Visual Fields

Chapters:

1. Introduction
2. Mapping the Visual Field with Perimetry
3. Visual Field Testing for Children
4. Visual Field Abnormalities and the Visual Pathway
5. Interpreting the Goldmann Kinetic Perimetry Results
6. Interpreting Automatic Static Perimetry Results
7. Developmental Implication of Visual Field Loss

CHAPTER 1: Introduction

MAYER: We do differentiate between visual acuity and visual field, visual acuity being the centermost part of vision where we focus on things, we fixate, we see details.

Everything else is the visual field.

Even though it's really one continuous surface, there really is no separation in our vision or in our minds between visual acuity and visual field.

Some important things about the visual field is first of all, as I showed you, if you do this, you hold your finger when you can't see it, you bring it forward. And you see it, you're aware of it out in your field, and out here.

That's the fullest extent of your field. And it's actually a little more than 180. It's actually a little more than 90 degrees from fixation, which is where we really like to count in this field.

NARRATOR: We see a pencil sketch of an adult male face head-on, with the left eye covered by the left hand.

A shaded, semi-circular wedge shape depicting the horizontal range of the right visual field extends from the eye along a horizontal plane and is bisected by a line, dividing the wedge into the nasal and temporal fields.

The nasal field is described by an arc of 60 degrees. The temporal field on the other side of the axis is 100 degrees for a total range of 160 degrees in the right eye.

MAYER: And then when you're thinking about the upper field, the farthest position up you see is about 60 to 70 degrees. And the farthest position you could see out, the farthest amount of degrees, is actually way down here, but I'll bring it up so my finger is seen. It's 80 to 90 degrees, so it's very big.

NARRATOR: A second sketch shows an adult male head in profile.

A shaded, semi-circular wedge shape extends from the eye in a vertical plane, and is bisected by a line representing the horizontal axis, dividing the wedge into upper and lower fields.

The upper field limit is 60 degrees from the axis, the lower field 75 degrees, for a total range of 135 degrees.

MAYER: Your vision off to the side is coarser or rougher, and you don't see colors as well, you don't see details really very well at all. You do see big, gross patterns, you see contrast differences.

So, for example, I can see the wall contrast over there when I'm just looking at your face. And that's really important for understanding what peripheral vision is for and what it does.

NARRATOR: A third sketch shows a male figure looking at a chart of concentric circles that intersect horizontal and vertical axes at ten degree increments.

It is a Goldmann perimeter chart.

A dotted line describes a rough, oval shape and marks the plotted limits of the right visual field. The elongated and largest part of the field is to the right of the vertical axis.

MAYER: So if we think about what the peripheral field does do for us, we can think about when we move around. When we move around through obstacles, go downstairs, reach for something, do any physical activity, sports, ride a bicycle. All those things of daily life that take physical movement, we're using peripheral vision. It's really important for that.

It's not that we are not also using our detail vision, because we are. Because we're scanning around. We see something to the side, we scan to it. That's being cued by peripheral vision to a target out to the side. So that's really important.

There's another aspect of peripheral vision that's very important, too, and it's for doing detailed tasks. For example, for reading, when you're reading a page, you fixate on a word, and you're anticipating... you're reading off to the right, and that's in your peripheral vision. So you have to be aware of those word images.

You may even see some of them as you're scanning to the right. You really need peripheral vision for fluent reading as well. And it's one of the problems with people who have visual field loss, particularly on the right side. They don't scan very easily to the right. And so what they'll do is they'll jump their eye way off, and then scan back, and then jump way off. Because they don't see just to the right of fixation. They don't see that word just to the right.

 

CHAPTER 2: Mapping the Visual Field with Perimetry

MAYER: So we have to measure the visual field in a quantitative way. And we have to relate where you see the target in your peripheral field to a point in space that has some kind of metric, that we can say it's 60 degrees from fixation.

I can say, well, you see it right here and you don't see it here. But what's that difference? Is this 90 degrees? Is this 60, 70, and so forth? So we really need to quantify that, and we need it to be able to describe it to other people, to show it to previous exams, and to really follow how a person's visual field is holding together when they have a disease.

We use something called a hemispheric perimeter. It's actually a white, painted hemisphere, very smooth, completely simple inside. And now what the instrument will do is it projects a light onto that surface. And that light can appear in any place in the field. It can be moved, it can be static. You move the target, it's kinetic. And that was the old way of doing things, and we used something called a Goldmann kinetic perimeter to do that.

NARRATOR: In a photograph, we see a hemispheric perimeter of the type described.

Red arrows point to a chin and brow rest, which allow the head to remain in a steady position during testing, thus aiding focus on a fixation point at the center of the hemisphere, which is also noted by a red arrow.

A bright point in the hemisphere is the light target, and it is also identified with an arrow.

Next, we see the device from the back with an examiner peering through a scope that extends from the interior fixation point. Using a Goldmann perimeter chart, the examiner can pick a point at which the light target will be presented inside the perimeter. The results are then plotted by the examiner.

MAYER: The Goldmann has been superseded now for adults, for testing adults. So in most clinical settings with adults, they still use a hemisphere perimeter, but now everything is done with a target with light being presented in one position, so statically.

It's actually automated, run by a computer. So there's no longer an examiner who has to do all of this positioning and plotting by hand. It's all done by computer. So a person does the same thing they do with the old version, with a Goldmann.

I didn't quite describe that, but puts their chin in a chin rest, and their forehead against this. Looking into the globe, watching a tiny, small central spot and waiting for the light to come.

NARRATOR: In a photo, we see a young boy being tested by an examiner. His chin and forehead rest in a fixed position, and in his hand he grasps a buzzer. The examiner peers through the scope at the back of the machine.

MAYER: When they see the light, they press a buzzer. So, the same thing is done in the Goldmann, and in the automated static perimetry. Only the light moves in one situation, and it doesn't in the other.

NARRATOR: We see a photograph of a patient seated at an automated static perimeter device. In his right hand is the buzzer that he will depress when a target is sighted.

Since only one eye is tested at a time, he wears a patch over his right eye. A screen displaying the plot results is visible on the side of the machine.

MAYER: The reason why not moving the target — presenting it in one position — is really good, it's very precise and you can vary the brightness of that target up and down. So you can see just how dim a target will that person be able to see. And that's really important for measuring fields in people who have optic nerve and retinal disease.

Now, the Goldmann is still very good for testing the peripheral field. And it's also really good for testing children who can't sit for the amount of time it takes for an automated, static perimetry test.

Pressing the buzzer, looking in, holding still, all of that. We can interact with a kid that we're testing with Goldmann. We can, you know, talk to them and say, "Oh, shall we take a break? "You want to try it this way?" We try to make it into a game for them.

 

CHAPTER 3: Visual Field Testing for Children

MAYER: I see children, many of whom I can't test with a Goldmann perimeter. They have a possibility of a visual field loss because they have damaged somewhere along the pathway. But they're in wheelchairs or they can't speak. They aren't going to be able to hold their chin in a chin rest. They're visual, they look around.

What do I do with them? How do I test them?

The way that I use, which I think is, you know, each of us has our own particular way of testing children's visual fields. All doctors will do something like what I'm going to do. My way is — and what's very important is you have to have a target that the child looks at, fixates — and this is my Count.

NARRATOR: Luisa Mayer displays a small figurine of the character the Count on the end of a long, thin rod.

She is about to describe and demonstrate how the Count fixates the child's attention as she introduces another target into the visual field, a white, Styrofoam-like ball on a long, thin rod.

MAYER: And the count wiggles like that, so he really gets a child's attention right to the center. But how do I get the child to look off the side?

Well, what I do is I bring a target — a big, white ball that comes into their field — and I wait for them to look at it. And when they do, the first time they do it, I go, "Oh, you found it. "You found the white ball. "He gets to eat it. The Count loves to eat the white ball."

And then I bring it in, in another place. "Oh, you found it again. He loves to eat that white ball." And I bring it in again, and so forth.

After that first trial, they're very excited, it's a game that they can understand. Even if they don't understand my words, they know what this action is on it. And that works really well in a lot of kids.

NARRATOR: In a photo, we see Dr. Mayer using the Count and ball to test the vision of a young girl, who is sitting on her mother's lap. The girl laughs as the Count eats the white ball.

MAYER: Now, what about the child that is fixating too strongly on the Count? And we think of children like this as having an attentional problem. They can't shift their attention very well. It might not be due to a peripheral field loss, but simply an attentional problem. So then we have to have two interesting targets — one that will keep attention at the center, and the other one that they will look at because they've seen him before, they like him.

NARRATOR: Again, Luisa is about to describe and demonstrate a vision evaluation. This time, she uses two, brightly colored figurines — Elmo and Big Bird — on the end of long, thin rods.

MAYER: They know this is Elmo, or I say, "Where's Elmo?" And I shake him a little bit.

Sometimes I have to go back and forth between them. "Okay, here's Elmo, now where's Big Bird?"

Back and forth to be sure that it's not that they're just neglecting because they really like to look at Elmo more than Big Bird, or vice versa.

So there are tricks about testing children's visual fields so that you're getting around their attentional problems, you're not just tapping into an attention problem, and you're actually really testing the visual field for a certain target.

So I find that bigger white sphere is really very good for most of the young visually impaired children that I see. Sometimes I have to go bigger, but usually not. And then there are children where you have to use a light, where the real object isn't going to work, and you have to have a light, maybe even a flashing light target for them to look at.

And those kids, often they're sort of just staring around like this. And you don't have to show them anything centrally, because that may in fact cause them to just stare. And you just bring it in, and then they will react to it. They may react to it a little late and see a little delay. But nevertheless, you will see that reaction.

So at least using this method — which is called confrontation — we can get a gross sense of whether there's a field loss, whether the field is very constricted. They only see it in here, they don't see it out here. And more or less like that, it's really much more qualitative than what we can do with a Goldmann or automated static perimetry. But it can be very informative.

 

CHAPTER 4: Visual Field Abnormalities and the Visual Pathway

MAYER: So, visual field defects can be caused by damage to structures that correspond to what we call the visual pathway. And that starts in the eye, the back of the eye, where the optic nerve and the retina are.

The optic nerve courses to the little area... tiny, little area in the part of the brain that's just behind the eyes called the chiasm. They cross, half of the fibers go to one side, to one hemisphere, the other half go to the other from each eye. And what's happening is that projection of the left field goes to the right brain, and the projection of the right field goes to the left brain.

And it occurs right after the chiasm. And there's a long pathway, actually, all the way from the eyes to the back of the brain, to the occipital lobe. So damage to any part of those structures can cause a visual field loss. Not just in the eye, but in the back of the brain, all parts of the brain.

NARRATOR: We see a graphic depiction of the way in which the human visual pathway and the various structures transmit and interpret visual information.

A green apple is presented in the left visual field, and a purple and white fish in the right field. Information from both fields enters each of the eyes, and is projected to the retinas.

At the chiasm of the optic nerve, half of the fibers from each eye cross into the opposite hemisphere of the brain and onto the visual cortex. The visual cortex of the left hemisphere processes information from the right visual field, and vice versa.

MAYER: So it's important to think about also what kinds of disorder, damage — or sometimes we call them lesions — are causing these visual field defects at different levels of the visual system. And in terms of the most common disorders, in the retina it would be some kind of hemorrhage or some kind of circulatory problem or a retinal degeneration.

I mean they're not common in the world of visual impairment, but in terms of people's serious problems, it's a retinal degeneration. Also, there's diabetic retinopathy, which causes problems in peripheral vision and need to be detected. In the optic nerve, for optic nerve defects, the biggest problem is really glaucoma. And that's one of the reasons why the static perimetry is so important because it's picking up glaucomatous field losses — that's what they're called — early, and where treatment may be more effective.

There are other causes of optic nerve lesions as well. Optic neuritis, neuropathies of various sorts for all kinds of reasons. Children can have congenital defects of the optic nerve that cause field defects, and those are very important to find.

One of the syndromes of the children that we see here at Perkins is CHARGE syndrome. And there can be a loss of tissue in the optic nerve and also in the retina that causes a characteristic field defect of the upper part of the field and maybe sometimes here.

And those actually are pretty good and easy to test because the person doesn't see anything in that field. But generally, optic nerve and retinal diseases are hard to test. And in most children, they're very difficult to test.

So in adults, you use automated perimetry and you do very well. Now, at the chiasm, when you have those crossing fibers, the most common cause of a visual field loss of the chiasm is a tumor. And so I see a number of little children who have tumors. And one of the really important things is to measure their visual fields. Because they can give us more information than this tiny, tiny little area called a chiasm.

Even an MRI doesn't give you the information that a visual field defect can give you. So then we get back into the brain, but it's all the brain, actually. But past the chiasm, the kinds of damage or disorders that cause visual field defects in the hemispheres are stroke and tumors.

And in children, some children can be born where there's been some kind of event that causes them to have low oxygen, poor blood flow to the brain, and they can have not really a stroke, but a loss or a damage to a certain part of the brain that affects the visual field. And those kids are really important to be able to do their visual field and find out if they have problems.

 

CHAPTER 5: Interpreting the Goldmann Kinetic Perimetry Results

MAYER: In the case of the Goldmann kinetic perimetry, we're going to have an oval, just like I described, which will be the farthest out a person sees that target. So that would be pretty easy to determine. You'd be able to find where is the central point that the person fixated, how far out did they see it. You want to have some norms to compare it to.

NARRATOR: We see a Goldmann field map that plots the outer perimeter of the visual field for a child with normal vision.

MAYER: A normal visual field of a child, let's say between five and eight years of age, has a certain size and confirmation. It will look very much like an adult's, maybe just be a little bit smaller. The right eye field will be a little constricted, as it is in adults. And the nasal field, the left eye field should be pretty far out.

You should be able to see two field plots, one with a very large target, and one with a smaller target showing sort of the mid-peripheral field. And you should also see a dark area for that right field plot right about here. And that is the normal blind spot where the optic nerves go back into the brain. If you've had a good test with a child, you're able to test the blind spot. So you normally see that little, dark spot there.

NARRATOR: We see the Goldmann chart of both the right and left eye as described. An oval perimeter is compressed slightly in the nasal field, and the dark mark denoting the blind spot is just to the temporal side of the fixation point in both eyes.

MAYER: Let me show you an abnormal field from a child who's five, six years old.

NARRATOR: We see a Goldmann field plot that shows the perimeter of a visual field for the child's right and left eyes. The right boundary of both plots is sharply delineated by the vertical axis.

MAYER: This is a right field loss. So if you think about that normal field we saw, a nice oval. Now, what you're going to see now is a field that's completely absent on the child's right.

Right to the vertical meridian, we call that the vertical meridian. He has a beautiful field on his left, and it's the same with the left eye and the right eye. No seeing, no field, there's no circles plotted on the right side of the field plot, but lots of fields represented on the left.

And if you look at his binocular field, that is with both eyes open, you see he has a very extensive field on the left, and no field on the right. He has a right field loss we call right homonymous hemianopia, a complicated term meaning same in each eye. And he's a boy with a very severe field loss.

 

CHAPTER 6: Interpreting Automatic Static Perimetry Results

MAYER: Automatic static perimetry mostly tests the central 30 degrees. You can test farther out, but you really want to see what's happening in that central area because that's where optic nerve and retinal diseases occur. And what you'll see is several different circles like this on this page.

NARRATOR: We see the graphic depiction of results from a static perimetry test on a child with normal vision.

MAYER: It will show these round circles that represent different aspects of the analysis of the visual field. And probably, you can ignore all of them but the one that's usually on the right, and it's a density plot. And it's showing in just different blacknesses and whitenesses of light, how abnormal that field is.

So a normal field would show mostly very light dots, white dots with some variation. And you'll notice there'll also be a blind spot. And that will be a little dark area on this right eye field off to the right, and below the horizon. And that's a normal blind spot.

And that's really important to test, and, of course, it always gets tested. Then we look at a child who's having the same test, but has an abnormal field. And this is a boy about ten years old.

NARRATOR: Now we see the plot of a child with a vision abnormality and the results are interpreted.

MAYER: For his right eye — again, also the right eye — shows abnormality in the nasal portion. remember we talked about the nasal field and the temporal field that's on the left.

There are dark areas all along that rim, and that represents non-seeing. Where it's black, he doesn't see the target. Where it's gray, the target has to be quite bright for him. And where it's white off to the right in his temporal field, he's seeing it normally.

So he has what we call a nasal field constriction. And his plot shows good reliability and also not within normal limits. Beyond that, you have to go to the doctor and ask for more interpretation. In relationship to wherever his damage is, and his is in the retina.

 

CHAPTER 7: Developmental Implication of Visual Field Loss

MAYER: If I see a child who is at risk of having a field loss, and I measure that, and I come up with they do have a left-sided field loss or a quadrant of their field is missing, what implications does that have for the child and the parent? Well, there are lots of things to think about.

One thing is, of course, moving around. I said that peripheral vision is important for moving around. So if a person has a left field loss, they might bump into things on the left, not be able to judge distances and depth very well if they're going in that direction, or if they're reaching in that direction.

I see children who have cerebral palsy. And so they may have a hemapheresis on that side. They also have a field loss. Their hand is not used very well. Well, that hand is in the non-seeing field. So what I try to do is say well, what are the implications for daily life for all of the things at the developmental of that child. Where they are. Are they walking, are they reaching?

And I try to help — and teachers of the visually impaired are really important in this, and an orientation mobility specialist —to judge, "Well, how can we help the child, and the parent, and the teacher place things in the right place for the child, "give them an opportunity to have that non-seeing hand "over in their seeing field, "move things over so they can see things, let them move things if they want to?" That kind of thing.

NARRATOR: In a series of two photographs, a young boy is sitting with his neck supported while a purple ball inside a bright, yellow frame is introduced into his field of vision.

In the second photo, the ball is moved to the boy's right visual field, and his eyes look toward the ball.

MAYER: I want to say, again, reemphasize that getting a specialist who works with the child, an educator, who works with the child who is probably a teacher of the visually impaired, and specifically and importantly, an orientation mobility specialist is very important.

Those people will evaluate the child in their functional environment. I'm just measuring the field. And I see some of the things they might do or not do in a clinical setting, but nothing like how they go up and down stairs, how they you know, hit a ball when they're batting or catch a ball, how they ride a bicycle, if they're able to do that, or just simply walk around.

That has to be done and helped, the parents have to be helped in understanding the consequences of their field loss by these specialists.