Sudden blindness in my 16mth old husky

Hi all my pup went blind literally overnight , with. No warning or reason , vet can’t find anything wrong with his eyes /retinas etc and all his bloods are clear , he is still his usual happy mischievous self and at times seems to be able to see something but mainly his eyes are just fixed and dilated and he is using his sense of smell and hearing , has anyone else had this happen where there is no case of glacoma or cataracts etc and no head trauma , thanks in advance
Donna xx