equine-corneal-ulcers-a-systematic-approach-to-diagnosis-and-treatment

Introduction to Equine Corneal Ulcers

Equine corneal ulceration is a condition frequently encountered in equine veterinary practice, with a range of cases seen from mild, self-limiting ulcers to severe cases that necessitate surgical intervention. It is critical for equine practitioners to emphasize a thorough and systematic examination when diagnosing this condition to ensure a tailored and appropriate treatment plan for each horse.

Common Causes of Corneal Ulcers

Trauma

Trauma is recognized as the primary cause of corneal ulceration in horses, which can arise from both external and endogenous sources:

• External factors: This includes physical injuries from environmental elements such as branches, barbed wire, or abrasive surfaces that can scratch or penetrate the cornea.

• Endogenous factors: An example of this is entropion, a condition where the eyelids invert, causing lashes to rub against the cornea and leading to ulceration.

Bacterial and Fungal Sources

The cornea can be affected by various microbial agents:

• Common bacteria: Staphylococcus, Streptococcus, and various species of Aspergillus are frequently implicated in cases of corneal ulceration.

• Fungal infections: Although they are rare in the UK, fungal ulcers, particularly those caused by species like Fusarium or Aspergillus, present significant challenges in the U.S.

Clinical Signs of Corneal Ulcers

Symptoms

Horses with corneal ulcers typically exhibit several clinical signs, which may include:

• Blepharospasm: This refers to the involuntary closing of the eyelids, often a reaction to pain.

• Epiphora: Excessive tearing is a prominent sign and can lead to wetness around the eyes.

• Reddened conjunctiva: This signifies inflammation of the outer membrane of the eye.

• Corneal edema: Cloudiness or a noticeable opacity of the cornea can indicate deeper issues.

• Swollen eyelids and other signs: There may also be miosis (constriction of the pupil) and photophobia (sensitivity to light), particularly if anterior uveitis accompanies the ulcer.

Diagnosis of Corneal Ulcers

Techniques

Diagnosing corneal ulcers involves several techniques:

• A comprehensive eye examination using an ophthalmoscope is essential to assess the condition of the cornea and surrounding structures.

• Application of fluorescein dye helps in locating the ulcer, as a positive result will reveal areas of epithelial damage. If Descemet's membrane is exposed, the risk of rupture increases significantly.

• Rose Bengal stain: This dye is particularly valuable in identifying fungal ulcers that may otherwise be overlooked.

Additional Testing

In cases of rapidly progressing or persistent ulcers, additional testing may be necessary:

• Bacterial and fungal cultures should be obtained to identify the causative agents and guide antimicrobial therapy.

• It is also important to recognize secondary anterior uveitis, which is commonly associated with corneal ulcerations and can complicate treatment outcomes.

Types of Corneal Ulcers

Superficial Ulcers

These are the most common type and usually heal rapidly without causing long-term damage to the eye.

Melting Ulcers

Caused by elevated levels of proteinases in the tear film, which induce degeneration of the corneal stroma. These ulcers require prompt treatment to avert severe damage.

Indolent Ulcers

Characterized by superficial, non-healing ulcers with redundant epithelial borders, these may be resistant to standard treatments and require specialized management.

Mycotic Ulcers

Rare in the UK but present with distinct clinical features. Diagnosis typically requires culture to identify the fungus responsible.

Viral Keratitis

This condition leads to superficial lesions of the cornea, often associated with equine herpesvirus type 2.

Treatment of Corneal Ulcers

Uncomplicated Superficial Ulcers

The treatment regimen typically includes:

• Topical broad-spectrum antibiotics: Options such as chloramphenicol, ciprofloxacin, and gentamicin are used to combat bacterial infection.

• Systemic NSAIDs: Medications like flunixin are administered to alleviate pain and inflammation.

• Mydriatic drugs: Such as atropine are used to manage anterior uveitis and provide comfort for the horse.

More Severe Forms

For more complicated cases, treatments may include:

• Anticollagenase Treatment: Using topical serum or EDTA can help accelerate the healing process for melting ulcers.

• Subpalpebral Lavage Systems: This technique helps administer medication to horses that are uncooperative with traditional topical applications.

• Debridement: Surgical removal of necrotic tissue may be necessary to facilitate healing.

Surgical Interventions

Techniques

When medical management fails, surgical options may be considered:

• Conjunctival Grafts: This involves suturing conjunctival tissue over the ulcer to protect it, enhancing blood supply and facilitating healing.

• Amniotic Membrane Flaps: Provides a biological covering that promotes healing while reducing scarring.

• Corneal Transplantation: Though more invasive, it is effective for severe ulcers that cannot heal through other means, utilizing fresh donor corneas.

Considerations

When considering surgical intervention, it's crucial to weigh the potential risks of corneal scarring against the benefits of preserving the functional integrity of the eye. Successful outcomes greatly depend on early diagnosis and timely treatment.

Conclusion

Management of corneal ulcers in horses can be challenging yet rewarding. With early recognition and appropriate treatment strategies, many cases can be effectively managed, significantly improving the quality of life for equine patients.

References

A compilation of comprehensive studies and articles outlining standardized practices for the diagnosis and treatment of equine corneal ulcers.