There should be several inches of room between the top of your head and the cap to allow air circulation so sweat can evaporate, thus cooling the head. Tight-fitting caps are a bad idea, because they increase heating. Regular exposure to UV radiation leads to cataracts and other eye disorders. Fishers are at higher risk because water reflects UV rays, providing a double threat. Polarized sunglasses help reduce glare.
Glare is the kind of thing that causes cataracts and retinal aging.
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