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Laura Liebermann, Sarah R. Hatt, David A. Leske, Jonathan M. Holmes; Variability of Fusional Convergence in Childhood Intermittent Exotropia. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6379.
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Measures of fusional convergence may provide information regarding severity of intermittent exotropia (IXT), but the variability of fusion in IXT is unknown. We evaluated change in measures of fusional convergence over the course of a day, in children with IXT.
Eleven children with IXT (aged 6 to 13 years) were evaluated during 4 (n=10) or 3 (n=1) sessions (2 hours apart) over the course of a day and repeated on a second day. Convergence fusion break point (prism diopters; pd) was measured at distance and at near, fixing on an accommodative target, using a fixed prism bar. A subnormal value was defined as lower than the 5th percentile of a population of normal 6 to 13-year olds (12 pd distance, 18 pd near). For each day, patients were categorized as either always subnormal, always normal, or variable (some measurements above and some measurements below normal threshold).
For distance fusional convergence, on day 1, 5 patients were always subnormal, 2 always normal, and 4 variable. Of the patients categorized as subnormal on day 1, 4 remained subnormal on day 2 and one became variable. The 2 patients that were always normal remained always normal for day 2. Of the 4 patients that were variable on day 1, 1 remained variable on day 2, 2 became always normal, and 1 became subnormal. For near fusional convergence, on day 1, 1 patient was always subnormal, 4 always normal, and 6 variable. The patient who was always subnormal on day 1 remained subnormal on day 2. Of the 4 patients always normal on day 1, 3 remained always normal and 1 became variable. Of the 6 patients that were variable on day 1, 4 remained variable on day 2 and 2 became always subnormal.
Measures of fusional convergence are variable in many children with IXT, often changing between normal and subnormal throughout the course of a day and often not following the same pattern on a subsequent day. Isolated measures of fusional convergence may not be representative of an individual patient with IXT and multiple measurements may be needed.
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