||Andrew G. Lee, MD, Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, TX, Professor of Ophthalmology, Weill Cornell Medicine; Christine Tang, Baylor College of Medicine, Class of 2023
||Summary: • Homonymous hemianopsia -easy to identify when it's either on right or left side -lesion is behind chiasm because it's homonymous hemianopsia -therefore, lesion is on contralateral side from the homonymous field defect • 2 homonymous hemianopsias juxtaposed together o Occurs with bilateral lesion -i.e. bilateral occipital infarction, or prior temporal lobe infarct and now a new occipital lobe infarct o Easier ones to identify: checkerboard pattern like BMW logo -one field is a right denser inferiorly homonymous quadrant hemianopsia and the other side is a juxtaposed left superior quadrant hemianopsia -Similarly, right denser superiorly homonymous quadrant hemianopsia juxtaposed to a left inferior denser inferiorly quadrant hemianopsia o Harder ones to identify -not a checkerboard -Left homonymous hemianopsia juxtaposed to right homonymous hemianopsia but both superior -acuity is normal because they can see 20/20 with bottom part of macula -structural eye exams and the disc will be normal as well • Looks like altitudinal defect bilaterally -caused by nerve fiber loss from eye diseases like branch artery occlusion or old ischemic optic neuropathy • Similarly, same defect can occur inferiorly -left inferior quadrant hemianopsia juxtaposed to a right inferior homonymous quadrant hemianopsia -altitudinal character • Differentiating juxtaposed homonymous hemianopsias -presence of macular sparing o Macular sparing in homonymous hemianopsia, even with juxtaposition of another homonymous hemianopsia -preservation of vertical step o Presence of macular sparing helps us to differentiate that 2 homonymous hemianopsias are juxtaposed together • Conclusion: o If 20/20 acuity, normal pupil exam, structural eye exam normal -with field defect on both sides of vertical meridian -look for vertical step o If checkerboard -juxtaposed homonymous hemianopsia o If altitudinal -cover one side to uncover homonymous nature of field -look for either sparing of macula or respect to vertical meridian in remainder of field -juxtaposed homonymous hemianopsia [Transcript of video] "So today we're going to be talking about juxtaposed homonymous hemianopsia, and an easy homonymous hemianopsia is when it's either on the right or the left side. And as you know, we project the field as if the patient is looking at their own field, so in this example the shaded portion represents the right homonymous hemianopsia and so that's usually an easy field to diagnose. You know that the lesion is behind the chiasm because it's homonymous hemianopsia, so you know the lesion is on the contralateral side from the homonymous field defect. What's harder is when you have two homonymous hemianopsias juxtaposed together and that occurs when you have a bilateral lesion-for example, a bilateral occipital infarction, or you have prior temporal lobe infarct and now you have a new occipital lobe infarct. That combination will produce a juxtaposed homonymous hemianopsia, and so one of the easiest ones is when one field is a right denser inferiorly homonymous quadrant hemianopsia and the other side is a juxtaposed left superior quadrant hemianopsia. And as you can see this generates kind of like a checkerboard pattern like the BMW logo. And this right here happens to be an example of one of these checkerboard fields, where you have a right denser superiorly homonymous quadrant hemianopsia juxtaposed to a left inferior denser inferiorly quadrant hemianopsia, so it generates this kind of a checkerboard field. The one that's harder is if it's not a checkerboard and if you have something that looks like this. So, you have a left homonymous hemianopsia juxtaposed to a right homonymous hemianopsia but they're both superior. And if they're both superior, it's going to look like an altitudinal field defect bilaterally to you. So normally altitudinal field effects occur from nerve fiber layer loss from disease in the eye-for example, a branch artery occlusion or old ischemic optic neuropathy or something that's damaging the nerve fiber layer from below. And in a juxtaposed homonymous hemianopsia, the tip-offs are going to be: number one, the acuity is going to be normal because they can still see 20/20 with this bottom part of the macula. Of course, the pupils in retro-chiasmal disease involving the occipital cortex, for example, are not going to have any pupil abnormalities. The rest of these structural eye exams are going to be normal and the disc is going to be normal, so in a bilateral occipital infarction that is affecting the inferior calcarine cortex bilaterally, you'll get juxtaposed homonymous hemianopsias that will look like a bilateral altitudinal field defect. And the same defect can occur inferiorly of course, where you have a left inferior quadrant hemianopsia juxtaposed to a right inferior homonymous quadrant hemianopsia, and again you'll get the altitudinal character. So, one of the things that can help differentiate these juxtaposed homonymous hemianopsias is the presence of macular sparing. And so, if we spare the macula in a homonymous hemianopsia, and even if you juxtapose another homonymous hemianopsia onto that, you'll still have preservation of the vertical step. And the presence of that macular sparing will help us to differentiate that this is actually two homonymous hemianopsias juxtaposed together. One is more complete, then the other one is denser superiorly, but this kind of visual field is also juxtaposed homonymous hemianopsia. So the major key kicking point is, if you have 20/20 acuity, a normal pupil exam and the normal fundus and the rest of the structural eye exam is normal, and you see a field defect that's on both sides of the vertical meridian, the key feature is looking for that vertical step. If it's a checkerboard, that's pretty easy. If it's altitudinal, we're going to want to cover one side so we can uncover the homonymous nature of this field, and we're going to be looking for either the sparing of the macula or respect to the vertical meridian in the remainder of the field, so that we don't think this is an arcuate scotoma from glaucoma or some other optic neuropathy fields, when you're really dealing with juxtaposed homonymous hemianopsias."