The tropicamide eye drop test in Parkinson's disease

The dementia of Parkinson's disease (PD) and Alzheimer's disease (AD) share neurochemical and neuroanatomical characteristics. Pupillary supersensitivity to dilute pilocarpine and to the cholinergic antagonist tropicamide were described in AD, although the specificity has been debated. In the present work we examine whether a similar supersensitivity of the pupil exists in PD patients with and without dementia. PD patients ( n = 36,13 demented) and 14 neurologically healthy age-matched controls were examined. The pupil size was determined at baseline and 30 min after the instillation of 0.01% tropicamide, and measured using the Goldmann perimeter. All 13 demented PD patients, but only eight of the 23 non-demented patients (35%), had a mydriatic response to dilute tropicamide. Among controls, only 2 14 (14%) had mydriaris ( p < 0.001). This supersensitivity of the pupil of demented PD patients to a cholinergic antagonist may reflect either a reduced parasympathetic tone or an artifact of increased corneal permeability and decreased lacrimation and blinking. We conclude that the tropicamide eye drop test is not useful as a diagnostic tool for dementia in PD.