Characteristics of divergence excess type intermittent exotropia in Asian children

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.

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.

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.

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.