PUPIL-DILATION TO TROPICAMIDE IS NOT SPECIFIC FOR ALZHEIMER-DISEASE

Background: The extent of pupil dilation after instillation of a dilut e tropicamide solution was proposed as a noninvasive neurobiological d iagnostic test for Alzheimer disease (AD). Pupils in patients with AD dilated 23% vs only 5% in control subjects. Objective: To determine wh ether pupil dilation in response to tropicamide distinguishes patients with AD from control subjects without dementia. Methods: There were 5 0 patients with AD and 51 control subjects; no participant had primary ocular pathological conditions or took drugs that affected cholinergi c 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 i lluminated the eye with a low-level infrared source and measured pupil diameters, fixation, and light level every 16.7 milliseconds during e ach 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 wa s 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 min utes 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 bet ween patients with AD and control subjects. Eye color and corneal mois ture did not affect these results. The extent of pupil dilation in pat ients with AD was not related to clinical estimates of dementia severi ty. Conclusion: Pupil dilation in response to instillation of 0.01% tr opicamide is not useful as an antemortem diagnostic test for AD.