ANATOMY AND PHYSIOLOGY
Two cortical centres of ocular control are recognised:
1. Middle gyrus of frontal lobe (frontal eye field).
2. Occipital cortex.
slow following -pursuit movement.
Activation results in slow movement of the eyes to the ipsilateral side.
Occipitomesencephalic pathway Both project to the oculomotor trochlear IV and abducens VI cranial nuclei
Pathways for horizontal eye movement involving the III and VI nuclei are clearly delineated (as shown) but those controlling vertical eye movement are less well understood
Origin of fast rapid eye movement - saccadic movement - either voluntary or reflex. Activation results in jerk deviation of the eyes to the opposite side
Origin of fast rapid eye movement - saccadic movement - either voluntary or reflex. Activation results in jerk deviation of the eyes to the opposite side cranial nuclei
VI cranial nuclei
_____- Medial longitudinal fasciculus
- Paramedian pontine reticular formation (although not a discrete anatomical entity) -sometimes described as the 'lateral pontine gaze centre'
Note that the cortical descending pathways from one side activate the ipsilateral III nucleus and the contralateral VI nucleus thus swinging the direction of gaze to the opposite side.
It is important to distinguish between saccadic and pursuit movement. When following an object a slow pursuit movement maintains the image on the macular area of the retina. To fixate on a new object, rapid saccadic movement aligns the new target on the macular area. When locked into the new target, pursuit movement maintains fixation.
Eye movement occurs voluntarily in a conjugate (parallel) manner in any direction. Eye movements also occur reflexly to labyrinthine stimulation.
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