Mastering Equine Ophthalmology: Systematic Examination Techniques for Modern Practice

Equine eye examinations require specialized techniques and equipment distinct from small animal ophthalmology. Dr. Rachel Allbaugh’s comprehensive approach to equine ocular evaluation provides practitioners with the confidence to perform thorough examinations and manage common conditions affecting horses.

The Systematic Approach

Successful equine ophthalmic examination follows a structured sequence that maximizes efficiency while ensuring patient safety and diagnostic accuracy.

Patient Preparation and Restraint

Safety Considerations:

• Secure restraint is essential for both patient and examiner safety
• Consider chemical restraint for fractious animals
• Adequate lighting is crucial for proper visualization
• Position equipment within easy reach before beginning

Positioning Techniques:

• Approach the horse from the side, never directly from front or back
• Use halter and lead rope with assistant control
• Consider stocks for detailed examination
• Maintain calm, steady movements throughout procedure

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Equipment Selection

Essential Instruments

Basic Examination:

• Direct ophthalmoscope with multiple aperture settings
• Indirect ophthalmoscope for wide-field fundus examination
• Penlight or transilluminator
• Magnification loupes (2.5x recommended)
• Tonometer for intraocular pressure measurement

Advanced Diagnostics:

• Fluorescein stain strips for corneal evaluation
• Rose bengal stain for tear film assessment
• Schirmer tear test strips
• Gonioscopy lens for drainage angle evaluation

Medication Preparation

• Topical anesthetic (proparacaine 0.5%)
• Mydriatic agents (tropicamide 1%, atropine 1%)
• Fluorescein sodium 0.25%
• Sterile saline for irrigation

Examination Sequence

1. Distance Observation

Initial Assessment:

• Observe both eyes simultaneously for asymmetry
• Note head position and behavioral signs
• Assess eyelid position and movement
• Evaluate pupil size and symmetry in ambient lighting

Common Findings:

• Blepharospasm: Indicates pain or irritation
• Epiphora: May suggest blocked nasolacrimal system
• Head tilting: Often compensates for visual field defects
• Asymmetric eyelid positioning: May indicate neurological issues

2. Adnexa Examination

Eyelid Assessment:

• Palpate for masses, swelling, or temperature changes
• Evaluate eyelid margins for trichiasis or distichiasis
• Check for adequate eyelid closure (Bell’s phenomenon)
• Assess third eyelid position and appearance

Conjunctival Evaluation:

• Note color, texture, and vascular patterns
• Look for follicle formation or chemosis
• Evaluate fornices for foreign material
• Check for symblepharon or adhesions

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Corneal and Anterior Segment Assessment

Corneal Evaluation Techniques

Gross Examination:

• Assess clarity, smoothness, and luster
• Note any opacities, vessels, or pigmentation
• Evaluate corneal thickness and contour
• Check for epithelial irregularities

Fluorescein Staining Protocol:

1. Apply topical anesthetic (proparacaine)
2. Wait 30 seconds for adequate anesthesia
3. Apply fluorescein strip to lower fornix
4. Irrigate excess stain with sterile saline
5. Examine under cobalt blue light

Interpretation:

• Green uptake indicates epithelial defects
• Dendritic patterns suggest viral keratitis
• Geographic lesions may indicate bacterial infection
• Full-thickness staining indicates corneal perforation risk

Anterior Chamber Assessment

Depth and Clarity:

• Normal anterior chamber depth varies by breed
• Assess for flare (protein) or cells (inflammation)
• Note iris color, pattern, and pupillary border
• Evaluate lens clarity and position

Pupillary Light Reflexes:

• Test direct and consensual responses
• Normal equine pupils constrict rapidly and completely
• Assess for Marcus Gunn pupil (afferent pupillary defect)
• Note pupillary shape irregularities

Fundoscopic Examination

Preparation and Technique

Mydriasis Induction:

• Tropicamide 1%: Onset 15-20 minutes, duration 2-4 hours
• Atropine 1%: Onset 30-45 minutes, duration 7-14 days
• Choose based on examination needs and follow-up requirements

Examination Approach:

1. Begin with indirect ophthalmoscopy for overview
2. Progress to direct ophthalmoscopy for detail
3. Systematically examine optic disc, vessels, and peripheral retina
4. Document findings with diagrams or photography

Normal Fundus Characteristics

Optic Disc:

• Oval to round with distinct margins
• Pink to orange coloration
• Central physiologic cup may be present
• Retinal vessels radiate from disc margins

Retinal Vessels:

• Arterioles appear narrower and brighter than venules
• Normal arterial-to-venular ratio approximately 2:3
• Vessels should have smooth, continuous walls
• No arteriovenous crossing changes in normal eyes

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Common Equine Ocular Conditions

Corneal Conditions

Corneal Ulceration:

• Most common emergency in equine ophthalmology
• Often secondary to trauma or foreign bodies
• Requires aggressive treatment to prevent complications
• Subpalpebral lavage may be indicated for severe cases

Fungal Keratitis:

• More common in warm, humid climates
• Often presents with dense, white infiltrates
• Requires prolonged antifungal therapy
• May necessitate surgical intervention

Uveitis Syndromes

Equine Recurrent Uveitis (ERU):

• Leading cause of blindness in horses
• Characterized by recurring episodes of inflammation
• Requires long-term management strategies
• Early recognition improves long-term prognosis

Clinical Signs:

• Blepharospasm and photophobia
• Conjunctival hyperemia
• Corneal edema
• Miosis and aqueous flare

Advanced Procedures

Subpalpebral Lavage System

Indications:

• Frequent medication administration required
• Patient fractious or dangerous to handle repeatedly
• Corneal perforation risk necessitates continuous therapy
• Owner compliance concerns with frequent dosing

Placement Technique:

1. Sedate patient and provide local anesthesia
2. Create small incision through upper eyelid
3. Thread lavage tube through incision and position in fornix
4. Secure tube with skin sutures
5. Connect to extension tubing for easy medication delivery

Post-Placement Management:

• Monitor for tube displacement or occlusion
• Maintain strict aseptic technique during medication administration
• Assess daily for complications or inflammation
• Remove when intensive therapy no longer required

Documentation and Follow-Up

Examination Records

Essential Elements:

• Detailed description of all findings
• Photographic documentation when possible
• Treatment plan with specific medications and frequencies
• Client education provided
• Follow-up schedule established

Medicolegal Considerations:

• Thorough documentation protects both patient and practitioner
• Clear communication of prognosis and treatment expectations
• Written instructions for home care
• Emergency contact protocols for complications

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Key Takeaways for Practitioners

1. Systematic approach ensures comprehensive evaluation and reduces missed findings
2. Proper restraint and positioning are essential for safety and examination quality
3. Equipment familiarity improves efficiency and diagnostic accuracy
4. Documentation quality protects both patient outcomes and professional liability
5. Client education about normal findings builds trust and improves compliance

Dr. Allbaugh’s structured approach to equine ophthalmology provides the foundation for confident diagnosis and management of ocular conditions in horses. The combination of thorough examination techniques with appropriate diagnostic tools enables practitioners to provide optimal care while maintaining safety for both patient and examiner.

Successful equine ophthalmic practice requires dedication to continuing education, as new diagnostic techniques and treatment modalities continue to evolve. Regular participation in specialized continuing education programs ensures practitioners remain current with best practices in this challenging but rewarding field.

References

• VetOnIt CE. “Introduction To Equine Ophthalmology with Dr. Rachel Allbaugh.” Course materials and transcript. 2023.
• American College of Veterinary Ophthalmologists. “Guidelines for Equine Ophthalmic Examination.” 2025.
• Equine Veterinary Journal. “Current approaches to equine ophthalmology diagnosis and treatment.” 2025.
• Veterinary Ophthalmology. “Systematic review of equine ocular conditions in practice.” 2024.