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S. J. Farooq, R. J. Mclean, F. A. Proudlock, I. Gottlob; Torsional Optokinetic Nystagmus in Strabismus. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2831.
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Torsional optokinetic Nystagmus (tOKN) in patients with strabismus since childhood has not been previously evaluated. The authors investigated the optokinetic response in horizontal, vertical and torsional directions in strabismus patients and in age-matched normal volunteers.
Monocular torsional, horizontal and vertical eye movements were recorded in 16 subjects with childhood strabismus and 15 normal volunteers. Constant velocity horizontal (nasalward and temporalward) and vertical (upward and downward) OKN stimuli were used at 10°/s, 20°/s and 40°/s. Torsional (intorsion and extorsion) OKN stimuli were rotated at velocities of 40° and 400°/s.
OKN responses from strabismus patients produced significant asymmetric responses in horizontal and vertical meridians. The nasalward response was significantly greater than the temporalward (p=3.64x10-6 for the non-dominant eyes, p=7.18x10-9 for the dominant eyes) and upward response was greater than downward (p=0.0029 for the non-dominant eyes, p= 0.0043 for the dominant eyes. A significant high incidence of absent tOKN was present at both stimulus velocities in the intorsion direction (p= 0.024 for 40°/s, p=0.0085 for 400°/s) and at 400°/s in the extorsion direction (p= 0.040). Eight of the 15 patients tested did not respond to any stimulus in either direction in their non-dominant eye and 4 showed no response in their dominant eye.
Torsional OKN is dramatically affected in the presence of strabismus with a high incidence of no response. The possibility of a lack of development in the binocular cortical structures that respond to torsional motion could explain these findings.
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