Pupil dilation response to tropicamide: a biological test for Alzheimer's disease?

The pupil dilation response to tropicamide has been proposed as a simple test for demonstrating the central cholinergic deficit present in Alzheimer's disease (AD). We examined this response in 20 patients with clinically diagnosed mild probable AD and in 20 unrelated, cognitively intact, age-matched controls. A marked increase in pupil diameter was observed within 30 minutes in both groups. Differences between the groups did not attain statistical significance. The ability of the proposed test to discriminate between AD patients and healthy controls may be influenced by experimental procedures and by the ethnic background of the subjects under study. At present the pupil dilation response to tropicamide cannot be considered a useful diagnostic aid.