Changes in pupil reaction to light in Alzheimer's disease patients: a preliminary report

The aim of this preliminary study was to compare the pupil reaction to light in Alzheimer's disease (AD) patients before and after treatment and in normal controls. Ten AD patients diagnosed according to DSM-IV and NINCDS-ADRDA criteria (five medication-free and five under anticholinesterase treatment) and five age- and gender-matched controls took part in the study. Drug-free patients and all control subjects were free of any medication for at least four weeks. An optical method was used to assess the pupil reaction to a single flash. Medication-free AD patients manifested shorter latency and lower amplitude of maximum response to light in comparison to controls. These findings are in agreement with the presence of a cholinergic deficit in AD patients. Pharmacological treatment with donepezil, which is an anticholinesterase agent partially improves this deficit. The results of this preliminary investigation suggest that dynamic pupillometry could be a useful adjunct to assist the diagnosis of early AD, and the differential diagnosis between different types of dementia. AD patients seem to manifest a specific pattern of pupil reaction to light, and some characteristics of this pattern are detectable even in patients receiving anticholinesterase medication. However, this is only a preliminary report and further research is mandatory.