Rapid Survey of Blindness: RAAB Method Accurate

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Researchers led by a team based in Hong Kong set out to assess the diag­nostic accuracy of the survey method known as RAAB (for rapid assessment of avoidable blindness). They found that RAAB has high diagnostic accura­cy for the detection of the prevalence of blindness, visual impairment (VI), and VI due to cataract.¹ “RAAB is a valuable alternative in areas where cost and logistical factors prohibit the use of conventional epidemiologic surveys,” said coauthor Dennis S.C. Lam, MD, FRCOphth, at the Chinese University of Hong Kong.

A note on RAAB. This method is endorsed by the World Health Orga­nization for population-based surveys of blindness and VI in people aged 50 years and older in a specific geograph­ic area. Each RAAB survey involves an eye examination, with the use of a penlight, and a fundus exam via direct ophthalmoscopy. The exams are held in the participant’s home. “The major advantages of this method are its sim­plicity, rapid conduct, lower cost, and use of standardized assessments,” said Dr. Lam.

In the field. This study involved 2,145 people aged 50 years and older in 45 villages located in the Chaonan Region of southern China. All partici­pants were examined according to the RAAB protocol; they were then offered a more extensive examination in a mobile eye clinic that was set up in a village center on the same day.

Exams in the mobile clinic included standardized visual acuity (VA) tests using logMAR charts, refraction, slit-lamp biomicroscopy, and a dilated fundus exam with a binocular indirect ophthalmoscope. Blindness and economic blindness were defined as having VA in the better-seeing eye of <20/400 and <20/200, respectively. VI was defined as having VA of <20/60 in the better eye. The primary cause of blindness and VI was defined according to the cause of VI in the participant’s better eye.

Results. Of the 2,145 participants who were screened with RAAB, 327 (15.2%) refused to attend the mobile eye clinic, and two (0.1%) were unable to undergo the more in-depth exam­ination.

Sensitivities ranged from 89.5% to 90.3%, and specificities ranged from 97.7% to 99.3% for detection of differ­ent levels of VI—and these results pro­vide “strong support for the diagnostic accuracy of the RAAB methodology for the detection of blindness and VI,” the researchers wrote.

With regard to blindness and VI owing to cataract and refractive error, RAAB was highly accurate for cataract but less so for refractive error.

Limitations. The authors noted that it is possible that their results over­estimate the impact of cataract and underestimate those of glaucoma and posterior segment diseases on the prev­alence of blindness and VI. Nonethe­less, they said, the RAAB methodology “remains an important tool for inform­ing research and policy for blindness prevention.”

—Arthur Stone

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1 Zhang XJ et al. Am J Ophthalmol. Published online Dec. 14, 2019.

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Relevant financial disclosures—Dr. Lam: None.

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