In dogs but not cats, an enzyme in the corneal stroma converts glucose to sorbitol causing diabetic dogs to be at risk for irreversible cataract formation.
What is this enzyme?
Aldose reductase
What is the simplest test for confirming patency of the nasolacrimal duct (also called the Jones test)?
Application of fluorescein stain on the eye, and observation for its emergence at the nares.
Which species normally has the least prominent retinal vessels on funduscopic visualization of the optic disc: ovine, bovine, equine, canine, or feline?
Equine
In which order should the following ophthalmic diagnostic tests be conducted on a patient?
- A. Bacterial culture swab
- B. Fluorescein stain
- C. Schirmer tear test
A → C → B
Bacterial samples first, to reduce contamination; Schirmer second, to avoid interference by artificial tears used with fluorescein stain (last).
For ophthalmoscopy, which gives a more complete view of the whole fundus: direct or indirect?
Indirect ophthalmoscopy
(lens held in hand)
It also allows visualization through both eyes using a headset.
Hyphema makes it impossible to see a patient’s posterior chamber. Ultrasound reveals an undulating membrane tracing a wavelike course through the posterior chamber.
What is the diagnosis?
Retinal detachment
You need to choose between two topical ointments, one containing corticosteroids, and one without, for the treatment of conjunctivitis.
What is an important condition to rule out before dispensing the medication?
Corneal ulceration
If present, topical corticosteroids are contraindicated as they can delay healing and increase risk of infection.
Which components of the eye make up the uvea?
- Choroid
- Ciliary body
- Iris
Observing symmetry of eye position and pupils tests which cranial nerves?
CN III, IV, and VI
(oculomotor, trochlear, and abducens, respectively)
They innervate the extraocular muscles.
What is the difference between microphthalmia and phthisis bulbi?
Both are smaller than normal globes, but:
- microphthalmia is congenital
- Phthisis bulbi is acquired shrinkage of the globe secondary to trauma or inflammation
What is hypopyon?
An accumulation of white blood cells (pus) in the anterior chamber of the eye
A cat presents with sudden blindness. Fundic exam reveals retinal hemorrhages and detachment. Assess what systemic parameter to identify a potential underlying cause?
Blood pressure
Retinal hemorrhage and detachment in cats and dogs commonly results from systemic hypertension; measuring blood pressure helps identify and manage this underlying cause.
Why may it be useful to distinguish between superficial and deep corneal vascularization?
- Superficial suggests superficial corneal or external ocular disease
- Deep suggests corneal stromal or intraocular disease
Superficial: e.g., keratitis, chronic irritation, ulceration
Deep: e.g., uveitis, deep stromal keratitis, endothelitis
A canine patient has an intraocular pressure of 7 mmHg (normal: 10-30 mmHg). What is the most likely diagnosis?
Uveitis
(< 10 mmHg)
With glaucoma, the IOP is > 30 mmHg.
Name two ways to confirm a suspected diagnosis of retinal detachment in a blind animal.
- Fundic examination
- Ocular ultrasound
Ultrasound is the only method if there is severe hyphema or corneal opacity obscuring the anterior and posterior chambers.
Why does a very deep corneal ulcer show no central uptake of fluorescein, and what is this called?
The ulcer has reached the level of Descemet’s membrane, which does not absorb fluorescein
(This is called a descemetocele)
At this stage, the cornea is extremely thin and at high risk of perforation, so use care to avoid pressure on the eye.
What is the difference between ectopic cilia, distichiasis, and trichiasis?
- Ectopic cilia: aberrant individual eyelashes arising from meibomian glands and growing through conjunctiva towards the globe
- Distichiasis: presence of an additional row of eyelashes on the eyelid margin, in addition to the normal lashes
- Trichiasis: normal eyelashes (or facial hair) that rub on the conjunctiva or cornea (e.g., skin fold on the muzzle of a bulldog)
In the normal eye, how is aqueous humor produced and drained, and how does this relate to glaucoma?
- Produced by the ciliary body
- Drains mainly through the trabecular meshwork (+/- via the uveoscleral route, varying by species)
- Glaucoma (increased intraocular pressure) occurs when drainage is impaired or production‑drainage balance is disrupted
What are hallmark findings on ophthalmic examination indicative of a flare-up of uveitis?
- Aqueous flare (protein or cells in the anterior chamber)
- Miosis
- Corneal edema
- Conjunctival/episcleral hyperemia
- Blepharospasm
- Epiphora
- Low intraocular pressure in acute cases
Uveal inflammation disrupts the blood‑aqueous barrier, causing inflammation and pain.
Which ocular nerve blocks are commonly used to facilitate enucleation in cattle?
Retrobulbar 4‑point or Peterson block plus an auriculopalpebral block (or other eyelid motor block)
Blocking both the motor function (eyelids) and sensory/optic nerve prevents reflex bradycardia and allows safe globe removal.
Name one veterinary species that has 100% decussation of optic nerve fibers at the optic chiasm.
- Birds
- Fish
In these species, all optic nerve axons cross to the contralateral side, unlike mammals, where only a portion cross due to binocular vision and more frontal eye placement.
Which nerve block is commonly used to facilitate ophthalmic examination in horses, and what is its effect?
Auriculopalpebral nerve block; it temporarily paralyzes the orbicularis oculi muscle, preventing blinking
Blocking this motor branch of the facial nerve allows the examiner to hold the eyelids open without causing discomfort.
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