Can tropicamide eye drop response differentiate patients with progressive supranuclear palsy and Alzheimer's disease from healthy control subjects?

Pupillary dilation in response to dilute tropicamide eye drops has been proposed as a noninvasive diagnostic test to identify patients with Alzheimer's disease (AD). We examined 14 patients with progressive supranuclear palsy (PSP), another related neurodegenerative disorder characterized by severe widespread cholinergic deficits and known central hypersensitivity to cholinergic blockade, to determine whether they also showed a marked pupil dilation after administration of dilute tropicamide eye drops. Both PSP patients and healthy age-matched control subjects had a similar pupillary response comparable with that previously reported in AD patients. Given its lack of specificity, physicians should be very cautious in using this test for identification of patients with AD.