Uhthoff sign

[ōōthŏf]
n.
  1. An indication of multiple sclerosis in which vasodilation from exposure to heat or from exertion may cause transient visual impairment or weakness.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.