Ophthalmology on the NAVLE is high yield for a few specific traps: glaucoma vs uveitis IOP distinction, indolent ulcers in Boxers, and equine recurrent uveitis. Know the IOP direction for each condition and you will handle most ophthalmic questions correctly.
Basic Ophthalmic Examination
Schirmer Tear Test (STT): Done BEFORE any eye drops. Normal ≥15 mm/min in dogs; <10 mm/min = KCS (dry eye). Tonometry: Normal IOP 10–25 mmHg in dogs/cats; 15–30 mmHg in horses. Glaucoma = elevated IOP (>30 mmHg); uveitis = DECREASED IOP (ciliary body inflamed → reduced aqueous production). This is the classic NAVLE trap. Fluorescein staining: Positive = corneal epithelial defect. Descemet's membrane does NOT stain with fluorescein (negative staining = descemetocele). Menace response: CN II afferent, CN VII efferent. Pupillary light reflex: CN II afferent, CN III efferent—intact even with cortical blindness (subcortical pathway).
Corneal Ulcers
Indolent ulcers (SCCED): Boxers and Corgis, middle-aged/older dogs. Non-healing despite normal epithelium—basement membrane adhesion defect. Loose epithelial edges that can be wiped away with a dry swab. Antibiotics alone will NOT heal these. Requires grid keratotomy (needle) or diamond burr debridement to stimulate healing.
Melting ulcer (keratomalacia): Pseudomonas most common; protease production → rapid stromal lysis; gelatinous appearance. Treatment: serum eye drops (anti-proteases), topical ciprofloxacin or tobramycin, EDTA, atropine for secondary uveitis.
Glaucoma
Primary glaucoma breeds: American Cocker Spaniel (most common in US), Basset Hound, Chow Chow, Shar Pei, Siberian Husky. Primary glaucoma in cats is rare—most feline glaucoma is secondary.
Treatment: Acute: mannitol 1–2 g/kg IV over 20–30 min (fastest IOP reduction). Long-term: topical dorzolamide (carbonic anhydrase inhibitor), timolol (beta-blocker), latanoprost (prostaglandin analog—BEST for primary glaucoma; CONTRAINDICATED in uveitis). ATROPINE IS CONTRAINDICATED IN GLAUCOMA—it increases IOP by blocking ciliary muscle.
Uveitis
Inflammation of uveal tract (iris, ciliary body, choroid). Signs: miosis (pain-induced), ciliary flush, aqueous flare (cells and protein in anterior chamber), hypotony, blepharospasm.
Canine causes: Brucella canis (always test — zoonotic), systemic mycoses (Blastomyces, Histoplasma), Leishmania, lens-induced uveitis from cataract leakage, trauma. Feline causes: FIP, toxoplasmosis, FHV-1, lymphoma. Equine: Equine Recurrent Uveitis (ERU)—most common cause of blindness in horses; Leptospira pomona association; Appaloosas overrepresented.
Treatment: Topical atropine (mydriasis prevents posterior synechiae—iris adhesion to lens), topical prednisolone acetate 1% (if no corneal ulcer), systemic NSAIDs, treat underlying cause.
Hereditary Eye Disease
Collie Eye Anomaly (CEA): Collies and Shelties; choroidal hypoplasia; diagnosable in puppies at 5–8 weeks (before pigmentation obscures lesions). Autosomal recessive; genetic test available. Progressive Retinal Atrophy (PRA): Bilateral symmetric retinal degeneration; nyctalopia (night blindness) first sign; many breeds; genetic test available. Hereditary cataracts: Labrador, Golden Retriever, Standard Poodle, Boston Terrier. Diabetic cataracts in dogs are bilateral and form rapidly (osmotic sorbitol mechanism)—rare in cats.