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I. Hamazaki, S. Hasebe, H. Ohtsuki; Inferior Oblique Weakening Surgery Affects Compensatory Ocular Countertorsion . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2477.
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While keeping the head tilted laterally for several seconds, otolith–ocular reflex (OOR) induces static compensatory countertorsion. Recently, this phenomenon has been confirmed by MRI imaging analysis to which should contractile thickening of the oblique muscles (Demer J & Clark RA, Neurophysiol 2005). To elucidate this observation, the effect of surgery to weaken the inferior oblique (IO) muscle on compensatory ocular countertorsion was studied.
Subjects and Methods: :
Compensatory countertorsion was measured in 5 patients (mean age, 54.3 years) with unilateral decompensated superior oblique palsy using a light–weigh head–mounted measuring system (Hasebe S et al, Arch Ophthalmol 2003) while the head is held steady for 20 seconds at each head tilt angle of 10, 20, 30 and 40 degrees. Countertorsion at each head tilt angle was calculated by measuring the inclination of a line connecting the two centroids of the characteristics iris pattern and corneal light reflex on digital image flames captured with CCD cameras. Then the ratio of countertorsion of the paretic eye for each head tilt angle (gain) between before and after the IO weakening surgery on the paretic eye were compared.
When the head was tilted ipsilaterally, the postoperative mean (SD) ratio (%) of compensatory countertorsion of the paretic eye to each head tilt angle did not significantly differ from that preoperatively (9.9+/–1.7% for preoperatively and 8.0+/–5.2% postoperatively). Whereas, when the head tilted contralaterally, the postoperative mean ratio (%) of compensatory countertorsion of the paretic eye was significantly decreased compared to that preoperatively (19.3+/–3.3% preoperatively and 13.3+/–5.8% postoperatively, p<0.05).
Our observation suggests that contractile activity of the IO muscle plays an important role in static compensatory ocular countertorsion as an extorter of the globe.
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