Glaucoma in Cats: High Eye Pressure, Corneal Cloudiness and Vision Rescue

1. Pathophysiology: Aqueous Humor Dynamics

Aqueous humor is continually synthesized by the non-pigmented ciliary epithelium and circulates through the pupil into the anterior chamber, where it exits via the iridocorneal drainage angle (trabecular meshwork) into systemic venous circulation.

When inflammatory debris, cellular infiltrates, or fibrous synechiae occlude this drainage sieve while fluid production proceeds, intraocular pressure surges rapidly, halting axoplasmic transport at the optic disc.

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2. Secondary Etiologies in Cats: Uveitis, Tumors, and Luxation

Primary congenital glaucoma is exceptionally rare in felines. Overwhelmingly, cases stem from secondary disease:

• Feline Chronic Anterior Uveitis: The leading culprit. Inflammatory cells, fibrin, and posterior synechiae clog the drainage pathways. Commonly secondary to FIP, FIV, FeLV, or Toxoplasmosis.
• Intraocular Neoplasia: Feline diffuse iris melanoma (FDIM) or ocular lymphoma directly infiltrating the filtration angle.
• Lens Luxation or Subluxation: Anterior displacement of the crystalline lens creates physical pupillary block.

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3. Clinical Presentation: Identifying the Red, Cloudy Eye

Feline glaucoma signs can be insidious initially before sudden decompensation:

• Corneal edema: High hydrostatic pressure overwhelms the corneal endothelial pump, leading to hydration of the stroma and a hazy, milk-blue appearance.
• Fixed dilated pupil (Mydriasis): The iris sphincter muscle is paralyzed by pressure ischemia, failing to constrict when illuminated.
• Episcleral vascular engorgement: Prominent corkscrew-like red vessels radiating across the white sclera.
• Buphthalmos: Physical enlargement and stretching of the globe in chronic, end-stage cases.

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4. Diagnostic Triage: Applanation and Rebound Tonometry

Definitive evaluation requires prompt physical measurement of pressure:

• Rebound Tonometry (TonoVet): Instantly measures IOP without topical anesthetic; pressures >25-30 mmHg in an inflamed eye confirm glaucoma.
• Slit-lamp biomicroscopy: Assesses aqueous flare, keratic precipitates, and lens stability.
• Ocular ultrasonography: Evaluates posterior segment anatomy, retinal detachment, or retrobulbar masses.

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5. Emergency Medical Protocols and Surgical Management

Immediate clinical goals are reducing IOP to preserve viable photoreceptors and relieve chronic headache:

• Topical Carbonic Anhydrase Inhibitors (CAIs): Dorzolamide 2% or brinzolamide 1% drops every 8 hours directly suppress aqueous humor production. These are the gold-standard first-line agents in felines.
• Beta-blockers: Timolol 0.5% combined with CAIs to enhance pressure reduction.
• Caution with Prostaglandin Analogs (Latanoprost): Unlike in dogs, latanoprost is less effective in cats due to species-specific receptor differences and may exacerbate underlying uveitis.
• Surgical intervention: In permanently blind, chronically painful eyes with buphthalmos, enucleation or intraocular evisceration provides immediate, curative pain relief.

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Scientific Sources and References

• Maggs, D. J., Miller, P. E., & Ofri, R. (2018). Slatter's Fundamentals of Veterinary Ophthalmology, 6th ed. Elsevier.
• McLellan, G. J., & Miller, P. E. (2011). Feline glaucoma—a comprehensive review. Vet Ophthalmol, 14(s1), 15-29.
• Stiles, J. (2014). Ocular manifestations of systemic disease in cats. Compend Contin Educ Vet, 36(6), E1-E9.