Nine-year incidence of visual impairment in the Barbados Eye Studies

Abstract

Objective: To describe the 9-year incidence of visual impairment and primary causes of blindness among black participants of the Barbados Eye Studies (BES).

Design: Population-based prospective cohort study.

Participants: The BES followed a nationally representative cohort selected by simple random sampling, aged 40 to 84 years at baseline, with reexaminations after 4 years (Barbados Incidence Study of Eye Diseases [BISED]) and 9 years (BISED II). BISED II included 2793 (81%) of those eligible.

Methods: Cumulative 9-year incidence rates were estimated by the Product-Limit approach. The study was reviewed and approved by the institutional review boards of collaborating institutions.

Main outcome measures: Best-corrected visual acuity (VA) was assessed by the Ferris-Bailey chart, following a modified Early Treatment of Diabetic Retinopathy Study protocol. Low vision and blindness were defined by World Health Organization (WHO) criteria as VA <6/18 to 6/120, and <6/120, respectively, in the better eye, and by U.S. criteria as VA < or =20/40 and < or =20/200, respectively. Vision loss was defined as a decrease of 15 letters or more read correctly in the better eye between baseline and follow-up examinations.

Results: The 9-year incidence was 1.0% and 2.1% for blindness and 6.0% and 9.0% for low vision, by WHO and U.S. criteria, respectively. Older age at baseline was associated with higher incidence of low vision and blindness, reaching 23.0% (95% confidence interval [CI], 18.8-28.0) and 4.3% (95% CI, 2.7-6.9) at age 70 years or more, based on WHO criteria. The primary causes of incident bilateral blindness (U.S. criteria) in 126 eyes were age-related cataract (48.3%), open-angle glaucoma (OAG) (14.3%), combined cataract and OAG (6.3%), diabetic retinopathy (8.7%), and optic atrophy (7.1%). Age-related macular degeneration (2.4%) rarely caused blindness.

Conclusions: Incident visual impairment is exceedingly high in this population. Cataract, OAG, and diabetic retinopathy remain the major causes of blindness, underpinning the clinical and public health significance of these conditions in this and similar populations.

Figure 1

Primary causes of incident bilateral blindness (visual acuity ≤20/200) (n=126 eyes). AMD= age-related macular degeneration; DR=diabetic retinopathy; OAG= open-angle glaucoma