🩺 Vet’s 2025 Guide to Equine Recurrent Uveitis (Moon Blindness) in Horses 👁️🐴

Equine Recurrent Uveitis (ERU), often known as moon blindness, is the leading cause of blindness in horses today. With up to 28% of affected horses blind in one or both eyes at first examination, this disease is a serious threat to equine vision and well-being. In this 2025 guide, Dr. Duncan Houston breaks down the condition’s causes, signs, and modern treatment strategies for protecting your horse's sight. 🌙🧪

🌘 What Is Equine Recurrent Uveitis (ERU)?

ERU is a chronic, painful condition characterized by repeated episodes of inflammation in the uvea—the pigmented, vascular part of the eye. The term “moon blindness” dates back centuries, when people believed flare-ups occurred with lunar cycles. We now know ERU is not related to moon phases, but is an autoimmune disorder that may have genetic, infectious, and environmental triggers. 🧬👁️

🔁 What Makes ERU “Recurrent”?

Unlike one-time uveitis episodes, ERU involves recurring flares of eye inflammation that progressively damage the eye, potentially leading to:

• 👁️ Cataracts
• ⚫ Glaucoma
• 🌫️ Retinal detachment
• 🔚 Blindness

Each episode further deteriorates ocular structures, making early recognition and management essential. ⏳🛡️

🧫 Causes and Risk Factors of ERU

ERU is thought to be immune-mediated, meaning the horse’s own immune system attacks its eye tissues. But several underlying causes and contributors are linked to the disease. 📉🧬

🦠 Leptospirosis: The Most Common Infectious Trigger

Leptospirosis is a bacterial disease spread through contaminated water. Horses contract it by drinking from ponds, streams, or water contaminated by urine from:

• 🦌 Deer
• 🐄 Cattle
• 🐖 Pigs
• 🐀 Rodents

After exposure, the initial infection may be mild or unnoticed, but ocular symptoms can appear 15–24 months later. Because the connection is delayed, it’s often overlooked as a cause of ERU. 💧🧪

🧬 Genetic Predisposition

Some breeds are more likely to develop ERU, and more severely:

• 🐴 Appaloosas – Especially those with the leopard complex; they are 8x more likely to develop ERU and 4x more likely to go blind
• 🐎 Warmbloods – Often show subtle, chronic forms
• 🟣 Knabstruppers – Share the leopard gene and similar risk to Appaloosas

In these breeds, inflammation is more insidious and often goes unnoticed until advanced. Genetic counseling and regular eye screening are advised. 🧬👀

🔍 Diagnosing ERU vs. Non-ERU Uveitis

It’s important to distinguish ERU from a single episode of uveitis caused by injury or other factors. Both present similarly but have very different treatment paths. 🩺🧠

⚠️ Signs of Uveitis (Acute Flare):

• 😣 Squinting or eye sensitivity
• 😢 Tearing and discharge
• 🌫️ Cloudy or bluish cornea
• 🔴 Redness of the sclera
• 🕳️ Constricted pupil

If the condition returns after treatment—or symptoms become chronic—the horse may have ERU. Only an equine ophthalmologist can make a definitive diagnosis using tools like ocular ultrasound, fluorescein staining, and intraocular pressure testing. 👁️🔬

💊 Treatment Options in 2025

ERU is not curable, but modern veterinary medicine offers effective tools to manage inflammation, minimize pain, and preserve vision. Treatment often includes:

1. 🧴 Topical Therapy

• 💊 Corticosteroids (e.g., prednisolone acetate)
• 🧼 Nonsteroidal anti-inflammatories (e.g., flurbiprofen)

2. 💊 Systemic Medications

• 🩺 Oral NSAIDs like phenylbutazone or flunixin
• 💊 Oral steroids in severe flare-ups

3. 💉 Intraocular Injections

• 🔬 Low-dose gentamicin (may reduce Leptospira load)
• 🧪 Triamcinolone to suppress inflammation

4. 🌱 Suprachoroidal Cyclosporine Implant

This slow-release implant offers long-term immune suppression directly to the eye. It reduces recurrence significantly and is often used in advanced or recurrent cases. 🛡️🧠

5. 🧼 Vitrectomy (Surgical Option)

Removal of the vitreous humor helps eliminate inflammatory mediators and bacteria. Most effective in early-stage ERU linked to Leptospira. 🧪🔧

🛡️ Prevention and Long-Term Management

While ERU cannot be entirely prevented, there are proactive steps owners can take to minimize risk and severity:

🚰 Safe Water Management

• 💧 Use clean, trough-based water—not ponds or streams
• 🚫 Prevent access to wildlife-contaminated sources

🧬 Breed-Specific Monitoring

• 📅 Schedule regular ophthalmic checkups for Appaloosas and Warmbloods
• 🧠 Watch for subtle signs of chronic inflammation

📈 Owner Vigilance

• 👀 Monitor for eye squinting, discharge, or cloudiness
• 📸 Take photos of flare-ups to share with your vet
• 📞 Contact your vet immediately during any acute eye issue

📱 Use Ask A Vet for Fast Help

The Ask A Vet app provides immediate access to veterinary support when your horse experiences an eye flare:

• 📷 Upload eye photos for urgent review
• 📅 Track treatment and flare-up frequency
• 💬 Consult an equine vet 24/7

Download the Ask A Vet app today to safeguard your horse’s vision. 🐴📲

🧠 Final Thoughts: Be Proactive, Be Prepared

ERU is a serious condition that requires diligent care, especially in genetically prone breeds. Early recognition and ongoing treatment can preserve vision and reduce suffering. Whether managing a mild flare or a chronic case, your partnership with a knowledgeable vet—and the use of modern tools—can make all the difference. 👁️❤️

For more expert guidance, visit AskAVet.com or consult your equine ophthalmologist through the app. Together, we can fight moon blindness—one eye at a time. 🌙🩺