Dr. Ho touches upon the aims of visual fields, glaucomatous visual field defects and non-glaucoma causes of visual field loss. Dr. Ho presents images of visual filed and points out to the lesions.
DR HO: Hello? Okay. Good morning, everyone. So today I’ll be giving a small talk on visual field defects. So it’s a bit different from what we’ve been doing so far. You’ve done a lot of retina, a lot of glaucoma, and cataracts. So I’ll touch on a bit of neuro-ophthalmology. So this is something you can do even without a slit lamp. You’ve got visual field facilities in your hospital. So we’ll just go through some cases. So these are the reasons why we do visual fields. The aims of the visual fields allows you to identify abnormal fields, as well as to follow up patients who have abnormal visual fields. Our visual fields also have a normative database that we can compare. And in patients whom we follow up, we can also see if they are stable or if they are getting worse. So for patients who have glaucoma, the visual field defect should correspond to the nerve fiber bundle defect. So here’s an example. If you have an area here that is damaged… You get a corresponding visual field defect here. All right. Sorry. So here you get a superior lesion. And over here, you get an inferior visual field defect. So, similarly, in this picture, there’s an inferior defect. And on visual fields, you see a superior defect. So this is quite simple so far. But what about not glaucoma? So this is not glaucoma. So we suspect that the visual fields are not because of glaucoma if they have these features. Sorry. We will suspect a patient does not have glaucoma if he has these features. So if the optic disc has less cupping than expected for the visual field loss… Based on the optic disc appearance, you see that the area of thinning does not correspond to the visual field defect. If the disc is more pale than cupped. So for the next point, it’s excessive progression of visual field, but you can also get that in glaucoma. And if the pattern of the visual field defect respects the vertical midline, you would be very suspicious of something not glaucoma. So if you see this visual field defect, where is the lesion? Anyone else? That’s right. So this is a classic bitemporal hemianopia. And so we look for what we call the suprasellar lesion. Suprasellar tumor. So what else would you look for in these patients? So if you have a patient who comes in with a bitemporal hemianopia, what other features can you look for? Anyone else?
>> Can we see this again? MRI?
DR HO: So yeah, MRI is good. CT can also show you the lesion, but generally for patients who have any intracranial neurological causes, we prefer MRI. The reason for this is because, for the CT scan, it shows bone very well, but MRI is better for soft tissue. So we need to look for signs of the chiasmal syndrome, for patients who have a pituitary gland lesion or a suprachiasmal, a suprasellar lesion, with these features. So patients may have see-saw nystagmus. Does anybody know what this is? So the eye movements will look like a see-saw pattern. They will move like that. Like a see-saw. There’s a feature called hemifield slip. I just wrote it down here. You can take a look at it. I’ll just pull these up. Okay. So for hemifield slip, the patients may actually complain of double vision, even though it doesn’t affect the third, fourth, and sixth cranial nerves, which control your motility. But you can actually get diplopia. The patient may also say that they’re not able to see anything beyond what is in front of them. So if you hold a target up in front of them, they can’t see what is behind the target.
>> In hemifield slip?
DR HO: Yes. And you look at the optic nerve on examination. They have bow tie atrophy patterns. So it looks like a bow tie. For these patients, because the lesion is in the suprasellar area, you need to ask about features of hypersecretion. Hypersecretion of pituitary hormones. So in patients who have oversecretion of growth hormone, you can get acromegaly. And for patients who have hypersecretion of prolactin… For females, you ask about a history of amenorrhea and galactorrhea. And for men, you can ask about infertility or impotence. And if they have hypersecretion of ACTH, they may have features of Cushing’s syndrome. So what are your differentials? These are differentials of a bitemporal hemianopia. So you mustn’t rule out any retinal causes, such as any nasal retinal reasons. They can be from panretinal photocoagulation, sectoral or panretinal photocoagulation, retinitis pigmentosa, or retinoschisis. You may also have optic nerve lesions, such as coloboma, tilted optic disc, and eyelids. Eyelids can also cause blockage of the temporal fields. So what about this visual field? Does anyone know where the lesion is? Anyone?
>> It’s at the junction between the optic nerve and the chiasm.
DR HO: That’s right. So where is the chiasm in relation to the lesion?
>> Anterior to the pituitary gland.
DR HO: So between the chiasm and the lesion, which one is in front of which? Okay. So this is what we call a junctional scotoma. And the chiasm is actually behind the lesion. So typically what you’d get is: One of the optic nerves at this site is affected by the tumor. And on the other eye, you get a temporal field defect. So this is what you get. So the scotoma on one side, and on the other side, a temporal field defect. There we are. So the reason why you get a superior field defect on the other side is because of the crossing of the fibers of the optic nerve. So how does the relationship of the chiasm affect the visual field defect? You know the answer. Okay. Very good. Let me just bring this all out. Okay. So if there’s a central lesion directly over the sellar area, you get a bitemporal. So that was the first visual field defect we saw. For a prefixed lesion, this means that the chiasm is anterior to the pituitary gland. And what you get here would be an incongruous homonymous hemianopia. And so these may actually mimic the postchiasmal lesion. So you get a typical homonymous hemianopia. Homonymous hemianopia. Okay? So where are we? I think we went through — we’ve kind of been through all of this already, right? So I’ll move on.
>> Yes, move on.
DR HO: So if the chiasm is behind the pituitary gland… You get a junctional scotoma. So this is the one that we have — the case we discussed before. Yeah. So patients also have a relative afferent pupillary defect. In addition to the visual field defect. So this is just a schematic diagram showing where the nerves go. So if you have a chiasmal lesion here, your nasal fibers that cross here are affected. So that’s why you get a bitemporal field defect. If you have a prefixed lesion, so the chiasm is… Sorry. The chiasm is in front of the lesion… So the lesion will lie here… So the lesion — sorry, the lesion is posterior to the crossing… So you get a homonymous defect. If the chiasm is postfixed, the lesion is in front. And you get a junctional scotoma. So if you have a lesion like this, which part of the visual pathway is affected? Anyone? Okay. So it’s the lateral geniculate body. And what you get is a homonymous horizontal sectoranopia. So in this kind of setting, the lateral choroidal artery is affected. Okay. What about this one?
DR HO: This is also the lateral geniculate body. Okay? So you get a quadruple sectoranopia. And this time the distal anterior choroidal artery is involved.
>> I’m sorry. This is artery of the brain?
DR HO: Yes. So these are if you get strokes. So lateral geniculate body lesions can give you these very strange visual field defects. So they may also have contralateral sensory or motor deficits. Okay. So now something more easy. Where is the lesion here? Which side is it? So this is the visual field as you see it. So this one would be the left side. This is the right side. That’s right. Yeah. So it’s a left-sided lesion. And where in the brain is the lesion? Anyone? So you get a similar — this is a similar lesion, except on the other side.
>> Can you say it again?
DR HO: This is a left-sided lesion. This one’s a right-sided lesion. So you can see on the Goldmann the right-sided — it’s a right-sided field defect. So these are temporal lobe lesions. So most likely temporal lobe… So what else would you ask the patient who has a temporal lobe lesion? Anyone? Sorry? You can ask for history of trauma, yeah. But if you want to decide which lobe the lesion is actually in, is there any other questions you want to ask the patient? Or anything else you want to look for on examination? Okay. So there are actually other non-visual findings that you can ask the patient as well. So patients with temporal lobe lesions can get auditory hallucinations. They may have language problems. Deja vu and jamais vu. Deja vu is the feeling that you’ve been there before. And jamais vu is a feeling that is not familiar. So it’s kind of the opposite of deja vu. The patient may also have epilepsy, like seizures. So they can have unusual tastes on their mouth and smells. And there may be also movement of the lips or around the mouth. And on the side of the lesion, they may also see visual hallucinations. So what about this one? Where is the lesion?
>> Parietal lobe.
DR HO: Yes, very good. On which side?
>> On the opposite side. The right side.
DR HO: So this is the left eye and this is the right eye. So where is the lesion? Which side? Which parietal lobe is it?
>> On the right side.
DR HO: That’s right. So always remember: Postchiasmal lesions, it’s always on the opposite side. And pie in the sky is for temporal lobe. This is pie on the floor. For the parietal lobes. So the parietal lobes are a bit more complicated, because then we divide it into dominant and non-dominant lobe.
>> Dominant and non-dominant?
DR HO: But before we move onto that, yeah — in the clinic, you can also ask the patient to look at the eye movements for any pursuit problems. So in terms of eye movements, the frontal lobe controls saccades, and the parietal lobe controls pursuits. So frontal lobe — the front controls saccades. So quick movements from one side to the other. Parietal is scanning movements. Pursuits. So in a parietal lobe lesion, you get a pursuit problem to the same side as the parietal lobe lesion. And so in the left parietal lobe lesion, the patient will have problems pursuing to the left. And what you can also do is use the OKN drum. And you also look for asymmetry. So parietal lobe lesions, because it’s pursuit, the OKN drum also gives you an idea of how the eye movements are. Because when the drum rotates, the eyes also follow. So this is like pursuits. So when you rotate away from the lesion, the other side, this is normal pursuit. But when it goes to the other side, the opposite side, you get asymmetric pursuit. So it’s not smooth anymore. Okay. So this is the… The features of the dominant lobe and non-dominant lobe. Most people are left-side dominant. Left-side — the left lobe is dominant. And the right lobe is non-dominant. So in a patient with dominant lobe lesions, what are the other things you look for? Anyone know?
>> A language problem?
DR HO: Yeah, that’s right. Very good. Anything else? So these are actually very useful, because you can ask the patient in the clinic. You don’t need any special equipment. So after you find the lesion with the visual fields, you can actually examine for them and ask some questions. So for dominant lobe lesions, you get Gerstmann syndrome. And then non-dominant lobe — does anyone know what we find?
>> Problems with calculating?
DR HO: Yes. That’s right. So patients will have impaired construction. So constructional apraxia.
>> What does that mean?
DR HO: So you ask them to draw something. They can’t draw it. Yeah. Not able to calculate properly. They might neglect that side. What about this one? Where is the lesion? Start slowly first. Which side is the lesion?
>> Left side.
DR HO: Left side. So on the screen, they are not able to see this side. It means the lesion is on the other side. Yeah. Yeah. So in this case, because you see that on the left side — this is the left — left side, he’s not able to see — the lesion is in the right side. So this lesion is very symmetrical, up and down. Looks very congruous. So the lesion is most likely posterior. So the more posterior you are, the more similar the two sides are. So this looks like an occipital lobe lesion. So you get a very congruous defect. But what other defects can you get? So the occipital lobe is special in that it gets two different blood supplies. Blood supplies. The two arteries supply the occipital lobe. The medial cerebral artery and the posterior cerebral artery. Okay. So in lesions where the medial cerebral artery is not involved, they’re macula-sparing, which means that the macula area is still good. Yes. And in that case, the patient gets a very tunnel-like visual field. But if the macula — if the lesion affects both arteries, the posterior and the middle cerebral, then the entire field will be gone. So key points to interpreting visual fields. So the fields are opposite in location to the damaged area. So this is quite good. When you first see a visual field printout, you first identify which side is the lesion. So if the field defect is only in one eye, it’s anterior to the chiasm. So it only affects one side. And therefore you get a relative afferent pupillary defect on the same side as the lesion. So if you see a relative afferent pupillary defect, there are two possibilities. It’s either anterior to the chiasm, where it’s the optic nerve itself is involved, or it can be posterior to the chiasm, on the other side. If the field defect is in both sides, then the problem is either behind the chiasm or it’s either bilateral retina problems or optic nerve problems. So if you see a printout and you see that both eyes are affected, the lesion is either behind the chiasm or we mustn’t forget retina problems and optic nerve problems on both sides. So you need to find out where the location of the lesion is. And you need to decide where the location of the lesion is for each eye independently. So for bitemporal defects… Lesions at the chiasm. If it’s homonymous, then you suspect something behind the chiasm. So what about binasal defects? Anything else? Don’t worry. Okay. So where can the lesion be to cause a binasal? So usually these cases — you think about retina. And what can cause a retina problem that can give you a binasal defect? RP. Yes, that’s right. Yep. Anything else? So you can go step-wise. Is it retina? Is it optic nerve? Or is it behind the optic nerve? So for retina, like you rightly said, RP is good. Other things that could cause it would be — if you had laser to that side, laser to the temporal side of the retina. Or even retinal detachments on both sides. But temporally. For optic disc lesions, it may be tilted optic disc. So you need to consider glaucoma, non-glaucoma, or retina problems. So what about nasal hemianopia? Just remember that the lesion will be on the temporal side of the optic nerve, so on the opposite side. And if it’s a central defect, it’s most probably an optic neuropathy or a macular problem. So this is just a schematic diagram, showing where the sites of lesions could be. So if you cut the nerve here… You get a scotoma on this side. You get a field loss on this side, but the other eye is spared, because this is not affected. Here’s the chiasmal lesion of the bitemporal hemianopia. And over here you see a postfixed lesion. Where it’s at von Willebrand’s knee. So therefore you get a junctional scotoma. And we’ve discussed that posterior to the chiasm, you can get these kinds of field defects. So the more posterior you get, the more congruous the defects are.
>> Congruous means continuous?
DR HO: So it looks similar on both sides.