Analysis of the Clock-Reading Ability in Patients with Cognitive Impairment: Comparison of Analog Clocks and Digital Clocks.

Background: Time disorientation is one of the main symptoms observed in patients with dementia; however, their clock-reading ability has not been fully reported.
Objective: This study aimed to investigate the clock-reading ability of both digital and analog clocks in patients with dementia. We newly devised the clock-reading test (CRT) and the number-reading test (NRT) to assess cognitive factors that may affect clock-reading ability. Furthermore, the discriminating power of the CRT was calculated.
Methods: 104 participants were categorized based on their Mini-Mental State Examination (MMSE) scores as follows: subjective cognitive decline ∼ mild cognitive impairment (SCD∼MCI, N = 43), early Alzheimer's disease (AD) (N = 26), and middle-to-late AD (N = 35). Their cognitive abilities were evaluated using the clock-drawing test (CDT), CRT, and NRT.
Results: Cognitive decline leads to impairment of clock-reading ability which is more pronounced in the analog clocks than digital ones. This deficit in clock-reading is attributed to a loss of semantic memory regarding clocks at all stages. Additionally, visuospatial dysfunction and reduced ability of number recognition may lead to deficit in clock-reading in the advanced stage of AD. The discriminating power of the CRT (analog) (AUC = 0.853) was high enough to detect cognitive decline.
Conclusion: Digital clocks are more readable by patients with dementia. Since reading clocks is closely associated with daily life, the CRT has proved to be a useful tool. A decline of analog clock-reading may be an early detector for the onset of dementia in elderly patients.