TL;DR: Anisocoria, or unequal pupil size, is a serious clinical sign in cats that requires immediate veterinary attention to diagnose potential eye diseases or neurological emergencies.
What is anisocoria and how does it affect my cat's eyes?
Anisocoria is the medical term used to describe a condition where a cat's pupils are of unequal size. You may notice one pupil is a thin slit while the other is wide and round, or simply a noticeable difference in diameter between the two. This is not a standalone disease but rather a clinical sign that something is affecting your cat’s eyes or their neurological system.
Is it a veterinary emergency if my cat’s pupils are different sizes?
- High Urgency: Anisocoria is a high-priority condition, and your cat should be seen by a veterinarian as soon as possible.
- Serious Potential Causes: The cause can range from localized eye issues like glaucoma or uveitis to severe systemic problems such as head trauma, feline leukemia, or neurological disorders.
- Immediate Danger Signs: Seek emergency care immediately if the pupil change is accompanied by sudden blindness, stumbling, or a change in temperament.
Why should I take a photo of my cat's eyes for the triage process?
- Capture a Static Record: Because pupils react to light, their appearance may change by the time you reach the vet; a photo preserves the imbalance as it appeared at home.
- Help the Veterinary Team: A clear photo in normal lighting helps the clinical team assess the severity of the condition more accurately.
- Identify Secondary Symptoms: Photos allow the veterinarian to look for additional signs like redness, cloudiness, or discharge that might fluctuate during transport.
Clinical Context (Merck Veterinary Manual)
Anisocoria in cats warrants investigation into several potential etiologies. Diagnostic differentials include dysautonomia, intracranial diseases (pituitary masses, paranasal masses, meningiomas, or lymphosarcoma), systemic diseases (such as canine distemper, mycosis, protothecosis, or granulomatous meningoencephalomyelitis), neoplasia, trauma, and orbital cellulitis. Clinical confirmation of dysautonomia may be aided by contrast radiography of the esophagus and reduced lacrimal secretion (<5 mm/min when measured by the Schirmer tear test). Pilocarpine (0.1%) applied to the cornea causes profound miosis within 10-15 minutes due to denervation hypersensitivity but has no effect on a healthy cat.
Chapter: Neurology
Source: The Merck Veterinary Manual, 11th Edition (Page 1256)