“What everyone wants to know is how quickly does this measurement change?” In the studies to date, patients have had their disease for about 8–10 years, and there is only about a 10-micrometer difference in RNFL thickness between MS patients and controls.
If RNFL thickness changes at a steady rate, this translates to about a micrometer per year—which falls within the margin of error. However, longitudinal data may show periods of more rapid progression and periods of relative stability, said Dr. Calabresi.
“What we're finding in OCT is that over a 2-year period, 10%-15% of people have stepwise declines of up to 10 micrometers … It's not that everyone is just losing a little bit. Some people will have subclinical attacks and not necessarily even know that they had an optic neuritis episode.”
Dr. Calabresi and his colleagues are currently working on a longitudinal study of about 1,000 patients that they've been tracking. The results are expected in the next year.
OCT is already showing promise in the clinical trial setting, where it could be used at frequent intervals to track the effectiveness of a drug on halting MS progression. The technique is being used in optic neuritis drug trials, and several companies are interested in using OCT as an assessment tool in MS trials.
Dr. Calabresi reported that he does not have any relevant conflicts of interest.
RNFL thickness map shows the right eye of an MS patient.
Areas of Red and yellow show areas of abnormality.
RNFL thickness (black line) for 0–360 degrees in right eye (top): Bottom image is a tomogram of the right eye's RNFL. Images courtesy Dr. Peter Calabresi