 Now we're going to show a couple of examples of perinode syndrome, which is the dorsal midbrain syndrome. Here we're asking the patient to gaze laterally. Lateral eye movements seem full. Fairly smooth as well. Rapid refixation saccades appear normal. Now we're asking the patient to look upward. Notice that saccades in the up direction are certainly impaired and in fact you can see some convergence, retraction, and stagmus. This is the other component of perinode syndrome. Vertical gaze palsies, convergence, retraction, and stagmus, light near dissociation, Collier sign, those are common features of the dorsal midbrain syndrome. The differential is somewhat age dependent. In younger patients, multiple sclerosis, encephalitis, those should be disorders that you should think of. In older patients, vascular disease becomes much more prominent. The lights are off and what you can see is that there is some response to light reaction with these eyes, although not particularly brisk. There again, we're really flooding that eye and it really doesn't react well. Now we're asking the patient to evoke the near response to see how the patient reacts to near stimulation. We're asking the patient to follow the target up and there's certainly an impaired upward pursuit. In superimposed, you can see these convergence, retraction, and stagmus. Here's another example of a perinode's or dorsal midbrain syndrome. Patients being asked to follow the target upward and I think that you can see pursuit is impaired. Not as bad in the downward direction. Certainly abnormal in the upward direction. But as you can see, horizontal movements are spared. Those functions are subserved predominantly from pontine structures. Now look at this. Regular, ocular stimulation, you can see that vertical gaze is much more normal.