[Hypersensitivity in the pupil dilation response to a cholinergic antagonist in patients with Alzheimer's disease and Down's syndrome].

In 1994, Scinto et al. reported hypersensitivity in the pupil-dilation response to topical application of a cholinergic antagonist, tropicamide, in patients with Alzheimer-type dementia. Similar tests on Japanese subjects showed significant differences in pupil response between subjects with Alzheimer-type dementia (under age 70 years) and age-matched controls. The present study included 24 patients with early-onset Alzheimer-type dementia, 29 patients with late-onset Alzheimer-type dementia, 15 healthy controls (all spouse of patients with Alzheimer-type dementia), 9 patients with vascular dementia and 5 patients with Down's syndrome. After adapting to semi-darkness (10 lux), a solution of tropicamide (Midrin-P, Santen Co, Ltd) was instilled into the right eye. Pupil diameters were measured every 5 to 10 min, and the maximum pupil diameter for each eye was used in the data analysis. The solution was diluted until the tropicamide concentration reached 0.01%. Pupil diameters were measured, and differences between baseline and maximum pupil diameter were computed. Among 18 patients with early-onset Alzheimer-type dementia (mean age 63.9 years) the pupils dilated by 1.12 +/- 0.52 mm (mean +/- SD) as compared with 0.20 +/- 0.75 mm in 7 age-matched controls (mean age 57.8 years); this difference was significant (T-test, p < 0.05). Correlations between the degrees of pupillary dilation and the scores on the revised version of Hasegawa's Dementia Scale were not significant. These data suggest that in subjects under 70 years of age, the diagnostic methods described by Scinto et al. can be used to distinguish those with Alzheimer-type dementia from those without dementia, but those methods may not be effective in subjects over 70 years of age.