Tuesday, June 14, 2011

Can a Stroke Cause Blindness

A stroke can cause symptoms from hallucinations to complete blindness. These symptoms depend on where in the occipital lobe they occur.

When the stroke affects most of the occipital lobe on one side of the brain the result is called homonymous hemianopsia, the loss of half of the field of view on the same side in both eyes. This occurs frequently in stroke and brain injuries because of the connections and wiring of the wiring system in the brain.

Visual images on the right side travel from both eyes to the left side of the brain, while visual images on the left side in each eye travels to the right side of the brain. So damage to the right side of the posterior portion of the brain causes vision loss of the left viewing in both eyes. Damage to the left posterior brain causes a loss to the right field of vision.

Central vision is processed in the occipital pole in the brain. Central vision is what you see when you look straight ahead, the center of your vision.

A person affected in this area may have trouble looking straight in someone's face, they may not be able to see noses, upper lips, or the lower half of a person's eye on the affected side. They could however see the person's shoulder, and the top of their head on that side. These cases are rare, but when they do occur, they are referred to as, 'central visual defect'.

When the occipital lobes of the brain are completely affected by the brain it is called 'cortical blindness'. This is what we know as 'blindness', but doctors use this term to convey to each other the reason for the blindness stems from damage to the brain cortex.

People with cortical blindness also suffer sometimes from what is called visual Anosagnosia syndrome. This is a lack of awareness about a physical or mental impairment caused by damage to one or more parts of the brain. People with this anosagnosia are incapable of understanding that they have an impairment.

Other symptoms of occipital lobe stroke are visual illusions, visual hallucinations, visual agnosias, Balint syndrome which is the coming together of three symptoms because of a stroke at the border of the parietal and occipital lobes of the brain.

Symptoms of Balint syndrome are:

The inability to voluntarily look around in space.
  • Inability to grab an object while looking at it, due to an imbalance of eye and hand movements.
  • A tendency to only see one object in the visual field at one time.

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