Research has been done that links the night-blindness gene to a particular gene that causes few spots and snowcaps in appaloosas...100% of them are affected by night-blindness (although I guess it can be to varying degrees). Other horses can be affected as well, there just happens to be a link to these two coat patterns. Basically they can not see in dim light.
My horse is not a homozygous snowcap appy, because his mama is a palomino and not an appy, so it isn't the appy coat pattern gene that would indicate his nightblindness....BUT he has shown other behavior to make me wonder.
Sometimes he puts his head really low, turns his head to the side, and twists his eye to look up at the sky or barn roof....very strange! I have never seen another horse do this. Has anyone else?