The Influence of Vision Impairment on the Measurement of Cognition in Older Adults in India: Findings From LASI-DAD.

Background and Objectives: Prior investigations have not considered whether poor vision biases cognitive testing. However, such research is vital given increasing evidence that vision impairment (VI) may be an important modifiable risk factor for dementia, particularly in low- and middle-income settings where the prevalence of VI is high. Research Design and Methods: This study employed data from 3 784 participants in Wave 1 of the Longitudinal Aging Study in India-Diagnostic Assessment of Dementia (LASI-DAD) who underwent both visual acuity and cognitive function testing. We used multiple indicators and multiple causes models to assess differential item functioning (DIF; eg, bias) in cognitive testing by objectively measured distance and near VI. Multivariable linear regression was used to model the association between VI and cognitive factor scores before and after DIF adjustment. Analyses were performed for general cognition and separate cognitive domains, corresponding to memory, language/fluency, executive functioning, and visuospatial performance. Models were adjusted for demographic, health, and socioeconomic covariates. Results: Participants in our sample were 60 and older. Most participants with VI were 60-69 years old (59.6%) and 50.8% were female. Individuals experiencing both distance and near VI tended to be older, have lower educational attainment, be married, reside in rural settings, and belong to lower consumption and BMI categories. Both distance and near VI were associated with poorer cognition before and after DIF-adjustment. Differences between DIF-unadjusted and -adjusted scores were small compared to the standard error of measurement, indicating no evidence of meaningful measurement differences by VI. Discussion and Implications: In well-conducted large-scale surveys, bias in cognitive testing due to VI is likely minimal. Findings strengthen previous evidence on the association between VI and dementia by showing that such associations are unlikely to be attributable to vision-related measurement error in the assessment of cognitive functioning.