Equine infectious ulcerative keratitis uveitis (Proceedings)
Uveitis classification: any cause of blood-ocular barrier breakdown
Introduction
o Moon Blindness, Periodic Ophthalmia
o Most common cause of blindness in horses
• 2-5% of US horses
o Recurrent episodes of intraocular inflammation separated by quiescence
o What causes ERU?
• Genetic
• Environment
• Cause of initial uveitis
o Etiology debatable, but agreement that a dysregulated ocular immune response causes the disease
• Positive corticosteroid effects
• Inflammatory recurrences
• Lack of antibiotic tx success
o Unilateral vs bilateral disease
• May be either
• Recurrences may be either
• If 2+ years pass without disease in second eye, vastly reduced chance of developing disease
Uveitis Classification: any cause of blood-ocular barrier breakdown
o Primary: any etiology causing inflammation
• Trauma: blunt vs penetrating
• Infectious
√ Bacterial: Brucella, Borrelia burgdorferi, Leptospira, Rhodococcus equi, Streptococcus
√ Viral: EHV-1, EHV-2, Equine influenza, EVA, Parainfluenza type 3
√ Parasitic: Onchocerca, Strongylus, Toxoplasma
• Miscellaneous: endotoxemia, neoplasia, septicemia, tooth root abscess
o Equine Recurrent Uveitis
• Two or more episodes observed
• Two+ years w/out an episode diminishes risk
• Labeled: active / acute, quiescent, or end-stage
• Three clinical syndromes
√ Classic
• Most common
• Inflammation of iris, ciliary body, and choroid and adjacent cornea, anterior chamber, lens, vitreous, retina
• Attacks become more frequent / more severe
• Sequelae include blindness, phthisis bulbi, cataract, synechia
√ Insidious
• Low grade inflammation not outwardly painful
• Gradual destructive effect
• Draft and appaloosa breeds
√ Posterior
• Vitreous, retina, choroid and some anterior segment associated inflammation
• Blindness, vitreal cloudiness, retinal detachments
• Warmbloods, Europeans, draft breeds
Clinical Appearance
o No gender preference
o Variable clinical signs
o Over half of cases present before 12 years of age
o Anterior Segment
• Pain
• Epiphora
• Blepharospasm
• Miosis*
√ Unless dilated or synechia present
• Hypotony
√ IOP = 5 – 15 mmHg
• Aqueous flare
• Iris color change
√ Dull, rubeosis
• Corneal edema
• Deep, short perilimbal vessels common
• Fluorescein dye test – negative uptake
• Calcific band keratopathy w/chronic disease
• Uncommon – corneal cellular infiltrates, extensive neovascularization
o Posterior Segment
• Difficult to assess – anterior segment inflammation
• Vitritis (debris, murky, "glow")
• Vitreal liquefaction / floaters / traction bands
• Fundus obscured
Chronic End Stage Disease
o Posterior synechia, capsular pigment, focal / diffuse cataracts
o Lens luxation / subluxation
o Secondary glaucoma
o Retinal Detachment
o Chorioretinal scarring (peripapillary region)
• Non-tapetal area: small, circular focal depigmentation with central hyperpigmentation
• Wing-shaped hypopigmentation nasal and temporal to disc = Butterfly Lesion
DDX / Diagnostics
o Dx determined by characteristic clinical signs and historical clinical bouts
o DDX
• Corneal diseases (ulcer, abscess, foreign body, neoplasia, immune-mediated, viral)
• Non-ERUveitis
• Glaucoma
o Diagnostic tests:
• CBC/Profile
• Leptospiral serology: questionable value / tests previous exposure
• Aqueous humor / serum leptospiral serology more helpful
√ Microagglutination titers (MAT)
√ Positive C value: aqueous MAT value / serum MAT value
• Suggests intraocular production of antibodies against the organism
• Equine leukocyte antigen (ELA) typing: may help determine genetic susceptibility
• Fecal
• Lyme and EVA titer / Western blot analysis
Leptospira
o Linked to spontaneous ERU around the world
o Initial report linking leptospirosis to ERU in 1940 in Germany
o Abundant research generated since then
o Precise pathogenesis of disease (induction, role of organism in uveitis) remains poorly understood
• 1985 – UF detected AB specific to L. interrogans
• 1985 – Argentina demonstrated antigentic relationship between cornea and Leptospira, suggesting molecular mimicry
Appaloosa Horses
o Significantly higher risk: 8.3 times higher than other breeds combined
o Clinically distinct from classic ERU cases
o Often insidious course without bouts of pain
o Age of onset variable
o Secondary complications / sequelae biggest problem
o Bilateral – 80% of cases
o Glaucoma affected 21%
o Sequelae: posterior synechia, iris color change, cataracts, luxation/subluxation, vitritis, retinal detachments, phthisis bulbi, blindness
o Coat color pattern: significant finding
• Light base coats with focal darker spots**
√ Leopard pattern
• Dark base coats with light rump blanket least likely affected
o Equine MHC may play a factor in susceptibility
Medical Treatment
o Two main goals
• Reduce inflammation: corticosteroids and NSAIDs
• Reduce discomfort: mydriatic- cycloplegic
o Medication categories
• Topical steroids
√ Prednisolone acetate 1%
• Indication – potent anti-inflammatory with excellent penetration
• Dose – q 1 to 6 hours
• Risk – predisposes to corneal fungal infection
√ Dexamethasone 0.5-1.0%
• Indication – potent anti-inflammatory with excellent penetration
• Dose – q 1 to 6 hours
• Risk – predisposes to corneal fungal infection
• Topical NSAIDs
√ Flurbiprofen 0.03% / Diclofenac 0.1%
• Indication – anti-inflammatory with good penetration
• Dose – q 1 to 6 hours
• Risk – decreases corneal epithelialization
• Mydriatic – cycloplegic
√ Atropine 1%
• Indication – cycloplegic / mydriatic (minimize synechia / pain relief)
• Dose – q 6 to 24 hours
• Risk – may predispose to colic by decreasing gut motility
√ Phenylephrine 10%
• Indication – use combined with atropine; not great in horse but may provide some added help (alpha agonist)
• Systemic anti-inflammatory medications
√ Flunixin meglumine
• Indication – potent ocular anti-inflammatory
• Dose – 0.5 mg/kg PO, IV, IM x 5 days, then 0.25 mg / kg
• Risk – long term use may predispose to gastric / renal toxicity
√ Phenylbutazone
• Indication – anti-inflammatory
• Dose – 4.4 mg/kg PO, IV
• Risk- long term use may predispose to gastric / renal toxicity
√ Dexamethasone (Azium)
• Indication – potent anti-inflammatory
• Dose – 5-20 mg / day PO or 2.5 – 5.0 mg/day IM
• Risk – frequent side effects, laminitis formation so use with caution and as a last resort, taper off dose, alter management (decrease confinement, stress, starches while increasing forage and access to paddocks / pastures)
√ Prednisone
• Indication – potent anti-inflammatory
• Dose – 100-300 mg / day PO, IM
• Risk - see dexamethasone
• Subconjunctival injection
√ Trimacinolone
• Indication – potent anti-inflammatory, 7-10 day duration of action
• Dose – 1-2 mg
• Risk – severe predisposition for bacterial or fungal keratitis; cannot remove once administered
• Intravitreal antibiotic
√ Gentocin – 4 mg
• Systemic antibiotic?
√ Doxycycline - 12 mg/kg PO BID for one month
√ Enrofloxacin - 7.5 mg/kg PO QD for one month
Surgical Treatment
o Suprachoroidal cyclosporine sustained-release implants
• Constant therapeutic drug delivery to affected tissues
• By-passes some of blood-ocular barriers
• Reduces / eliminates need for regular tx by owner
• Release rates well below toxic drug levels
• Patient convenience
• Blocks transcription of IL-2 production and the responsiveness of the T-
o Rapamycin injection
Prognosis
o See chronic end-stage disease
o Corneal ulcers
o Pthisis bulbi
o Enucleation
o Poor for sight: 50-60% of ERU cases in studies experienced blindness in one or two eyes
o Appaloosas that were seropositive for Leptospirosis had the worst visual prognosis
