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Neuro-Ophthalmology - part 6

Trong một bệnh nhân stereoblind với lác, Danh sách máy bay của hai mắt bình thường trong hình dạng, tức là tương đối phẳng, nhưng thay đổi định hướng của họ tùy thuộc vào mắt là fixating [62]. Hiệu ứng này có lẽ hầu hết do để vergence chỗ ở do. | Fig. 2. Top view of both eyes during symmetric and asymmetric convergence movements. The visual target moves from far to near arrow . In a stereoblind patient with strabismus the Listing s planes of the two eyes were normal in shape i.e. relatively planar but changed their orientation depending on which eye was fixating 62 . This effect was most probably due to accommodation-induced vergence. Asymmetric Vergence Movements and Hering s Law Hering s law of equal innervation implies that equal version and vergence commands are sent to both eyes and that the binocular motor output represents the sum of the two signals. The analysis of asymmetric vergence movements fig. 2 can give some indication whether Hering s law holds 63 64 or whether the two eyes are independently controlled as advocated by Helmholtz 65 66 . As we will see there are arguments for both theories. During static convergence on a target in front of one eye i.e asymmetric convergence only the inferior oblique muscle contracts in this eye as demonstrated with MRI contraction of the same muscle apart from contractile changes in the lateral and medial rectus muscles is also seen in the fellow eye which is directed inward 47 . During rapid gaze shifts along the line of sight of one eye which calls for asymmetric vergence the horizontal peak accelerations of the two eyes are similar despite different position trajectories 67 . This finding suggests equal saccadic pulses for each eye according to Hering s law together with an additional vergence signal. After human subjects were trained to have a vertical vergence component during symmetric horizontal vergence the vertical vergence component could also be demonstrated during smooth pursuit of targets in depth both along the line of sight of one eye 68 . Thus symmetric smooth pursuit seems to be combined with vergence to produce Disconjugate Eye Movements 95 asymmetric slow eye movements which speaks against monocular control of these movements. Some subjects