When fishing, condensation on our lenses can be a real pain to deal with. It occurs thanks to the temperature difference between our body and the surrounding air.
Condensation is not normally a problem when just strolling to the local pond. But if you have to hike in over a steep hill, or paddle hard it can really cause sunglasses to fog up.
Some sunglass designs trap a lot more condensation and steam than the others.
I have found the best way to reduce the chance of condensation forming, is to wear sunglasses that have a minimal frame. Such frames allow more airflow which helps clear away any moisture before it gets a chance to settle on our lenses. Preventing condensation is all about maximizing airflow between the face and lens.
Does anti-condensation coatings and sprays help?
Some sunglasses come with coatings that are supposed to reduce condensation. I honestly have not seen one that works.
The same applies to the aftermarket sprays and wipes, that are supposed to keep condensation away.