The retinal nerve fiber layer is the one part of the brain where nerve cells are not covered with the fat and protein sheathing called myelin, making this assessment specific for nerve damage as opposed to brain MRI changes, which reflect an array of different types of tissue processes in the brain.

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This is done by examining the combined concentration of gray and white matter, or nerve cells and fiber tracts, in parts of the brain not normally used for verbal processing the hippocampus and cerebellum, normally associated with memory and motor learning.

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