Unfortunately, big dogs do not always make very good "Little" Angels. The halo needs to be light weight for the dog's comfort. (Plus, I have to be able to bend whatever material is used for it.) A very large halo flops and sags. The "E" measurement (side of neck to nose) is what determines the halo diameter. Even though your dog may be considered medium size, an "E" measurement of 10" or 11" is large for a halo. Over 12" rarely ever works.
Also, a large halo will wipe everything off a coffee table or bookshelf. In addition, the halo can lasso other dogs.
Instead, I would suggest that you consider the Mesh Eyewear (http://angelvest.homestead.com/mesheyewear.html). It seems much more comfortable and safer than Doggles (goggles for dogs) and will protect the eyes from things that might scratch.
If you really want to try it, I can make the vest in a heavy, stiff fabric (when available) for better support. If it doesn't work you may return it for a $15 refund, if requested within 30 days of receiving the vest.