Pupil response to tropicamide in Alzheimer's disease and other neurodegenerative disorders.

Excessive mydriatic response to dilute tropicamide has been suggested as a possible non-invasive diagnostic test in patients with Alzheimer's disease (AD). To further evaluate the sensibility and specificity of this test we studied the pupillary response to tropicamide in 24 patients with AD, 30 age-matched controls, 7 patients with dementia other than AD and 13 patients with extrapyramidal disorders (EXD). Maximum dilatation response over baseline was much higher in AD with significant differences compared to controls (p < 0.001) and to EXD (p < 0.05). However, there was a quite wide range of overlap between AD and controls and no cut-off point was found with a high enough specificity to consider this a conclusive diagnostic test. Lower dilatation response in the overlapping range (13%), however, may be useful because of its negative predictive value (93.5%) and as a screening tool due to its sensitivity (87.5%).