Veterinary Ophthalmology Flashcards

A dog presents with acute, painful unilateral blindness, a mid-dilated unresponsive pupil, corneal edema, and intraocular pressure of 58 mmHg. The most likely diagnosis is:

Answer: Acute primary glaucoma

Acute primary glaucoma (most commonly closed-angle in dogs) presents with markedly elevated IOP (>30 mmHg, often 40–70 mmHg), corneal edema from endothelial damage, fixed mid-dilated pupil, and rapid onset of blindness. It is an ocular emergency requiring immediate IOP reduction. Uveitis typically causes miosis and low-to-normal IOP. Retinal detachment causes blindness without pain or elevated IOP. Corneal ulcers cause pain and discharge but not elevated IOP.

Equine Recurrent Uveitis (ERU) is the leading cause of blindness in horses worldwide. The most commonly implicated infectious agent in leptospiral-associated ERU is:

Answer: Leptospira interrogans serovar Pomona

Leptospira interrogans serovar Pomona is the most frequently isolated serovar associated with ERU in North American horses. The proposed mechanism involves molecular mimicry between leptospiral proteins and uveal antigens, triggering autoimmune inflammation. Vitreous humor PCR or antibody titers support the diagnosis. Other serovars (Grippotyphosa, Bratislava) are also implicated. Onchocerca can cause periocular inflammation but is less directly linked to recurrent uveitis.

A cat presents with a ventromedial corneal opacity that appears yellow-brown and is firmly adherent to the cornea. There is no fluorescein stain uptake. What is the most likely diagnosis?

Answer: Corneal sequestrum (corneal nigrum)

Corneal sequestrum (also called corneal nigrum or corneal mummification) is unique to cats and is characterized by a focal area of corneal stromal necrosis that appears amber, brown, or black. It does not stain with fluorescein (no epithelial defect initially) and is firmly embedded in the stroma. It is most common in brachycephalic breeds. Treatment is surgical keratectomy. Eosinophilic keratitis has a white/pink vascularized plaque appearance; indolent ulcers have loose epithelial edges and do stain.

The direct pupillary light reflex (PLR) assesses integrity of which anatomical pathway?

Answer: Optic nerve → pretectal nucleus → bilateral Edinger-Westphal nucleus → ciliary ganglion → pupillary sphincter

The PLR pathway does NOT require cortical processing. Afferent signal travels via the optic nerve (CN II) → optic chiasm → pretectal nucleus (midbrain) → bilateral Edinger-Westphal (parasympathetic) nuclei → oculomotor nerve (CN III) → ciliary ganglion → short ciliary nerves → pupillary sphincter muscle. The bilateral projection from the pretectal nucleus explains the consensual (indirect) PLR. Lesions in the visual cortex do not abolish the PLR.

Pannus (chronic superficial keratitis) in dogs is most prevalent in which breed and is thought to be exacerbated by which environmental factor?

Answer: German Shepherd Dog; ultraviolet radiation

Pannus (chronic superficial keratitis, CSK) is a bilateral immune-mediated inflammatory condition most common in German Shepherd Dogs and Belgian Shepherd Dogs. UV radiation worsens the condition, explaining its higher prevalence and severity at high altitudes (e.g., Colorado) and in dogs with more outdoor sun exposure. Treatment includes topical corticosteroids and/or tacrolimus (cyclosporine) long-term to control immune-mediated vascularization and pigmentation.

A cherry eye (prolapse of the nictitating membrane gland) in a young Bulldog should be managed by:

Answer: Surgical repositioning (pocket or tacking technique) to preserve glandular tear production

The third eyelid (nictitating membrane) gland contributes approximately 30–50% of the aqueous portion of the tear film. Excision was historically performed but leads to an unacceptably high rate of keratoconjunctivitis sicca (KCS/dry eye). Current standard of care is surgical repositioning using the 'pocket technique' or anchoring sutures to preserve the gland's tear-producing function. Medical management alone is generally ineffective for established prolapse.