NAVLE Special Senses

Equine Ocular Trauma Study Guide

📅 March 28, 2026 ⏱ 25 min read

Overview and Clinical Importance

Ocular trauma is one of the most common ophthalmic emergencies encountered in equine practice. Horses are uniquely predisposed to eye injuries due to their large, laterally positioned, prominent globes that protrude from shallow bony orbits. Combined with their flighty temperament, curious nature, and environments containing potential hazards such as bucket handles, fencing, and vegetation, horses frequently sustain ocular injuries ranging from minor corneal abrasions to globe rupture.

The equine globe measures approximately 48mm horizontally and 44mm anteroposteriorly in adult horses, making it one of the largest eyes among land mammals. This large surface area increases vulnerability to traumatic insults. Any suspected ocular trauma should be treated as an emergency requiring evaluation within 12 hours of discovery, as delayed treatment can result in permanent vision loss or globe loss.

Clinical Sign	Description and Significance
Blepharospasm	Involuntary eyelid closure; indicates ocular pain. Note eyelash orientation - normally horizontal, vertical orientation suggests pain.
Epiphora	Excessive tearing; may be clear (irritation) or purulent (infection). Creates a wet streak down the face.
Photophobia	Light sensitivity; horse closes eye when exposed to bright light. Common with uveitis and corneal disease.
Corneal Edema	Cloudy, blue-gray cornea indicating fluid accumulation. Suggests endothelial damage or inflammation.
Miosis	Constricted pupil; classic sign of uveitis. Accompanies most significant ocular trauma.
Periorbital Swelling	Swelling around the eye; may obscure the globe. Can indicate trauma, infection, or orbital fracture.

Clinical Presentation and Initial Assessment

Clinical Signs of Ocular Trauma

Horses with ocular trauma typically present with one or more of the following signs, which may be unilateral or bilateral depending on the mechanism of injury:

Systematic Ophthalmic Examination

A complete ophthalmic examination requires adequate sedation and regional anesthesia. Begin by observing the horse from a distance before approaching to assess head carriage, facial symmetry, and how the horse navigates its environment.

Required Nerve Blocks

NAVLE TipThe auriculopalpebral block provides MOTOR paralysis (akinesia) but NO analgesia. Always combine with the supraorbital block or topical anesthesia for painful procedures. If the horse still reacts to finger pressure at the intended procedure site, additional local anesthetic or sedation is needed before proceeding with sharp instruments near the eye.

Essential Diagnostic Tests

Fluorescein Stain: The cornerstone of corneal ulcer diagnosis. The dye adheres to hydrophilic stroma when epithelium is absent, fluorescing bright green under cobalt blue light. Apply liberally as a concentrated solution since painful eyes have increased tear production that dilutes the stain.
Pupillary Light Reflex (PLR): Tests retinal and optic nerve function. Present PLR is encouraging for vision preservation. Absent PLR with trauma requires assessment of reversibility.
Ocular Ultrasound: Essential when corneal opacity prevents visualization of deeper structures. Evaluates lens position, retinal attachment, vitreous hemorrhage, and globe integrity.
Tonometry: Measures intraocular pressure. Elevated IOP indicates glaucoma; decreased IOP may indicate uveitis or globe rupture.

Nerve Block	Technique	Effect
Auriculopalpebral	Inject 2-3 mL local anesthetic subcutaneously at the highest point of the zygomatic arch	Motor block of CN VII - eliminates forceful eyelid closure (akinesia)
Supraorbital (Frontal)	Inject local anesthetic at the supraorbital foramen within the frontal bone	Sensory block of CN V - provides analgesia to the central upper eyelid

Corneal Ulcers

Corneal ulceration (ulcerative keratitis) is the most common ocular injury in horses, representing erosion of the corneal epithelium with potential stromal involvement. The equine cornea is approximately 0.6-1.0mm thick, with central areas being thinner than peripheral areas.

Classification of Corneal Ulcers

High-YieldA descemetocele does NOT retain fluorescein stain because Descemet's membrane is hydrophobic, unlike the hydrophilic stroma. The classic appearance is a clear area in the center of a fluorescein-positive ulcer. This is a surgical emergency as the globe may rupture with minimal trauma or even from blinking.

Treatment of Corneal Ulcers

Treatment intensity depends on ulcer classification. Remember the Five A's of complicated corneal ulcer treatment:

Exam Focus: NEVER apply topical corticosteroids or steroid-containing ophthalmic preparations to an eye with a corneal ulcer. Steroids inhibit epithelial healing, promote collagenase activity, and potentiate fungal and bacterial infection. This is one of the most common causes of iatrogenic worsening of equine corneal ulcers.

Subpalpebral Lavage Systems

A subpalpebral lavage (SPL) system is an ophthalmic catheter that allows topical medication administration without directly manipulating painful or fragile eyes. The system consists of silicone tubing passed through the eyelid with a footplate resting in the conjunctival fornix, running along the neck to an injection port near the withers.

Indications for SPL placement:

Complicated corneal ulcers requiring frequent medication (greater than q4h)
Severe uveitis or stromal abscesses
Fractious horses difficult to medicate conventionally
Eyes at risk for rupture where manipulation could cause additional damage
Owner/caretaker unable to safely administer topical medications directly

Type	Characteristics	Healing Time	Prognosis
Simple/Superficial	Epithelial loss only; clean margins; no infection; minimal stromal involvement	3-7 days	Excellent
Complicated/Infected	Stromal involvement; cellular infiltrate (white/yellow); irregular margins; may have melting appearance	Weeks to months	Guarded to good with aggressive treatment
Indolent (SCCED)	Superficial; non-adherent epithelial lip at margins; fails to heal despite appropriate therapy	Prolonged without debridement	Good with debridement
Descemetocele	Full stromal loss; only Descemet's membrane remains; does NOT retain fluorescein (membrane is hydrophobic)	Surgical emergency	Guarded - high rupture risk

Eyelid Lacerations

Eyelid lacerations are frequently referred to as "bucket handle tears" because horses commonly injure their eyelids on bucket handles, hooks, nails, or other protruding objects when they jerk their heads up quickly. The eyelids have an excellent blood supply, which promotes healing but also causes significant hemorrhage and rapid swelling after injury.

Key Principles of Eyelid Repair

Preserve tissue: Do NOT debride eyelid tissue unless it is obviously necrotic (cold and leathery). The excellent blood supply allows survival of tissue that would necrose elsewhere.
Align the lid margin precisely: The eyelid margin must be anatomically aligned to prevent exposure keratitis. A step defect causes failure of tear film distribution and chronic corneal ulceration.
Two-layer closure: Close the conjunctival/deep layer with absorbable suture (6-0 Vicryl), then close skin with figure-of-eight at the margin followed by simple interrupted sutures.
Protect the cornea: Keep suture knots away from the corneal surface. Use soft, absorbable suture material.
Always assess the globe: Before repair, perform fluorescein staining to rule out concurrent corneal ulceration from the original trauma.

Prognosis: Good with prompt, accurate repair. Lacerations repaired within the first few hours before significant swelling occurs have the best outcomes. Even extensive lacerations can heal with minimal scarring if treated appropriately.

High-YieldWhen cleaning periorbital wounds, use dilute povidone-iodine SOLUTION, never povidone-iodine SCRUB. Scrub, chlorhexidine, and alcohol are all toxic to the cornea and can cause severe chemical keratitis.

The Five A's	Description and Examples
Antibiotics	Topical broad-spectrum: Triple antibiotic, chloramphenicol, or fluoroquinolones (ciprofloxacin, ofloxacin). Frequency varies from q6-8h (simple) to q1-2h (complicated).
Antifungals	Required in geographic regions with high fungal prevalence. Options: Natamycin 5%, voriconazole 1%, miconazole 1%. Common pathogens: Aspergillus, Fusarium.
Atropine	Topical 1% for cycloplegia and mydriasis. Reduces ciliary spasm pain, prevents synechiae formation. Use q12-24h until pupil dilates, then reduce frequency.
Anti-inflammatories	Systemic NSAIDs (flunixin meglumine 1.1 mg/kg IV/PO q12-24h) for secondary uveitis. NEVER use topical steroids with active corneal ulceration.
Anti-collagenase	Autologous serum or EDTA to inhibit collagenase enzymes causing stromal melting. Critical for melting ulcers. Apply frequently (q1-2h initially).

Orbital and Periorbital Trauma

Orbital Fractures

Orbital fractures commonly occur when horses rear and strike their heads on ceilings, trailers, or other objects, or from kicks by pasture mates. The bones most commonly involved are the frontal bone (forming the dorsal orbital rim) and the zygomatic arch (the prominent bony process lateral to the eye).

Clinical Signs and Diagnosis

Severe periorbital swelling, which may completely obscure the eye
Facial asymmetry and abnormal contour of the orbital rim
Crepitus on palpation of the orbital rim
Epistaxis (associated with sinus involvement - indicates more severe trauma)
Subcutaneous emphysema if sinus communication exists

Diagnostic imaging: Radiography can diagnose most orbital fractures, but CT provides superior detail of fracture configuration, sinus involvement, and soft tissue damage. CT is particularly valuable for surgical planning.

Treatment Considerations

Many orbital fractures can be managed conservatively with rest, NSAIDs, and antimicrobials if open. Surgical repair is indicated for:

Significantly displaced fragments impinging on the globe
Fragments causing nasolacrimal duct obstruction
Cosmetic concerns (depression fractures) in performance horses
Associated sinusitis requiring drainage

Prognosis: Favorable for most orbital fractures. In one study of 18 horses, 13 returned to their previous use. Prognosis worsens with concurrent sinusitis, epistaxis, or zygomatic process involvement.

Globe Rupture and Perforation

Globe rupture represents full-thickness loss of corneal or scleral integrity. It may result from sharp trauma (lacerations with better prognosis) or blunt trauma (rupture at weak points such as the limbus or equator with worse prognosis). The globe is essentially filled with incompressible fluid, so rapid rises in intraocular pressure from impact cause the eye wall to yield at its weakest points.

Clinical Signs Suggesting Globe Rupture

Visible iris prolapse through a corneal or scleral defect
Collapsed or soft globe on palpation (decreased IOP)
Hyphema (blood in the anterior chamber)
Fibrin or vitreous in the anterior chamber
Severe chemosis and hemorrhage obscuring visualization
Absent or severely diminished PLR and dazzle reflex

Decision Making: Repair vs. Enucleation

NAVLE TipProptosis (forward displacement of the globe) is uncommon in horses without concurrent orbital fractures and profound globe injury, unlike in brachycephalic dogs. When seen in horses, it indicates severe trauma and carries a poor prognosis for globe salvage.

Consider Surgical Repair When:	Consider Enucleation When:
Dazzle reflex or PLR is present	No light perception (absent PLR and dazzle)
Short corneal lacerations (less than 15mm)	Optic nerve avulsion or severance
Sharp trauma with clean margins	Completely collapsed globe
Injury less than 2 weeks old	Chronic injury with phthisis bulbi
Referral to ophthalmologist is possible	Severe intraocular infection or pain

Secondary (Traumatic) Uveitis

Virtually all significant ocular trauma causes secondary uveitis, inflammation of the uveal tract (iris, ciliary body, and choroid). Traumatic uveitis is a reflex response to corneal injury and must be treated aggressively to prevent permanent complications including synechiae formation, cataract development, and phthisis bulbi.

Clinical Signs of Secondary Uveitis

Miosis: Constricted pupil due to iris sphincter spasm
Aqueous flare: Protein and cells in the anterior chamber causing a cloudy appearance
Hypopyon: White blood cell accumulation in the ventral anterior chamber
Hyphema: Blood in the anterior chamber
Decreased IOP: Ciliary body inflammation reduces aqueous humor production
Corneal edema: Often accompanies anterior uveitis

Treatment of Secondary Uveitis

High-YieldIt is CRITICAL to distinguish primary uveitis from secondary (reflex) uveitis caused by corneal disease. Treatment differs drastically - topical steroids are essential for primary uveitis without corneal involvement, but are absolutely contraindicated when corneal ulceration is present. Always perform fluorescein staining before initiating topical steroid therapy.

Drug Class	Examples and Dosing	Mechanism/Notes
Systemic NSAIDs	Flunixin meglumine 1.1 mg/kg IV q12-24h initially; phenylbutazone 2.2-4.4 mg/kg PO q12h for maintenance	Inhibits prostaglandin synthesis; critical for controlling intraocular inflammation. Flunixin preferred for acute phase.
Topical Atropine 1%	q6-12h until pupil dilates, then q24-48h to maintain dilation	Cycloplegia reduces ciliary spasm pain; mydriasis prevents synechiae. May decrease GI motility - monitor for colic.
Topical Corticosteroids	Prednisolone acetate 1% or dexamethasone 0.1% q6-12h	ONLY if cornea is fluorescein-negative. Potent anti-inflammatory but contraindicated with corneal ulceration.

Enucleation

Enucleation (surgical removal of the globe) is the most commonly performed ophthalmic surgery in horses. It is indicated when the eye is blind and painful, when vision cannot be restored, or when intraocular pathology poses risk to the horse's comfort or health.

Indications for Enucleation

Blind, painful eye from any cause
Severe trauma with globe rupture and no visual potential
End-stage equine recurrent uveitis with phthisis bulbi
Uncontrolled glaucoma
Intraocular neoplasia
Severe intraocular infection (panophthalmitis)

Surgical Techniques

Enucleation may be performed under general anesthesia or standing with sedation and regional anesthesia. Two primary techniques exist:

Transpalpebral: Eyelids are sutured closed with towel clamps, and an elliptical incision is made through the skin 1cm from the lid margin. The entire globe, conjunctiva, and nictitating membrane are removed en bloc. Preferred when neoplasia or infection is present.
Subconjunctival: The conjunctiva is incised at the limbus and dissection proceeds posterior to the globe. Faster but with increased risk of orbital contamination.

Prognosis: Excellent for comfort following enucleation. Most horses adapt well to unilateral vision loss and can return to previous work. In one study, 34 horses returned to work after unilateral enucleation. Bilateral enucleation requires significant management commitment but is possible.

Memory Aids for Exam Success

The Five A's of Complicated Corneal Ulcer Treatment

Antibiotics - Antifungals - Atropine - Anti-inflammatories - Anti-collagenase

UVEITIS Mnemonic

Ulcer first rule out (fluorescein before steroids!) Very small pupil (miosis) Edema of cornea common IOP decreased Treat with atropine and NSAIDs Iris may adhere to lens (synechiae) Steroids topical only if fluorescein negative

NAVLE TipWhen you see a horse with blepharospasm, epiphora, and a cloudy eye on the NAVLE, your differential diagnosis should include corneal ulcer, uveitis, glaucoma, and stromal abscess. The fluorescein stain result is the key differentiator - positive uptake indicates epithelial loss (ulcer), while negative uptake with the same clinical signs points toward uveitis or stromal abscess.

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