A symptom of multiple sclerosis (MS) in which a person’s vision becomes blurred when the body gets overheated from hot weather, exercise, fever or saunas and hot tubs. It is thought to be a residual symptom of optic neuritis, even if the person was unaware that they ever had optic neuritis.
This is an example of a pseudoexacerbation, rather than a relapse, because vision returns to normal after body temperature returns to normal. No permanent damage is done.
The term also is occasionally used to refer to temporary worsening of other MS symptoms due to heat, such as numbness, tingling or weakness.