The Rapid Assessment of Avoidable Blindness (RAAB) has been developed as a simple and rapid survey methodology that can provide data on the prevalence and main causes of blindness.

Aim

To assess the prevalence and main causes of avoidable blindness and visual impairment in people aged 50 and above in Mongolia.

Methods

The RAAB uses a standard methodology which is documented in the RAAB Instruction Manual (Hans Limburg, International Centre for Eye Health, London School of Hygiene and Tropical Medicine). 

Assuming an estimated prevalence of blindness in persons aged 50+ of 2.14% and a non-compliance of 5%, with a variation to 25% around the estimate of 2.14% at 95% probability, the required sample size was calculated at 4,040: 101 clusters of size 40. Visual acuity (VA) was measured with a Snellen tumbling E chart, using optotype size 18 (60) on one side and size 60 (200) on the other side. The lens status of all participants was assessed by both torch and distant direct ophthalmoscopy, by an ophthalmologist in a shaded or dark environment. The data were analyzed using RAAB Version 4.02 (ICEH, London) for pre-defined reports relating to both crude and age and gender adjusted results.

Results

The survey included 4,040 people aged 50 years and older, of whom 4,029 were actually examined. The coverage was 99.7%. 7 persons (0.2%) were absent and 4 (0.1%) refused to participate in the study. The prevalence of bilateral blindness with available correction in the better eye is 2.2 % (95% CI, 1.7 - 2.7%); 2.4% in males and 2.2% in females. The prevalence of bilateral severe visual impairment (SVI) is 2.1% and bilateral moderate visual impairment (MVI) is 10.8%. The prevalence of functional low vision, requiring low vision services, is 4.5%. In people aged 50+, untreated cataract is the most common cause of bilateral blindness with 38.9%, followed by glaucoma (20.0%), non-trachomatous corneal opacity (13.3%), and other posterior segment disease (7.8%).

Conclusion: Untreated cataract and uncorrected refractive errors are the major causes of avoidable blindness and low vision in Mongolia, respectively. Priority should be given to cataract surgery, followed by the development of optical services and PHC and PEC services, as these are the most cost-effective interventions. These three interventions will address about three thirds (67.8%) of the causes of blindness and have most impact.

Pp. 65-71, Tables 5, Figures 3, References 15

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