Understanding field of vision: why does my child climb up to the slide, but then refuse to go down it?

Image: view looking down from the top of a grey slide onto the wood chip ground below.

In my last blog post, I talked about visual acuity, which is probably the most commonly recognised and used measure of vision. However, there are many other aspects of vision, besides visual acuity.

Visual field, or ‘field of vision’ is another very important aspect of a person’s visual profile. Visual field is described in the dictionary as: the entire area that a person is able to see when their eyes are fixed in one position. Where you are sitting right now, while reading this post on your computer, tablet, or phone, consider what other information is actually visible to you. While looking at the words on the screen, you are most likely aware of things to either side of you, and above and below you. Keeping your eyes on the words here, think about how far out to the sides you can see. You are probably aware of furniture within the room you are sitting in. If you are near a window, you will probably be aware of light from the window. If someone were to walk into the room you are in and approach you, you would notice them once they entered your field of vision.

For each eye, while looking straight ahead, we can perceive things out to around 100 degrees to our side, and about 60 degrees across the midline of our body. The below diagram attempts to illustrate this visual field

Image: on the left side is a bird's-eye view of a person, with a yellow arc illustrating a normal horizontal visual field for the left eye, extending from the eye, out to 100 degrees to their side (temporally) and 60 degrees across their body midline (nasally).  On the right side is the same bird's eye view of a person, with a blue arc illustrating the corresponding horizontal visual field for the right eye.

Of course, we usually use both our eyes together, so our binocular field of vision extends horizontally out to around 180 degrees, and we can see things within an approximate semi-circle, where straight ahead is the 90 degree point.

Image: a bird's-eye view of a person, with the yellow arc representing left visual field, combined with the blue arc representing right visual field.  The area where the two 'fields' overlap is coloured green.

In the above illustration, the area where the two ‘fields’ overlap is the area where we have binocular vision - we can see this area with both eyes, and it is by combining these two images that we are able to judge depths.

If you hold a finger out to each side and move it slowly behind you, you can get an approximate idea of the horizontal boundaries of your visual field, which should be similar to that pictured in the diagram.

Our vertical visual field extends around 60 degrees superiorly, and 70 degrees inferiorly

Image: a diagram of a person in profile with a grey arc showing their vertical visual field extending approximately 60 degrees superiorly, and 70 degrees vertically.

Various conditions can cause a reduction to our visual fields. One of the most common ones is glaucoma, which causes a gradual loss to our peripheral vision. The problem here is that, while our peripheral vision is very important to our visual function, most of us are surprisingly bad at noticing gradual loss of vision in this area. This is why having regular eye tests is so important, to check for changes indicative of glaucoma. Glaucoma can usually be managed successfully with eye drop medications, but if the vision has already been lost, we have no way of restoring it.

In people with cerebral visual impairment (CVI), we frequently find significant restrictions to visual fields. Many people with CVI have significant loss to their lower visual field. This causes a lot of problems for them because it is very difficult to get around safely when you can’t see in your lower field.

Here’s one example of why it’s difficult to get around safely when you can’t see things in your lower visual field. Below is an image taken in our building.

Image: Three tiled grey steps, leading down, in the foreground with contrasting edges and hand railings to each side, leading to a high contrast Braille mat. Beyond is a white wall with a clear glass door.

Now here is what it might look like if you have no lower field.

Image: the same image as previous, but with the lower half cropped, so the stairs are no longer visible.

With the lower field removed, we can no longer see the stairs or the Braille mat. We don’t know how many stairs there are, and we may not even realised that there are stairs if we are busy trying to get to the door.

For people with a lower field defect, getting up the stairs is easier. Let’s look at why that is.

Image: A grey tiled floor with a Braille mat, leading to three tiled grey steps, leading up, with contrasting edges and hand railings to each side.  There is another high contrast Braille mat at the top of the steps.

When we approach the steps from below, they appear in our upper visual field. Let’s see how it looks to someone with a lower field defect.

Image: the same image as previous, but with the lower half cropped.  The grey tiled floor is no longer visible, but the steps can be seen in the upper visual field.

From this direction, the steps are clearly visible and the person will be prepared for them.

Now consider it is a young child, or an adult with intellectual disability who is missing their lower field. They likely will not be able to articulate this issue to those who care for them. Parents and carers are left bewildered by the fact that the person gets up the stairs without issue, yet has so much difficulty going down the stairs, even the same stairs they climbed up! If you didn’t consider vision and understand visual field, this might seem like pretty confusing behaviour. Maybe you think the person is just being difficult. Or maybe you conclude that they just don’t like whatever is at the top of the stairs. Not an unreasonable conclusion.

A frequent report we hear from parents of children being assessed for CVI is that they will climb up the slide, but then either refuse to slide down, or will only come down head-first. Based on what we have previously discussed, does this behaviour seem a little less bewildering now?

Image: same as the first picture: view looking down from the top of a slide, but with the lower part of the image cropped, so you can no longer see the slide or where it leads to..

Once we understand that the issue is with the lower field, we can get help devising compensatory strategies. We even have specialised professionals who can help with this; they are called Orientation and Mobility Specialists.