 We're going to show you here an example of a third nerve palsy. Now this is a relatively young patient who had acute onset of a third nerve palsy, and when worked up was found to have a dolicoactatic basilar artery. Most likely it was compressing the left third nerve because this patient had pupillary involvement. The pupil is relatively involved on the left side. Going through ductions now, you can see that that left pupil doesn't medially duct, doesn't infiduct well either, and see that at AB ducts quite well, six nerve function. And superduction is obviously impaired, and I think if you watch, you can also see that there is pupillary involvement. The anisecory is greater in light than dark. Now what we're doing is trying to demonstrate secondary and primary deviation. Patient was fixating with his parietic eye, and you can see the secondary deviation that resulted. When fixating with the good eye, there's the primary deviation. Patients fixating with his poor eye, look at that big deviation. When fixating with his good eye, not quite as much. That follows the general rule that secondary deviations are greater than primary deviations. And we're just going to demonstrate that here. The uncovered eye now has a greater deviation than now. What we're going to show here is the anisecoria, and again, it's much more prominent when the light is on. This would simply indicate a parasympathetic defect to the pupil.