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Blepharitis in horses refers to inflammation of one or both eyelids. It may be associated with swelling, redness, irritation, crusting, hair loss, and discomfort around the eyes.
Horses with blepharitis may also show excessive tearing, eye discharge, squinting, or sensitivity to light, especially if inflammation extends to other parts of the eye.
Blepharitis can develop from numerous causes, including infections, allergic or inflammatory reactions, photosensitization, or injury. Because eyelid swelling can also accompany painful eye conditions such as corneal ulcers and uveitis, identifying the underlying cause is essential for guiding treatment and preventing serious eye damage.
Learn how to recognize the symptoms and causes of blepharitis, how veterinarians diagnose and treat the condition, and how to manage affected horses and reduce the risk of recurrence.
Blepharitis in Horses
Blepharitis is a general term for inflammation of one or both eyelids in horses. The inflammation may affect only the eyelid or occur alongside problems involving other parts of the eye, including the conjunctiva and cornea. [1][2]
Illustration: Dr. Ana Mesa, PhD
Blepharitis can develop from several underlying problems, including: [1][2][3][4][5][6][7]
- Bacterial and fungal infections
- Allergic or immune-related inflammation
- Photosensitization
- Trauma
- Habronemiasis around the eye
Affected eyelids may become swollen, red, painful, or irritated, and some horses develop crusting, scaling, hair loss, or sores around the eye.
Some common signs of blepharitis include: [1][2][5][6][7]
- Excessive tearing
- Eye discharge
- Squinting
- Sensitivity to light
What's your top priority with your horse's health?
What's your top priority with your horse's health?
Associated Symptoms
Symptoms associated with blepharitis vary depending on the underlying cause and whether inflammation is limited to the eyelids or also affects the surrounding skin or other parts of the eye. [1][2]
Common symptoms in horses include: [1][2][3][5][6][7]
- Swollen or thickened eyelids
- Redness around the eyelids
- Crusting or scaling of the eyelid or surrounding skin
- Hair loss around the eye
- Sores on or around the eyelids
- Excessive tearing
- Eye discharge
- Squinting or frequent blinking
- Sensitivity to light
- Rubbing or irritation around the eye
The appearance of the eyelids and surrounding skin can provide clues to the underlying cause. Fungal blepharitis may produce well-defined, scaly areas with hair loss, while habronemiasis around the eye causes raised, inflamed sores and thick discharge. [4][5]
Photosensitization may cause redness, scaling, crusting, and more widespread skin problems, particularly on unpigmented areas of the horse’s body, in addition to blepharitis and other eye inflammation. [7]
Blepharitis can also occur alongside conjunctivitis, corneal disease, or uveitis. Marked squinting, sensitivity to light, or eye discharge may indicate that other parts of the eye are affected. [3][6][7]
When to Call the Veterinarian
Same-day veterinary evaluation is recommended for new or unexplained eyelid inflammation in horses accompanied by: [3]
- An eye that is partly or completely closed
- Significant squinting or sensitivity to light
- Excessive tearing or discharge from the eye
- Sudden or severe eyelid swelling
- An eyelid wound or other trauma around the eye
- A change in the color or appearance of the eye
- Signs of impaired vision
Prompt evaluation helps determine whether the problem is limited to the eyelid or involves the cornea or structures inside the eye.
Causes of Blepharitis in Horses
Blepharitis can develop from infections, parasites, allergic or inflammatory reactions, photosensitization, or injury to the eyelid or skin around the eye. [1][2]
The appearance of the eyelid alone does not always reveal the underlying cause. Many of the symptoms associated with blepharitis also occur with several different eye and skin conditions, so veterinarians consider the horse’s other symptoms and recent history when investigating blepharitis. [1][2][3]
Infectious Causes
Bacterial infections can involve the tissues around the eye or develop alongside inflammation of the conjunctiva and cornea.Â
Fungal organisms can also infect the eyelid, although blepharitis appears to be uncommon in equine cases of fungal infection. [4]
Because bacterial and fungal infections can resemble other causes of eyelid inflammation, the appearance of the lesion does not identify the organism responsible. Veterinarians diagnosing infectious causes take samples from the affected eye or skin to determine whether infection is involved. [1][2][4][6]
Parasites
Habronema larvae can cause inflammation when flies deposit them on moist tissues or damaged skin around the horse’s eye.
Instead of completing their normal life cycle, the larvae remain in the tissue and trigger a strong inflammatory reaction. This condition is known as periocular habronemiasis and is sometimes referred to as a form of “summer sores.” [5]
Affected horses may develop swollen, raised, or irritated areas around the eyelids and conjunctiva. [5]
Periocular habronemiasis is most likely to occur during periods of increased fly activity. Given this, blepharitis may develop during warmer months when insect activity is highest. [5]
Allergic & Inflammatory Causes
Allergic reactions and other non-infectious inflammatory conditions can cause pronounced swelling of the eyelids and surrounding tissues. The loose tissues around the horse’s eye can become noticeably swollen when inflammation develops, sometimes making it difficult for the horse to open the affected eye normally. [1][3]
Inflammation may also occur alongside irritation of the conjunctiva or other structures around the eye. Horses may show tearing, squinting, redness, or sensitivity in addition to eyelid swelling.
Because these signs can also occur with infection, trauma, or more serious eye disease, significant or persistent swelling requires veterinary evaluation. [1][2][3]
Photosensitization
Photosensitization occurs when certain conditions make the skin unusually sensitive to sunlight. Areas with little pigment or hair protection are most vulnerable, which means the skin around the eyes and muzzle may be affected. Horses can develop redness, scaling, crusting, and more severe skin damage following sun exposure. [7]
Photosensitization may be a temporary side effect of some medications or a serious sign of advanced liver disease. In horses, liver disease is most commonly associated with different forms of poisoning, especially toxic plant intakes. [2]
Eye and eyelid problems can occur at the same time, and photosensitization can affect more than the skin. When blepharitis occurs alongside sun-sensitive skin on the face or other unpigmented areas, veterinarians may consider plant exposure and other causes of photosensitization as part of the investigation. [7]
Trauma & Irritation
The eyelids can be injured by kicks, collisions with fences or stall fixtures, branches, and other objects in the horse’s environment. Even relatively small injuries may cause noticeable swelling because the tissues surrounding the eye are delicate.
More significant trauma can result in cuts, bruising, or damage involving nearby structures of the eye. [1][3]
Local irritation may also cause a horse to rub the face or eye area, leading to additional swelling or skin damage. Insects, dust, foreign material, or an already painful eye can contribute to rubbing and make the surrounding tissues more inflamed. [1][2]
Table 1. Causes of blepharitis in horses
| Cause | Examples | Typical features |
|---|---|---|
| Bacterial infection | Moraxella spp. | Blepharitis with conjunctivitis, tearing, and discharge from the eyes |
| Fungal infection | Trichophyton equinum | Scaly, well-defined areas of hair loss around the eyelid |
| Parasites | Habronema spp. | Raised, inflamed areas, often during warmer months |
| Allergic inflammation | Allergic reactions | Rapid eyelid and conjunctival swelling |
| Photosensitization | Wild parsnip exposure | Redness, scaling, and crusting, particularly on unpigmented skin |
| Trauma and irritation | Kicks, collisions, rubbing | Localized swelling, inflammation, or visible eyelid injury |
Diagnosis of Blepharitis in Horses
Diagnosing blepharitis involves determining the underlying cause of the eyelid inflammation and checking whether other parts of the eye are affected. A complete eye examination is important because eyelid swelling can also occur with conditions such as corneal ulcers and uveitis. [3]
Depending on the appearance of the eyelid and suspected cause, your veterinarian may include diagnostic tests such as: [3][4][5]
- Fluorescein staining
- Cytology
- Bacterial culture
- Fungal culture
- Skin scrapings
- Biopsy
- PCR
The appearance and location of changes to the eyelid can help narrow down the possible cause. Crusting, hair loss, swelling, sores, discharge, and signs of injury can help distinguish between different conditions.
The veterinarian will also check the horse’s eye for problems such as conjunctivitis, corneal ulcers, or inflammation inside the eye. [3][4][5]
Similar Conditions
Several different eye and skin conditions in horses can cause swelling, redness, tearing, or discomfort around the eye that resembles blepharitis. [1][2][3]
Conditions a veterinarian may rule out include: [1][3][5][8]
- Conjunctivitis
- Corneal ulcers or keratitis
- Uveitis
- Tumors on or around the eyelids, including squamous cell carcinoma
- Foreign bodies
- Traumatic injuries
Some of these conditions affect the eye itself rather than primarily affecting the eyelids. Since corneal ulcers and uveitis can cause significant pain and require prompt treatment, eyelid swelling should not automatically be assumed to be a minor skin problem. [3]
Treatment of Blepharitis in Horses
Treatment for blepharitis depends on the underlying cause and the severity of the inflammation. [3][4][5][7]
Possible treatments your veterinarian may consider for your horse include: [3][4][5][7]
- Antibiotic medications
- Antifungal medications
- Deworming medications
- Anti-inflammatory medications
- Removing or surgically reducing larger areas of inflamed tissue
- Wound repair
- Protecting the horse from sunlight
- Treating other affected parts of the eye
The horse may require more than one type of treatment, especially if the inflammation affects both the eyelids and other parts of the eye. Treatment may also need to change as the inflammation improves or when diagnostic testing identifies a specific infection or other underlying cause. [3][5]
While waiting for veterinary evaluation, practical steps to reduce the risk of harm and discomfort to the horse include: [3][5][7]
- Keeping the horse in a clean, shaded environment
- Preventing rubbing or further injury to the affected eye
- Using a clean fly mask when appropriate
- Reducing exposure to flies and other insects
- Monitoring for increasing swelling, discharge, squinting, or sensitivity to light
- Avoiding application of eye medications unless directed by a veterinarian
Measures such as shade and a face mask can also be particularly useful when photosensitization is suspected, while fly control is important when the cause is suspected to be related to parasites. [5][7]
Prognosis
The prognosis for blepharitis depends on the underlying cause and whether other structures of the eye are affected.
Cases involving fungal infection, periocular habronemiasis, bacterial infection, and photosensitization typically improve or resolve following appropriate treatment. [4][5][6][7]
Preventing Blepharitis in Horses
Not all cases of blepharitis are preventable, but reducing exposure to common causes of eyelid inflammation and addressing eye or skin problems promptly may lower the risk. Preventive measures depend partly on the conditions that predispose an individual horse to blepharitis. [3][5][7]
Management strategies owners can implement to reduce the risk of blepharitis and other eye disorders include: [3][5][7]
- Using fly masks and appropriate insect control during periods of high fly activity
- Keeping stalls, paddocks, and manure areas clean to reduce fly populations
- Checking feeders, buckets, fencing, and other equipment for areas that could injure the eyelids
- Monitoring the eyes and surrounding skin for swelling, wounds, crusting, or other changes
- Addressing persistent rubbing or irritation before it results in eyelid injury
- Limiting sunlight exposure when photosensitization is suspected
- Checking hay and pasture for potentially harmful plants when photosensitization is a concern
Preventing recurrent eyelid swelling and other vision problems depends on identifying and managing the underlying cause of inflammation.
Frequently Asked Questions
Here are some frequently asked questions about blepharitis in horses:
Blepharitis is inflammation of one or both of a horse's eyelids. It may occur on its own or alongside inflammation affecting the conjunctiva, cornea, or other parts of the eye. [1][2]
Common symptoms include swollen or thickened eyelids, redness, crusting, scaling, hair loss, sores, excessive tearing, and eye discharge. Affected horses may also squint, blink frequently, rub the eye, or become sensitive to light. [1][2][3][5][6][7]
Blepharitis can result from bacterial or fungal infections, allergic and immune-related inflammation, parasites, photosensitization, trauma, or local irritation. Because several eye and skin conditions cause similar symptoms, the appearance of the eyelid alone may not identify the underlying cause. [1][2]
New or unexplained eyelid inflammation accompanied by significant squinting, light sensitivity, discharge, sudden swelling, trauma, or changes in the appearance of the eye requires same-day veterinary evaluation. Any eye injury or sudden change in vision should be treated as a medical emergency. [3]
Flies can contribute to blepharitis by depositing Habronema larvae on moist tissues or damaged skin around the eye. The larvae can trigger raised, inflamed sores known as periocular habronemiasis, which is more likely to occur during warmer months when fly activity is high. [5]
Photosensitization can cause blepharitis along with redness, scaling, crusting, and skin damage, particularly on unpigmented areas around the eyes and muzzle. When these signs develop after sun exposure, a veterinarian may investigate medication reactions, plant exposure, liver disease, and other possible causes. [2][7]
Blepharitis primarily affects the eyelids, while conjunctivitis involves the conjunctiva. However, both conditions can occur together and may cause overlapping signs such as redness, tearing, discharge, swelling, and discomfort. A veterinary eye examination can determine which structures are affected. [1][2][3]
Diagnosis typically begins with a complete eye examination to identify the cause of the eyelid inflammation and check the cornea and other eye structures. Depending on the suspected cause, testing may include fluorescein staining, cytology, bacterial or fungal culture, skin scrapings, biopsy, or PCR. [3][4][5]
Treatment depends on the underlying cause and may include antibiotics, antifungal or deworming medications, anti-inflammatory medication, wound repair, sunlight protection, or treatment of other affected eye structures. Some horses require more than one treatment, particularly when inflammation extends beyond the eyelid. [3][4][5][7]
Keep the horse in a clean, shaded environment and prevent rubbing or further injury to the eye. A clean fly mask may be appropriate, but avoid applying eye medications unless directed by a veterinarian. Monitor for worsening swelling, discharge, squinting, light sensitivity, or changes in the eye's appearance. [3][5][7]
Not every case is preventable, but fly control, clean facilities, safe fencing and equipment, and regular monitoring of the eyes and surrounding skin may reduce the risk. Limiting sunlight exposure and checking hay or pasture for harmful plants may also be appropriate when photosensitization is suspected. [3][5][7]
Summary
Blepharitis causes inflammation of one or both eyelids in horses and may occur alone or alongside disease affecting the conjunctiva, cornea, or internal structures of the eye.
- Signs can include swollen or reddened eyelids, crusting, hair loss, sores, tearing, discharge, squinting, and sensitivity to light
- Underlying causes include bacterial or fungal infections, parasites, allergic inflammation, photosensitization, trauma, and local irritation
- Veterinary diagnosis may involve a complete eye examination, fluorescein staining, cytology, microbial culture, skin scrapings, biopsy, or PCR testing
- Treatment is directed at the underlying cause and may include medication, wound repair, or removal of inflamed tissue
- Prompt evaluation is important when swelling occurs with marked pain, discharge, trauma, or signs of impaired vision
References
- Gilger. B. C. Ed. Equine Ophthalmology, 4th ed.. Wiley-Blackwell. 2022.
- Reed. S. M. et al. Equine Internal Medicine, 4th ed.. Saunders. 2018.
- Dwyer. A. E. Ophthalmic Emergencies in the Field. Veterinary Clinics of North America: Equine Practice. 2021.
- Ural. K. et al. Mycotic Blepharitis Due to Trichophyton equinum in a Horse and Treatment With Topical Terbinafine. Fırat University Veterinary Journal of Health Sciences. 2008.
- Verhaar. N. et al. Case Series: Periocular Habronemiasis in Five Horses in the Netherlands. Veterinary Record. 2018.
- Seeger. M. G. et al. Isolation of Moraxella spp. from Horses with Conjunctivitis in Southern Brazil. Brazilian Journal of Microbiology. 2021.
- Winter. J. C. et al. Photodermatitis and Ocular Changes in Nine Horses after Ingestion of Wild Parsnip (Pastinaca sativa). BMC Veterinary Research. 2022.
- Estell. K. Periocular Neoplasia in the Horse. Veterinary Clinics of North America: Equine Practice. 2017.
