Diagnostic Eye Scan Technique Developed for Multiple Sclerosis

A five-minute eye exam might prove to be an inexpensive and effective way to measure and track the debilitating neurologic disease multiple sclerosis (MS), potentially complementing costly magnetic resonance imaging (MRI) to detect brain shrinkage--a characteristic of the disease's progression.

A Johns Hopkins University- (Baltimore, MD, USA)-based study of a group of 40 MS patients used a process called optical coherence tomography (OCT) to scan the layers of nerve fibers of the retina in the back of the eye, which comprise the optic nerve. The process, which uses a desktop device similar to a slit-lamp, is simple and painless. The retinal nerve fiber layer is the one area 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 a variety of different types of tissue processes in the brain.

Results of the scans were calibrated using accepted norms for retinal fiber thickness and then compared to an MRI of each of the patient's brains--also calibrated using accepted norms. Investigators found a correlation coefficient of 0.46, after accounting for age differences. Correlation coefficients represent how closely two variables are related--in this case MRI of the brain and OCT scans. In a subset of patients with relapsing remitting MS, the most common form of the disease, the correlation coefficient jumped to 0.69, suggesting an even stronger association between the retinal measurement and brain atrophy.

"This is an encouraging result,” said Johns Hopkins neurologist Peter Calabresi, M.D., lead author of the study, which appears in the October 2007 issue of the journal Neurology. "MRI is an imperfect tool that measures the result of many types of tissue loss rather than specifically nerve damage itself. With OCT we can see exactly how healthy these nerves are, potentially in advance of other symptoms.”

In addition, according to Dr. Calabresi, OCT scans take about one-tenth as long and cost one-tenth as much as an MRI scan, which means they are faster and less expensive to use in studies that monitor the effectiveness of new treatments for MS.

MRI of the brain, which can measure total volume, has long been the primary tool used to monitor MS. But MRI scanning, aside from being expensive and uncomfortable, is often misleading since brain inflammation--also a symptom of the disease--can distort brain volume readings. Furthermore, the brain begins shrinking relatively late in the progression of the disease, so MRI is not as effective at detecting the disease in its early stages when treatments are most effective. OCT scans look directly at the thickness, and therefore, health, of the optic nerve, which is affected early on in the disease, frequently before the patient suffers permanent brain damage.

In the study, researchers recruited 40 patients from the Johns Hopkins MS clinic. Twenty had relapsing remitting MS, 15 had secondary progressive MS, and five had primary progressive MS. Researchers also recruited 15 healthy control patients free from ophthalmologic or neurologic disease as a comparison group.


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