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The Equine Eye: What Horse Owners Need to Know
Suzanne Jaynes, MVB Ocean State Equine Associates
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The Horse’s Vision What can a horse see?
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Field of Vision • visual field nearly 360 degrees, minus tail area • binocular vision until 3-4 feet away • color vision, blues and reds
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Anatomy
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Ophthalmic Examination
Note lash position. This is often the FIRST, and
most subtle change you will see.
Note size of the eyes. Look for facial symmetry.
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Use a BRIGHT light in a DARK area.
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Can the horse see? • Menace response
• Dazzle response
• Pupilary light response
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Note Pupil Size
Normal size Mydratic Miotic
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Colors
Red White Blue
Hyphema Stromal Abscess Corneal Edema
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Signs of Trouble
Ocular Discharge Tearing & Squinting Periocular Swelling
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Nerve Blocks to Facilitate Examination
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Fluorescein Eye Stain • Detects defects in the cornea such as abrasions, ulcerations & lacerations • Moisten strip with saline and gently touch to the horse’s sclera. • Diluted fluorescein can miss minor abrasions.
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Assessment of Tears
Rose Bengal Stain • Assesses tear film • Fungal ulcers at earliest
stage will be negative to fluorescein but positive to Rose Bengal
• Must be diluted Schirmer Tear Test • Give a quantitative
measure of tear production
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Measuring Eye Pressure
• Tonometry
• Will be elevated with glaucoma
• Usually low with uveitis
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Corneal Ulcers & Abrasions
• Very common – prominent eyes
• Sight-threatening • Requires early
confirmation & treatment appropriate treatment
• Ranges from minor abrasion to full-thickness perforation
• Require aggressive treatment, regardless of size
• Very painful
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The Corneal Environment
• Corneal thickness = 1.0 to 1.5 mm in center, 0.8 mm at periphery
• Healing of superficial, non-infected ulcers is 5-7 days
• Cornea always exposed to bacteria & fungi – protected by epithelium
• Defect in corneal epithelium allows bacteria & fungi to adhere and initiate infection
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Medical Treatment - Antibiotics
Topical Antibiotics
• Bacitracin-Neomycin-Polymixin B **
• Ciprofloxacin
• Tobramycin
• Gentamicin
• Chloramphenicol
• Cephazolin
• Ointments vs. Solutions
• Administered every 2 to 8 hours, depending on medication
• Used based on bacterial sensitivity
• Often combined with anti-fungal medications (plant debris, southern states)
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Treating Secondary Uveitis
Topical Atropine Sulfate 1%
• Reduces protein leakage
• Minimizes pain from ciliary muscle spasm
• Reduces synechia formation by dilating the pupil
• Given every 4-6 hours until dilated, then reduced immediately
• Risk of colic due to slowed gut transit time
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Treating Secondary Uveitis
Systemic Anti-Inflammatories
• Banamine – Aids in reducing ocular pain and inflammation
• Start with full dose twice daily & tapered as healing progresses
• Equioxx
• Bute
Topical anti-inflammatories
• May be used in if uveitis is severe
• Flurbiprofen
• Diclofenamic acid
• Profenol
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Tear Film Proteases
• Enzymes that provide surveillance & repair damaged cells
• Balanced with inhibitory factors to prevent excessive degradation of normal tissue
• Excessive levels can lead to rapid degradation of collagen causing corneal “melting.”
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Collagenolysis Prevention
• Serum is biologically non-toxic & has antiprotease activity
• Helps reduce tear film & corneal proteases
• Apply topically as much as possible
• Replace with new serum every 8 days.
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Surgical Treatment
Conjunctival Flaps/Grafts
• Used for deep, melting or large corneal ulcers
• Used for severe lacerations or perforated ulcers
Amnion
• Less scarring
Suturing of Lacerations
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Amnion for Repairing Melting Ulcer
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Inappropriate Therapy for Ulcers
Topical Corticosteroids
• Encourage growth of bacteria and fungi by interfering with non-specific cellular immunity
• One dose can reduce healing time by several weeks.
• Systemic corticosteroids also contraindicated
DO NOT USE!!!
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READ the Drug Labels Closely!
NO STEROIDS STEROIDS