Equine Entropion Study Guide

Overview and Clinical Importance

Entropion is an inward rolling of the eyelid margin that causes the eyelashes and periocular hair to contact the corneal surface, resulting in ocular irritation, pain, and potential corneal damage. This condition is one of the most common eyelid abnormalities in foals and represents an important topic for the NAVLE examination due to its clinical prevalence and the critical nature of early recognition and intervention.

In horses, entropion primarily affects the lower eyelid and is most frequently observed in neonatal foals, though it can also occur in adults secondary to ocular pain, trauma, or cicatricial changes. Understanding the pathophysiology, clinical presentation, diagnostic approach, and treatment options is essential for preventing serious secondary complications including corneal ulceration and potential blindness.

Etiology and Classification

Equine entropion can be classified based on its underlying cause. Understanding these classifications is crucial for determining the appropriate treatment approach.

Primary (Congenital) Entropion

Primary entropion occurs in newborn foals due to conformational abnormalities, excess eyelid skin, or developmental factors. This is the most common form encountered in equine practice. Contributing factors include:

• Anatomical excess of eyelid skin
• Microphthalmos (abnormally small globe)
• Prematurity with enophthalmos (recession of globe)
• Dehydration causing orbital fat atrophy and enophthalmos
• Malnutrition or failure to thrive

Secondary (Acquired) Entropion

Secondary entropion develops in adult horses and is typically associated with:

• Spastic entropion: Caused by chronic ocular pain leading to orbicularis oculi muscle spasm (blepharospasm). The most common form in adults.
• Cicatricial entropion: Results from eyelid scarring following trauma, surgery, or chronic inflammation.
• Phthisis bulbi: End-stage globe shrinkage causing secondary enophthalmos.

Breed and Age Predispositions

Clinical Signs and Presentation

Recognition of clinical signs is essential for early diagnosis and prevention of corneal damage. The clinical presentation varies based on severity and duration.

Primary Clinical Signs

Diagnostic Approach

Physical Examination

Diagnosis of entropion is primarily clinical and based on direct visualization of the inverted eyelid margin. A complete ophthalmic examination should include:

• Visual inspection: Observe both eyes for symmetry, lid position, and evidence of ocular discomfort
• Eyelid examination: Confirm inward rolling of the eyelid margin with hair or lashes touching the cornea
• Manual eversion: Gently roll the eyelid outward to assess degree of entropion and response to correction
• Corneal examination: Evaluate for cloudiness, edema, vascularization, or ulceration

Fluorescein Staining (Critical Diagnostic Test)

Fluorescein staining is MANDATORY in all cases of entropion to assess for secondary corneal ulceration. This test should be performed:

• At initial presentation: To establish baseline corneal status
• During treatment: To monitor for ulcer development or healing
• Post-intervention: To confirm resolution

Fluorescein Staining Technique

Apply fluorescein dye strip to the conjunctival surface after moistening with sterile saline. The dye adheres to the exposed hydrophilic corneal stroma when the epithelium is damaged, appearing as a bright green fluorescent area when examined with a blue (cobalt) light or Wood's lamp.

Exam Focus: A positive fluorescein test indicates corneal ulceration and upgrades the urgency of treatment. Simple ulcers should heal within 7 days with appropriate therapy. Ulcers that fail to heal or progress may indicate secondary infection (bacterial or fungal) and require more aggressive intervention.

Additional Diagnostics

In foals with entropion, consider evaluating for underlying systemic conditions:

• Complete blood count and chemistry: If systemic illness suspected
• IgG testing: To rule out failure of passive transfer
• Hydration status assessment: Dehydration can cause enophthalmos contributing to entropion

Treatment Options

Treatment selection depends on the patient's age, severity of entropion, presence of corneal damage, and underlying cause. The primary goal is to prevent corneal damage while the condition resolves or until definitive correction can be performed.

Treatment Summary Table

Temporary Tacking Sutures (First-Line Treatment in Foals)

Temporary tacking sutures are the treatment of choice for neonatal entropion. This technique everts the eyelid margin while preserving tissue for normal growth.

Technique

• Restraint: Sedate foal if needed; may place in lateral recumbency
• Local anesthesia: Apply topical anesthetic to cornea; perform line block in eyelid tissue
• Suture material: Use 4-0 to 5-0 non-absorbable suture (nylon or silk) with P3 needle
• Placement: Place vertical mattress sutures 2-3 mm from eyelid margin, perpendicular to lid margin
• Number of sutures: Two to four sutures depending on extent of entropion
• Tension: Apply enough tension to slightly OVERCORRECT the entropion (as sutures will loosen)

Medical Management

Concurrent medical therapy is essential in all cases of entropion:

Complications of Untreated Entropion

If left untreated, entropion can lead to serious and potentially irreversible ocular damage:

• Corneal ulceration: Constant abrasion from hair/lashes causes epithelial erosion
• Secondary infection: Bacterial or fungal colonization of corneal ulcers
• Corneal scarring: Permanent opacity affecting vision
• Corneal perforation: In severe cases, deep ulcers may perforate
• Reflex uveitis: Inflammation of the uveal tract secondary to corneal disease
• Blindness: End-stage complication of severe corneal damage
• Enucleation: May be required for severely infected or perforated eyes

Prognosis

The prognosis for equine entropion is generally excellent with early intervention. Key prognostic factors include:

• Congenital entropion in foals: Many cases self-resolve as the foal grows; temporary tacking highly effective
• Early treatment: Prevents corneal damage and has excellent outcome
• Presence of corneal ulcer: Prognosis depends on depth and infection status
• Cicatricial entropion: May require permanent surgical correction; guarded prognosis if extensive scarring

ENTROPION = IN-tropion (eyelid rolls IN)

Remember: ENtropion rolls IN, ECtropion rolls EXIT (out)

FOAL Treatment Mnemonic: "T.A.C.K."

• T = Temporary treatment only (no permanent surgery in foals!)
• A = Assess for corneal ulcer with fluorescein
• C = Consider underlying causes (dehydration, sepsis)
• K = Keep sutures in 7-14 days