Critical flicker fusion in primary degenerative dementia of the alzheimer’s type (PDDAT): Clinical implications (II)

Abstract

Critical Flicker Fusion Threshold (CFFT) and the difference between fusion and flicker thresholds were examined in 23 female and three male patients with Primary Degenerative Dementia of the Alzheimer’s type (PDDAT). The control group consisted of age, sex, and occupational class-matched, normal volunteers. Patients had a mean age of 81.7 years ±6.05 (range 67–89); diagnosis was based on DSM-IIIR criteria.The psychophysical method of limits was used to measure three ascending (fusion) and three descending (flicker) means the average being the CFFT.Both the CFFT and the flicker thresholds were able to distinguish between patients and volunteers at a high level of statistical significance (t=2.054, df=50, p<0.0018 and t=−4.903, df=50, p<0.0000 respectively). Sixty-five percent of patients had CFFT scores below 1.96 SD of the volunteer CFFT mean and 85 percent of patients had flicker thresholds below 1.96 SD of the volunteer flicker mean. The fusion thresholds were not significantly different in the two groups but the fusion thresholds were significantly greater than the flicker thresholds in patients (t=5.617, df=25, p<0.0000).One interpretation of the results in that patients with PDDAT have a significant reduction in the sensitivity of the Central Nervous System to suprathreshold flicker.Accurate diagnosis of early PDDAT (probable Alzheimer’s disease) continues to remain one of the most difficult areas in dementia research. The use of simple quantitative measures such as CFFT may have an important role to play in the overall assessment of patients with PDDAT.