| 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 |
So, today we're going to be talking about the wedge sectoranopia, and basically it's just like it sounds. We have a sector of not seeing (wedge sectoranopia) that's in the shape of a wedge. So, patients who have a visual field defect normally when we have a retrochiasmal field defect, we get some form of homonymous hemianopia. Normally, when you have a homonymous hemianopia up is up and down is down, and by that I mean if you have a superior field defect, whether it's a superior homonymous hemianopia, or an inferior field defect an inferior homonymous hemianopia-the "pie in the sky and pie in the floor,"or even an altitudinal field defect, the field defect is in the opposite area of the visual system. So, a superior field defect is from an inferior nerve fiber damage. So when we have a "pie in the sky" homonymous hemianopia that normally means you're in the temporal lobe because that's the inferior radiations which is the Meyer's loop, and the same thing with "pie on the floor," parietal lobe localization. But the wedge sectoranopia is neither denser superiorly nor inferiorly-it either involves or spares this wedge. So, it's a strange kind of homonymous hemianopia because it's not really lining up on the midline, and so we can either have involvement of this wedge in a homonymous fashion or sparing of that wedge in a homonymous fashion. And that is localizing to the lateral geniculate body. The reason is the geniculate body has a very unusual blood supply, and so we have supply from the anterior choroidal artery and we have supply from the lateral choroidal artery. If we have an anterior choroidal artery infarct, we have this kind of field defect that spares that wedge, the fixation. The alternative is you could have an hourglass kind of field defect. So If we have an hourglass configuration in that field defect, that is a bilateral geniculate body lesion. That's because the blood supply of the anterior and the lateral choroidal artery supply or spare or involve that wedge inside the lateral geniculate body. So, as opposed to up is up and down is down in the rest of the pathway, the wedge sectoranopia (either Pac-Man or hourglass) are both geniculate fields because of the unique blood supply of the geniculate body, the anterior and lateral choroidal artery, involving or sparing this wedge of fixation. And we call that the wedge sectoranopia. So, a wedge sectoranopia, is homonymous, it's on the contralateral side to the lesion, it does not respect the vertical meridian, it does the wedge to fixation, either sparing or involving that wedge, and if you see Pac-Man or the hourglass, pick geniculate body. |
