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Kristina Irsch, David L Guyton, Howard S Ying; Lingering fusional adaptation influences the Bielschowsky head tilt test in superior oblique paresis.. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1332.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate how fusion influences the Bielschowsky head tilt test in unilateral superior oblique paresis.
In eight fusing patients, we correlated haploscopic-determined fusional mechanisms with Bielschowsky head tilt test differences.
Five patients used the vertical recti for vertical fusional vergence and had a mean Bielschowsky head tilt test difference ± SD of 22 ± 8 PD. After a 30-minute patch test one of those, in whom the test was performed, showed a decrease of 10 PD. Two patients used the “paretic” superior oblique muscle and the contralateral superior rectus muscle to fuse, and had a mean Bielschowsky head tilt test difference ± SD of 6 ± 8 PD. The Bielschowsky head tilt test difference of one, in whom a patch test was performed, increased by 11 PD. The remaining patient used the “paretic” superior oblique muscle and contralateral inferior oblique muscle to fuse, and had a Bielschowsky head tilt test difference of only 3 PD, increasing to 21 PD after patching.<br /> <br /> One explanation for this behavior in the last patient involves lingering vergence adaptation of the “paretic” superior oblique muscle and contralateral inferior oblique muscle, which makes these muscles more effective when activated on ipsilateral head tilt, lessening the expected increase in hyperdeviation. Similarly, in our patients with oblique/rectus-mediated fusion, the vergence-adapted “paretic” superior oblique muscle and contralateral superior rectus muscle are activated on ipsilateral and contralateral tilt respectively, lessening the hyperdeviation in both directions. In the other five patients, however, the vergence-adapted ipsilateral inferior rectus muscle and contralateral superior rectus muscle are activated on contralateral tilt, accentuating the Bielschowsky head tilt test difference.
Fusion influences the Bielschowsky head tilt test difference, either decreasing or increasing this difference depending on the particular muscle groups that are being used for fusion. The absence of a positive Bielschowsky head tilt test should not be relied upon to rule out the diagnosis of superior oblique paresis. In suspected superior oblique paresis patients with fusion, performing the Bielschowsky head tilt test after a patch test may be necessary to bring out the Bielschowsky head tilt test difference supporting the diagnosis.
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