| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (BL) Class of 2022, Baylor College of Medicine, Houston, Texas |
| Transcript |
Today we're going to be talking about the macular ganglion cell layer, and it's in the macula obviously, and the retinal ganglion cell in the macula can be measured with OCT. Today we have Jared with us, who will serve as our guide today through the macular ganglion cell. So, the macular cube, built in the ZEISS machine and the Heidelberg, we have no proprietary issues. So, here's a ganglion cell analysis using a macular cube (and Jared maybe you could just show the camera there), and you can see in the color coding scheme, that we have a very, very sharp delineation between the macular ganglion cells surrounding the fovea and this big bright color indicates that we have good thickness of macular ganglion cell layer. So the reason to have this is we can tell (and the machine is saying we're in the green zone which is good), how many macular ganglion cells we have left. So in patients who have vision loss, we can tell how much of that vision loss is from actual ganglion cell loss, and that is the utility of macular ganglion cell. Because in some patients we cannot use the normal things that we're looking at. The normal things we're looking at are looking at the retina and looking at the optic nerve. However, what if the optic nerve is pale, but only a little bit pale, or pale but you can't tell how much pallor (right Jared), by looking at a disc, how much vision they have or don't have? But the machine can turn that pallor into a quantitative assessment of how many ganglion cells we actually have. And in the end, the number of ganglion cells matters, because that's the cell body that's going to supply that axon. And so, if we have a patient who has optic disc edema, the disc is swollen, over time that nerve is going to become pale and become optic atrophy. However, in the disc edema phase we really don't know how much fiber is sick and how much is dead. But the macular ganglion cell can tell us whether this nerve is actually going to be heading to the red zone with decreased nerve fiber layer and optic atrophy or maybe this optic disc edema if treated is going to resolve completely with preservation of the macular ganglion cell. So, the macular ganglion cell layer is really good when we can't rely upon the other things that we'd normally would use-the disc appearance, the OCT of the retinal nerve fiber layer. These things are the normal things that we'd use on OCT, but the ganglion cell layer actually measures quantitatively the ganglion cell layer. And so, we can use it both for prognosis and for diagnosis. The other interesting thing about using the macular ganglion cell is that we can tell when we have loss that is hemianopic. And so in a patient who has homonymous hemianopia, and the rest of their structural eye exam is normal, we can actually see the homonymous hemianopia in the macular ganglion cell layer, and in those patients, what we see is a hemianopic pattern in the ganglion cell loss. And that hemianopic pattern in the ganglion cell loss is not visible to us ophthalmoscopically, and OCT of the retinal nerve fiber layer cannot see that either. This is a trans-synaptic type of degeneration, so even though the lesion is in the occipital lobe, producing a homonymous hemianopia, because that lesion is seen by the ganglion cell in the macular ganglion cell layer, we can document this person had homonymous hemianopia.What's fascinating about this type of technology is we now longer have to depend on the patient-so the visual field is a very subjective test, and what if the patient can't do a visual field or there is no visual field because they're in the ICU or the hospital or whatever reason they can't do a visual field. Structural analysis can be done using the macular ganglion cell layer to show us a homonymous hemianopia without testing the visual field. And so to me, the macular ganglion cell layer is a really great test for diagnosis, prognosis, when we can't use the normal things-looking at the disc, doing an OCT of the disc. |
