NAVLE Special Senses

Feline Glaucoma Study Guide

📅 March 28, 2026 ⏱ 25 min read

Glaucoma is a neurodegenerative disease characterized by progressive optic nerve damage and retinal ganglion cell loss, ultimately resulting in irreversible vision loss.

Overview and Clinical Importance

Glaucoma is a neurodegenerative disease characterized by progressive optic nerve damage and retinal ganglion cell loss, ultimately resulting in irreversible vision loss. In cats, glaucoma is typically an insidious and gradually progressive condition that is often underdiagnosed due to its subtle clinical presentation. Unlike dogs, cats rarely exhibit the acute, painful presentation common in canine glaucoma.

Feline glaucoma accounts for approximately 1 in 367 cats presenting to veterinary teaching hospitals, though prevalence is likely higher due to underdiagnosis. It represents 29% of all feline enucleation submissions to pathology laboratories. Critically, 73% of cats with glaucoma are already blind at the time of initial presentation.

High-YieldSecondary glaucoma accounts for 95-98% of all feline glaucoma cases, with chronic uveitis being the most common underlying cause. Primary glaucoma is RARE in cats, unlike dogs.

Parameter	Normal Value	Clinical Significance
IOP (TonoVet)	15-25 mmHg (mean ~20 mmHg)	Greater than 25 mmHg is abnormal
IOP (Tono-Pen)	12-23 mmHg (mean ~18 mmHg)	Underestimates IOP greater than 30 mmHg
Inter-eye difference	Less than 8 mmHg	Difference greater than 8 mmHg warrants investigation
Circadian variation	4-5 mmHg higher at night	Single IOP reading may not reflect true status

Anatomy and Aqueous Humor Dynamics

Aqueous Humor Production and Outflow

Aqueous humor is produced by the non-pigmented epithelium of the ciliary processes through both active secretion (primarily) and ultrafiltration. It provides nutrition to the avascular lens and cornea and maintains intraocular pressure (IOP) and globe shape.

Aqueous Humor Outflow Pathways in Cats

Conventional (trabecular) pathway: Accounts for greater than 97% of aqueous outflow in cats. Aqueous flows from the posterior chamber, through the pupil to the anterior chamber, then exits via the trabecular meshwork to the angular aqueous plexus and intrascleral venous plexus.

Uveoscleral (unconventional) pathway: Accounts for less than 3% of outflow in cats (much less than in dogs). Aqueous passes through the iris and ciliary body stroma to the suprachoroidal space.

High-YieldThe feline iridocorneal angle is WIDER and more open than in dogs or humans. The pectinate ligament fibers are delicate and widely spaced. This anatomical difference explains why primary angle-closure glaucoma is rare in cats.

Normal Feline Intraocular Pressure

Cause	Mechanism	Key Features
Chronic Uveitis	Inflammatory debris, posterior synechiae, pre-iridal fibrovascular membranes obstruct outflow	MOST COMMON cause. Often idiopathic. Associated with FIP, FIV, FeLV, toxoplasmosis
Intraocular Neoplasia	Tumor cells infiltrate trabecular meshwork; neovascular membranes cause angle closure	Diffuse iris melanoma most common. Also lymphoma, post-traumatic sarcoma
Lens Luxation	Pupillary block; vitreous prolapse	Usually SECONDARY to uveitis or glaucoma (unlike dogs where it can be primary)
Trauma/Hyphema	Blood clots, fibrin, inflammatory cells obstruct drainage angle	Also consider hypertension as cause of hyphema in older cats
Aqueous Misdirection (FAHMS)	Aqueous diverted posteriorly into vitreous; causes anterior displacement of lens-iris diaphragm	Middle-aged to older cats. Shallow anterior chamber. Female predisposition

Classification of Feline Glaucoma

Secondary Glaucoma (95-98% of cases)

Secondary glaucoma occurs when an identifiable underlying disease process impairs aqueous humor outflow. It may be unilateral or bilateral depending on the underlying cause.

Causes of Secondary Glaucoma in Cats

NAVLE TipWhen you see an older cat with BILATERAL glaucoma and a SHALLOW anterior chamber, think Feline Aqueous Humor Misdirection Syndrome (FAHMS). This is UNIQUE to cats and has not been described in dogs.

Primary Glaucoma (2-5% of cases)

Primary glaucoma occurs without antecedent ocular disease. It is rare in cats compared to dogs. Breed predispositions include Siamese, Burmese, and Persian cats.

Primary Congenital Glaucoma (PCG): A mutation in the LTBP2 gene has been identified as the cause of autosomal recessive congenital glaucoma in Siamese cats. Affected kittens show elevated IOP by 8 weeks of age, globe enlargement, and elongated ciliary processes.

Memory Aid - Feline Glaucoma = "SECONDARY UVEITIS" S - Secondary glaucoma is most common (95-98%) E - Elevated IOP greater than 25 mmHg C - Chronic and insidious presentation O - Often BLIND at presentation (73%) N - Neoplasia is a major cause (melanoma, lymphoma) D - Dorzolamide is first-line treatment A - Anterior uveitis is #1 cause R - Rarely primary (unlike dogs) Y - Young cats with PCG = LTBP2 mutation

Clinical Sign	Description	Comparison to Dogs
Buphthalmos	Globe enlargement; may be dramatic in young cats	Common in both species with chronic glaucoma
Mydriasis	Fixed, dilated pupil; poor PLR	Common in both species
Corneal Edema	Mild to moderate cloudiness	LESS pronounced in cats than dogs at comparable IOP
Pain/Blepharospasm	Often minimal; cats mask pain well	LESS pronounced than in dogs
Episcleral Injection	Minimal to absent	Prominent in dogs; RARE in cats
Haab's Striae	Tears in Descemet's membrane from globe stretching	Rare in cats; seen with chronic buphthalmos
Vision Loss	Often the presenting complaint	73% of cats are BLIND at presentation

Clinical Signs and Presentation

Feline glaucoma is characterized by subtle clinical signs that often progress slowly over months. Unlike dogs, cats rarely display acute pain, episcleral injection, or dense corneal edema.

High-YieldThe feline eye is remarkably RESILIENT to glaucomatous damage. Cats may maintain some vision even with gross buphthalmos. Optic disc cupping is difficult to appreciate in cats due to lack of myelination of the normal feline optic nerve head.

Tonometer	Type	Anesthesia	Key Limitation
TonoVet	Rebound	Not required	Must be held horizontal
Tono-Pen	Applanation	Required	Underestimates IOP greater than 30 mmHg

Diagnosis

Tonometry

Accurate IOP measurement is essential for diagnosis. The TonoVet rebound tonometer is preferred for cats because it does not require topical anesthesia, is well-tolerated, and is more accurate at elevated IOP ranges compared to applanation tonometers.

Tonometer Comparison in Cats

Additional Diagnostic Procedures

Gonioscopy: Evaluates the iridocorneal angle. In cats, it can be performed without a goniolens due to the wide angle. Useful for identifying angle abnormalities and differentiating primary from secondary glaucoma.

Ocular Ultrasound: Essential for evaluating intraocular masses, lens position, anterior chamber depth (especially in FAHMS), and vitreous abnormalities.

Systemic Workup: CBC, chemistry panel, FeLV/FIV testing, blood pressure measurement, +/- toxoplasmosis titers to identify underlying causes of uveitis.

Drug Class	Drug	Dose	Mechanism	Notes
Carbonic Anhydrase Inhibitor	Dorzolamide 2%	1 drop q8h	Decreases aqueous production	FIRST-LINE therapy. ~45% IOP reduction. May cause hypersalivation
CAI + Beta-blocker	Dorzolamide/Timolol	1 drop q8-12h	Decreases aqueous production	Synergistic effect. Avoid with cardiac/respiratory disease
Beta-blocker	Timolol 0.5%	1 drop q12h	Decreases aqueous production	Causes miosis - avoid if pupil block. Risk of bradycardia
Prostaglandin Analog	Latanoprost	N/A	Increases uveoscleral outflow	INEFFECTIVE in cats due to lack of FP receptors. NOT recommended
Osmotic Diuretic	Mannitol	1-2 g/kg IV over 30 min	Dehydrates vitreous	Emergency use only. Effect lasts 6-10 hours

Treatment

Treatment goals include reducing IOP to less than 25 mmHg (ideally 10-15 mmHg), preserving vision when possible, managing pain, and treating the underlying cause. The prognosis for vision preservation is guarded to poor in most cases due to late presentation.

Medical Management

High-YieldPROSTAGLANDIN ANALOGS (latanoprost, travoprost) are INEFFECTIVE in cats due to lack of FP receptors in the feline ciliary body. They also cause intense MIOSIS which can worsen pupil block. Do NOT use prostaglandin analogs in cats!

Surgical Management

Enucleation: The treatment of choice for blind, painful eyes and when intraocular neoplasia is suspected. Provides definitive pain relief and allows histopathologic diagnosis. CAUTION: In cats, excessive traction on the optic nerve during surgery can damage the optic chiasm and cause contralateral blindness due to the short feline optic nerve.

Cyclophotocoagulation: Laser ablation of ciliary body. Less successful in cats than dogs, possibly due to sparse pigmentation in feline ciliary body. Contraindicated with uveitis.

Gonioimplants: Drainage shunts may fail more frequently in cats due to pre-existing uveitis and small globe size.

Intravitreal Gentamicin: Generally CONTRAINDICATED in cats due to risk of post-traumatic ocular sarcoma development.

NAVLE TipOn the NAVLE, if asked about treatment of a blind, painful glaucomatous eye in a cat with suspected intraocular neoplasia, the answer is ENUCLEATION. Also remember that intravitreal gentamicin injection is contraindicated in cats due to risk of post-traumatic sarcoma.

Prognosis

The prognosis for vision preservation is guarded to poor in most cases of feline glaucoma due to late presentation and chronic nature of disease. Medical therapy can often maintain comfort and may preserve residual vision for months to years in some cases. The prognosis for life depends on the underlying cause - cats with glaucoma secondary to lymphoma or metastatic neoplasia have a poorer systemic prognosis.

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