Design, methodology, and preliminary results of the Handan Eye Study

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Design, methodology, and preliminary results of the follow-up of a population-based cohort study in rural area of northern China: Handan Eye Study

Over half of China’s 1.4 billion people live in rural areas, yet research on their eye health remains limited. For decades, most studies focused on urban populations, leaving critical gaps in understanding diseases like glaucoma, cataract, and age-related macular degeneration (AMD) in rural communities. The Handan Eye Study (HES)—a landmark population-based cohort study in northern China’s Hebei Province—aims to fill this gap. Its 2012–2013 follow-up, building on a 2006 baseline, provides the first long-term data on 6-year eye disease incidence, progression, and risk factors in rural adults. Here’s what you need to know about its design, methods, and early findings.

Who Conducted the Study?

The follow-up was led by researchers from the Beijing Institute of Ophthalmology, Beijing Tongren Eye Center, Beijing Tongren Hospital, and Capital Medical University (Beijing, China), with contributions from the Handan Eye Study Group. Co-first authors include Kai Cao, Jie Hao, and Ye Zhang, and the corresponding author is Prof. Ning-Li Wang (Beijing Institute of Ophthalmology).

Study Design & Methodology

The HES is a population-based cohort study tracking rural adults in Handan, a city in Hebei Province (northern China). The 2006 baseline enrolled 6,830 adults aged 30 or older from 13 villages in Yongnian County—chosen for its representative income (median for northern rural China) and demographic similarity to national rural populations.

The 2012–2013 follow-up aimed to:

  1. Measure 6-year cumulative incidence of vision-threatening eye diseases.
  2. Assess disease progression and its impact on quality of life.
  3. Evaluate risk factors for eye disease and death.

Inclusion & Exclusion Criteria

  • Included: Adults aged 36 or older (6 years after baseline), local residents (or those living in the area for ≥6 months), and volunteers who provided informed consent.
  • Excluded: Under 36, short-term residents (≤6 months), or those refusing participation.

Recruitment Strategy

To maximize participation:

  • Village leaders and local doctors used TV/radio broadcasts and face-to-face talks to explain the study.
  • Home visits were made for residents unable to attend central clinics, with abbreviated exams for disabled participants.

Data Collection

Trained interviewers and experienced ophthalmologists (who worked on the baseline) collected data through:

  1. Questionnaires: Socio-demographics (age, gender, education), medical history (hypertension, diabetes), cognitive function (Mini-Mental State Examination, MMSE), general quality of life (EuroQol-5D), and eye-specific symptoms. New in follow-up: The 8-item Short-Form Health Survey (SF-8), 12-item Near Vision-Related Quality of Life (NVR-QOL), and a 15-item visual quality questionnaire.
  2. Ocular Examinations: Best-corrected visual acuity (BCVA), intraocular pressure (IOP), slit-lamp exams, fundus photography, retinal nerve fiber layer imaging, and refraction testing. New in follow-up: Color vision testing, near vision measurement, and trachoma screening.

Key Preliminary Results

Of the 6,830 baseline participants, 5,394 (85.3%) completed follow-up—a strong rate for cohort studies. 929 were lost to follow-up (mostly working away from home or refusing), and 507 died.

Group Comparisons

Researchers compared three groups: followed-up, lost to follow-up, and dead. Key findings:

  • Dead group: Older (average 66.5 years vs. 51.4 in the followed group), more male (59% vs. 44.6%), lower education (65.9% finished middle school vs. 85.5%), and higher rates of chronic diseases (36.7% hypertension, 8.2% diabetes vs. 20.2%/1.8% in the followed group). Vision was also worse (BCVA 0.37 logMAR vs. 0.08 in the followed group).
  • Lost to follow-up vs. followed: Minor differences (younger, more male, slightly lower BMI/systolic blood pressure), but no gaps in critical eye parameters (BCVA, IOP, corneal thickness, axial length).

Factors Linked to Death

Multivariate analysis identified three predictors of death over 6 years:

  1. Age: Each additional year increases death risk by 9% (OR = 1.09, 95% CI: 1.07–1.11).
  2. Gender: Males are 2.2 times more likely to die than females (OR = 0.32, 95% CI: 0.22–0.45).
  3. BCVA: Better vision reduces death risk by 72% (OR = 0.28, 95% CI: 0.16–0.50).

Data Quality

The study’s data is robust:

  • Scale Reliability/Validity: Questionnaires like EuroQol-5D (Cronbach’s α = 0.63) and SF-8 (α = 0.90) had strong consistency and validity (cumulative variance ≥0.61).
  • Measurement Consistency: Exams (IOP, visual acuity) had high inter-operator agreement (Intraclass Correlation Coefficient, ICC ≥0.80). Diagnoses of glaucoma, AMD, and diabetic retinopathy (DR) were consistent between ophthalmologists (Kappa ≥0.69).

What Does This Mean for Rural Eye Health?

The HES follow-up is a milestone for rural Chinese eye health. It’s one of the first large cohort studies to track long-term eye disease trends in northern rural populations—providing data on:

  • Incidence of blindness, low vision, and major eye diseases (cataract, glaucoma, AMD).
  • Risk factors for disease progression and death.
  • Normative data for rural adults (e.g., IOP, refraction).

Strengths

  • High Follow-Up Rate: 85.3% is well above the average for cohort studies, reducing bias.
  • Rigorous Quality Control: Trained staff, consistent measurements, and valid scales ensure reliable data.
  • Low Bias Risk: Minimal differences between followed and lost groups mean results are generalizable.

Limitations

  • No Young Adults: All participants are ≥36, so findings don’t apply to younger populations.
  • Incomplete Gonioscopy: Not all participants had angle exams, so we can’t distinguish angle-closure vs. open-angle glaucoma.
  • Rare Diseases: Small sample size for low-incidence conditions (e.g., macular retinoschisis).

Conclusion

The Handan Eye Study follow-up provides unprecedented insights into rural northern China’s eye health. Its high follow-up rate, rigorous methodology, and strong data quality make it a valuable resource for researchers and policymakers. Future analyses will reveal 6-year incidence rates for eye diseases and how factors like age, gender, and chronic illness affect outcomes—helping design targeted interventions to protect rural communities’ vision.

Original study: Cao K, Hao J, Zhang Y, et al. Design, methodology, and preliminary results of the follow-up of a population-based cohort study in rural area of northern China: Handan Eye Study. Chinese Medical Journal 2019;132(18):2157–2167. doi:10.1097/CM9.0000000000000418

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