 This is a young man who has bilateral ladies' pupils. And what we're showing here is the right eye, slit lamp exam, but the light's being turned on and off. It's subtle, but what I want you to look at is the iris stroma and the relative contraction of all the segments around the iris. I think you can see that perhaps the segment at 11 o'clock is not quite contracting as briskly as the others. This will be much more prominent in the other eye. Again, it's subtle in this right eye. We're going to focus in here on some segments at around 7 o'clock and let's see what happens with the lights on and off. Notice how the areas around that segment contract briskly, but that segment at 7 is a little sluggish. It seems to be drawn in by the segments around there. This is a sector palsy, something that's clinically observable at the slit lamp, but the scene should suggest parasympathetic denervation. Now, here we're asking the patient to perform a near response. And you can see that the segments contract fairly well, but on redilation it takes quite some time. Here's the left eye. Now, look at that segment around 2 to 4 o'clock. It contracts, but pretty slowly. The rest of the pupil is pretty quiet. See that? That's fairly obvious as compared to the right eye. That's a fairly dramatic sector palsy, extending pretty much from 1.30 to 2 o'clock all the way around the pupil to about 6 to 7 o'clock. Again, what you can see is the iris folding in around 2 to 3 o'clock and maybe 4 o'clock. Those are active segments that are contracting, although not normally, but the rest of the iris is pretty quiet. I think it shows up very well here. We're going to focus in on those segments just a little bit better. Now, keep in the back of your mind how poorly this pupil is reacting to light. Again, showing the same thing just so that you can get a good feel for what a sector palsy looks like. Now, watch what we're going to do. We're going to have the patient evoke a near response. You see how that pupil is quite a bit more constricted than it was to light stimulation? Look at that. It comes down pretty nicely. That's a very good example of light near dissociation. Now, watch it redialate slowly, slowly, slowly. Very characteristic of a tonic pupil. Now, we're evoking the near response again. See, the pupil comes down pretty well, including those segments between 2 o'clock around the nasal aspect of the pupil to around 5. Those segments weren't working well to light before, but notice how to near stimulation, they contract quite well. And characteristic of an 80s or any tonic pupil for that matter, is to get redialates very, very slowly. Now, what we're doing is trans-illuminating an infrared light, both pupils. And what I want you to look at, this is the right pupil. Look at these segments at around perhaps 1 o'clock and maybe 7 o'clock. There's a little bit of dip in the normal coloration of the iris rough. Those are iris defects and suggest that those segments aren't working quite well. I think there's another segment that you can see quite well at 8 o'clock. Just a little divot around the pupillary rough. And those segments correlate fairly well with segments that aren't contracting well to light. This is a nice technique and supplements your clinical exam. What we're doing is we're shining light in the opposite eye and showing how that pupil contracts to light. There it is again. And see how those defects tend to close up a bit to light stimulation. Now, here we are in the opposite eye. Look at all of those segment defects. I think one can easily be seen at about 3.30 to 4 o'clock. It's a large one. There's another one at about 6 to 7 o'clock. In fact, actually between maybe 3.30 and 8 o'clock, there's some patchy defects. Now, look at here. We're asking the patient to evoke the near response and those segments close up fairly well. But to redialation, look how slowly the pupil redialates. That's characteristic of a tonic pupil. Let's look again. There, I think you can see quite well all of the iris defects. Here we go with the near response. And again, that pupil just sort of creeps out as it dilates very slowly. We'll see in the next example how light near dissociation is not only caused by an 80s pupil but by many other disorders.