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