Heat-Related Internuclear Ophthalmoparesis Monitors Multiple Sclerosis Therapies

Monitoring internuclear ophthalmoparesis (INO) in a clinical setting could provide a sensitive test to determine a patient's susceptibility to other heat-related multiple sclerosis (MS) symptoms, as well as a way to monitor the effectiveness of treatments.

Scientists studied an aspect of MS called Uhthoff's phenomenon, named for the German ophthalmologist who reported in 1889 that some people have temporary vision problems after exercise or in hot weather. This and other symptoms of MS, such as fatigue or problems with coordination, worsen in the heat for most people with the disease.

A bodysuit that heats or cools a patient, combined with painless measurements of eye movements, provided multiple sclerosis investigators from University of Texas (UT) Southwestern Medical Center (Dallas, TX, USA) with a new tool to study the link between body temperature and severity of MS symptoms. The study demonstrated that as body temperature rises, the severity of INO also increases. Normally, eyes move at the same speed, but when a person with INO looks rapidly from one object to another, one eye moves more slowly than the other does eye does. The study was reported in the March 25, 2008 edition of the journal Neurology.

The scientists used a whole-body suit, riddled with tubes for circulation of water that can change body temperature; a pill-like thermometer that measures core body temperature after being swallowed; and an infrared camera that painlessly tracks eye movements. The subjects wore a lightweight device, fitted on a headband that used infrared light to track their eye movements as they followed a random sequence of blinking lights.

In the subjects with INO, increasing the body temperature worsened the differences between their two eyes' relative motion. Conversely, cooling the body made the eyes synchronize better. "With this new technique, we can objectively test new therapies that specifically treat a host of MS-related symptoms,” said Dr. Frohman, professor of neurology and ophthalmology, director of the Multiple Sclerosis Program and Multiple Sclerosis Clinical Center at UT Southwestern and senior author of the study.

The next step, according to Dr. Frohman, is to use this system to measure the effectiveness of a drug that appears to relieve heat-induced symptoms in people with MS.


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University of Texas Southwestern Medical Center