|Uhtoff's phenomenon = Uthoff's phenomenon refers to visual problems
that occur in persons with MS that are brought on during periods of increased
body temperature. The usual history is of "black spots" appearing in the
visual fields of one or both eyes while the person is exercising, in the
sauna, taking a hot shower, or having a fever. This phenomenon is felt
to reflect areas of impaired but still functioning myelin that breaks down
in transmitting electrical impulses when the surrounding fluid heats up.