Background: The head-tilt phenomenon (difference between the vertical deviati ons with an ipsilateral and contralateral headtilt by 45 deg. each) occurring in patients with a superior oblique palsy has traditionally b...Background: The head-tilt phenomenon (difference between the vertical deviati ons with an ipsilateral and contralateral headtilt by 45 deg. each) occurring in patients with a superior oblique palsy has traditionally been explained by the lacking contraction of the superior oblique muscle within the synkinetic movemen t of ocular counterrolling. However, using a computer model, Robinson showed that the superior oblique palsy itself causes only a relatively small head-tilt ph enomenon. Adaptive mechanisms amplifying the otolith reflex were suggested to ex plain the increase of the head-tilt phenomenon in the course of time. In order to reduce the abnormal head posture required for binocular vision, the otolith r eflex would be amplified, accepting the greater vertical deviation when the head is tilted to the paretic side [23]. Question: If the head-tilt phenomenon were solely caused by the lacking contraction of the superior oblique muscle, it sho uld be greater in bilateral than in unilateral superior oblique palsies. If an a daptive mechanism were acting to reduce the abnormal head posture, the head-til t phenomenon should not be greater, and could even be smaller in bilateral than in unilateral superior oblique palsy, because in bilateral (symmetric) trochlear nerve palsies the vertical deviation at straight gaze is already small or absen t without adaptation. Patients and Methods: We have carried out a retrospective comparison of 10 patients with bilateral symmetric superior oblique palsies and 10 patients with unilateral superior oblique palsy. In all cases, the palsy was acquired and had been present for at least 1 year. Results: The patients with bi lateral superior oblique palsy had a head-tilt phenomenon ranging from 0 to 7 d egrees (median, 2 deg.). The patients with unilateral superior oblique palsy had a head-tilt phenomenon between 2 and 13 degrees (median, 8 deg.). The differen ce was significant (p=0.0117). Conclusions: The head-tilt phenomenon is smaller in long-standing bilateral symmetric superior oblique palsies than in long-st anding unilateral superior oblique palsy. This finding supports the hypothesis t hat in unilateral superior oblique palsy, an adaptive mechanism augments the hea d-tilt phenomenon by an amplification of the otolith reflex. However, we presum e that the amplification of the otolith reflex is only a side effect of the adap tive change of the vertical fusional vergence tonus and thus the price of the im proved vertical fusion, rather than a compensatory mechanism.展开更多
文摘Background: The head-tilt phenomenon (difference between the vertical deviati ons with an ipsilateral and contralateral headtilt by 45 deg. each) occurring in patients with a superior oblique palsy has traditionally been explained by the lacking contraction of the superior oblique muscle within the synkinetic movemen t of ocular counterrolling. However, using a computer model, Robinson showed that the superior oblique palsy itself causes only a relatively small head-tilt ph enomenon. Adaptive mechanisms amplifying the otolith reflex were suggested to ex plain the increase of the head-tilt phenomenon in the course of time. In order to reduce the abnormal head posture required for binocular vision, the otolith r eflex would be amplified, accepting the greater vertical deviation when the head is tilted to the paretic side [23]. Question: If the head-tilt phenomenon were solely caused by the lacking contraction of the superior oblique muscle, it sho uld be greater in bilateral than in unilateral superior oblique palsies. If an a daptive mechanism were acting to reduce the abnormal head posture, the head-til t phenomenon should not be greater, and could even be smaller in bilateral than in unilateral superior oblique palsy, because in bilateral (symmetric) trochlear nerve palsies the vertical deviation at straight gaze is already small or absen t without adaptation. Patients and Methods: We have carried out a retrospective comparison of 10 patients with bilateral symmetric superior oblique palsies and 10 patients with unilateral superior oblique palsy. In all cases, the palsy was acquired and had been present for at least 1 year. Results: The patients with bi lateral superior oblique palsy had a head-tilt phenomenon ranging from 0 to 7 d egrees (median, 2 deg.). The patients with unilateral superior oblique palsy had a head-tilt phenomenon between 2 and 13 degrees (median, 8 deg.). The differen ce was significant (p=0.0117). Conclusions: The head-tilt phenomenon is smaller in long-standing bilateral symmetric superior oblique palsies than in long-st anding unilateral superior oblique palsy. This finding supports the hypothesis t hat in unilateral superior oblique palsy, an adaptive mechanism augments the hea d-tilt phenomenon by an amplification of the otolith reflex. However, we presum e that the amplification of the otolith reflex is only a side effect of the adap tive change of the vertical fusional vergence tonus and thus the price of the im proved vertical fusion, rather than a compensatory mechanism.
