Evaluating the effect of spectacle correction for refractive errors and presbyopia on cognitive function in rural older adults in China: protocol for a randomised, parallel-group, superiority trial.

BACKGROUND

Vision impairment and mild cognitive impairment are highly prevalent in ageing rural populations of low- and middle-income countries. Observational studies suggest that vision correction may slow cognitive decline, but robust causal evidence-particularly from rural China-is lacking, despite an ongoing randomised controlled trial (RCT) in India. Our RCT will evaluate whether providing near and/or distance vision correction can slow cognitive decline among older adults in rural China, generating context-specific evidence to guide national policy and global healthy ageing strategies.

METHODS

This study is designed as an assessor-blind, parallel-group, individually RCT. A total of 964 participants (482 per arm) aged 60-79 years with correctable refractive error-related visual impairment at distance and/or near (presenting visual acuity <6/12 in the better-seeing eye, improving to ≥6/7.5 in either eye with spectacle and/or near visual acuity <6/12 at 40 cm when measured binocularly, improving to ≥6/7.5 in either eye with spectacle), rural household registration, normal hearing (defined as a hearing threshold <40 dB in at least one ear, assessed using the HearX HearTest) and Mini-Mental State Examination, Second Edition, Simplified Chinese version scores above education-specific cut-offs will be enrolled. After comprehensive eye examinations at township health centres or village clinics, intervention participants will receive distance, near or bifocal spectacles while controls will receive a prescription and spectacles at trial closeout. The primary outcome is the change in global cognitive function from baseline to the 36-month follow-up, assessed using the Chinese version of the Montreal Cognitive Assessment Basic, with and without adjustment for baseline score, age, gender, education and other potential confounders.

ETHICS AND DISSEMINATION: The protocol is approved by the Institutional Review Board of West China School of Public Health and West China Fourth Hospital, Sichuan University, China (approval number: (HXSY-BEC-S2026005)). Results will be published in a peer-reviewed journal and presented at scientific meetings.

TRIAL REGISTRATION NUMBER: NCT06836440, 21 April 2025, (https://clinicaltrials.gov/study/NCT06836440).