Marcus Gunn Pupil and Argyll Robertson Pupil – Pupillary Disorders

00:01 Okay.

00:02 Again, just to review.

00:04 So when we have light shining in one eye, we get a direct light reflex and we have had a consensual light reflex in the other eye because of that signaling going through the Pretectal nucleus and Endinger-Westphal nucleus, the ciliary, you know, cranial nerve, all that stuff, okay.

00:22 Direct and consensual.

00:24 But there are some lesions that prevent that from happening.

00:28 So if you have abnormal processing in one eye.

00:31 So the normal eye is being shined, the light is shining there and we have a good direct light reflex.

00:38 And we have miosis in the other eye, a consensual light reflex.

00:42 Now, I'm telling you that the patient's right eye, on the left-hand side here, the right eye has got abnormal processing of light, it's not going to understand exactly how it should respond.

00:54 So I shine the light in that eye remove the flashlight over, there it goes.

01:00 And I only get a little tiny bit of reflex and not only that I'm not getting any direct reflex, I'm not getting consensual.

01:08 So as it goes back and forth, see that we lose the direct and consensual light reflex because of abnormal processing in that right eye.

01:17 What's going on here? Well, this is the Marcus Gunn, so-called Marcus Gunn Pupil named after Dr. Marcus Gunn, who discovered it, he should have named it after his patient, but he named it after himself.

01:28 And what is going on here is that we have a defect in the optic nerve or in the retina of the abnormal eye.

01:36 So again, the right eye here has got a defect and you see it as a big X there in the optic nerve, it can also be in the retina on that side.

01:44 And when the light shines in that abnormal eye, or the abnormal optic nerve, I don't get the director consensual response.

01:53 But when I go down to the normal eye at the bottom where everything is intact.

01:59 Perfect, good.

02:01 So this is an Afferent defect.

02:03 Afferent processing defect, meaning coming off the eye.

02:06 The problem is very proximal in the entire chain of things.

02:11 So possible etiologies for Marcus Gunn Pupil.

02:14 You can have lesions of the optic nerve and the visual path pathway very proximal to the eye.

02:20 You can have lesions of the retina in that eyes, so it's not perceiving light appropriately.

02:25 We could have a patient who's developed Amblyopia.

02:27 Remember, this is central brain failing to process information that's being sent by the eye.

02:35 We had a whole session where we talked about amblyopia and strabismus, right remember? Go back and review.

02:41 And you can have eyes that have, they're not always perfectly matched in terms of the diameter of the pupil.

02:48 And some people walk around with one people bigger than another and that's just their normal state.

02:53 So they may have an apparent Marcus Gunn Pupil.

02:57 Okay, that's Marcus Gunn.

02:58 Let's look at one other way that we can mess up the pupillary response.

03:02 This is the Argyll-Robertson Pupil.

03:05 And this is the green box at the top is typically classically associated with syphilis.

03:11 And the syphilitic lesion will occur in the Eringer-Westphal nucleus.

03:16 Actually just a little bit dorsal to that.

03:19 So that little spiral gates responsible for the syphilis are getting in that area where we have the X.

03:26 So now what is happening, we shine the light and none of that information is getting through.

03:31 So light doesn't make the pupils respond.

03:35 They're non-responsive to light either as the direct or the consensual response.

03:41 But see, when the fly goes in, the eyes rotate towards that, that's accommodation.

03:47 And normally when eyes come close and look at something close to the nose, such as that fly coming in.

03:53 Then the pupils do also undergo miosis.

03:58 That's to limit the amount of light.

03:59 You don't need as much light when you're looking up close.

04:02 So the pupils in these patients with Argyll-Robertson due to the syphilis involving the Edinger-Westphal nucleus, don't respond but they do accommodate.

04:14 So in a less politically correct time, many many years ago, when I was a medical student, the way that we remember this, was that okay this is a disease associated or a lesion associated with syphilis, the Argyll-Robertson Pupil.

04:29 And in Argyll-Robertson Pupil, the pupils don't respond but they accommodate and because of association with syphilis, the way to think about this and remember this was that it was like a lady of ill repute who would accommodate you but wouldn't necessarily respond.

04:48 So that's a less politically correct environment.

04:51 I'm not even sure that joke is going to make it into the final cut, but hopefully it will.

04:55 And now we've talked about Marcus Gunn, Argyll-Robertson, miosis, mydriasis.

05:00 You've learned some other drugs.

05:01 And we'll quit there.

05:03 Thank you very much.

05:04 See you later.