Date Published: February 20, 2018
Publisher: Public Library of Science
Author(s): Kimie Miyata, Tadanobu Yoshikawa, Masayuki Morikawa, Masashi Mine, Nozomi Okamoto, Norio Kurumatani, Nahoko Ogata, Kewei Chen.
To determine whether there is a significant association between prior cataract surgery and cognitive function in an elderly Japanese cohort.
Nara Medical University, Nara, Japan.
The Fujiwara-kyo Eye Study was a cross-sectional epidemiological study.
The subjects were ≥ 68-years who lived in the Nara Prefecture and responded to recruitment notices. All of the subjects received comprehensive ophthalmological examinations, and answered questionnaires on their socio-demographic and medical history including prior cataract surgery. The association between prior cataract surgery and cognitive function was determined.
A total of the 2764 subjects whose mean age was 76.3±4.8 years (±standard deviation) was studied. Of these, 668 individuals (24.2%) had undergone cataract surgery. Of these, 150 (5.4%) had dementia as determined by the Mini-Mental State Examination (MMSE) score ≤23, and 877 individuals (31.7%) had mild cognitive impairment (MCI; MMSE score 24–26). The subjects who had prior cataract surgery had significantly lower odds ratio (OR) of having MCI (OR = 0.78, 95% confidence interval; CI 0.64–0.96, P = 0.019) than those who had not had cataract surgery after adjusting for age, sex, body mass index, education, hypertension, diabetes, depression, and history of stroke. The OR was still lower when the visual acuity was also added to the adjusted factors (OR 0.79, 95% CI 0.64–0.97, P = 0.025). However, prior cataract surgery did not contribute significantly to the low OR for dementia.
Cataract surgery may play a role in reducing the risk of developing MCI independently of visual acuity but not for dementia.
The number of older individuals is rapidly increasing worldwide, and the cost of medical care and social security benefits have correspondingly increased. It is known that both visual and cognitive impairments increase with advancing age [1–3], and these impairments will contribute to the cost of medical care. The incidence of dementia was estimated to be 15% and mild cognitive impairment (MCI) was 13% in individuals ≥65 years in Japan in 2010. Thus, 28% of individuals ≥65 years have some degree of cognitive impairments . Visual and cognitive impairments can limit the activities of daily living and the quality of life (QOL), and earlier studies [5–8] and population-based epidemiological studies [9–14] involving older individuals have shown that there is a strong association between visual impairments and cognitive function. We have also found a significant association between visual impairments and cognitive function in elderly Japanese .
Data was available on 2,764 individuals on the status of the crystalline lens or prior cataract surgery (S1 Table). All of these individuals had been examined by MMSE. The mean age of subjects was 76.3 ± 4.8 years (mean ± standard deviation, SD). Of the 2,764 subjects, 5.4% were placed in the dementia group, 31.7% in the MCI group, and 62.8% in the normal cognitive function group. The mean age of the dementia group and the MCI group was significantly higher than that of the normal cognitive function group (P <0.001, Table 1). The number of subjects with ≥13 years of education was lower in the dementia group (13.3%) and the MCI group (18.2%) than that in the normal cognitive function group (26.1%; P <0.001, Table 1). The mean BCVA was significantly worse in the dementia group and the MCI group than that in the normal cognitive function group (P <0.001, Table 1). Our results showed that prior cataract surgery significantly reduced the risk of having MCI (OR = 0.78) but did not reduce the risk for dementia. Cataracts are frequent in the elderly and are the leading cause of visual impairments in the elderly worldwide. An earlier study reported that there was a significant correlation between the visual acuity and cognition , and subjects with good visual acuity had a 63% lower risk for developing dementia over an 8.5-year period . Similarly, elderly individuals with decreased visual acuity were 5 times more likely to show diminished cognitive performance than elderly individuals with good vision . We also reported earlier that the prevalence of both cognitive and visual impairments increased with increasing age in this cohort . Furthermore, subjects with mild visual impairments (BCVA >0.2 logMAR unit) had 2.4 times higher risk of having dementia than those without visual impairments after adjusting for age, sex, and length of education. These results indicate that it is important to maintain good visual acuity to reduce the risk of developing dementia, however the effects of cataract surgery on preventing cognitive impairment were not analyzed in the Fujiwara-kyo study.