Pupil dilation to tropicamide is not specific for Alzheimer disease
J. H. Growdon, K. Graefe, M. Tennis, D. Hayden, D. Schoenfeld and S. H. Wray
Department of Neurology, Massachusetts General Hospital, Boston, USA.
BACKGROUND: The extent of pupil dilation after instillation of a dilute
tropicamide solution was proposed as a noninvasive neurobiological
diagnostic test for Alzheimer disease (AD). Pupils in patients with AD
dilated 23% vs only 5% in control subjects. OBJECTIVE: To determine whether
pupil dilation in response to tropicamide distinguishes patients with AD
from control subjects without dementia. METHODS: There were 50 patients
with AD and 51 control subjects; no participant had primarily ocular
pathological conditions or took drugs that affected cholinergic tone. All
participants received 1 drop of 0.01% tropicamide in 1 eye and 1 drop of
0.9% saline solution in the other eye in random order. Pupil measurements
were obtained using a pupil and corneal reflection tracking system (RK-426
PC system, ISCAN Inc, Burlington, Mass) that illuminated the eye with a
low-level infrared source and measured pupil diameters, fixation, and light
level every 16.7 milliseconds during each 30-second-measurement. Pupil
measurements were obtained from each eye at baseline and 5, 10, 15, and 30
minutes after drop instillation. RESULTS: The increase in pupil size after
tropicamide instillation was equal between patients with AD and control
subjects. The mean (+/- SD) pupil diameter increased from 4.5 +/- 1.1 to
5.5 +/- 1.1 mm after 30 minutes in patients with AD and from 4.7 +/- 0.9 to
5.8 +/- 0.9 mm in control subjects. Anisocoria and the mean rate of
dilation did not differ between patients with AD and control subjects. Eye
color and corneal moisture did not affect these results. The extent of
pupil dilation in patients with AD was not related to clinical estimates of
dementia severity. CONCLUSION: Pupil dilation in response to instillation
of 0.01% tropicamide is not useful as an antemortem diagnostic test for AD.
