When you become dehydrated from perspiration and strenuous activity, it tends to affect the eyes long before other body systems. Dehydrated eyes produce less tears and the all-important and protective tear film, which is critical to vision, quickly becomes under-moisturized.
As a result of not enough water, the salt concentration in the tear film increases proportionately, causing burning, discomfort, fatigue, etc. Too little moisture and too much salt in the tear film can very quickly begin to cause ulceration of the protective membrane over the cornea. If nothing is done about it, this can eventually lead to permanent eye damage and even blindness.
The good news is that beginning corneal ulcerations usually heal quickly once the tear film’s water/salt balance is restored. Still, it is wise not to take changes or let it go too long.
Solar glare, snow glare, wind, pollution and UV radiation can also cause tear film moisture loss, thereby increasing salt concentration.
Now you might ask, if the tear film is made up of salt, water and oil, and perspiration is also made up of salt, water and oil, why is to so uncomfortable to get sweat in your eyes? The answer is that perspiration contains far too much salt. Just a little perspiration in the eyes can cause the tear film to start eating into the cornea’s protective membrane.
Suggestions: Wear your sunglasses or goggles, wear your headband and if you can, drink lots of water before and after your activity, AND … carry a pure-water eye mist moisturizer that, when applied to the eyes, will instantly restore the tear film’s water-to-salt ratio.