Red Eyes in Cats: Causes & Treatment

Red eyes in cats are a common presenting complaint that always warrants veterinary investigation, as redness reflects underlying inflammation, infection, injury, or disease affecting ocular structures. Because cats' eyes are complex and delicate organs essential for vision and wellbeing, any abnormality demands prompt evaluation. Red eyes may result from benign causes (temporary irritation from dust or mild allergic response) or serious conditions threatening vision (corneal ulceration, glaucoma, uveitis). The critical distinction is that red eyes that persist for more than a few hours or are accompanied by discharge, pain, swelling, squinting, or vision changes represent medical emergencies requiring urgent veterinary care. Understanding what causes red eyes, recognising that persistent redness is abnormal, knowing which symptoms indicate emergency, and understanding the diagnostic approach helps cat owners respond appropriately and protect their cat's sight.

This comprehensive guide explores the anatomy of eye redness, details the most common causes of red eyes, discusses clinical presentation, presents diagnostic procedures, explains treatment approaches, addresses prognosis, and provides guidance on when emergency care is essential.

Understanding Red Eyes in Cats

Why Do Eyes Become Red?

Eye redness occurs when blood vessels in the eye become dilated (enlarged), allowing more blood to flow through the eye tissue, making redness visible.

What Causes Blood Vessel Dilation:

• Inflammation: Immune response to irritation, infection, or injury triggers blood vessel dilation
• Infection: Bacterial, viral, or fungal infections cause inflammation and redness
• Injury/trauma: Scratches, lacerations, or blunt force cause local inflammation
• Increased eye pressure: High intraocular pressure physically dilates vessels
• Allergic reaction: Immune response to environmental triggers causes histamine release and vasodilation

Which Eye Structures Can Be Red

• Conjunctiva: Membrane covering eyeball and lining eyelids; appears as pink/red tissue
• Sclera: White part of eye; normally white, appears red when inflamed
• Eyelids: Can become red, swollen from inflammation
• Interior eye structures: Inner inflammation (uveitis) may show as redness in specific eye areas

Common Causes of Red Eyes in Cats

1. Conjunctivitis (Inflammation of the Conjunctiva) — Most Common

Conjunctivitis is the most frequent cause of red eyes in cats, involving inflammation of the conjunctival membrane covering the eye.

Types of Conjunctivitis:

• Allergic conjunctivitis: Allergic reaction to environmental allergens (pollen, dust, mold spores)
• Infectious conjunctivitis: Bacterial, viral, or fungal infection of conjunctiva
• Traumatic conjunctivitis: Injury to conjunctiva from scratches, foreign objects
• Irritant conjunctivitis: Response to irritants (smoke, sprays, chemicals)

Symptoms:

• Conjunctival redness: Visible pink/red conjunctival tissue
• Eye discharge: May be clear (viral/allergic) or coloured (bacterial)
• Squinting (blepharospasm): Eye held partially closed; indicates discomfort
• Excessive tearing: Watery eyes; tears running down face
• Mild swelling: Eyelids may be slightly swollen

2. Upper Respiratory Infections (Feline Herpesvirus/Calicivirus)

Viral upper respiratory infections commonly affect eyes simultaneously, causing conjunctivitis and sometimes corneal disease.

Feline Herpesvirus (FHV-1):

• Most common cause viral conjunctivitis: FHV-1 directly infects conjunctival and corneal tissue
• Clinical signs: Conjunctivitis, keratitis (corneal inflammation), sometimes corneal ulcers
• Systemic signs: Sneezing, nasal discharge, fever accompanying eye disease
• Reactivation risk: FHV-1 reactivates during stress; cats may have recurrent episodes
• Anterior uveitis possibility: FHV-1 can trigger anterior uveitis (inner eye inflammation)

Calicivirus:

• Causes conjunctivitis: Conjunctival inflammation and discharge
• Systemic signs: Respiratory symptoms, oral ulcers

3. Corneal Ulcers (Keratitis) — Serious

Corneal ulcers are painful injuries to the cornea (eye surface) and represent serious eye emergencies requiring immediate treatment.

What Causes Corneal Ulcers:

• Trauma: Scratches, cat fights, foreign objects, self-trauma from rubbing
• Feline herpesvirus: FHV-1 causes keratitis and ulcer formation
• Corneal erosion: Defect in corneal surface exposes underlying tissue
• Infection: Secondary bacterial infection of corneal defect

Symptoms:

• Severe eye redness: Intense redness from severe inflammation
• Severe pain: Affected cat squints severely; shows obvious pain behaviour
• Excessive tearing: Profuse tearing; tears running down face
• Light sensitivity (photophobia): Avoidance of bright light; eye held shut
• Cloudiness: Cornea appears cloudy/hazy (epithelial defect or scar)
• Visible defect: Close inspection shows crater-like defect on cornea surface
• Frantic eye rubbing: Aggressive pawing/rubbing at affected eye; risk of self-trauma

Why Urgent Treatment Critical:

• Rapid progression: Corneal ulcers deteriorate quickly; can lead to perforation
• Perforation consequences: Corneal perforation causes loss of eye contents; permanent blindness
• Vision threat: Scarring from healed ulcers may impair vision permanently
• Pain severity: Corneal ulcers extremely painful; pain management essential

4. Glaucoma — Emergency

Glaucoma is dangerously high intraocular pressure (IOP) that damages the optic nerve; progressive sight-threatening emergency.

What Happens in Glaucoma:

• Elevated intraocular pressure: Normal IOP ~15–25 mmHg; glaucoma >25–30 mmHg (varies)
• Optic nerve damage: High pressure damages optic nerve cells; causes permanent vision loss
• Irreversibility: Glaucoma often irreversible; priority is preventing vision loss, not restoring lost vision

Symptoms of Glaucoma:

• Eye redness: Intense redness from pressure and inflammation
• Severe ocular pain: Severe, often excruciating pain
• Enlarged eye (buphthalmia): Eye appears abnormally enlarged; stretched from pressure
• Dilated, unresponsive pupil: Pupil fixed and dilated; doesn't respond to light
• Cloudy cornea: Corneal oedema (swelling) from high pressure makes cornea cloudy
• Vision loss: Sudden blindness; cat may show behaviour changes from sight loss

Secondary Glaucoma:

• Complication of other disease: Uveitis, corneal ulcer, anterior chamber bleeding can trigger glaucoma
• Serious complication: Glaucoma developing from other eye disease worsens prognosis significantly

5. Uveitis (Intraocular Inflammation) — Serious

Uveitis is inflammation of the uveal tract (iris, ciliary body, choroid); serious condition potentially threatening vision.

What Causes Uveitis:

• Infection: Toxoplasmosis (most common infectious cause in cats), FeLV, FIV, FIP, bacterial infections, fungal infections (cryptococcosis, blastomycosis)
• Immune-mediated: Autoimmune disease; immune system attacking uveal tissue
• Trauma: Eye injury causing secondary uveitis
• Neoplasia: Tumours (iris melanoma most common) causing ocular inflammation
• Secondary: Reaction to corneal ulcer or other ocular disease
• Idiopathic: In many cats, cause undetermined despite investigation

Symptoms of Uveitis:

• Intense eye redness: Sclera and conjunctiva intensely red
• Severe ocular pain: Severe pain; cat avoids eye contact, hides
• Squinting: Eye held partially or completely closed
• Light sensitivity: Avoidance of bright light; photophobia
• Cloudy appearance: Interior eye turbidity from inflammatory cells/proteins
• Clear watery discharge: Serous discharge from inflammation
• Vision problems: Difficulty seeing; vision loss if inflammation affecting retina
• Pupillary changes: Miotic (constricted) pupil; pupil may be irregularly shaped

Complications of Untreated Uveitis:

• Secondary glaucoma: High pressure developing from inflammation
• Corneal ulcers: Secondary corneal disease from chronic inflammation
• Posterior synechiae: Iris sticking to lens; causes vision-threatening complications
• Cataracts: Lens opacity from chronic inflammation
• Retinal detachment: Inflammation causing retina to separate from eye wall; blindness
• Lens luxation: Lens dislocating from position; vision loss

6. Eye Injuries and Trauma

• Scratches/lacerations: Injuries to eye or eyelid from cat fights, sharp objects
• Foreign objects: Plant material, dust, debris irritating eye
• Chemical injury: Exposure to caustic substances
• Thermal injury: Burns from hot liquids or surfaces
• Results: Redness, pain, tearing, potential for secondary infection

7. Allergies and Environmental Irritants

• Allergens: Pollen, dust, mold spores, dander triggering allergic response
• Irritants: Smoke, strong perfumes, cleaning products, air pollutants
• Typically mild: Usually causes mild redness and tearing; more uncomfortable than serious
• May be seasonal: Pollen-related allergies worse certain times of year

8. Dry Eye (Keratoconjunctivitis Sicca)

• Reduced tear production: Inadequate tears leave cornea and conjunctiva dry
• Causes redness: Dry tissue becomes irritated; blood vessels dilate
• Secondary causes: Autoimmune destruction of tear-producing glands; medications; systemic disease
• Symptoms: Redness, mucoid discharge, squinting, pain

Discharge Types and What They Indicate

• Clear watery discharge: Suggests viral infection or allergic reaction; tear overflow
• Yellow/green discharge: Suggests bacterial infection; requires antibiotic treatment
• Thick mucoid discharge: Indicates severe inflammation or bacterial infection
• Bloody discharge (haemorrhage): Suggests severe trauma or high intraocular pressure

Diagnosis of Red Eyes in Cats

Physical Examination

• Visual inspection: Assess which eye structures red; degree of redness; presence of discharge, swelling
• Observation of behaviour: Squinting, light avoidance, head position indicate pain level

Fluorescein Staining Test

• Purpose: Detects corneal defects (ulcers, erosions, scratches)
• Procedure: Fluorescein dye applied to cornea; stains defects bright green under light
• Critical for: Identifying corneal ulcers requiring urgent treatment

Intraocular Pressure (IOP) Measurement

• Tonometry: Measures pressure inside eye; detects glaucoma or elevated pressure
• Normal IOP: ~15–25 mmHg in cats; higher suggests glaucoma
• Essential test: Must be performed with uveitis and suspected glaucoma

Schirmer Tear Test (STT)

• Measures tear production: Evaluates whether cat has dry eye
• Procedure: Tear production paper placed under eyelid; measures tear strip wetness
• Normal values: >15 mm in 60 seconds; <5 mm suggests dry eye

Slit Lamp Examination (Advanced)

• Magnified examination: Detailed view of anterior and sometimes posterior eye structures
• Identifies: Corneal defects, iris changes, lens problems, internal bleeding
• Usually performed by ophthalmologist: Specialised equipment and training needed

Blood Tests and Diagnostics

• FHV-1/Calicivirus testing: Viral PCR or serology for viral infections
• Toxoplasmosis testing: Serology for feline uveitis most common infectious cause
• FeLV/FIV testing: Screen for retroviral infections causing uveitis
• Other blood work: Complete blood count, chemistry panel assessing systemic disease

Treatment of Red Eyes

Topical Medications (Eye Drops/Ointments)

Antibiotics:

• For bacterial infections: Tobramycin, ofloxacin, moxifloxacin (most common antibiotics prescribed)
• Application: Typically multiple times daily; frequency depends on severity
• Duration: Usually 7–14 days minimum

Antivirals:

• For FHV-1: Cidofovir (most effective; compounded); applied multiple times daily
• For herpes ulcers: Critical for healing; prevents recurrence

Anti-inflammatory:

• Corticosteroids: Prednisolone, dexamethasone reducing inflammation
• NSAIDs: Flurbiprofen (Ocufen) reducing inflammation and pain
• Caution: Steroids contraindicated in corneal ulcers (risk of perforation); only use when ulcers ruled out

Pain Relief:

• Atropine: Dilates pupil; reduces pain from iris inflammation; prevents iris sticking
• NSAIDs: Topical pain management

Systemic (Oral/Injectable) Medications

• Oral antibiotics: For severe infections or when topical insufficient
• Systemic NSAIDs: Pain relief and anti-inflammation (use with caution in cats)
• Systemic corticosteroids: For severe uveitis; significant side effects risk in cats; used cautiously
• Antiviral medication: Famciclovir oral for FHV-1

Treating Underlying Disease

• If toxoplasmosis: Antitoxoplasma therapy
• If systemic disease: Treatment of FeLV, FIV, FIP, other systemic conditions
• If glaucoma: IOP-lowering medications (beta blockers, prostaglandin analogues)

Surgical Treatment

• Severe trauma: Repair of corneal perforations or serious injuries
• Uncontrolled glaucoma: Drainage procedures to lower IOP
• Severe uveitis with uncontrollable inflammation: Sometimes enucleation (eye removal) necessary
• Lens removal: If cataract or lens-induced uveitis

Important: NEVER Use Human Eye Medication

• Human eye drops may contain: Decongestants or NSAIDs harmful to cats
• Risk: Human medications can worsen feline eye conditions
• Always use veterinary-approved medication only: Formulations specifically designed for cats

Prognosis and Outcomes

Mild Conjunctivitis:

• Excellent prognosis: Usually resolves completely with treatment
• Recovery time: 5–10 days typical

Corneal Ulcers:

• Depends on depth: Superficial ulcers generally good prognosis; deep ulcers guarded
• Scarring: May retain permanent scar affecting vision slightly
• Treatment crucial: Early treatment dramatically improves outcomes

Glaucoma:

• Sight-threatening: Often irreversible once present; goal is preventing further vision loss
• Long-term medication: Usually requires lifelong IOP-lowering therapy
• Blindness risk: Progressive blindness possible despite treatment

Uveitis:

• Variable: Some cases transient (resolve within weeks); others chronic (lifelong treatment)
• Underlying cause matters: Some infectious causes resolve; others require indefinite management
• Complications risk: Without aggressive treatment, vision loss complications common

When to Seek Emergency Veterinary Care

• Sudden blindness: Inability to see suddenly; EMERGENCY
• Severe swelling: Eyelids or eye dramatically swollen; EMERGENCY
• Cloudy eye: Cornea appears white/cloudy; suggests pressure or infection; URGENT
• Eye injury: Visible injury, bleeding, obvious trauma; EMERGENCY
• Bleeding from eye: Blood in or from eye; EMERGENCY
• Extreme pain: Cat in obvious severe pain, unable to open eye; EMERGENCY
• Enlarged eye: Eye appears abnormally large; suggests glaucoma; URGENT
• Unable to open eye: Complete inability to open eye; URGENT
• Persistent redness: Redness lasting >24 hours; requires evaluation within 24–48 hours

This guide is based on research from VCA Animal Hospitals, University of Tennessee College of Veterinary Medicine, Feline Ophthalmology Series (Cat Fanciers' Association), Today's Veterinary Practice, DVM360, Colorado State University Veterinary Health System, and ACVO (American College of Veterinary Ophthalmologists). Conjunctivitis most common cause red eyes. FHV-1 DNA documented in aqueous humour of cats with anterior uveitis negative for other known causes; may enter eye via axonal transport. Anterior uveitis can trigger secondary glaucoma. Iris melanoma most common primary ocular neoplasm in cats; can mimic uveitis. Corneal ulcers extremely painful; brachycephalic cats at higher risk. Most common eye drops: tobramycin, ofloxacin, moxifloxacin; cidofovir compounded for FHV-1 ulcers. Topical corticosteroids contraindicated in corneal ulcers—risk perforation. Systemic steroids risk side effects diabetes, heart disease in cats; used cautiously. Atropine prevents posterior synechiae (iris sticking to lens) major complication uveitis. Topical antiviral cidofovir most effective FHV-1 treatment. Life-long topical medications for chronic uveitis in <5% complication rate. Lens-induced uveitis from cataract rupture may be uncontrollable; secondary glaucoma often results; enucleation often necessary. Diagnostic tests (Schirmer, tonometry, fluorescein) must be performed initial uveitis evaluation. Toxoplasmosis most common infectious cause uveitis in cats. Normal IOP 15–25 mmHg; clinical signs glaucoma if IOP >25–30 mmHg. Atropine-induced reactivation FHV-1 documented; monitor closely if steroids prescribed. Emergency referral ophthalmologist recommended if vision-threatening conditions suspected. Early aggressive treatment essential to prevent secondary glaucoma, synechiae, vision loss complications.