A technique that relies on infrared scanning of the eyes has been developed to measure the severity of symptoms that people with multiple sclerosis suffer as a result of slight changes in their core body temperature.

It has long been known that some multiple sclerosis patients exhibit internuclear ophthalmoparesis, a condition where one eye moves more slowly than the other when body temperature is increased. Under normal conditions, eyes move at the same speed. There has not previously been a reliable way to measure the response or to gauge its severity.

Dr. Elliot M. Frohman (left) uses an infrared eye-tracking device to study symptoms associated with multiple sclerosis. Courtesy of the University of Texas Southwestern Medical Center.

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A research team led by Dr. Elliot M. Frohman at the University of Texas Southwestern Medical Center at Dallas used a head-mounted infrared eye-tracking device manufactured by SR Research Ltd. of Osgoode, Ontario, Canada. The setup painlessly tracked a test subject’s eye movements at a sampling rate of 500 Hz as the eyes followed a series of blinking LEDs positioned in front of them at a distance of about 100 cm.

The test subjects also wore a full body suit into which water was circulated to increase or decrease core body temperature by one-half of a degree. They also swallowed a pill-like thermometer to monitor their core temperature.

A total of 24 people were tested. Eight had multiple sclerosis accompanied by internuclear ophthalmoparesis, eight others had multiple sclerosis but did not suffer from the eye disorder, and the final test subjects were healthy controls.

In test subjects with internuclear ophthalmoparesis, researchers observed and measured the abnormal difference between the relative motions of the eyes as body temperature increased. Conversely, the synchronization of the eyes improved when body temperature cooled.

Details of the research were reported in the March 25 issue of Neurology.