Scans Predict Future Visual Health

Photo: Brown male eye

A new imaging technique helps
analysing a disease of the eyes
often going along with MS; © SXC

The condition occurs most often as a result of Multiple Sclerosis (MS). "We see this as part of a battery of tests we hope to give patients within the next decade to help our clinical assessment and tailor it to an optimal treatment," says lead author Robert T. Naismith. "It may also help further refine our basic understanding of MS in terms of expanding our insights into where and how damage occurs and why it can affect patients differently."

Regular MRI scans can detect optic neuritis but offer no information on its severity and potential lasting consequences for a patient's vision. Currently in use clinically to detect and follow up on strokes, DTI uses a rapid series of MRI scans to track water diffusion in tissue. Noting that inflammation and the cell damage it causes would likely alter water diffusion in the affected tissues, the scientists hypothesised that this information might allow them to assess the severity and potential for lasting damage of MS flare-ups.

For the study, researchers used DTI to image the optic nerves of twelve healthy volunteers, twelve patients who had begun to suffer from optic neuritis within the past month and 28 patients with a history of earlier outbreaks. They gave participants with optic neuritis or a history of it detailed assessments of their visual health.

In the healthy subjects, DTI scans showed that the water diffusion along the length of the subjects' optic nerves, a characteristic known as axial diffusivity, averaged about 1.66 micrometers squared per millisecond. In three patients with acute optic neuritis, those levels went down as much as 0.45 micrometers squared per millisecond.

"As the inflammation breaks down the structure of the axons or branches of the optic nerves, the normal water diffusion in this direction is impeded," Naismith explains. "After several months, though, the debris is cleared away, and this value and another characteristic known as radial diffusivity then start to increase."

In acute patients, the initial decrease in axial diffusivity correlated with decreased sensitivity to visual contrast one month and three months later. In patients with a history of optic neuritis, the increase in radial diffusivity was a good predictor of lower scores on several tests of visual health.; Source: Washington University in St. Louis