A higher prevalence of chronic conditions such as diabetes, hypertension, and heart disease consistent with past studies, is strongly associated with vision impairment among older people (Crews et al., 2017). Consistently, the present study found that vision impairment is significant associated with reporting diabetes among older individuals. Again, studies have found patients with diabetes militias to be at an increased risk of developing vascular dementia and Alzheimer’s disease (Arvanitakis, Wilson, Bienias, Evans, & Bennett, 2004; Exalto, Whitmer, Kappele, & Biessels, 2012; Peila, Rodriguez, & Launer, 2002). Hence, establishing a link that relates diabetes and vision impairment with cognitive functioning is required that may allow more effective screening for and prevention of vision impairment and/or cognitive decline to be developed in the future.
Vision impairment as a post-stroke disability has been well-acknowledged in the literature (Sand et al., 2013, 2016). Concordant with past studies that have shown that people who experienced a stroke were at higher risk of visual defects than people without experiencing stroke (Suchoff et al., 2008), results of the present study showed that stroke is significantly associated with visual impairment among older adults. Further, clinical studies found that high blood pressure increases the risk of developing diabetic retinopathy and other retinal vascular diseases (Duke-Elder, 2007; Wong et al., 2001). In line with this, we found a significant association of hypertension with vision impairment among the study participants. Moreover, multiple studies have found that compared with older adults who have normal vision, visually impaired persons had higher chances to have heart diseases and cardiovascular mortality (Dianed Zheng et al., 2012; Evans et al., 2002; Hsueh et al., 2019; Liew, Wong, Mitchell, Cheung, & Wang, 2009). Similarly, the present study found a significant positive association of heart disease with reporting visual impairment in the older participants.
Cataracts are found to be the leading cause of blindness and visual impairment worldwide, especially in developing countries (Bourne et al., 2013). A meta-analysis of all available population-based studies found that the highest percentages of visual impairment caused by cataracts were recorded in the South Asian region (Khairallah et al., 2015). The present analysis also shows that after controlling for socio-demographic variables, the chances of reporting vision impairment among older adults who had cataracts were almost six times higher than their counterparts. Although cataracts and resultant impairment cases can be avoided with early detection and timely intervention, the delivery of surgical interventions continues to be a challenge in developing countries (Khanna, Pujari, & Sangwan, 2011).
On the other hand, vision impairment among aging populations is closely associated with their cognitive and behavioral manifestations (Clemons, Rankin, & McBee, 2006). Consistently, our results suggested a significant relationship between visual and cognitive impairment, an association not previously demonstrated in any population-based studies in India. Findings from several cross-sectional and longitudinal studies in other countries, however, support such an association (Anstey et al., 2001; Davies-Kershaw et al., 2018; Luo et al., 2018; Mandas et al., 2014). Another Japanese study found that older adults with both impaired vision and hearing had higher odds of cognitive impairment (Mitoku, Masaki, Ogata, & Okamoto, 2016). Further, such studies suggested that better visual acuity by means of cataract surgery or refractive correction and wearing glasses seem to correlate with better cognitive functioning (Albers et al., 2015; Rogers & Langa, 2010; Spierer et al., 2016; Tamura et al., 2004). Contrarily, some of them found that vision-enhancing interventions did not lead to short-term improvements in functioning or cognitive status (Elliott, McGwin, & Owsley, 2009).
While the strength of this study is that it uses data from a large, nationally representative, population-based survey to examine a comprehensive list of chronic conditions in conjunction with vision impairment and its association with a cognitive deficit, it is subject to several limitations. First, the data is cross-sectional in nature; we, therefore, cannot confirm whether a cognitive decline preceded vision impairment or vision impairment preceded a cognitive deficit, and we cannot infer causality between chronic illnesses and vision impairment. Second, the data excludes people living in nursing homes and other institutional settings, who may report higher rates of vision impairment. Third, the vision question in BKPAI is a self-reported measure of function and does not capture the severity of vision problems or different eye diseases.