation lag was 0.1 mm (range: 0.0–0.3 mm) in normal subjects and 0.3 mm (range: 0.0–1.6 mm) in Horner's patients. A dilation lag of 0.4 mm or more was 100% specific for differentiating Horner's syndrome from physiologic anisocoria, but the sensitivity was 48%. There was no significant correlation between the magnitude of the baseline anisocoria and the amount of dilation lag nor between the amount of dilation lag and postcocaine anisocoria. Conclusions: This photographic technique is a simple and readily available nonpharmacologic method to detect pupillary dilation lag and confirm unilateral Horner's syndrome. However, not all Horner's patients demonstrate a significant amount of dilation lag. Thus, the absence of dilation lag (less than 0.4 mm) does not rule out Horner's syndrome and, in suspected cases, cocaine testing is recommended.