The conjunctiva serves several important functions:

• Protects the eye from debris and microorganisms
• Produces components of the tear film
• Contains immune cells that respond to pathogens
• In allergic conditions, it becomes a site of excessive immune response

Type I Hypersensitivity (Immediate)

• Most common form
• Mediated by IgE antibodies and mast cells
• Occurs within minutes of allergen exposure
• Causes histamine release and inflammation

Type IV Hypersensitivity (Delayed)

• Cell-mediated immune response
• Takes hours to days to develop
• Often associated with contact allergens

Allergic conjunctivitis often occurs alongside:

• Atopic dermatitis
• Allergic rhinitis
• Food allergies
• Flea allergy dermatitis
• Seasonal allergies

Environmental (Aeroallergens)

• Pollens (grass, tree, weed)
• Dust mites
• Mold spores
• Dander from other animals

Contact Allergens

• Household cleaning products
• Shampoos and grooming products
• Topical medications
• Plants (direct contact)
• Fabric or carpet fibers

• Fall: Weed pollens (ragweed)
• Year-round: Dust mites, mold, indoor allergens

Dogs More Commonly Affected

• West Highland White Terriers
• Bulldogs (English, French)
• Labrador Retrievers
• Golden Retrievers
• Boxers
• Shar-Peis
• Dalmatians
• Most breeds with atopic dermatitis

Cats

• Less commonly diagnosed with primary allergic conjunctivitis
• Often occurs secondary to upper respiratory infections
• Siamese and Himalayan cats may be predisposed to atopy

• Living in highly pollinated areas
• Indoor allergen exposure
• Concurrent atopic dermatitis
• Age: Usually develops in young adults (1-3 years)
• Previous allergic conditions

Eye Redness (Hyperemia)

• Pink to red discoloration of conjunctiva
• Visible blood vessels
• May affect one or both eyes
• Often worse with allergen exposure

Eye Discharge

• Clear, watery discharge (serous)
• May become mucoid (thicker, stringy)
• Usually not purulent (yellow/green) unless secondary infection
• Discharge may dry around eyes

Itching (Pruritis)

• Rubbing eyes with paws
• Rubbing face on carpet or furniture
• Squinting or blinking frequently
• Pawing at face

Swelling (Chemosis)

• Swollen, puffy conjunctiva
• May appear as fluid-filled bubble on eye surface
• Eyelids may be swollen

Tearing (Epiphora)

• Excessive tear production
• Tear staining beneath eyes
• Wet fur around eyes

• Third eyelid elevation
• Photophobia (light sensitivity)
• Head shaking
• Concurrent skin symptoms (if atopic)

• Eosinophilic keratitis may occur
• Often have concurrent upper respiratory symptoms

• Cloudy or blue-tinged cornea
• Change in pupil size
• Vision changes
• Yellow-green discharge (infection)
• Trauma to the eye

Key questions to answer:

• Duration and pattern of symptoms
• Seasonal or year-round?
• Both eyes or one eye?
• Concurrent skin symptoms?
• Response to previous treatments?
• Environmental changes (new products, moving, etc.)?

Standard Eye Exam

• Visual inspection of eyes and adnexa
• Assessment of discharge character
• Evaluation of conjunctival appearance
• Corneal examination
• Pupil light responses
• Intraocular pressure if indicated

Schirmer Tear Test

• Measures tear production
• Rules out dry eye (keratoconjunctivitis sicca)
• Normal values vary by species

Fluorescein Staining

• Detects corneal ulcers or scratches
• Rules out corneal damage from rubbing
• Essential before prescribing steroids

Conjunctival cytology can help identify:

• Eosinophils: Strongly suggests allergic cause
• Neutrophils: May indicate bacterial component
• Lymphocytes/Plasma cells: Chronic inflammation
• Bacteria: Secondary infection
• Mast cells may also be present

Intradermal Testing

• Gold standard for environmental allergies
• Requires specialist (dermatologist)
• Tests reaction to injected allergens
• Used to formulate immunotherapy

Serum Allergy Testing

• Blood test for allergen-specific IgE
• Less invasive than intradermal
• Can be performed by general practitioner
• Results used for immunotherapy

Elimination Diet Trial

• For suspected food-related allergies
• 8-12 week strict novel protein diet
• Helps identify food triggers

Must differentiate from:

• Bacterial conjunctivitis
• Viral conjunctivitis (especially in cats)
• Keratoconjunctivitis sicca (dry eye)
• Foreign body
• Eyelid abnormalities (entropion, ectropion)
• Corneal disease
• Uveitis
• Glaucoma

Antihistamine Eye Drops

• First-line for mild cases
• Options: olopatadine, ketotifen
• Used 1-2 times daily
• Safe for long-term use
• May take 1-2 weeks for full effect

Mast Cell Stabilizers

• Prevent mast cell degranulation
• Options: lodoxamide, nedocromil
• Best used prophylactically before allergen exposure
• Can combine with antihistamines

Corticosteroid Eye Drops

• Very effective for inflammation
• Options: prednisolone acetate, dexamethasone
• NEVER use if corneal ulcer present (fluorescein test first!)
• Use short-term when possible
• May increase risk of infection

Cyclosporine/Tacrolimus

• Immunomodulatory agents
• Options: cyclosporine (Optimmune), tacrolimus
• Excellent for chronic management
• Takes 2-4 weeks for full effect
• Steroid-sparing properties

NSAID Eye Drops

• Anti-inflammatory without steroids
• Options: ketorolac, diclofenac
• Useful when steroids contraindicated
• May delay corneal healing

Artificial Tears

• Flush allergens from eye surface
• Provide lubrication
• Use preservative-free for frequent application
• Can apply 4-6 times daily as needed

Oral Antihistamines

• Help with concurrent allergic symptoms
• Options: diphenhydramine, cetirizine, hydroxyzine
• Variable efficacy for eye symptoms alone
• Safe for long-term use

Oral Corticosteroids

• Reserved for severe cases
• Short courses preferred
• Monitor for side effects

Apoquel (Oclacitinib) - Dogs

• Janus kinase inhibitor
• Very effective for atopic symptoms
• May help with ocular component
• Prescription only

Cytopoint (Lokivetmab) - Dogs

• Injectable anti-IL-31 antibody
• Monthly injection
• Targets itch pathway
• May provide some eye relief

When allergens can be identified:

• Dust mites: HEPA filters, frequent cleaning, washable bedding
• Pollen: Limit outdoor time during peak seasons, wipe face/paws after outside
• Mold: Reduce humidity, clean high-moisture areas
• Contact allergens: Identify and remove specific products

• Keep windows closed during high pollen times
• Wash pet bedding weekly in hot water
• Consider hypoallergenic beds
• Regular vacuuming with HEPA vacuum
• Limit carpeting in home

• Hypoallergenic, fragrance-free shampoos
• Wipe face and around eyes with damp cloth
• Consider omega fatty acid supplements for skin health

Subcutaneous Immunotherapy (SCIT)

• Traditional allergy shots
• Gradual increase in allergen dose
• Modifies immune response over time
• Takes 6-12 months to see full effect
• 60-70% success rate
• Lifetime commitment in many cases

Sublingual Immunotherapy (SLIT)

• Allergen drops given under tongue daily
• Easier to administer than injections
• Similar efficacy to SCIT
• Growing option in veterinary medicine

• Monitor for secondary infections
• Adjust treatment based on seasonal patterns
• Watch for medication side effects
• Keep symptom diary

• Recurrent corneal ulcers
• Severe or unusual presentation
• Suspected concurrent eye disease
• Chronic cases requiring advanced management

Corneal Ulceration

• From chronic rubbing and scratching
• Can become infected or deep
• May require intensive treatment
• E-collar essential to prevent further trauma

Secondary Bacterial Infection

• Inflammation predisposes to infection
• Yellow-green discharge develops
• Requires antibiotic treatment

Keratoconjunctivitis Sicca (Dry Eye)

• Chronic inflammation can damage tear glands
• May develop secondary dry eye
• Requires lifelong tear supplementation

Chronic Corneal Changes

• Pigmentation of cornea
• Scarring
• May affect vision if central cornea involved

Eosinophilic Keratitis (Cats)

• White-pink plaque on cornea
• Associated with allergies and herpesvirus
• Requires specific treatment

For Allergic Conjunctivitis

• Generally good with appropriate management
• Most pets controlled with combination therapy
• Quality of life usually excellent
• May require lifelong treatment
• Symptoms often wax and wane with seasons

Factors Affecting Prognosis

• Ability to identify and avoid allergens
• Response to immunotherapy
• Compliance with treatment
• Presence of concurrent atopic dermatitis
• Development of complications

Most pets with allergic conjunctivitis:

• Live normal, comfortable lives
• Enjoy normal activities
• Have minimal visual impact (usually)
• Require ongoing but manageable care

Key points for pet owners:

• This is usually a chronic, manageable condition
• Treatment may be lifelong
• Symptoms may flare seasonally
• Avoid rubbing (use E-collar if needed)
• Regular medication compliance is important
• Watch for signs of worsening or complications