Equine Ophthalmology 3 Flashcards
Uveitis (general) vs Equine Recurrent Uveitis (ERU) (the disease)
- end results
- signalment?
(all cases of ERU are uveitis, but not all cases of uveitis are ERU)
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All causes of uveitis can prime the eye for ERU
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End result of both:
* Breakdown of the blood ocular barrier and inflammation
* One severe case of uveitis or several attacks of ERU can blind a horse
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General uveitis: no breed, age, or sex predisposition
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ERU: Appaloosa > TB > StB
Uveitis
- episodes
- causes
- signs
- relapse?
- therapy
- result?
Single episode
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Various causes
* Trauma, ulceration
* Corneal ulceration
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Typical clinical signs
* Miosis, low IOP
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Relapse: 2-6 weeks
* Pseudo-recurrence
* Mimics ERU
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Taper therapy: 6-8 weeks
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Can be blinding
ERU
- episodes
- causes
-syndromes
- therapy length
- result?
2+ episodes with quiescence in between
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Various causes
* Immune-mediated
* Leptospirosis
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3 syndromes
* Classic: typical uveitis, any breed
* Insidious: low grade inflammation, Appaloosa
* Posterior: vitritis and retinitis, Warmbloods
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Months of therapy
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Leading cause of blindness
Classic ERU presentation, signs
Classic
- Initial episode/Acute classic attack followed by periods of quiescence
- C/S: the intermittent “flare-ups” increase in severity with each recurrence
Insidious ERU presentation, signs, breeds
- Low grade uveitis that never fully resolves….just lingers along
- C/S: minimal outward signs of pain, but cataract formation results in blindness
- Predisposed breeds: Appaloosa, draft breeds
Posterior ERU presentation, signs, breeds
- Inflammation of the vitreal, retinal, choroid, very mild anterior uveitis
- C/S: vitritis, chorioretinitis (“butterfly” lesions) that chronically
→ cataracts, retinal detachment, vitreal degeneration - Predisposed breeds: Draft, Warmblood, European
Posterior Signs for ERU - fundic observations
Chorioretinal lesions
- “Butterfly” lesions
- “Bullet-hole” lesions = depigmented spots with pigmented center
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Vitreal lesions
- Vitreal traction bands
- Vitreal degeneration
Chronic – End-stage ERU (any form) lesions
- Haab’s stria (yellow arrows) from glaucoma
- Diffuse corneal edema from
glaucoma - Mature cataract
- Pigment on anterior lens capsule secondary to
posterior synechia touch points (yellow arrow
heads), capsule/subcapsular cataracts (yellow
arrows)
ERU Diagnosis
Ocular examination
* Ocular ultrasound (mass, vitreal/retinal integrity)
* Tonometry – a difference of 10 mmHg between eyes supports uveitis
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Physical examination
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Testing:
> Serology:
- Leptospira titre (pomona, bratislava, autumnalis) > 1:400 (may be present for years)
- Toxoplasma titre
- Brucella titre
- viral titres – only if clinical signs are present (multifocal pinpoint corneal ulcers)
> PCR (vitreal/aqueous samples) -Leptospira
> Conjunctival biopsy: -Onchocerca microfilaria
ERU Medical treatment
Use Conventional Therapy for Uveitis:
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Antibiotic: Penicillin, Tetracycline, Oxytetracycline, Enrofloxacin
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Anti-inflammatory
* Steroidal vs NSAID
> Topical (Dexamethasone 0.1%, Prednisolone acetate 1%, Diclofenac) > Do not wean off too quickly.
Taper for ~2 weeks after
clinical signs have resolved.
> Systemic (Flunixin, Phenylbutazone, Dexamethasone, Prednisone) > For refractory cases
> Subconjunctival (Triamcinolone)
> Intraocular: tissue plasminogen activator (TPA) - referral
> Intravitreal: gentamicin – typically referral
ERU Treatment Rules:
Do not wean off medications too quickly > or we can see rebound
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Systemic steroidal medication
* Used for refractory cases
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Antibiotic medication in cases of Leptospirosis
* Penicillin
* Tetracycline
* Oxytetracycline
* Enrofloxacin
ERU Surgical Treatment
- Cyclosporine A implants - how it works, efficacy
- Permanent implant (6.5 mm) imbedded between the sclera and posterior uvea
- Blocks transcription of IL-2 production and prevents the activation of T lymphocytes
- 18% recurrence rate
ERU Surgical treatment
Vitrectomy
- what we do? success rate?
- Removal of vitreous
- Irrigation with diluted gentamicin (0.2 mg/ml)
- Requires specialized equipment
- 85-98% success rate
ERU Surgical treatment
Vitreal injections - how to? complications?
- General anesthesia
- Lateral recumbency
- 8 mm posterior to the limbus at the 12 o’clock position aim in direction of the optic nerve
- Vitreous sample withdrawn first
- 4 mg of gentamicin (IV formulation)
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Complications: - Vitreal hemorrhage, progression of cataract, retinal detachment
ERU Prevention
Genetic testing:
Appaloosa breed has high risk for ERU
* Leopard complex spotting (LP) coat pattern
> May not correspond to phenotype seen
* Homozygous > Heterozygous > Normal
> Monitor homozygous and heterozygous
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Vaccination:
Leptospirosis – associated ERU
* New vaccine available (Zoetis)
* Studies still needed to determine “protective” effect
* Use of at-risk Appaloosas???
