| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (PZ) Class of 2023, Baylor College of Medicine, Houston, Texas |
| Transcript |
So today, we're just going to be talking about non-organic vision loss, and we're going to be covering the most common ways that a non-organic patient comes to neuro-ophthalmology. So, the first one is easy. The patient is complaining about very severe loss: no light perception, light perception but only in one eye, in this example on the right. Now, that is one of the easiest things to do because if you really are no light perception in one eye only then we really have to have a relative afferent pupillary defect in that right eye. So as soon as they don't have a RAPD, we already are suspicious that this person is non-organic. However, it's always best to prove that someone is non-organic as well as labeling them as non-organic in the chart, and what we have to do here is prove that this person can see better than they claim they're seeing. So, if for example, the fellow eye in this case is 20/20 and the right eye is no light perception, we already don't have an RAPD which is already tipping us off that this is a non-organic patient. And so, one of the things we can do is we can do is we can take a four base down prism and put it in front of the good eye. So as you know, a prism will displace the light and so if we're looking at the letter E here, for example a 20/40 letter E, if we put this 20/40 letter E onto the chart and have the patient view with their 20/20 left eye they will see an E that's displaced. But if this supposed no light perception eye see's nothing then they'll only see one E. However, if the patient reports that they see two E's, one on top of each other, then we know that the second E is actually coming from the supposed no light perception eye. And we don't even have to check the vision in the supposed no light perception eye because we already know that this is the 20/40 E. And so, the key thing about this test is we're putting it in front of their good eye. We tell the patient we're testing the good eye. We tell them we're going to put this prism in front of the good eye and that it's going to split the image and then we put it over the good eye. It causes them to see this. We ask them what do they see. I see two E's, one on top of each other. That already proves that this eye can see 20/40. That is the end of the test. So, this is a monocular vertical prism test. It's really great and it doesn't have to be no light perception. You can put any level of acuity here: 20/100, 20/60, 20/80, because you're testing the good eye under monocular conditions. It would be one E but under binocular conditions we should have two E's. If the organic response is given, they only see one E then that supports the hypothesis that they're telling the truth. So, it works both ways. It can prove someone is non-organic, but it also could suggest that someone actually has an organic problem that needs to be dealt with. The second most common thing that we see in terms of non-organic is visual field defects. And as you know, the arc subtended by the visual angle is a constant. The only thing that changes is as you're getting farther and farther away, the size of the circle that we are subtending is bigger. So, when we move from a 1-meter target to a 2-meter target, the arc subtended and angled is the same, but the field has to expand. But for whatever reason, patients who have a 5-degree field like to claim a tunnel field. So, it'll look 5 degrees at 1 meter. I'll be 5 degrees at 2 meters. It's 5 degrees at 3 meters. So, a normal organic field expands like a funnel. This is an organic field and that's why you can look at things that are very far away like the moon or the stars or whole galaxies and you can fit it on your retina. Because it's far enough away, but patients who are non-organic have a tunnel field. So, tunnel is non-organic. Funnel is organic. The problem is residents write in people's charts who are organic that they have a tunnel field. But what you really wrote was this person is non-organic. A tunnel has an entrance and an exit and they're the same size. It's a tunnel. So please don't write tunnel when you meant funnel. Funnel is organic. Tunnel is non-organic. We can test this field at one meter and two. The last non-organic field I want to talk to you about with our little time together is when you have monocular visual field loss. So, as you know, we look at the field right and left as if the patient is looking at it. So, in this particular example, the patient is claiming that they can't see in this right eye temporally, but this eye is normal. There's not going to be any RAPD because they're non-organic. If they do have an RAPD, they're organic. If they have that field defect in one eye only and you're no RAPD, then the test is to test that field again with both eyes open. And because this part of the field in the left eye overlaps with this field and the fellow eye (the nasal portion of this left eye overlaps with the temporal field), if you test the field with both eyes open and it's organic, a normal field will result. However, a non-organic patient will persist in claiming that they can't see. And so, if we do the both eyes open field and they still have the field defect and the other eye's normal, that is evidence for a non-organic field. So, I prefer the term non-organic for these patients. You don't know who has the DSM-5 diagnosis of malingering, which requires a secondary gain. You don't know who has conversion disorder, which does not require secondary gain. They have some deep-seated psychological conflict that is manifesting in a somatic way. They are actually unconsciously doing this. They don't know that they can't see. In fact, they believe they can't see. And you are in no position to judge whether someone is malingering or conversion disorder. That is determined by a different specialty and that's not you. So non-organic vision loss. The three most common things: monocular loss no RAPD, tunnel versus funnel field, and any kind of field defect in one eye but especially a monocular hemianopia field test. Tests with both eyes open. And then non-organic. Don't tell them they were faking because if they're a malingerer they already know that information. If they're a conversion disorder, they won't believe you so there's no point in telling them this. I usually just tell the patients, ‘Look, we don't find anything organic. We can see that your vision is actually better and that you're just going to get better.' And I give them a little small window to escape out of it. I usually don't send them for psychological evaluation unless there's some other DSM-5 reason for doing it. And I just write in the chart that they're non-organic. |
