Prevalence of Presbyopia (Near Vision Fatigue) and Related Factors Among Working Adults Aged 30 to 55 Years in Shanghai (FOCUS)

This cross-sectional observational study will investigate the prevalence of presbyopia (near fatigue) and associated factors among working adults aged 30-55 years in Shanghai, China. Eligible participants must have worked in their current position for at least one year and provide written informed consent.

Industry-stratified two-stage sampling will be used, with the ISIC Rev.5 classification as the industry stratification framework. At the first stage, workplaces are randomly selected from candidate workplace rosters within each industry stratum; the study plans to include at least 15 independent workplaces covering at least 5 ISIC Rev.5 sections. At the second stage, eligible employees are randomly sampled from complete, de-duplicated employee rosters of the selected workplaces; if the number of eligible employees in a workplace does not exceed the planned invitation quota, all eligible employees are invited. The target is at least 1,366 participants with valid primary outcome data. Allowing for an estimated combined nonresponse and unusable primary outcome data rate of 20%, at least 1,708 individuals will need to be invited.

Data collection will include questionnaires and standardized ophthalmic examinations. Questionnaires will assess demographic and occupational characteristics, near-work demands, screen exposure, sleep, outdoor activities, lifestyle, ocular symptoms, awareness of presbyopia, previous correction, and correction needs and preferences. The NAVQ-P and OSDI questionnaires will assess near-vision difficulties and ocular surface symptoms. Examinations will assess distance, intermediate, and near visual acuity, refraction, near addition power (ADD), accommodative function, and ocular health. NVC mini-program outputs, including presbyopia severity categories and recommended ADD ranges, will also be recorded.

The primary outcome is the prevalence of presbyopia. Presbyopia is defined as binocular near visual acuity worse than N8 at 40 cm under best distance correction, improving by at least one line to N8 or better with additional positive spherical lenses, after excluding other ocular diseases sufficient to explain the reduction in near vision.

Secondary assessments will describe visual function, the relationship between accommodative amplitude and age, awareness of presbyopia, and correction needs. Associations with demographic, occupational, refractive, behavioral, and dry-eye-related factors will be examined. Analyses will account for industry stratification, workplace clustering, and unequal sampling probabilities as appropriate.

Agreement between NVC outputs and subjective refraction ADD will be assessed using overall percent agreement, the proportions of classifications differing by one grade and by two or more grades, and Kendall's tau-b correlation between NVC grades and clinical grades. The proportion of reference ADD values falling within the NVC-recommended ranges will also be calculated. No treatment will be assigned as part of this observational study.