 The young man has a resolving optic neuritis, and you can see that he has an afferent pupillary defect on the left. We're putting a small filter over the right eye to try and balance that defect. And you can see that when the light is shined in the left eye, there's still a dilation indicating that there's not enough filter placed over the normal eye. Now 0.6 log unit filter is placed over the right eye. And again, you can see that it's not quite large enough to balance this defect. I want to point out that in between each testing, what you need to do is to re-bleach the amount of light entering both eyes as I'm doing here. And that's to prevent any asymmetric bleaching of the eyes while the filter has been placed over it. We're getting close, but I think you can still see that there's a relative dilation of the left pupil. So we're not quite there yet. Sometimes the endpoint is a little bit mushy, and a judgment call has to be made in terms of how much filter to place over the eyes. One good endpoint would be if you've placed too much filter over the eye and induced an afferent defect in the normal eye, then you know you've gone too far. I think that you can see that we're just about balanced here.