Prevalence and Causes of Functional Low Vision in School-Age Children: Results from Standardized Population Surveys in Asia, Africa, and Latin America Clare E. Gilbert,1 Leon B. Ellwein,2 and the Refractive Error Study in Children Study Group3 PURPOSE. Data on the prevalence and causes of functional low The World Health Organization’s (WHO’s) International vision (FLV) in adults and children are lacking but are impor- Classification of Diseases (ICD)-10 categories of visual loss tant for planning low-vision services. This study was conducted define low vision as “a corrected visual acuity in the better eye to determine the prevalence and causes of FLV among children of Ͻ6/18 (Ͻ20/63) down to and including 3/60 (20/400).” recruited in eight population-based prevalence surveys of vi- This definition includes all individuals, regardless of the cause sual impairment and refractive error from six countries (India of visual loss. A major limitation of the ICD-10 categories of [2 locations]; China [2 locations]; Malaysia, Chile, Nepal, and visual loss is that they do not allow refractive errors to be South Africa). assessed as a cause of visual impairment, and so the WHO METHODS. Using the same protocol, 4082 to 6527 children aged recently suggested that “presenting visual acuity” (i.e., visual 5 (or 7) to 15 years were examined at each site. Uncorrected acuity tested with distance spectacles, if usually worn), as well and presenting visual acuities were successfully measured with as uncorrected visual acuity, be used in all population-based retroilluminated logMAR tumbling-E charts in 3997 to 5949 surveys. Most individuals who have a presenting visual acuity children; cycloplegic autorefraction was performed and best in the better eye of Ͻ6/18 down to and including 3/60 require corrected acuities assessed. All children were examined by an spectacles, surgery (e.g., cataract surgery), or other treatment ophthalmologist and a cause of visual loss assigned to eyes with to restore sight and thus do not require assessment for low- uncorrected acuity Յ6/12. The prevalence of FLV was deter- vision interventions (e.g., optical devices). mined overall and by site; associations with gender, age, pa- At a meeting of low-vision specialists in 1993, it was realized rental education and urban/rural location were assessed with that neither the original ICD-10 definition of low vision nor the logistic regression. revision using presenting acuity adequately identifies individu- RESULTS. The prevalence of FLV ranged from 0.65 to 2.75 in als who might benefit from low-vision services after assess- 1000 children, with wide confidence intervals. The overall ment. The following definition of low vision was therefore prevalence was 1.52 in 1000 children (95% CI 1.16–1.95). FLV derived for use in population-based prevalence surveys: “a was significantly associated with age (odds ratio [OR] 1.13 for person with low vision is an individual, who after refraction each year, P ϭ 0.01), and parental education was protective and medical or surgical treatment, has a best corrected visual (OR 0.75 for each of five levels of education, P ϭ 0.017). acuity of Ͻ6/18 to light perception in the better eye, but who Retinal lesions and amblyopia were the commonest causes. uses, or has the potential to use vision for the planning and/or CONCLUSIONS. More studies are needed to determine the prev- execution of a task.” However, it should be acknowledged that alence and causes of FLV in children so that services can be others may also have the potential to benefit from low-vision planned that promote independence, improve quality of life, services (e.g., those with better visual acuity but loss of con- and increase access to education. (Invest Ophthalmol Vis Sci. trast sensitivity).1 This definition differs in four ways from the 2008;49:877–881) DOI:10.1167/iovs.07-0973 revised ICD-10 definition: (1) best corrected visual acuity rather than presenting vision is used; (2) a broader range of espite there being some population-based data on the visual acuities is included; (3) individuals whose visual acuity Dprevalence of blindness in children, there are no data on could be improved by surgical and/or medical treatment are the prevalence and causes of functional low vision in children. excluded; and (4) there is a functional component (e.g., the These data are urgently needed for rational planning of low- ability to navigate independently should also be assessed). In vision services for children. this article we use the term “functional” low vision (FLV) to represent the 1993 definition. Data from only two population- based surveys have been analyzed using the FLV definition to From the 1London School of Hygiene and Tropical Medicine, date, one in India2 and another in Pakistan3: the former in- London, United Kingdom; and the 2National Eye Institute, National cluded all age groups and the latter included adults Ն30 years Institutes of Health, Bethesda, Maryland. 3 of age. The Study Group members are listed in the Appendix. The purpose of this study was to determine the prevalence Supported by the World Health Organization (WHO) under Con- tract N01-EY2103 from the National Eye Institute; WHO New Delhi, and causes of FLV in school-age children who were examined India; and other nongovernment organizations. in eight sites in Asia, Africa, and Latin America using the Submitted for publication July 30, 2007; revised September 26, standard methodology developed by the Refractive Error Study October 19, and November 1, 2007; accepted January 11, 2008. in Children (RESC) Group.4 The sites were in urban and rural Disclosure: C.E. Gilbert, None; L.B. Ellwein, None areas: Jhapa District in Eastern Nepal (rural)5; Mahabubnagar The publication costs of this article were defrayed in part by page district near Hyderabad in Southern India (rural)6; the Liwan charge payment. This article must therefore be marked “advertise- area of Guangzhou, China (urban)7; the Shunyi District near ment” in accordance with 18 U.S.C. §1734 solely to indicate this fact. Beijing, China (semiurban)8; the La Florida area of Santiago, Corresponding author: Clare E. Gilbert, International Centre for 9 Eye Health, Clinical Research Unit, London School of Hygiene and Chile (urban) ; the Trilokpuri segment of New Delhi, India 10 Tropical Medicine, Keppel Street, London WC1E 7HT, UK; (urban) ; a contiguous area within the South and West Re- [email protected]. gions of Durban, South Africa (semiurban/urban)11; and the Investigative Ophthalmology & Visual Science, March 2008, Vol. 49, No. 3 Copyright © Association for Research in Vision and Ophthalmology 877 Downloaded from iovs.arvojournals.org on 09/30/2021 878 Gilbert and Ellwein IOVS, March 2008, Vol. 49, No. 3 Gombak District in Kuala Lumpur, Malaysia (urban).12 The rected visual acuity Յ6/12 if one or more of the following criteria were surveys were conducted between 1998 and 2003. met: (1) esotropia, exotropia, or vertical tropia at 4 m fixation, or Human subject research approval for the RESC study pro- exotropia or vertical tropia at 0.5 m; (2) anisometropia of 2.00 spher- tocol was obtained from the WHO Secretariat Committee on ical equivalent diopters or more; or (3) bilateral ametropia of at least Research Involving Human Subjects. Implementation of the ϩ6.00 spherical equivalent diopters. At the discretion of the examiner, study at each location was approved by the appropriate human eyes that did not meet these explicit criteria were also deemed to have subject review committee. The research protocol adhered to amblyopia as the principal cause of low vision. the provisions of the Declaration of Helsinki for research in- volving human subjects. Quality Assurance Interobserver reproducibility was monitored throughout the course of METHODS each study. For visual acuity in right eyes, unweighted ␬ statistics ranged from 0.53 to 0.83, with 0.0% to 4.1% of repeat measurements Details of the methods have been published, as have the specific details differing by two or more lines. In left eyes, ␬ statistics ranged from 0.53 4–12 of each survey. to 0.81 with 0.0% to 3.3% of measurements differing by two or more lines. Children with uncorrected visual acuity of Յ6/12 (in either eye) Sample Selection and approximately 5% to 10% of other children had test–retest evalu- Each of the RESC study populations was obtained by random sampling ations of uncorrected visual acuity. The repeat testing was conducted of geographically defined clusters. The originally calculated sample independently by a second examiner who was masked to the findings size of 5194 children aged 5 to 15 years (per study site) was based on from the initial testing. estimating a prevalence of refractive errors of 22% within a 20% error bound with 95% confidence with upward adjustment to accommodate Data Management, Definitions, and Analysis 4 nonparticipation (10%) and cluster sampling (25%). As there were no Enumeration and examination data forms were reviewed in the field reliable population-based data from the study areas that could be used for accuracy and completeness before computer data entry at a central to modify the calculation, this sample size, or larger, was used in study headquarters at each site. Measurement data ranges, frequency planning each survey. distributions, and consistency among related measurements were checked with data-cleaning programs. Enumeration As defined herein, children were considered to have FLV if they had Using house-to-house visits within the randomly selected clusters, a best corrected visual acuity of Ͻ6/18 down to and including light information on the name, age, gender, and schooling of each eligible perception in the better eye and visual loss was not due to a treatable child, along with the educational level of the parents, was obtained cause in one or both eyes (e.g., cataract).