Editor's Note: This article is part of TheHorse.com's ongoing coverage of topics presented at the 2012 American Association of Equine Practitioners' Focus on Ophthalmology conference, held Sept. 6-8 in Raleigh, N.C.
The equine eyelid might seem like an uncomplicated structure that simply opens and closes over the horse's eye, but there are a number of problems that can plague the anatomy. And what's more, these ailments are relatively common in horses.
At the 2012 American Association of Equine Practitioners' Focus on Ophthalmology conference, held Sept. 6-8 in Raleigh, N.C., Andrew Matthews, PhD, Dipl. ECEIM, hon Member ACVO, FRCVS, an equine practitioner and ophthalmologist from Ayrshire, Scotland, discussed the different disorders, diseases, and ailments of the equine eyelid.
"What you see doesn't always appear in the textbooks," he said, explaining why he wanted to show practitioners some of the uncommon disorders they might encounter in the field.
Matthews conducted a brief review of equine eyelid anatomy with the veterinary attendees before starting the discussion of eyelid problems with lacerations.
Eyelid Lacerations--Matthews said that although trauma and lacerations to the equine eyelid are common occurrences, they typically have positive healing potential as a result of the eyelid's good blood supply. If surgical repair is needed, he said, it can be carried out under standing, local anesthesia or general anesthesia, depending upon the severity of the wound. In other cases, surgical intervention isn't required and lacerations can be managed medically ("Horses can tolerate flapping upper lids as long as the cilia [eyelashes] don't contact the cornea," he noted).
If surgery is needed, Matthews said veterinarians will often delay wound closure for 12 to 24 hours to allow any associated swelling to subside.
Entropion and Ectropion--Entropion (inward rolling of the eyelids) rarely occurs in adult horses but is a common neonatal congenital abnormality, Matthews said. He stressed that it's important to fix this problem promptly to avoid permanent corneal scarring.
Conversely, ectropion (outward rolling of the eyelid) is a very rare condition that is usually always acquired, Matthews said. While this disorder can be surgically corrected, he warned that there is limited tissue to work with. Additionally, he noted, many ectropion cases are actually innocuous and no surgical or medical intervention is required.
Eyelid Coloboma--This uncommon disorder--in which the horse is "missing" a section of eyelid--can occur on the upper or lower lids, Matthews said, often in the middle of the eyelid. In most cases, there is little cause for concern and horses will live comfortably with the disorder. Surgical correction should be considered, however, if secondary problems (keratitis, recurrent ulceration, and/or trichiasis [more on that in a moment], for example) arise.
Trichiasis and Distichasis--Trichiasis (when the eyelashes are bent in toward the eye and rubs on cornea) and distichasis (abnormally sited eyelashes and/or ectopic hairs) are both uncommon disorders, however both require surgical correction, Matthews noted.
Vitiligo--Vitiligo is the term used to describe the depigmentation of previously pigmented sections of skin, Matthews said. He noted that he sees the disease most commonly in Arabian horses, and that there is no known cause or effective treatment. That said, it does not appear to have any impact on affected horses.
Solar Blepharodermatitis--Simply put, this eyelid inflammation caused by sun exposure typically occurs on nonpigmented eyelids and can result in redness and ulceration. It is also often considered a precursor for squamous cell carcinoma of the eyelid (more on that in a moment). Matthews said that ultraviolet blocking fly masks, creams, and tattoos have all been used to reduce the unpigmented skin's sun exposure. "You could also just move to Scotland," he joked.
Allergic Blepharoconjunctivitis--This eyelid inflammation caused by exposure to an irritant, which generally remains unknown, Matthews explained. This ailment can affect one or both eyes and although it can be gruesome to look at, it does not appear to cause any ocular pain, he said. There is often a very acute onset with this disorder, he said, characterized by "dramatic" eyelid and conjunctival swelling. Allergic blepharoconjunctivitis requires treatment, Matthews said, and generally heals well when treated with topical and systemic glucocorticoids.
Parasitic Blepharoconjunctivitis--This condition occurs when parasites--namely habronema spp.--cause a granuloma to form at the mucocutaneous junction of the eyelid. Matthews said that the granuloma can cause corneal abrasions if left untreated, so he recommends using local corticosteroids to combat the problem. "Regular deworming, fly sprays, and fly masks will help prevent further infestation," Matthews noted.
He added that in some cases, parasitic blepharoconjunctivitis can be confused for mast cell tumors (more on those in a moment). Prior to treating, it's important to ensure the diagnosis is accurate.
Infectious Blepharitis--This unusual disorder typically appears following trauma to the eyelid, Matthews said. These areas of inflammation have the potential to abscess and should be treated with systemic antibiotics. "Watch for foreign bodies (in the wound) and rim fractures" associated with the swelling, he stressed, and treat those accordingly.
Mebominitis and Chelazion--These two conditions are similar, but have distinct differences that differentiate them from each other. Matthews said that mebomianitis is an inflammation of the mebomian glands, which are located at the eyelid margins and secrete the lipid-based portion of the tear film. Affected horse experience ocular discomfort, swelling, and discharge from the mebomian glands, he said. The cause of this disorder is unknown; however it is treated with topical corticosteroids and antibiotics.
Chelazion, on the other hand, is a thickening of the lipid in the mebomian gland and is a rare occurrence in horses. Chelazion causes firm swellings and granuloma that can be seen through the conjunctiva, Matthews said. The growths can cause corneal abrasions and must be removed surgically, he noted.
Periocular Sarcoids--Another common eyelid ailment is the periocular sarcoid, Matthews said. If sarcoids aren't difficult enough to treat on other parts of the horse, those that appear on the eyelid are even more difficult because certain drugs are irritating to the eye, he added. Treatment options include Aldara cream, intralesional bacillus Calmette-Guerin or cisplantin injections, or radiotherapy, he said. Matthews cautioned, however, that "if one treatment modality fails then subsequent treatments are less likely to be successful."
Eyelid Melanoma--These tumors are most commonly seen in gray horses, Matthews said, and many can be surgically removed successfully. He cautioned that the eyelid margin must be preserved during surgery. If the tumor cannot be revomed surgically due to its location, cryotherapy is an option for removal, he said, and cimetidine can be used when complete excision cannot be achieved.
Mast Cell Tumors--Comprised of an accumulation of mast cells (type of cell found in the body), these tumors are uncommon in horses. Often nodular in appearance, Matthews said, mast cell tumors must be diagnosed via biopsy as several other eyelid abnormalities share a similar appearance. Many mast cell tumors can be surgically removed, however he cautioned that the eyelid margin must be maintained.
Squamous Cell Carcinoma--These common, cancerous growths on the eyelid are an unwelcome finding for most horses owners, as they often carry a relatively guarded prognosis compared to other locations of the eye, Matthews said. These locally invasive tumors should be treated early and aggressively to increase the chances of a positive outcome, he added. He recommended first debulking the tumor before treating it with an adjunct therapy, such as fluorouracil, mitomycin C, intralesional cisplantin, or cryotherapy. Surgical excision of the affected portion of eyelid can be used as a last resort, he said, as the outcomes typically are less favorable.
Ptosis and Horner's Syndrome--The term used for a drooping upper eyelid, ptosis is often associated with facial paralysis from head trauma or temporohyoid osteopathy, Matthews said; it is rarely associated with a neurologic disease, such as botulism or equine protozoal myeloencephalitis, he added.
Horner's syndrome (sympathetic nerve paralysis) is typically a second or third order disease in the horse (meaning it's prompted by another ailment). Ptosis is a common finding in Horner's syndrome patients, he said. Matthews recommended treating the root cause of the disease.
"Eyelid disorders are common," Matthews said. "Early diagnosis, if necessary by excisional biopsy, and therapeutic intervention will result in a favorable outcome in most cases."
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.