Traditionally, doctors use a tool, called the ophthalmoscope to look inside the eye for signs of disease or damage. For MS patients, the ophthalmoscope can be used to examine the optic nerve.
Peter Calabresi, M.D., Neurologist with Johns Hopkins Hospital, says a healthy optic nerve is typically bright yellow in color. Other colors, like pale white, are usually an indication of some amount of optic nerve damage.
While the ophthalmoscope exam may allow a physician to detect optic nerve disease, the tool isn’t sensitive enough to determine the degree of damage, or to detect minor changes over time in the health of the nerve fibers. Another tool, an MRI scan, can’t pick up damage in the small optic nerve fibers.
Calabresi is testing the use of another tool for MS patients. It’s called optical coherence tomography, or OCT. OCT works by focusing a beam of near-infrared light onto the back of the eye and measuring the intensity and position of the reflections as they bounce off the retina and optic nerve. Researchers have demonstrated a loss of thickness in the retinal nerve fiber layer in patients with a history of optic neuritis. Some degree of loss has also been found in MS patients without a history of optic neuritis, which suggests the damage occurs before patients begin experiencing any signs of a problem.
Currently, some ophthalmologists use OCT to follow patients with glaucoma. Use of the tool in neurology offices is under investigation and available only in a limited number of places. Calabresi says OCT may eventually be used to screen MS patients for early signs of optic nerve damage, follow those under treatment and to study the effects of new drugs on optic nerve health. However, he doesn’t see OCT as a replacement for MRIs. In fact, he hopes OCT scans will eventually be used in conjunction with MRI scans to provide more information about an MS patient’s overall health.