What is Moon Blindness in Horses?

SARAH: "I have an Appaloosa-Paint mix, and my farrier once mentioned to me to be careful about moon blindness. What is it, what breeds does it affect, what can be done to prevent it, and once it's contracted, what are the treatment options? Since my horse is a mix, is he less likely to contract moon blindness?"

DR LYDIA GRAY: There were like 12 questions in there.

SARAH: There were. I'll try to keep us on track.

DR LYDIA GRAY: So, moon blindness is what maybe the lay person would call it. A vet might use the term Equine Recurrent Uveitis or even Periodic Opthalmia. Those words give it away. So 'Equine Recurrent' means it comes and goes, it happens - it's chronic. And then 'uveitis' is inflammation - or 'itis' - of the uvea. And the uvea is internal eye structures.

It looks like a tearing eye, squinting, cloudy. Even the white part is red. That's how you notice it, so anytime you see that in your horse, that's an emergency. That's something you call your vet for. You do not put something in there that you have from last year or two years ago, because this treatment might include steroids. And in fact they say 'aggressive' anti-inflammatory agents - the FDA-approved medications. If you put a steroid in an eye that is tearing and squinting and cloudy but it's because of a corneal ulcer, you're done. It's bad. So eyes are something you should always contact your vet about.

Moon blindness - she does have an Appaloosa cross. There is a - what do they say? Appaloosas are overrepresented when it comes to moon blindness. There probably is a genetic component to this. It's an auto-immune disease, and - what triggers it though? Why do they get it? Cause not every Appaloosa is going to have this. However, when an Appaloosa does get moon blindness, they tend to have those waxing and waning bouts of inflammation and eventually, they can go blind from it.

Prevention-wise, we don't know what you can do to prevent it. Because there is probably an association with leptospirosis, a bacteria, things that reduce your horse's chance of getting infected with that like removing standing water would be helpful. Really, it's close observation of your horse. Use of a fly mask to protect the eye both before they have this and after really, and also to keep the sun away from them, is good.

Treatment is - like I said - aggressive anti-inflammatories, both intravenous, orally so you'll feed them, right in the eye. Might be something like Atropine, which dilates the eye, which means your fly mask is really important, because if their eye is artificially dilated, they can't close it to sun. It's painful then - the sun - so you need to put something that darkens it.

It's really, though, observation. Some of these horses, historically let's say, they will live on something like aspirin. So it's a mild anti-inflammatory, because sometimes you can't see even, the inflammation. But it's happening, and every time there's a bout of inflammation in the eye, it worsens and worsens and worsens which is what leads to blindness. It builds up and builds up over time and then you have a problem. These horses sometimes - and this is going to sound terrible - the eye is so painful that they will take it out. It's called enucleation. It's a pretty straightforward operation, but then you have a one-eyed horse, and so it doesn't look great and then you have to worry about him getting around, so it really makes sense to try and prevent this or watch for those bouts and manage them as best you can.

SARAH: Have you ever known in your barn a one-eyed horse?

DR LYDIA GRAY: Yeah.

SARAH: Yeah. They're very sweet, like they're very trusting.

DR LYDIA GRAY: And they actually do quite well.

SARAH: Yeah. They relate to people really well and they like to have their socket itched.

DR LYDIA GRAY: And they tend to have a buddy horse.

SARAH: Yeah.

DR LYDIA GRAY: There is usually another animal - sometimes a horse, sometimes it's something else - that takes care of them.

SARAH: Which is really sweet.

DR LYDIA GRAY: Yeah.