Severity and progression of visual impairment and risk of dementia.

INTRODUCTION: Visual impairment is associated with dementia risk, but the role of severity and longitudinal change remains unclear. We examined whether visual impairment severity and its progression were associated with incident dementia. METHODS: This territory-wide cohort study followed 15,576 community-dwelling older adults without dementia at baseline for 16 years. Incident dementia was ascertained using International Classification of Diseases, Tenth Revision diagnoses or Clinical Dementia Rating scores of 1 to 3. Visual acuity was measured using the Snellen chart. Cox models estimated hazard ratios, excluding dementia cases occurring within the first 6 years to minimize reverse causation and adjusting for demographic, comorbidity, and lifestyle factors. RESULTS: Moderate to severe visual impairment and faster visual acuity decline were associated with increased dementia risk. Severe visual impairment was associated with dementia onset 2.1 years earlier than normal vision. DISCUSSION: These findings strengthen the evidence for visual impairment as a dementia risk factor, supporting incorporation of visual assessment into dementia risk stratification. TRIAL REGISTRATION: The Chinese Clinical Trial Registry: ChiCTR1900023536.