Causes and associations of amblyopia in a population-based sample of 6-year-old Australian children.

Objectives: To describe the prevalence of amblyopia and associated factors in a representative sample of 6-year-old Australian children.

Methods: Logarithm of minimum angle of resolution visual acuity (VA) was measured in both eyes before and after pinhole correction, correcting cylindrical refractive components greater than 0.50 diopter (D), and with spectacles (if worn) in a population-based sample of 1741 schoolchildren. Retinal pathological abnormalities were excluded based on photographs. Amblyopia was defined using various best-available corrected VA measures in the absence of significant organic pathological abnormalities.

Results: Using the criteria of corrected VA less than 20/40 and at least a 2-line difference between eyes, amblyopia was diagnosed in 13 children (0.7%). The inclusion of children with amblyopia who had been successfully treated (n = 19) increased the amblyopia prevalence to 1.8%. Strabismus or strabismus surgery history was present in 37.5% of the children with amblyopia, anisometropia in 34.4%, both conditions in 18.8%, and isoametropia in 6.3%. Mean corrected VA in amblyopic eyes was 37.7 logarithm of minimum angle of resolution letters (Snellen VA equivalent < 20/40), ranging from 0 to 48 logarithm of minimum angle of resolution letters (Snellen VA equivalent < 20/200-20/25). Most amblyopic eyes (58.7%) were significantly hyperopic (spherical equivalent > or = +3.00 D); 8.7% were myopic.

Conclusions: A relatively low prevalence of amblyopia in a sample of 6-year-old children is documented. The majority of these children had already been diagnosed and treated for this condition.