Background:
Wide-ranging functional defects in eye movements have been reported in Alzheimer’s disease (AD) dementia. The detection of abnormal eye movements and reading problems may identify persons at risk of AD when clear clinical symptoms are lacking.
Objective:
To examine whether computer-based eye-tracking (ET) analysis of King-Devick (KD) test results differentiates cognitively healthy persons from persons with minor problems in cognitive testing or diagnosed mild AD.
Methods:
We recruited 78 participants (57 non-demented, 21 with mild AD) who underwent neurological examination, the Consortium to Establish a Registry for Alzheimer’s Disease neuropsychological test battery (CERAD-NB), and a Clinical Dementia Rating (CDR) interview. The non-demented participants were further divided into control (normal CERAD subtests, mean MMSE = 28) and objective mild cognitive impairment (MCI; decline in at least one CERAD memory score, mean MMSE = 27) groups. The KD reading test was performed using computer-based ET. The total time used for the reading test, errors made, fixation and saccade durations, and saccade amplitudes were analyzed.
Results:
We found significant differences between the control, objective MCI, and AD groups in regard to the mean saccade amplitude (3.58, 3.33, and 3.21 ms, respectively, p < 0.03) and duration (27.1, 25.3, and 24.8 ms, respectively, p < 0.05). The KD error scores in the AD group differed significantly (p < 0.01) from the other groups.
Conclusion:
Computed ET analysis of the KD test may help detect persons with objective MCI early when clear clinical symptoms are lacking. The portable device for ET is easy to use in primary health care memory clinics.
Summary Points:
- Both the duration and amplitude of saccades were significantly decreased in the MCI and AD groups compared to the control group. As expected, the controls were significantly faster on the KD test than the AD patients. The AD group had the highest number of reading errors, and less than half (38.9%) of the AD group managed to complete the KD test without making errors.
- The KD test is a standardized, commercially available reading test. We consider it to be a potential method of detecting cognitive impairment in neurodegenerative disorders, such as AD.
- New, objective methods that are easy to carry out to detect early signs of AD are important to identify because only early AD diagnosis and treatment initiation may delay progression of the disease and postpone the dementia stage and need for institutional care.
- We report that saccadic eye movement alterations occur very early in the disease course, even earlier than the other reports have indicated. These findings support the idea that eyes and eye functions are interesting research targets for new AD biomarkers