I know a lot of appy's have eye issues, particularly moon blindness. They are prone to flair ups and those can become painful. I would keep an eye on their eyes during the day because without appropriate care the uveitis they are talking about can lead to more painful conditions. The result of which is having the eye enucleated (removed).
Not to blow up your bubble on your horses bond with you. I am sure you both have a great relationship. That said, a lot of horses are less spooky and more trusting when they are loosing their vision. They have to trust their owners/riders because well really they have no other choice. Its part of the reason you can blindfold a scared horse and lead it somewhere. You can ride a blind horse for flat work but I would avoid jumping (that one I thought was obvious but I then I met someone who was really confused on that
I also know a few people who have guide horses for their blind horse. They put a bell on the companion and the blind horse can follow it around. Its sort of like a blind dog, you may not realize they have no vision until you move the furniture.