I'm not sure what you mean about the Guardian mask not working for you but I know it's spendy and that doesn't work for me! haha
If you think your mare has uvietis, you MUST get her a UV blocking flymask. Must. No ifs, ands, or buts. Must.
My mare has uvietis and was left untreated for years. Now she's living out her golden years as a mostly blind horse. She's happy but i wish her past owners had seen the signs, gotten her diagnosed, and helped her keep her vision.
This is a subject super close to my heart so hopefully I don't come off as harsh.
Cashel masks, the Guardian, and Kensington masks (I like the "Bug Eye" - that might be what Hemms is referencing: Kensington Web Bug Eye Fly Mask - Statelinetack.com
) are the masks on the market with UV protection.
Cashel and Kensington only have 70-something% UV protection and I've found that my girl will experience pain on the sunniest summer days if that's all she wears. They're fine for sunset/nighttime/morning/fall-winter but not for late spring and summer.
To deal with that, I made my own masks. I found UV blocking flymask material at a fabric store, deconstructed a flymask I didn't care about and liked the silhouette of as the pattern, and whipped out a couple flymasks. I was able to find 90% UV blocking "cloth" so these masks came out 90% UV blocking, which is only 10% or so less that The Guardian and for so much cheaper. Each of the masks I made probably cost $15 total.
So far they've been great. She's much more comfortable in them during the summer and her pain levels are dramatically decreased.
As far as seeing out of them, since they are really tightly woven mesh, that it not an issue. If you stick your head into one (I wondered too), it's darker - like you're wearing dark sunglasses, but you can still easily see. The coolest part is that the mesh is so tight that rain, mud, wind, etc, can't penetrate it so, since those things are triggers for some horses with ERU, all triggers=zapped.
Making a professional looking flymask was way easier than I thought. I was worried because you always see homemade flymasks that look......not great. However, I think that might be because they aren't using a good pattern or something because all of mine have come out fantastically!
I can post a picture if you would like. :)