Abstract

The ability to discriminate closely separated pairs of light flashes as being double is impaired in multiple sclerosis. The effects of altering body temperature on double flash resolution and on visual acuity were studied in four multiple sclerosis patients and in control subjects. At demyelinated sites heating impaired and cooling improved double flash resolution. Visual acuity behaved similarly. The double flash test was very sensitive, changing up to 75 ms in response to simple heating and cooling procedures that produced small variations in acuity. Apart from its diagnostic value, the double flash test furnishes a simple in vivo model to study the effect of temperature change (and potential symptomatic therapy) on conduction in partially demyelinated axons in the visual system.