, the team found that recovery of vision in patients with pituitary tumors is predicted by the integrity of myelin--the insulation that wraps around connections between neurons--in the optic nerves.
"Before the study, we weren't able to tell patients how much, if at all, they would recover their vision after surgery," explained David Paul, an M.D. candidate in the Department of Neurobiology and Anatomy, and first author of the study.
When pituitary tumors grow large, they can compress the optic chiasm, the intersection of the nerves that connect visual input from the eyes to the brain. Nerve compression can lead to vision loss, which usually improves after these tumors are surgically removed through the nose.
Paul and his colleagues used a technique called diffusion tensor imaging (DTI) to show how changes in a particular bundle of nerve fibers relate to vision changes in these patients.
"DTI measures how water spreads in tissue," explained Bradford Mahon, assistant professor in the Department Brain and Cognitive Sciences and the Department of Neurosurgery, and senior author of the study. "The myelin insulation normally prevents water from spreading within the nerves, which would cause the nerves to malfunction."
Paul describes myelin damage by analogy to an insulated copper cable. In the human brain, DTI can measure the "leakiness of the insulation," or how well myelin constrains the flow of water in brain tissue.