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1 EQUINE CORNEAL DISEASES & SURGERY: Stromal Corneal Diseases Gwendolyn Lynch, DVM, DACVO Eye Care for Animals at TLC The Life Centre & Marion DuPont Scott Equine Medical Center, Leesburg, Virginia Ulcerative Keratitis Serious eye disease of horses It appears that there is a greater risk of development of serious corneal infection in horses compared with other species In a sense vision i is more important in horses than pets Important to promptly & accurately diagnose and aggressively treat equine corneal ulcers, to prevent permanent vision loss and even loss of the eye itself Cornea Exam Essentials Must have Focal Light source Magnification Ex: Head loupe and transilluminator Cost-effective Eye Exam Essentials Slit Lamp= light source & mag together, plus other features Expensive Not strictly necessary 1

2 Nerve Block Ophthalmic Stains Anatomy of the Cornea Three main layers Epithelium Stroma Endothelium and Descemet's membrane Corneal Epithelium Epithelium 8-10 cell layers thick Hydrophobic Does NOT absorb fluorescein 2

3 Corneal Stroma Stroma Thickest layer (>90%) Precisely arranged lamellae of collagen Hydrophilic Absorbs fluorescein Layer attacked by collagenases ** Corneal Endothelium/ Descemet s Endothelium Innermost layer Single cell thick Descemet s membrane The acellular basement membrane of the endothelium Between endothelium & stroma Fungus has an affinity for this structure** Both are hydrophobic & do NOT take up fluorescein PRE-TEST Progressive Stromal Ulcer IDENTIFY THE TYPE OF ULCER! a. Melting Ulcer b. Progressive Deep Stromal Ulcer c. Stromal Abscess d. Descemetocele e. Corneal Laceration 3

4 Descemetocele Melting Corneal Ulcer Stromal Abscess Corneal Laceration 4

5 Keys to Successful Management Frequent Administration Frequent drug administration Prevention of self-trauma Appropriate drug selection Know when to refer or perform surgery Subpalpebral lavage Dorsal vs ventromedial Hospitalization (preferable) or very dedicated owners Protection Take Samples 1 st st! 5

6 Drug Selection Look at cytology slide yourself if possible Laboratory results take time Must make empirical drug selections based on: Type of ulcer Clinical suspicion Geographic location In-house cytology Can change later based on response to treatment and C & S results Common Pathogenic Isolates Bacteria Pseudomonas Beta Hemolytic Strep Staph spp Fungi Aspergillus Fusarium Penicillium Topical Antibacterial Agents Triple antibiotic Aminoglycosides- gentamycin, etc Fortified solutions- cefazolin, etc Chloramphenicol Fluoroquinolones Antifungal Agents Miconazole 1% Natamycin 5% Itraconazole in DMSO 1% (Ball et al. JAVMA 1997) Voriconazole (Clode et al. AJVR 2006) Silver Sulfadiazine (Betbeze et al. AJVR 2006) Betadine? 6

7 Anticollagenases Bacteria and fungi activate the cornea s endogenous proteases. The balance between proteases and antiproteases may be lost such that keratomalacia occurs even in the face of successful sterilization of the cornea. Treatment aimed at counteracting this process. Topical tetracyclines Oral Doxycycline (20 mg/kg/day?) EDTA N-Acetylcysteine Serum/plasma See Olliver et al. AJVR 2003 for excellent review Uveitis Therapy Secondary anterior uveitis is universally present with ulcers and the importance of addressing it cannot be over-emphasizedemphasized Reflex uveitis, not due to intraocular infection (exception= deep stromal abscess??) Bute, Banamine, or other NSAID Atropine (colic watch) What about PO dex, topical NSAIDS? Systemic Medical Options Doxycycline 20 mg/kg/day? Baytril? Fluconazole? 14 mg/kg PO once then 5 mg/kg/day OR 5 mg/kg BID X 7 days then 5 mg/kg/day Voriconazole 4 mg/kg/day PO When to Consider Referral or Pursuing Surgery Greater than 50% corneal depth All lacerations, descemetoceles, perforations Rapidly progressive Failure to respond to medical therapy Poor vascular response Preferably before involving large % corneal surface area Anytime you are uncomfortable 7

8 Available surgical options Surgical Options Direct suture (lacerations) Conjunctival pedicle flap Conjunctival Island Graft (Austr Vet J 2001) A-cell/ BioSist disk placement Amnion graft Corneal transplant- penetrating or lamellar Posterior lamellar keratoplasty (abscess) Case Study Patient 1 Case Studies History/Signalment: 12yo Irish Sport Horse Gelding w/ rapidly progressive ulcer Exam findings: Large deep stromal (variable depth to 85%) Fl+ ulcer with cloudy periphery Initial plan: Hmm 8

9 Case Study Patient 1 In-house cytology: fungus & more fungus Submit: Aerobic bacterial and fungal culture Decision: Intensive medical mgmt vs surgery Pros? Cons? Case Study Patient 1 Large conjunctival flap Does the job Vascular supply Support Significant visual impairment Alternatives? Case Study Patient 2 History/Signalment: 10yo Warmblood gelding w/ ulcer progression over 48hrs Exam findings: Fl + walls of lesion, Fl- centrally Initial plan: You tell me Case Study Patient 2 What about sampling on this one? SPL placement? 9

10 Conjunctival Pedicle Flap Samples at surgery Cytology results Mild suppurative inflammation No fungus* Culture results Strep zooepidemicus and Staph + Fungus - SPL at surgery Case Study Patient 3 History/Signalment: Shallow ulcer treated with BNP since 1 wk, rapidly progressed in past 36hrs Exam Findings: Large geographic variably deep Fl+ ulcer involving 80%+ corneal surface area; corneal stroma is gelatinous Large Melting Ulcer: What to do? Depends whether a blind eye is of any benefit Conjunctival flap will permanently blind this eye On the other hand, rupture is imminent Aggressive medical tx may be most sensible alternative Frequent in-hospital tx through SPL critical Empirical antibacterial, antifungal, anti-collagenase therapy to start Daily standing keratectomy? How Do You Want To Treat? Topical Antibacterial Gatifloxacin q1-2hrs Topical Antifungal Itraconazole in DMSO; Voriconazole? How often?* Anticollagenases Serum in EDTA (PTT) q 1-2hrs Doxycycline PO BID Systemic antibiotic Doxycycline Baytril? NSAID Banamine Atropine to effect 10

11 Case Study Patient 4 History/Signalment: 3yo track TB colt. Hx squinting 2wks ago- tx d with BNP until FL-, then BNP-H, now painful again 3 days Exam findings: Creamy tan- yellow well-circumscribed axial stromal opacity; stromal vessels Stromal Abscess-Medical Tx Felt to be initiated by micropuncture to cornea, which heals over leaving organisms behind in stroma May heal through vascularization i Use meds with good corneal penetration Fluoroquinolones Itraconazole in DMSO Stromal Abscess- Surgical Tx Fungi appear to have anti-angiogenic angiogenic proprties, however Fungi also have an affinity for Descemet s membrane Deep, poorly medication responsive lesions may benefit from surgery Posterior lamellar keratoplasty (PLK) Penetrating keratoplasty (PK) PLK>PK* (Andrew et al. Vet Ophthalmol 2000) Case Study Patient 5 History/Signalment: 7yo AQHA mare came in from field like this- treated with chloramphenicol X 48hrs Exam findings: Curvilinear corneal leison extending 90% depth, with large assoc d geographic Fl+ lesion with evidence of collagenolysis 11

12 Corneal Laceration What can be done now? What if she was seen 47hrs ago? Extra credit: do you believe my timeline? THE END 12