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The Equine Eye: What Horse Owners Need to Know
Suzanne Jaynes, MVB Ocean State Equine Associates
The Horse’s Vision What can a horse see?
Field of Vision • visual field nearly 360 degrees, minus tail area • binocular vision until 3-4 feet away • color vision, blues and reds
Anatomy
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.
Use a BRIGHT light in a DARK area.
Can the horse see? • Menace response
• Dazzle response
• Pupilary light response
Note Pupil Size
Normal size Mydratic Miotic
Colors
Red White Blue
Hyphema Stromal Abscess Corneal Edema
Signs of Trouble
Ocular Discharge Tearing & Squinting Periocular Swelling
Nerve Blocks to Facilitate Examination
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.
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
Measuring Eye Pressure
• Tonometry
• Will be elevated with glaucoma
• Usually low with uveitis
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
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
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)
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
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
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.”
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.
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
Amnion for Repairing Melting Ulcer
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!!!
READ the Drug Labels Closely!
NO STEROIDS STEROIDS
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