Managing equine ophthalmology diseases

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Without timely diagnosis of common equine eye diseases like squamous cell carcinoma (SCC), infectious keratitis, and uveitis, patients could quickly become blind, or even lose an eye entirely, according to Rachel Allbaugh, DVM, MS, DACVO, a professor of ophthalmology at Iowa State University in Ames. Because of this, it is crucial for early diagnosis, treatment, and monitoring to provide the outcome.¹

But can you recognize an equine eye disease when it presents itself at your clinic? During her lecture “You Can Do It! Recognizing and Treating the Top 3 Equine Eye Diseases” at the Fetch dvm360 conference in Kansas City, Missouri, Allbaugh, broke down how veterinary professionals can identify and manage equine eye diseases to help make them less frustrating while improving patient outcomes.¹

Squamous cell carcinoma

The most common tumor for equine eyes and adnexa is SCC, and it can occur on either eyelid, the third eyelid, conjunctive, libus, cornea, medial canthus, and even the orbit. SCC is commonly implicated by predisposing factors like ultraviolet radiation, breed, such as draft breeds with genetic cause, and light periocular hair/skin. Allbaugh explained that the disease typically starts as a hyperemic area on the eyelids and gradually moves to ulceration and then papillomatous masses. When it comes to other locations, SCC may show papillomatous or fleshy masses with variable degrees of necrosis, inflammation, and ulceration.¹

“When patients present in the early stages, there might be a hyperemic lesion, and then if it's affecting the eyelids, it actually could lead to ulceration appearance. We definitely can get papillomatosis… which I think is the more kind of classic appearance that people recognize, but because there are these varying degrees of ulceration, necrosis and inflammation, it's not always obvious that this is a cancerous process to our clients. So we, as veterinarians, want to keep it on our radar and help have owners watch for changes if they own these predisposed horses,” explained Allbaugh.

If a veterinary professional observes a lesion, they should conduct a biopsy to rule out granulation tissue, inflammatory conditions, habronemiasis, and other tumors to confirm the SCC diagnosis. Allbaugh explained that when treating SCC, the goal is to eliminate the tumor but also maintain ocular function and cosmesis. Treating SCC with a combination of surgical excision and additional therapy can help improve the success rate and adjunctive therapies such as chemotherapy, cryotherapy, immunotherapy, and photodynamic therapy can also be used.² However, Allbaugh told attendees that the most appropriate approach for your patient will depend on location, availability, financial considerations, and size.

SCC can recur, so veterinary professionals should reevaluate horses treated for SCC every 6 months, or earlier depending on if clients notice a developing lesion and communicate with them that repeat therapies may be needed. As for prognosis, eyelid SCC is worse when compared to other ocular sites, and early detection and treatment are important for a favorable outcome. Allbaugh told attendees that reducing ultraviolet radiation in horses that are predisposed or with prior disease and can be accomplished by utilizing a mask that blocks the majority of UV Light.¹

Uveitis and equine recurrent uveitis

Uveitis is the most common cause of blindness in equine patients and can form in any horse from systemic infectious diseases, blunt or penetrating trauma, neoplasia and idiopathic or immune-mediated inflammation. Horses with uveitis can present with multiple clinic signs, but a majority of clients notice ocular pain or vision compromise first.¹

“I always think of ophthalmology like a game of Clue. I'm trying to get as many clues as possible so that I can tell my story as to what all has happened. But things like aqueous flare can be pathognomonic for uveitis. Things like keratic precipitates, which we see in the ventral aspect, stuck to the endothelium in some horses can really clue you in about, yep, uveitis is what's going on here. A constricted pupil is expected with uveitis. If you have a bunch of signs of uveitis and the pupils widely dilated, well, then… Now I'm worried about it having a secondary glaucoma situation,” she explained.

“So again, just do that thorough examination. Try to get as many clues to your puzzle, and then that way you can come to your conclusion as to what is going on, qualify as many of the findings as you can, so that you can follow up with that more subjective evaluation at the recheck visits and know if things are looking better or getting worse,” Allbaugh continued.

Clinical signs and findings will vary with equine recurrent uveitis (ERU), and the disease can be unilateral or bilateral. Acute disease has active ocular pain and observable inflammation. When it comes to insidious uveitis, it can be more challenging to diagnose as equine patients may not be outwardly showing pain or subtle signs of low-grade on-go intraocular inflammation could be missed. Because they could be missed, veterinary professionals should consciously look for aqueous flare when in a darkened exam setting.¹

According to Allbaugh, active uveitis needs to be treated aggressively at first with therapy and slowly tapered over time with treatment extending 2 to 4 weeks past the resolution of signs. The therapy goal is to reduce pain and preserve vision with the most critical treatment component being anti-inflammatory therapy.¹

“Topical ophthalmic dexamethasone 0.1% (as neomycin/polymyxin B/dexamethasone) or prednisolone acetate 1% should be given 4 times daily or more frequently if needed. Concurrent topical NSAID therapy with ketorolac 0.5%, flurbiprofen 0.03% or diclofenac 0.1% may be needed in severe cases or can be utilized if steroids are contraindicated. Flunixin meglumine appears to be the most effective systemic NSAID, but phenylbutazone, firocoxib, or aspirin therapy may also be considered. Alternatively, oral steroid use may be necessary,” Allbaugh explained within her proceedings.¹

If an active Leptospira infection is suspected in the patient, systemic antibiotics can be administered. For more severe or frequently recurring cases could potentially require treatment from a specialist with intravitreal injections, vitrectomy, or suprachoroidal cyclosporine implantation³ to help improve chances for successful management.¹

ERU, also referred to as “periodic ophthalmia” or “moon blindness,” can affect any breed but are more associated with certain breeds such as Appaloosas and draft horses. ERU is not in every acute uveitis episode but can develop into ERU. Professionals should be warned of this disease process, and if 2 or more episodes of uveitis are observed a diagnosis of ERU can be made. Allbaugh told attendees that clients should contact a veterinarian for evaluation if similar occur signs occur and be cautioned against empiric treatment given the possibility of corneal ulceration, stromal abscessation, or foreign body presenting similarly.¹

Conclusion

These diseases, among others such as corneal ulceration and corneal stromal abscessation, are prevalent among horses, presenting a significant challenge in veterinary care. Early diagnosis and prompt, appropriate treatments are crucial for achieving successful outcomes. Effective management also requires vigilant monitoring to ensure that the condition improves as expected. When a disease proves difficult to diagnose conclusively, shows no improvement despite seemingly adequate therapy, or exceeds the limits of available treatment options, it is essential to consider a prompt referral to a specialist. This approach not only helps in providing the best possible care but also increases the likelihood of a favorable prognosis.

References

1. Allbaugh R. You Can Do It! Recognizing and Treating the Top 3 Equine Eye Diseases. Presented at: Fetch dvm360 Conference; August 23-25, 2024; Kansas City, MO.
2. Giuliano EA, MacDonald I, McCaw DL, et al. Photodynamic therapy for the treatment of periocular squamous cell carcinoma in horses: a pilot study. Vet Ophthalmol. 2008;11 Suppl 1:27-34. doi:10.1111/j.1463-5224.2008.00643.x
3. Gilger BC, Salmon JH, Wilkie DA, et al. A novel bioerodible deep scleral lamellar cyclosporine implant for uveitis. Invest Ophthalmol Vis Sci. 2006;47(6):2596-2605. doi:10.1167/iovs.05-1540