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S. R. Hatt, D. A. Leske, B. G. Mohney, M. C. Brodsky, T. Yamada, V. Karlsson, J. M. Holmes; Fusional Convergence Reserve, Control, and Stereoacuity in Children with Intermittent Exotropia. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1585.
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© ARVO (1962-2015); The Authors (2016-present)
In intermittent exotropia (IXT), poor motor control and reduced stereoacuity are often cited as indicative of increased severity. Motor control of an exodeviation relies on fusional convergence, but there are few data examining the relationship between fusional convergence reserve and control of the exodeviation or between fusional convergence reserve and stereoacuity. We evaluated correlations between fusional convergence reserves, control, and stereoacuity in children with IXT.
Seventy children (aged 3 to 17 years) with IXT were identified with distance and near measures of angle of deviation (by prism and alternating cover test [PACT]), control (using a previously reported 0-5 point control scale), stereoacuity and range of fusional convergence, at a single exam. We calculated a Fusion Reserve Ratio (FRR) as "fusional convergence break point/PACT." Spearman rank correlations were used to examine the relationship between FRR and control score at distance and near, and also between distance and near FRR and stereoacuity (Frisby Davis Distance [FD2] and Distance Randot [DR]), Frisby and Preschool Randot [PSR]).
There was a strong correlation between the distance FRR and distance control score (r= -0.77466, p<0.0001) and the near FRR and near control score (r = -0.68622, P <0.0001). There was a weaker correlation between distance FRR and distance stereoacuity using both DR (r= -0.38869, P=0.0009) and FD2 (r= -0.26914, P=0.02). At near, there was a correlation between near FRR and PSR stereoacuity (r= -0.28168, P=0.02) but not between near FRR and Frisby stereoacuity (r= -0.09808, P=0.4).
On a single exam, the FRR appears to correlate well with a single measure of control and with most measures of stereoacuity and therefore may be useful in grading the severity of IXT. Further study is needed to determine the repeatability of the FRR in IXT, and to determine whether there is role for measuring fusional convergence reserves in the management of children with IXT.
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