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Chapter 029. Disorders of the Eye (Part 22)

Horizontal Gaze Descending cortical inputs mediating horizontal gaze ultimately converge at the level of the pons. Neurons in the paramedian pontine reticular formation are responsible for controlling conjugate gaze toward the same side. They project directly to the ipsilateral abducens nucleus. A lesion of either the paramedian pontine reticular formation or the abducens nucleus causes an ipsilateral conjugate gaze palsy. Lesions at either locus produce nearly identical clinical syndromes, with the following exception: vestibular stimulation (oculocephalic maneuver or caloric irrigation) will succeed in driving the eyes conjugately to the side in a patient with a lesion of the paramedian. | Chapter 029. Disorders of the Eye Part 22 Horizontal Gaze Descending cortical inputs mediating horizontal gaze ultimately converge at the level of the pons. Neurons in the paramedian pontine reticular formation are responsible for controlling conjugate gaze toward the same side. They project directly to the ipsilateral abducens nucleus. A lesion of either the paramedian pontine reticular formation or the abducens nucleus causes an ipsilateral conjugate gaze palsy. Lesions at either locus produce nearly identical clinical syndromes with the following exception vestibular stimulation oculocephalic maneuver or caloric irrigation will succeed in driving the eyes conjugately to the side in a patient with a lesion of the paramedian pontine reticular formation but not in a patient with a lesion of the abducens nucleus. Internuclear Ophthalmoplegia This results from damage to the medial longitudinal fasciculus ascending from the abducens nucleus in the pons to the oculomotor nucleus in the midbrain hence internuclear . Damage to fibers carrying the conjugate signal from abducens interneurons to the contralateral medial rectus motoneurons results in a failure of adduction on attempted lateral gaze. For example a patient with a left internuclear ophthalmoplegia will have slowed or absent adducting movements of the left eye Fig. 29-19 . A patient with bilateral injury to the medial longitudinal fasciculus will have bilateral internuclear ophthalmoplegia. Multiple sclerosis is the most common cause although tumor stroke trauma or any brainstem process may be responsible. One-and-a-half syndrome is due to a combined lesion of the medial longitudinal fasciculus and the abducens nucleus on the same side. The patient s only horizontal eye movement is abduction of the eye on the other side. Figure 29-19 Rf l ifi ijqöu IIV - ul í I U d jjül pH- B5w MA c ïWASog LUƠ uoip ílj à luoipp kf Ú CH P i - j j j JBr fữ ỉvỊd ỊtiẢ s tiữSiiỉtH It ÙÍ 5ÍỠ1 ir U f uu r 10 S6UÍ11 IS j n H 3 .