Characteristics of divergence excess type intermittent exotropia in Asian children.

BACKGROUND: Exotropia is twice as common as esotropia in Asian children, with divergence excess intermittent exotropia contributing more than one half of exotropia cases. In this study, distance-near relationships and ratios of accommodative convergence to accommodation (AC/A) are compared using different measurement methods in Asian children with divergence excess intermittent exotropia.
METHODS: Children with intermittent exotropia and a distance deviation exceeding the near by at least 10(Δ) were consecutively recruited. After prism cover test measurements at 6 m and 33 cm, AC/A ratios were calculated using the heterophoria method and the gradient method with -2.0 D and +3.0 D lenses at 6 m and 33 cm, respectively. AC/A ratios were recalculated after 1 hour of monocular patching.
RESULTS: A total of 42 children (mean age, 6.9 years; range, 3-16 years) were included. The mean difference between distance and near deviation was 22(Δ) before occlusion and 14(Δ) after (P < 0.001). Approximately one third had a distance-near difference <10(Δ) after occlusion. With the heterophoria method, 100% of patients had high AC/A ratios before occlusion, with 71% continuing to have high AC/A ratios after. With the gradient method, 52% of patients had high AC/A ratios before occlusion, with 68% of this subgroup continuing to have high AC/A ratios after.
CONCLUSIONS: Pseudo-divergence excess was found in one third of the subjects. More children were diagnosed with high AC/A ratios using the heterophoria method than with the gradient method. Without monocular occlusion, approximately one third of the children with normal AC/A ratios may be mistaken to have high AC/A ratios when measured with either method. Identification of high AC/A ratio exotropic patients is critical due to the risk of developing consecutive esotropia at near after strabismus surgery.