(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (GP) Class of 2020, Baylor College of Medicine, Houston, Texas
Subject
Anatomy; Neuroanatomy
Description
Dr. Lee lectures medical students about pursuit eye movements.
Transcript
So last time we talked about saccades. I'm going to leave the saccade diagram up here for you because now we are going to switch gears and talk about pursuit. Pursuit is the slow movement, so we are pursuing a slow moving target. We don't need the fast movement, which is the saccade. The smooth pursuit is generated not from the frontal eye field but from the parietal-occipital-temporal region, and as opposed to the frontal eye field, which is contralaterally generated, the parietal-occipital-temporal lobe ipsilateral to the smooth pursuit is the site of origin of the pursuit mechanism. And just like what we talked about with the saccades, it has to use the same final common pathway. For the vertical gaze center in the thalamo-mesencephalic junction, that's cranial nerves III & IV, but in the pons, the parapontine reticular formation and the sixth nerve are for the horizontal gaze. So instead of contralateral frontal eye field firing for saccades, we have ipsilateral parietal-occipital-temporal lobe firing for pursuit. It runs down the exact same location in the pons for horizontal gaze. The sixth nerve nucleus talks to the third nerve nucleus via the interneuron, the medial longitudinal fasciculus, and we're off to the races, but instead of a saccade, a pursuit movement. So the supranuclear pathway is similar between the pursuit and the saccade pathways. The only difference is the site of origin in the cortex is contralateral frontal eye fields for saccades and ipsilateral parietal-occipital-temporal cortex for the pursuit. Everything else runs the same pathway, the same final common pathway.
