The tropicamide test in patients with dementia of Alzheimer type and frontotemporal dementia.

The tropicamide test was applied to 30 patients with probable Alzheimer's disease (pAD), 12 with frontotemporal dementia (FTD) and 46 healthy subjects. One drop of 0.01% tropicamide was instilled in one eye and one drop of saline solution in the other. The pupil diameter was measured with a Goldmann pupillometer in its basal condition and 10, 15, 20, 25, 30, 35, 45 and 55 minutes afterwards. The results do not show differences between pupil dilation observed in pAD and in FTD; in both groups, from the beginning of the test, the pupil dilated more than in healthy people. A high interindividual variability was observed. The best cutoff point is 38% of interpupillary difference at minute 25 (sensitivity = 63%, specificity = 80%). If we consider the prevalence of AD in a population over 40 years old to be 1.4%, the adjusted positive predictive value of the test would be 4.2%. According to these results, the test is not a true diagnostic marker of AD.