Detecting Pupillary Dilation Lag

Horner's syndrome produces an oculosympathetic deficit with ptosis, miosis, and abnormal pupillary dilation. The pupil findings are due to denervation of the iris dilator muscle, so the anisocoria in Horner's syndrome will be more pronounced in dim light or darkness. As the iris sphincter is intact in Horner's syndrome, the anisocoria will be minimal or disappear in bright light (Thompson, 1998).