ID MyHorse

Equine Immune-Mediated Keratitis (IMMK)

Have you ever had pinkeye? Do you remember how it itched and watered and looked awful? Pinkeye is inflammation of the lining of your eye, and the “white” of your eye. As painful and itchy as it is, it is not as severe as inflammation of the cornea.

Corneal Ulcer

Keratitis is inflammation of the cornea. The cornea consists of many layers. When inflammation or fluid invades the cornea, the layers are disrupted and the cornea becomes cloudy in appearance. If a defect appears on the cornea, that is an ulcer.

Kadeen’s Ongoing Struggle

As I wrote about in this blog, I have been struggling with Kadeen’s eyes. The veterinary ophthalmologist diagnosed Kadeen with equine Immune-Mediated Keratitis (IMMK) towards the end of last year. He had endured repeated episodes of corneal inflammation and ulceration.

Per the instructions of the ophthalmologist, he gets an anti-inflammatory ointment in both eyes on a daily basis. He was on a tapered schedule, and by mid-January, we were supposed to be able to taper it back again. Within a week of dropping the frequency, he had issues again. Therefore, I bumped it back to the previous schedule.


My fiance and I spent the last two weeks of January in beautiful Kauai, Hawaii. Unfortunately, we came home to a horse with a very painful, inflamed eye. My critter sitter had instructions to treat his eyes daily. After the fact, I learned his eye had been draining for a week.

I immediately scheduled an appointment with the ophthalmologist. However, by the time we were able to get there, his eye was ulcerated and showed evidence of neovascularization, or “new vessels”. That means that blood vessels had grown across his cornea as a result of the inflammation. That takes time…

We have a recheck in a few days. At that point, I will be over $450 in expenses (with a small vet discount included!) Of even greater concern is the fact that my horse has been suffering for over two weeks with a really painful eye. We may well be looking at an additional procedure (a lot more money) to get this under control. This is one of those times where my veterinary training is a liability. I know all of the things that can go wrong!

What are the signs of a horse with a painful eye?

Eye issues are an emergency. The first thing a horse owner might notice is a squinty horse with a partially or completely closed eye. Additionally, the eye may be red and watery or have a thick discharge. Possibly, the hair around the eye will be wet as a result of the increase in tear production.

While IMMK is not usually as painful as an ulcer, it does bother the horse. A horse with an itchy eye is going to do what? Rub it of course! And rubbing an itchy eye can create an ulcer on an already-compromised cornea. Watch for the other signs mentioned above, such as blood vessels creeping across the cornea. A horse with a painful eye is, in my opinion, fairly obvious. They are very uncomfortable!

What causes IMMK?

Veterinarians and researchers do not fully understand what causes IMMK. It might be related to the herpes virus. An over-reactive immune system is thought to be part of the problem.

It doesn’t usually create ulcers (unless your horse loves to rub his itchy eyes on anything and everything!) Often, it is unilateral, or only affecting one eye. In Kadeen’s case, both eyes have had issues. In this article by Andrew Matthews and Brian Gilger, IMMK is defined as:

… a progressive or chronic (>3 months in duration) nonulcerative persisting or recurring corneal opacity with mild to moderate signs of cellular infiltrate, corneal vascularization, and corneal edema.

Usually, infection is not present in this disease. A peek under the microscope at the ophthalmologist’s office did not reveal any bacteria evident in Kadeen’s painful eye. However, secondary infection can occur. Usually, anti-inflammatory medication placed in the eye on a regular basis will manage this disease.

My optho vet prepared me for a long course of tapering/maintenance therapy for Kadeen. Having dealt with how bad this can get in a short period of time, I am totally fine with regular/daily therapy to keep it at bay! As I mentioned in the previous post about this, I have this type of fly mask on Kadeen. It makes it harder for him to rub his eyes!

Recently, I received a weekly electronic newsletter from One of the articles discussed “three questions to never ask online!” Don’t ask, “How do I fix this?” when related to something like a horse bucking when asked to lope off. Don’t ask, “What bit should I use?” when there are so many variables involved in that decision. Lastly, don’t ask, “What do I do about this medical problem?” Call your vet if you have any concerns about your horse’s health!

In summary, eye issues are an emergency!

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4 thoughts on “Equine Immune-Mediated Keratitis (IMMK)”

  1. Hanna Leppimäki


    Do you still have the immk horse? If yes, I’d like to hear more of your story. Actully many would, so maybe you could tell it in Fb group IMMK?

    1. Hanna, I responded to you once before, but the site was having major issues and I believe the comment was lost? Anyway… YES, I still have the gelding, and he’s doing great. I figured out, WAY later than I should have, that his primary issue was the fact that I was utilizing a Hay Hut. Prior to building my barndominium, I had fed him twice a day using square bales. The round bale inside a Hay Hut was creating MAJOR allergy issues for him. Once I quit using that, he’s never looked back. I would be happy to post something on the IMMK FB group. Also, I wanted to let you know that ID MyHorse is collaborating with Horse Habit TV to produce a new podcast. One of our first guests is an ophthamologist at CSU, and she will be addressing equine eye issues. So watch for that!

  2. My horse has IMMK, after an eye injury the ophthalmologist at the emergency hospital was able to identify the cloudiness in her eye. A blessing in disguise maybe? However last year I also found out she has head shaking syndrome, we are thinking from an over reactive immune system. There isn’t a lot of research into this syndrome yet. We did allergy test and there’s a lot of allergies we are treating with shots. She flares up with the head shaking in summer (she is allergic to every insect) plus other grasses. I believe it all to be connected, her IMMK, head shaking syndrome and the allergies. I now have to be patient in a year and hope it all works.

    1. Wow, you have a lot going on with your horse! Kudos for all of the follow-through you are doing. I totally agree with you that immune-mediated issues go hand-in-hand with “allergies”. Allergic reactions are a wound-up immune system. I think my gelding’s eye issues were more related to a “standard” allergic response than they were/are to an eye-specific overzealous immune response. He still has a dry, allergic cough related to dusty hay, but we have had NO eye issues whatsoever once I got his head out of that hay hut. Good luck with your horse! And good luck with your patience factor! I am chomping at the bit to get back on my wounded guy… it can be hard to be patient!

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