Why does my vision get blurry when I get hot? It happens a lot in the summer and it is so annoying! Is there anything I can do about it?
Blurry vision is a very common symptom in patients with multiple sclerosis. Blurry vision that is triggered by heat typically occurs in the eyes of patients who have had a prior episode of optic neuritis. This phenomenon was first described an ophthalmologist in the 19th century and is called Uhtoff's phenomenon, in his honor.
Typically patients who have had optic neuritis will have very good recovery of visual acuity in the affected eye. However, if the body gets overheated (for example after vigorous exercise or in the summer heat) the vision in the previously affected eye will temporarily get blurry. Once the body cools off (air conditioning, or drinking an ice cold beverage) the blurry vision resolves rapidly.
Uhtoff's phenomenon is not considered an MS relapse but is a reminder that the optic nerve has suffered prior injury from the multiple sclerosis. If both eyes have had optic neuritis in the past then both eyes may become blurry in the heat.
The best way to prevent Uhtoff's phenomenon is to stay cool and well hydrated. Some patients with MS are so sensitive to the heat that they wear ice pack vests (these are vests with pockets which can be stuffed with ice packs) when going outdoors in the summer.
If you do notice that your vision becomes blurry but does not return back to normal after your body has cooled off, you should consider contacting your neurologist or ophthalmologist (in particular if the blurry vision lasts > 24 hours).
Benjamin Osborne, MD
Departments of Neurology and Ophthalmology
Georgetown University Hospital
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