As I sweltered in the newly tropical UK climate, I couldn’t help thinking about the impact of high temperatures upon eye health. I had more time to do this than usual, as a number of patients clearly felt it was just too hot to go for their eye check and failed to turn up.

When the weather is hotter than normally expected, the impact on the eyes can be varied and wide-ranging. Those struggling with the heat in general may find, as part of their general lethargy, a tendency to binocular decompensation. Ocular surface disorders, and in particular forms of allergic conjunctivitis, may be exacerbated while the reliance on fans to cool down may exacerbate existing dry eye problems.

In my recent review of pupil assessment, I mentioned a classic case of retrobulbar neuritis where the patient noticed their vision starting to go cloudy after having had a hot bath. Uhthoff’s phenomenon, or syndrome, was first described in 1890 by the German neuro-ophthalmologist after whom it was named and who observed how certain symptoms of multiple sclerosis (MS) worsened when the body’s temperature was raised. What he described as ‘difficulty seeing when somebody was exercising’ was eventually found to be an increased likelihood of optic neuritis when the body’s temperature is raised. Indeed, one of the wackier tests for MS introduced in the 1950s involved asking a patient to get into a hot bath to see how it affected their symptoms. Happily, things have moved on.

Alas, not in all areas. On the BBC news the other day, a serious scientist was asked what 40ºC was in Fahrenheit. She, obviously, did not know and I could not see why the question was asked, though I believe it is two gills, a furlong and three shekels.

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