Aim: To determine the prevalence of heterophoria, fusional convergence and divergence values and the degree of relationship between heterophoria and fusional vergence in preschool children.
Methods: For assessment of far and near heterophoria in 152 children aged 6-7, cover and prism cover tests were used. Far and near fusional vergences were measured by step vergence testing using prism bars.
Results: Orthophoria (-tropia) with the average values of heterophoria around 0 PD (prism diopter) were most common at far, and exophoria around 2 PD at near. The average break values of far fusional convergence and divergence were 13.7 ± 4.4 PD and 7.3 ± 2.1 PD, respectively. Near fusional convergence and divergence break values were 29.6 ± 6.6 PD and 16.2 ± 4.1 PD, respectively. The recovery values were from 1/3 to 1/2 lower than the break values. The correlation between heterophoria at far and far fusional convergence and heterohoria at near and near fusional convergence and divergence was weak, yet significant (r = 0.18 - 0.26; p less than 0.05).
Conclusion: In preschool children the prevalence of heterophoria, and values of fusional vergence were in the ranges of values for elementary school children and adults cited in the literature. Heterophoria and fusional convergence at far, and heterophoria and fusional vergences at near have shown a weak relationship.