Elsevier

Ophthalmology

Volume 112, Issue 7, July 2005, Pages 1275-1282
Ophthalmology

Original Article
Visual Acuity and the Causes of Visual Loss in a Population-Based Sample of 6-Year-Old Australian Children

https://doi.org/10.1016/j.ophtha.2005.01.052Get rights and content

Purpose

To describe the distribution of visual acuity and causes of visual loss in a representative sample of Australian schoolchildren.

Design

Population-based cross-sectional study.

Participants

One thousand seven hundred thirty-eight predominantly 6-year old children examined during 2003 to 2004.

Methods

Logarithm of the minimum angle of resolution (logMAR) visual acuity was measured in both eyes before and after pinhole correction and with spectacles if worn. Cycloplegic autorefraction (cyclopentolate) and detailed dilated fundus examination were performed.

Main Outcome Measures

Visual impairment was defined as any (visual acuity <20/40; <40 letters) or severe (visual acuity ≤20/200; 0–5 letters) for both better and worse eyes. Myopia was defined as spherical equivalent (SE) refraction ≤−0.50 diopters (D), and hyperopia as SE refraction ≥+2.0 D, deemed significant when ≥+3.0 D. Astigmatism was defined as cylinder ≥1.0 D and anisometropia as SE refraction difference between eyes at least 1.0 D. Amblyopia was defined as corrected visual acuity <0.3 logMAR units (<20/40; <40 letters) in the affected eye not attributable to any underlying structural abnormality of the eye or visual pathway, together with a 2-logMAR line difference between the eyes and presence of an amblyogenic risk factor.

Results

The mean visual acuity of this sample was 20/25 (49.3 letters). Uncorrected visual impairment was found in the better eye of 23 children (1.3%) and in the worse eye of 71 children (4.1%). The prevalence was higher in girls than boys and among children of lower socioeconomic status. Refractive error was the most frequent cause, accounting for 69.0%, followed by amblyopia (22.5%). Astigmatism was the principle refractive error causing visual impairment and was frequently uncorrected. Presenting visual impairment (using current glasses if worn) was found in the better and worse eyes of 15 children (0.9%) and 54 children (2.8%), respectively. This was mainly due to under corrected or uncorrected refractive error.

Conclusions

This study has documented a relatively low prevalence of visual impairment in a population of Australian children. Uncorrected astigmatism and amblyopia were the most frequent causes.

Section snippets

Population

The Sydney Myopia Study is a population-based survey of refraction and other eye conditions in a sample of 6- and 12-year-old school children residing in the Sydney metropolitan area. Methods used to identify and select the target sample, as well as a description of this sample and study procedures, were recently reported.10 The study area was stratified by socioeconomic status (SES), using Australian Bureau of Statistics (ABS) 2001 national census data. These data were used to select 34

Subjects

Of 2238 eligible children, 1765 (78.9%) children were given parental permission to participate, and questionnaire data were provided by parents. Of the 1765 children with a positive response, 24 were not examined, because they were absent from school during the examination period, and 1 9-year-old child was excluded from the analyses. The mean age of participants was 6.7 years (range, 5.5–8.4 years); 49.4% of children were female and 50.6% were male. Most (70.4%) were 6 years old, whereas a

Discussion

There are no universally accepted standards for visual acuity tests or norms in young children. Study results also differ, depending on whether an isolated or a surrounded optotype is used.2, 12 This report provides norms of distance linear visual acuity for 6- (and 7-) year-old children in a predominantly Caucasian sample. The mean visual acuity of children without ametropia in our sample was 50.1 letters (0.1 logMAR or 20/25 Snellen acuity). This is in close agreement with the value of 0.07

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    Manuscript no. 2004-316.

    Supported by the National Health & Medical Research Council, Canberra, Australia (grant no.: 253732); the Westmead Millennium Institute, University of Sydney; and the Vision Cooperative Research Centre, Sydney, Australia.

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