Equine Fungal Ulcers
written by: Dr. Kaylyn Andrews
2020-2021 PSEH Hospital Intern
What are fungi, and how do they affect me?
Fungi are normal microorganisms that live in a horse’s everyday environment, including in hay, grasses, shavings, straw, and dust. A normal horse can have bacteria and fungi living on its cornea and conjunctiva. 95% of horses living in Florida have fungi living on the surface of their eyes. These fungi do not routinely cause a problem until injury of the cornea occurs. This can lead to a fungal ulcer, also known as keratomycosis.
How do I know if my horse has an ulcer?
Signs to look for are squinting, discharge, redness, a “blue eye” or corneal edema, and pigment (yellow or brown) of the cornea. If you notice any of these signs, you should contact your equine veterinarian as soon as you can as early diagnosis of ulceration is key for a successful outcome. Initially, your equine veterinarian will apply fluorescein stain to the cornea to identify any disrupted corneal epithelium, showing an ulcer as a bright green spot on the eye.
How do I know if my horse has a fungal ulcer?
If your horse has a corneal ulcer that is not responding to initial treatment with antibiotics and pain medication, your horse may have a concurrent fungal infection. To know for certain that an ulcer is infected with fungi or bacteria, a sample of the infected area should be taken for examination under a microscope. This is known as a corneal cytology. A culture and sensitivity from this sample will also help guide treatment, and once diagnosed, proper antifungals and antibiotics can be prescribed.
What can I expect for treatment?
Treatment is twofold, treating the fungi as well as the subsequent inflammatory response caused by the fungi inside the eye. Antifungals are generally prescribed for an extended period of time to completely kill all of the fungi. Long term treatment is important with treating keratomycosis because anti-fungal drugs used in horses usually slow the growth of fungi as opposed to killing them. In addition, antibiotic treatment is indicated as concurrent bacterial infections are common. Uveitis is the name for inflammation of the middle layer of the eye, and this inflammation is always found with fungal ulcers in horses. This is treated with systemic NSAIDs, like Banamine. Topical atropine is also used to help keep the pupil dilated and for its pain-relieving effects. Serum from your horse’s blood may be used if the ulcer becomes soft or “melty”, when enzymes from bacteria or the body’s immune system cause the cornea to breakdown. Applied topically to the eye, serum has anti-enzymatic effects, and other medications with the same effect may be initiated. In many cases, an SPL, or subpalpebral lavage, may be indicated due to the frequency of treatment. This tubing system is basically an “eye catheter” that allows medications to be given often without having to pry your horse’s eye open and give medications directly. You can expect these ulcers to take week to months to heal, and dedicated, aggressive treatment multiple times a day is necessary.
Are there other treatment options?
Surgery may also be recommended by your equine veterinarian. A conjunctival graft would help allow blood vessels to reach the affected area, promoting faster healing. This is done by taking a part of the tissue surrounding the eyeball and stitching it over the ulcer. More severe cases may require a corneal transplant. In this case, the affected cornea would be removed and replaced with healthy cornea from a donor horse.
What can I do at home to ensure the ideal conditions for healing?
An eye mask or fly mask should be used to help protect the eye from trauma and flies while it is healing. These masks will also help protect an SPL, as the “eye catheters” can be delicate and can cause damage themselves if not in place and properly maintained. Horses that want to rub the affected eye may need a mask with a hard cup that fits over the eye for protection. Making sure your horse’s routine is not too severely altered is also very important. Adequate exercise, whether by small paddock turn-out or handing walking, in addition to monitoring eating/drinking habits and manure output is essential for horses with ocular lesions. Any change in lifestyle can predispose a horse to colic and staying vigilant will help you know when to seek veterinary care earlier.
How will this affect my horse’s vision?
Without aggressive treatment, ulcerative keratomycosis can be a serious threat to a horse’s eyesight. Whether it be medical or surgical, aggressive treatment should result in a positive visual outcome. With this being said, treatment is a long process and scarring of the cornea may be noticeable. Complications of corneal ulcers include a decrease in vision, corneal scarring, uveitis, eye rupture, and corneal abscessation. In some cases that do not respond to treatment, enucleation may be the only option to alleviate your horse’s pain.
References
Brooks, D. E. “Fungal Ulcers in the Equine Eye.” The Horse, Nov. 2017.
Brooks, D. E. Ophthalmology For The Equine Practitioner. Teton New Media, 2007.
Gelatt, Kirk N. Essentials of Veterinary Ophthalmology. Wiley-Blackwell, 2008.
