Sensory and cognitive association in older persons: findings from an older Australian population.

BACKGROUND

Explanations for associations found between sensory and cognitive function remain unclear.

OBJECTIVE

To assess in an older Australian population: (1) the correlation between sensory and cognitive function across groups with a narrow age range; (2) any independent association between sensory and cognitive impairment.

METHODS

We examined 3,509 non-institutionalised residents aged 50+ years in the second cross-sectional survey of the Blue Mountains Eye Study (1997-2000). Visual impairment was defined for best-corrected visual acuity (VA) < 6/12 in the better eye, moderate to severe hearing loss for hearing threshold > 40 dB (better ear), and likely cognitive impairment for Mini-Mental State Examination (MMSE) < 24 points.

RESULTS

We found likely cognitive impairment in 3.3%, vision impairment in 2.7% and moderate to severe hearing loss in 10.5% of this population. Correlation between VA or hearing threshold and MMSE score increased with age. After adjusting for age, weak but significant correlation was evident in the normal ageing sample between vision and MMSE (r = 0.12 with vision items included and r = 0.11 with vision items excluded, both p < 0.0001), and between hearing thresholds and MMSE (r = -0.12, p < 0.0001). After adjusting for age, sex, education and history of stroke, persons with vision impairment had a lower mean MMSE score than those with normal vision, regardless of whether vision-related items were included (27.1 vs. 28.6, p < 0.001) or excluded (19.8 vs. 21.0, p < 0.001). Similarly, persons with moderate to severe hearing loss had a lower mean MMSE score than those without hearing loss (28.1 vs. 28.7, p < 0.001). Persons with likely cognitive impairment also had lower mean VA and higher mean hearing threshold than those without, after adjustment.

CONCLUSIONS

We have documented an age-related correlation between sensory and cognitive function in a normal ageing sample. The association between sensory impairment and likely cognitive impairment remained significant after excluding vision-related MMSE items and adjusting for confounding factors. Our data suggest that age-related decline and the effect of visual impairment on the measurement of cognition only partly explain the association between sensory and cognitive impairments in older persons.