Last Updated on March 31, 2022 by Allison Price
Uveitis, a common cause for blindness in horses is still a mystery. It can also be difficult to treat in its recurrent forms. Although there is no cure, it does not necessarily mean that a horse will be permanently blind. A horse’s eyesight can be saved by careful management and treatment. Even if one eye is removed, many horses can continue to live normal lives and have successful competitive careers.Photo: Manbendu/AdobeStock
Uveitis refers to inflammation of the eye’s uveal tube, which is a layer of tissue between the outer layer of the eye (including the cornea) as well as its inner layer (the retina). It also includes the iris and ciliary bodies, and the choroid. It is delicate and can cause severe pain if it becomes inflamed.
Dr. Rana Bozorgmanesh, Hagyard Equines Medical Institute explained that the pupil contracts because of this. This causes a constricted pupil. “The ciliary muscles spasm and that can be quite painful. The blood capillaries in these areas become leaky and release proteins and cells. This is what we see.
These signs include squinting or tearing, light sensitivities, squinting or tearing, swollen eyes, or cloudiness or bluish haze. You might notice a bloodshot appearance to the white of your eye or pus or yellow deposits in the anterior chamber. There are subclinical cases, however, that may only show subtle symptoms.
Bozorgmanesh stated that you can have a smoldering form of uveitis without your knowledge. Tiny changes in the eyes may cause the eye to go blind. Many horse owners don’t realize the disease is present until their horse becomes blind. In other cases, you may see clinical signs during the active phase of the disease.
Causes for Uveitis
Uveitis may be a rare event, such as trauma to the eyes. This might not cause any problems in the future. Equine recurrent Uveitis (ERU), or moon blindness is a chronic, repeated form of uveitis that can cause permanent damage and eventual blindness. This is what horse owners are most concerned about.
Bozorgmanesh stated that “equine recurrent eyeitis is the most common cause of blindness in horses and it’s progressive.” It can vary depending on the horse’s breed and geographic location. However, the prevalence is generally between 2% to 25% in the United States. Bozorgmanesh stated that it is more common in appaloosa horses because they are genetically predisposed to the condition and can have as high as 25% prevalence. It is possible that German warmbloods could also be affected by this heritable condition. It’s more common in warmbloods, draft horses, and appaloosas than it is in quarter horses.Eye with chronic signs of uveitis, including discoloration of the iris and pupillary constriction.
Panuveitis is the most common form of uveitis in the United States. It tends to affect more the frontal part of the eyes. While posterior uveitis, which affects the back and retina of the eyes, is more common in Europe, it can also be seen in the United States.
Bozorgmanesh stated that people who bring warmbloods to the U.S. may see a different type uveitis.
ERU has existed for a long period of time.
Bozorgmanesh said that recurrent uveitis was once called “moon blindness”, a term that was first used in the 1600s. They noticed horses suffering from recurring eye problems or temporary blindness. They believed it was due to the phases of the moon at the time. It isn’t true, but it does show a waxing and waning.
Horse owners have known about the disease for centuries. However, it is still not well understood.
Bozorgmanesh stated that it is essentially an autoimmune disorder that has been linked to leptospirosis. However, this may not be true in all cases. It could also be due to the fact that we haven’t been able identify leptospirosis for every case. The exact cause of the disease is still unknown. It is possible that there is a genetic predisposition. For example, the coat pattern of the Appaloosa may be correlated. Genetic predisposition also affects immune system. If you have a particular type of immune response and are genetically predisposed to it, you may experience equine-recurrent uveitis if you receive a trigger like leptospirosis.
What to do if you suspect Uveitis
First, call your doctor immediately.
Bozorgmanesh stated that it is important to differentiate uveitis and recurrent uveitis. There is no single test that can determine if it’s ERU, or a single episode. Your veterinarian should first check for a primary cause. This could be an infection, eye ulcer, trauma, or any other reason that may have caused the horse’s uveitis. If there is a clear reason why your horse has developed uveitis, it will be better for both of you. It’s not uveitis that is the problem. This could lead to recurrent uveitis.
Horses with equine recurrent eye disease (equine uveitis) are likely to go blind as the condition progresses.
Bozorgmanesh stated that there are ways to slow down the process and that cases have been followed up on, they’ve had some success. “But unfortunately, there is no cure and most people will go blind over the long-term because of this. The prognosis is also worse if the ERU is leptospirosis-associated. Studies have shown that those who have leptospirosis-associated ERUs are more likely go blind.
There are many treatments that can slow down the progression of ERU.
Bozorgmanesh stated, “Even though it’s a rare case, you’ll still be treating the horse for many weeks.” “So be ready for that.”Eye with multiple signs of uveitis, including constriction of the pupil, deposits in the anterior chamber (beneath the cornea), as well as corneal abnormalities.
Photo: Courtesy of Dr. Rana Bozorgmanesh
and Dr. Nathan Slovis
The treatment goals are to control inflammation, reduce pain, minimize inflammatory mediators, and then re-establish the blood-ocular barrier. In other words, increase the leakage from blood vessels that release cells into the eye.
The most common treatment options are topical or systemic non-steroidal antiinflammatory drugs (like Banamine); anti-inflammatory corticosteroids; and medication to dilate the pupil. This will reduce pain. Your veterinarian might recommend a course of antibiotics for two to four weeks if there is concern about a horse suffering from leptospirosis.
The subpalpebral catheter, also known as a lavage catheter, can be used to make the treatment more efficient. A lavage system has a port at the base of the horse’s neck, which is attached to a tube that the veterinarian inserts into the horse’s eyelid. The user injects the medication through the port and then the medicine is transported through the tube to the eye. The downside is that the catheter cannot stay in horse’s eyes for long, but it can be kept in place for several weeks or months if necessary.
Bozorgmanesh stated that there are immuno-modulatory drugs you can use to suppress the immune response in the eye. “Hyperbolic cyclosporine is one of these medications, which can be used as an eye ointment.”
ERU cases can also be treated with cyclosporine (specifically cyclosporine A) via a sustained release device, which is a surgically implanted disk in the eye.
Bozorgmanesh stated that it is not always easy to inject medication into horses’ eyes. It depends on the horse. However, in these cases, you may be doing it as many as four times per day. It’s hard work and something that some horses don’t like. Their upper eyelid muscles can be some of the strongest in the world! If they don’t want it in their eyes, it won’t be possible. This work is eliminated by the implant.
Bozorgmanesh explained that implantation is a surgical procedure under general anesthesia. You want a healthy horse to do this. You must also make sure the eye is calm. If there is a severe flare-up, you cannot perform the surgery. The implant can be placed after the uveitis has subsided.
Bozorgmanesh stated that the implant can reduce the chance of uveitis recurrence in cases where it works. It has also been shown to reduce the duration and severity of each episode. It also improves the response time in patients who still need to be treated with topical medication.
Removal of vitreous humor is a surgical procedure that can be used to treat cases of posterior Uveitis, which is sometimes seen in horses from Europe. Bozorgmanesh stated that by removing the fluid, you are removing the immune mediators and the inflammatory debris that drive the immune response in this type of uveitis.
She said that the procedure was not designed to treat the more common panuveitis seen in the States.
Before you Treat
Bozorgmanesh warned that uveitis treatments such as corticosteroids can suppress the immune response of the eyes. It’s crucial to make sure that your horse is free from any infection or ulcers before starting treatment.
She said, “Otherwise, the treatment might make it 100 times worse.” Your vet should be checking your eye regularly, even if you’re using a steroid. It is important to know that your vet can check the eye for signs of an infection or a steroid reaction. If this happens, it is important to immediately stop using the steroid.
She said, “I always tell people to not just grab an eye ointment tube from your first-aid kit and then apply it to your horse’s eyes if they look painful.” “Different conditions require different medications.”
Removing an Affected eye
Horse owners may also want to consider taking out an eye that isn’t working.
Bozorgmanesh stated that there is no right or wrong in this situation. ERU can be painful for horses and is difficult for both horse and rider. It is important to decide if removing the eye is right for your horse and you. Each case is unique. If your horse is experiencing severe pain and you are unable to manage it, or if the medication doesn’t work as well as you would like, you might consider removing the eye.
Surgery to remove an eye does not necessarily mean the end of your horse’s activities or his competitive career. “Horses adapt very quickly,” Bozorgmanesh said. It’s nothing to fear. Many horses can live happy lives with one eye and still accomplish a lot. The benefits of living without pain for the vast majority of horses far outweigh any aesthetic advantages of having an infected eye.