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Discover how Heatstroke and UV Radiation Affect Your Eyes and Your Body

Posted on June 8th, 2021

As we head into hot summer days and we’re spending more time outdoors, it’s important to be mindful of our body temperature. Heatstroke can have an effect on many parts of the body, including the eyes.

Hyperthermia, as it’s clinically called, is the most severe form of heat illness and it can be considered a life-threatening emergency. Permanent neurological deficits due to heatstroke are rare but can extend into months of psychological and physiological effects. At its simplest, a heatstroke happens when your body temperature hits 40 degrees Celsius.

Heatstroke symptoms are often treated like heat exhaustion, so it can be easy to confuse the two. The truth is that it’s much more than just feeling a bit lightheaded, sleepy and overheated after a day in hot weather.

How do you get heatstroke?

The most well-known cause is prolonged sun exposure, but excessive exercise (called exertional heat stroke), can also be a culprit. Exertional heatstroke is one of the three most common causes of death in athletes.  

It can also be caused by overexertion in a warm environment, meaning sweating it out in your living room during the winter months can trigger a heatstroke just as easily as a prolonged summer session beside a pool.

Hyperthermia is, however, much more common during the summer months, as it becomes harder to regulate body temperature. Usually, heatstroke in the summer is paired with dehydration as your body sweats to remain cool.

How does heatstroke affect your eyes and your body?

A heatstroke is dangerous as it can cause neurological impairment, and with the optic nerve so close to the brain, increased body heat has been proven to affect the ocular blood flow. This can cause both increases and decreases in blood pressure. Studies have proven that body temperatures over 43 degrees Celsius may cause cell death. More than 30 minutes of eye exposure to temperatures reaching 43 Celsius (retinal hyperthermia) showed a breakdown of the blood-retinal barrier in the eye.

The good news is that heatstroke has not been proven to necessarily cause permanent damage to the optic nerve and most effects of hyperthermia on the body fade quickly.

Heatstroke is directly linked to triggering Uhthoff’s phenomenon and downbeat nystagmus.

For patients with multiple sclerosis, heat sensitivity manifests as Uhthoff’s phenomenon. It occurs because of the damage to the optic nerve caused by MS during overheating or overexertion. Signals between the eyes and the brain are disrupted, and temporary loss of vision may occur.

Downbeat nystagmus is another occurrence (though rarer) that has been recorded due to heatstroke. A study in the Neurology, Neurosurgery & Psychiatry Journal found a link between symptoms of downbeat nystagmus and cerebellar damage, proving that some individuals may be susceptible to that kind of thermal injury.

UV radiation has a big impact on your eye health

Overall, it’s the surrounding circumstances associated with prolonged sun exposure that can have serious effects on your eye health. One of the immediate signs of heatstroke is temporary vision loss or blurry vision, but what does extended UV exposure do to your eyes?

UV radiation has the power to damage delicate eye tissues, such as the cornea and lens. Often, the damage is painless, leading to repeated prolonged sun exposure over months and years. A buildup of damage caused by the sun can have powerful effects on eye health. Many unpleasant eye diseases occur in older age groups, and there is a connection between serious eye diseases and cancers and years’ worth of sun damage.

5 eye health conditions associated with UV exposure

1. Photokeratitis: A painful eye condition akin to a sunburn on your eye that can occur if your eyes are exposed to ultraviolet rays without protection.

2. Pinguecula: A benign, yellowish, noncancerous growth that develops on the white of your eye. This is a slightly raised growth that can make your eye dry and itchy, often causing irritation.

3. Pterygium: A fleshy, growth that occurs only at the sides of the eye. This growth can spread to distort the cornea, causing decreased vision and a feeling of something in your eye.  

4. Cataracts: A well-known eye condition that slowly but progressively clouds the lens of the eye with a yellow or white hardening, resulting in blurry vision and in some cases, blindness.

5. Age-related macular degeneration: A leading cause of blindness in the west, this condition often begins later in life. Links to UV exposure and photochemical damage have been shown to speed up the damage done to the structures of the eye.

Eye health conditions associated with dehydration due to sun exposure

Heatstroke and prolonged sun exposure often go hand in hand with dehydration. Dry eyes caused by lack of water are just as irritating and damaging as dry eye caused by other medical conditions such as allergies, screen exposure or weather exposure. With eye dehydration, you can expect sensitivity to light, a feeling of something in your eyes, or a burning sensation. Without proper lubrication to the tear film and aqueous layer, the tear film may become deficient, resulting in pain and blurry vision.

How can you prevent heatstroke and UV damage?

Thankfully, preventing heat stroke and sun damage is easy to do. The CDC recommends making sure you step indoors or to a cool area often and schedule and plan outdoor activities with rest times and cool-off periods. Staying hydrated and avoiding hot and heavy meals is a great way to reduce temperatures internally. Finally, UV damage can be avoided by wearing protective gear, including sunscreen, hats, and UV eye protection, like sunglasses. These are key to avoiding serious sun damage-related diseases to both the skin and eyes.

Tip: Bring eye drops and a thermometer with you when you plan outdoor activities in hot weather. It’s simple to keep your eyes moisturized and it’s easier to gauge how someone is feeling by getting an accurate reading of their temperature!

Heatstroke symptoms

According to the Centers for Disease Control and Prevention, the warning symptoms and signs of heatstroke are:

  • Fever (over 40 degrees Celsius)
  • Blurred vision
  • Fast, strong pulse
  • Dry, flushed skin (can also be sweaty)
  • Altered mental state (disorientation, agitation, confusion)
  • Nausea and/or dizziness
  • Headache
  • Losing consciousness

What to do:

If you notice signs of heatstroke in yourself or someone else, move to a cool place, loosen your clothes and take a cool bath or place cold cloths on your body. If you have the option to reduce your body temperature, do so. Anything over 40 degrees Celsius is a warning sign of heatstroke.

If you are vomiting, or if the heatstroke symptoms haven’t improved in 30 to 60 minutes, call 911 and ask for further directions.

If you’ve had previous experiences with heat exhaustion, heatstroke, or if you often find yourself outside without proper UV eye protection, it’s time to talk to a doctor. Book an eye exam at one of your local FYidoctors locations today.