Hemianopsia is one of the neurological disorders that show us to what extent vision is a process of complex functioning . We normally believe that what we see enters the eyes in the form of light and is represented in the brain as a unit, after our nervous system has taken charge of unifying the information received in “raw” format.
However, the sense of sight is working from a process that is not limited to collecting data and joining them together, but has a much more active role than it seems: it composes images that are not really equal to what the eyes capture.
In fact, the simple fact of having a pair of these sensory organs already makes this necessarily so, and hemianopsia helps us to understand this . Let’s look at it.
What is hemianopsia?
As far as we know, vision is one of the most important senses we have, but it is also true that it can fail in many different ways. Hemianopsia is one of them.
As its name suggests, hemianopsia has to do with the hemispheres, or rather, the hemicorbs, which are the sides of our body divided by a vertical axis (i.e., the left or right sides) as far as our nervous system is concerned. Specifically, hemianopsia is blindness in relation to one side of the visual field .
In other words, it is not that we do not see out of one eye and as a consequence our visual field narrows in the horizontal sense when one of its sides is reduced; it is that in one of the two eyes, or in both, one of the two halves of the visual field has ceased to exist
Hemianopsia may seem unusual and not as easy to understand as conventional blindness, but it is actually a neurological disease that affects vision. Therefore, all of its associated symptoms have to do with this kind of problem: orientation problems, confusion due to not finding a space, person or object , feeling of not knowing where you are, etc.
It is also possible that these symptoms are mixed with those of the accident or illness that has caused the hemianopsia, which as we shall see can be caused by very varied phenomena.
However, these symptoms also depend on the type of hemianopsia in question, as this disorder appears in different ways.
The main types of hemianopsia obey a first fundamental classification: unilateral and bilateral hemianopsia . In the first case, the alteration only affects one of the eyes, while in the second, it manifests itself in vision that depends on both eyes.
In turn, bilateral hemianopsia can be homonymous, if the affected side in both eyes is the same, or heteronymous , if in each eye the affected side is different: in one it affects the right, and in the other, the left.
Normally, hemianopsia is caused by injuries from trauma, stroke and tumors , all of which structurally affect the nervous system.
However, in some cases it may be due to transitory phenomena such as substance abuse or migraines with aura, which may generate temporary hemianopsies with very rapid remission of symptoms.
The parts of the nervous system that are usually behind hemianopsia are the optic chiasm or the last sections of the optic pathways on their way to the thalamus: the optic bands.
Difference with heminegligence
It is possible to confuse hemianopsia with heminegligence, a neurological disorder that also has to do with hemicorbs.
The main difference between the two is that in heminegligence, not only vision is affected , but also the experimentation of all the senses.
The second important difference is that in heminegligence the problem is not technically in the vision itself, but rather in the attention. The sensory data reach the brain , but are not processed as if they were relevant: they are “discarded”. For this reason, it has been seen that there is a kind of very meagre notion of what happens in the brain that is ignored, even though this information does not pass to the consciousness and the person believes that he or she has not noticed anything, as has been seen in experiments.
In the case of transitory hemianopsia, the intervention is limited to ensuring the well-being of the person until the effects wear off. The treatments aimed at intervening in non-transitory hemianopsia are of the neurological rehabilitation type , assuming that full recovery is unlikely to occur.
- Adel K. Afifi. (2006). Functional neuroanatomy: text and atlas. Mexico City: McGraw Hill p. 324.
- Caramazza, A.; Hillis, A. E. (1990). “Spatial representation of words in the brain implied by studies of a unilateral neglect patient”. Nature (Letter). 346 (346): pp. 267 – 269.
- O’Neill, E., O’Connor, J., Brady, J., Reid, I., and Logan, P. (2011). “Prism Therapy and Visual Rehabilitation in Homonymous Visual Field Loss. Optometry and Vision Science, Vol. 88(2).