Homonymous Hemianopia (New Vision in Absent Visual Field) Paper

This paper is a single case study, which means it follows one person. It is simply written and easy to follow. We have split our introduction into two parts, because it makes two very important points.

  • Part 1 Homonymous Hemianopia
  • Part 2 Unknown CVIs

Part 1 Homonymous Hemianopia

The patient, a girl, following a brain injury as a teenager, needed to have part of her left occipital lobe and part of her left posterior parietal lobe removed. The black area in the bottom right corner of Figure 1 (b) is an MRI image of the area that was removed.

The girl had a brain injury, and needed to have part of her left occipital lobe and part of her left posterior parietal lobe removed.The girl had a brain injury, and needed to have part of her left occipital lobe and part of her left posterior parietal lobe removed.

The occipital lobes are where the picture we see, in terms of colour, contrast and acuity, is created. Where a part of the occipital lobe is damaged, it can result in part of the picture being affected. The area of damage to the occipital lobe will affect the picture in the opposite corner, so for example the bottom left quarter of one occipital lobe will affect the top right quarter of the picture, as shown in the diagram.

Gordon N Dutton, Vision and the Brain, AFB Press, 2015

The girl had much of her left occipital lobe removed (the right occipital lobe remained intact), which affected the right side of the image her brain creates. Everything visually to the right, looking through both eyes, was absent. This absence of vision in a part of the visual field due to occipital lobe injury is called a hemianopia or homonymous hemianopia.

Homonymous is Greek meaning to be the same. This is because the visual field loss is the same from both eyes.

Hemianopia is also Greek:

  • hemi - meaning half
  • anopia - meaning without sight (or blindness)

Where a person has a homonymous hemianopia, it is generally not thought that vision can be restored in the area affected, for this girl the right side of her visual field.

Look at Figure 2. The first two diagrams are the results of visual field tests, taken in 2013. The dark brown crossed out areas show the visual field loss in both eyes, and it is clear that there is an almost complete absence of visual responses in the right visual field.

The two diagrams on the right of the page are the visual fields of the same girl, taken five years later in 2018 - just look at the difference! In five years, she has regained visual awareness across most of her right visual field - but how did she do it?

This case study explains that she used a different type of vision, a type of reflex vision, processed in a different part of the brain.

Reflex Vision

The world you see, is created by your brain, and is the combination of many separate processes all working in harmony and synchronicity - or should be! This way the visual world your brain creates is an accurate match for the world as you move through it. This point is further explained, briefly in our Newsletter (Issue 14), and in more detail in our Lessons and further detail in our What Is CVI? Sections.

Most vision is processed in parts of the cerebral cortex (see Lessons Level 1, The Brain), however reflex vision is processed deep in the centre of the brain, in an area called the thalamus.

Image of the side of the brain as it would be seen if cut through the middle from the forehead to the back (called a sagittal view), with the thalamus coloured pink, as indicated with the black arrow.Image of the side of the brain as it would be seen if cut through the middle from the forehead to the back (called a sagittal view), with the thalamus coloured pink, as indicated with the black arrow.

Reflex vision is designed to create a reflex, normally to do something very suddenly to protect yourself. For example, if a branch is hanging down from a tree you are walking under, that might strike you in the face, your reflex vision will make you blink, raise an arm to protect your face, or suddenly duck down, to protect you from physical harm.

Reflex vision is fast, and it is likely you would have reacted to the low hanging branch before you consciously saw it. Reflex vision comes from information through your eyes, but it does not contribute to the picture you see, it goes straight deep into the brain, and where necessary creates a quick reaction, or reflex. Reflex vision is triggered by movement, particularly fast movement from the sides.

There are different types of reflex vision, and some, including blindsight (explained below), are just that, a reflex...but not all.

There has been a comprehensive case study on a woman who, due to occipital lobe injury on both sides (bilaterally) could see none of the picture - essentially a double hemianopia affecting the whole visual field, yet she could see things, like her daughter's pony-tail swishing (for more information on this case study please review the Blindsight Newspaper Feature). What seemed to be happening was that the reflex vision, that typically just causes a reaction, was somehow finding its way into the conscious mind, so a woman who should be blind could see things (blindsight). The short film The Blind Woman Who Saw Rain explains this and is fascinating to watch. Where the reflex vision creates visual information the person is consciously and correctly aware of, like the blind woman who could see the swishing of her daughter's pony tail, this is called the Riddoch Phenomenon or Riddoch Syndrome.

Whilst Blindsight and the Riddoch Phenomenon have been well reported, there is not a great deal known about the other possible variants of blindsight, like this child who seems to have 'more than blindsight' but Riddoch Syndrome does not quite fit.

In a profoundly disabled child, severely affected by CVI, blindsight might evolve, so that the reflex, often with a startle or shock that a typical person experiences, is sort of de-sensitised, to allow a controlled response to movement, as one parent writes:

I know my child, registered blind due to CVI, has severely reduced visual attention. Without movement, everything outside of what they are looking at simply isn't there. As their looking and searching has improved over the last few years, I have noticed that the reaction to movement, particularly from the side, is less of a shock and more controlled. This is so useful for getting their attention in a calm way, to show different things to help their learning.

It could be that this child's primitive blindsight is evolving, to support a severely damaged visual system? Now, reported as less sensitive and shocking, it provides valuable visual support in an area the child is unable to see, broadening the child's access to their visual world.

The Paper

The girl in this paper had no vision on her right side. An expert suggested she might be able to regain some conscious awareness in her right visual field "through personal endeavour". She was "surprised that she had been able to accurately respond to [moving] stimuli in her right visual field, even though she felt she could not 'see' any image".

How could she see something she couldn't see?

With blindsight, hence the name:

  • Blind - unable to see
  • Sight - able to see

Reflex vision requires movement, so initially she practiced at home using head-nodding, and as explained in the paper, over time, used more and more opportunities to practice seeing in her right visual field, where she could not see. And the results are remarkable, look back at Figure 2 between the visual field tests performed in 2013 (on the left) and 2018 (on the right).

She did this - through personal endeavour!

Typically, people affected by hemianopia are not given the advice to try to re-gain conscious vision in their absent visual field, because there is little evidence to support this level of recovery. Many still think that it is not possible to see, where you cannot see - but this paper challenges that view:

This remarkable functional improvement supports the hypothesis that it is potentially possible for neuroplastic brain change to occur through focusing on the belief and expectation that things can change, while striving to gain greater conscious visual awareness, perhaps through modulating processes in the brain that control and facilitate change

Featured Paper

We believe there is a clear argument for more research, trials and case studies in approaches towards regaining conscious visual attention where vision is lost due to hemianopia.

Part 2 Unknown CVIs

We think this paper makes two really important separate points, the first, as explained above, is that there is enormous scope to regain visual awareness in an absent visual field due to hemianopia - that's big in itself, but there is an equally important second element to this case study.

This girl, in addition to the hemianopia, without knowing it for many years, was also affected by several other cerebral visual impairments. These unknown CVIs made her clumsy, and affected her confidence. Once she understood that she had further visual impairments, she no longer felt 'useless' and set to work trying to make the many changes needed in her world to both learn and be independent. This paper explains clearly and simply many exercises she trained herself in, simple exercises anyone affected could train themselves to do, in most places and at no cost, other than time and a lot of patience and motivation.

The overall conclusion of this case study is relevant to everyone affected by CVI. If empowered with the knowledge and understanding of their condition, and supported with the belief that they can make a difference themselves, then:

neuroplastic brain change can occur through simply the belief and expectation that things can change, if the patient has the desire to implement strategies, to bring about such change.

Featured Paper

Paper: Hemianopia and Features of Bálint Syndrome following Occipital Lobe Haemorrhage: Identification and Patient Understanding Have Aided Functional Improvement Years after Onset, McDowell N & Dutton G, Case reports in Ophthalmological Medicine, 25 March 2019

One final thought - the thalamus is not part of the cerebrum, it is in the centre of the brain, just above and closely connected to the midbrain (in the diagram below the cerebrum is coloured green, the pink and orange areas are the midbrain). Over the last thirty years the terminology around CVI has shifted from cortical blindness to cortical visual impairment to cerebral visual impairment (as explained in our Newsletter 17). Blindsight is in our view unquestionably a part of the complex profile that makes up cerebral visual impairments, so maybe it is a time for another new name? Maybe neurological visual impairments? But neuro is just about the nervous systems, although we know is more widely used. What word incorporates everything in the brain that can affect visual processing, which is potentially every part of the brain...BRAIN! Brain Related Impairments of Vision?


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