Sharpe James A
Division of Neurology, University Health Network WW5-440 TWH, University of Toronto, 399 Bathurst Street, Toronto, ON, Canada M5T 2S8.
Brain Cogn. 2008 Dec;68(3):241-54. doi: 10.1016/j.bandc.2008.08.015. Epub 2008 Nov 11.
Smooth pursuit impairment is recognized clinically by the presence of saccadic tracking of a small object and quantified by reduction in pursuit gain, the ratio of smooth eye movement velocity to the velocity of a foveal target. Correlation of the site of brain lesions, identified by imaging or neuropathological examination, with defective smooth pursuit determines brain structures that are necessary for smooth pursuit. Paretic, low gain, pursuit occurs toward the side of lesions at the junction of the parietal, occipital and temporal lobes (area V5), the frontal eye field and their subcortical projections, including the posterior limb of the internal capsule, the midbrain and the basal pontine nuclei. Paresis of ipsiversive pursuit also results from damage to the ventral paraflocculus and caudal vermis of the cerebellum. Paresis of contraversive pursuit is a feature of damage to the lateral medulla. Retinotopic pursuit paresis consists of low gain pursuit in the visual hemifield contralateral to damage to the optic radiation, striate cortex or area V5. Craniotopic paresis of smooth pursuit consists of impaired smooth eye movement generation contralateral to the orbital midposition after acute unilateral frontal or parietal lobe damage. Omnidirectional saccadic pursuit is a most sensitive sign of bilateral or diffuse cerebral, cerebellar or brainstem disease. The anatomical and physiological bases of defective smooth pursuit are discussed here in the context of the effects of lesion in the human brain.
临床上，平稳跟踪障碍表现为对小物体的扫视跟踪，并通过跟踪增益的降低来量化，跟踪增益即平稳眼动速度与中央凹目标速度的比值。通过影像学或神经病理学检查确定的脑损伤部位与有缺陷的平稳跟踪之间的相关性，可确定平稳跟踪所必需的脑结构。在顶叶、枕叶和颞叶交界处（V5区）、额叶眼区及其皮质下投射部位（包括内囊后肢、中脑和脑桥基底部核团）发生病变时，会出现向病变侧的轻瘫、低增益跟踪。同侧跟踪轻瘫也可由小脑腹侧副绒球和尾状蚓部受损引起。对侧跟踪轻瘫是延髓外侧受损的特征。视网膜定位跟踪轻瘫表现为在与视辐射、纹状皮质或V5区受损对侧的视觉半视野中出现低增益跟踪。急性单侧额叶或顶叶损伤后，平稳跟踪的颅骨定位轻瘫表现为在眼眶中点对侧的平稳眼动生成受损。全向扫视跟踪是双侧或弥漫性脑、小脑或脑干疾病最敏感的体征。本文将在人脑损伤影响的背景下讨论有缺陷的平稳跟踪的解剖学和生理学基础。
