The eyes can still see after a stroke, but the damaged brain cannot interpret visual signals. A personalized rehabilitation could achieve vision recovery.
Scientists in the UK have found that after a stroke there are areas of the brain that can still see, which will help design personalized rehabilitation programs for stroke survivors.
A stroke occurs when blood flow to part of the brain stops. Strokes are one of the leading causes of death and disability worldwide.
Visual field loss is a common and devastating complication of stroke. This type of vision loss affects one side of a person’s vision and is caused by damage to the visual pathway in the brain.
Currently, there is no unanimity about the possibilities of rehabilitating vision after a stroke, so what the new research has discovered is of significant importance.
The authors of this research used magnetic resonance imaging (MRI) to map the brain’s responses to visual stimuli after stroke.
They found that in stroke survivors with vision loss, light-sensitive neural areas survive that are not detected by current vision tests.
Visual field loss after stroke is usually diagnosed using perimetry, a technique that uses bright lights of varying size and brightness to assess a patient’s visual response.
However, perimetry only provides a rough map of residual visual function and cannot identify neural pathways that do not process visual information.
The authors of the new research combined detailed perimetry and multiple additional brain imaging data sets to map the affected visual pathways in the brain in four stroke survivors.
By measuring responses in the brain to visual stimuli with the new technique, they were able to observe the visual field of stroke survivors much more precisely, compared to perimetry.
When they overlaid their visual field maps with perimetry maps, they were able to see points in the visual field that still elicited a response from the brain.
“By examining different types of brain scans, we can see areas of ‘residual vision,’ places where the eyes and brain can still process images, even if this doesn’t reach consciousness,” explains Denis Schluppeck, lead author of the study, in a statement.
Eyes that see, brain that does not feel
The researchers explain that a common misconception with stroke-related vision loss is that it affects vision through a particular eye.
However, what actually happens is very different: the eyes continue to see, but the brain cannot process some of the visual information, so the person is not aware of all that they are seeing.
By using MRI to identify these areas of functional vision, doctors will be able to work with the stroke survivor and train them to regain some function in that particular location, the researchers say.
Rehabilitation strategies for vision loss in stroke consist of strengthening existing visual pathways or creating alternative pathways in the brain.
The combination of brain imaging and optometric testing provides a practical way to understand which areas of the brain to target for rehabilitation. The researchers note that their MRI protocol takes only an hour to perform.
In the future, the researchers plan to use what they have learned to understand other forms of vision loss.
Linking Multi-Modal MRI to Clinical Measures of Visual Field Loss After Stroke. Anthony Beh et al. Front. Neurosci., 05 January 2022.DOI:https://doi.org/10.3389/fnins.2021.737215