Conjunctivitis

Introduction

Conjunctivitis is the most commonly diagnosed ocular disease in general practice.

There are many primary causes of conjunctivitis, but the conjunctiva are also commonly secondarily inflamed with almost all ocular and periocular disease including corneal inflammation/ulceration, episcleral and scleral disease, orbital disease, lid and cilia abnormalities, uveitis and glaucoma. Uncomplicated conjunctivitis should not involve changes within the eye, and so any intraocular signs indicated intraocular disease which has to be investigated first.

Aetiologies for conjunctivitis include:

Viral conjunctivitis:

Canine Distemper Virus

Canine Adenovirus 1

Feline Calicivirus

Herpesvirus: in the dog, horse and cow

Bacterial conjunctivitis:

Can be acute or chronic, various pathogens may be involved

Chlamydophila felis

Mycoplasma

Mycotic conjunctivitis

Parasitic conjunctivitis: Thelazia

Sicca-related conjunctivitis: Keratoconjunctivitis Sicca (KCS)

Allergic/immune-mediated conjunctivitis

Eosinophilic conjunctivitis of cats

Miscellaneous: actinic-related conjunctivitis, lipogranuloma, ligneous conjunctivitis

Physical irritation

In rabbits keratitis and conjunctivitis are usually observed as an extension of dacryocystitis, seldom being encountered as primary clinical entities in rabbits. Foreign bodies in the conjunctival fornix are surprisingly uncommon, especially considering the frequency of their appearance in pet guinea pigs which are often kept under the same conditions of husbandry as pet rabbits. Harrenstien et al list trauma from dust or bedding, fight wounds and primary or secondary entropion, distichiasis or trichiasis as causes.

Clinical Signs

Hyperaemia: this is the hallmark of conjunctivitis and may vary in severity. The hyperaemia is diffuse, more severe towards the fornix and not restricted to a few large veins. It is usually located in the palpebral conjunctiva, but can involve all surfaces.

Chemosis: oedema of the conjunctiva is manifested by thicker folds of dorsal bulbar conjunctiva when the lid is rubbed against the bulbar conjunctiva. The scleral vessels are obscured by the chemosis and hyperaemia.

Ocular discharge: this is usually the presenting complaint. It may be minimal or absent, and mild with serous discharge from hypersecretion of the lacrimal glands due to irritation. Bacterial infections often lead to a mucopurulent discharge with polymorphonuclear cells and excess mucus. Some cats produce a black, waxy discharge.

Follicles: lymphoid follicles can be present on the conjunctival surfaces, and give them a cobblestone appearance. It is a non-specific reaction to conjunctival irritation.

Pain: this varies with the type of conjunctivitis and the species. Cats often have blepharospasm. Corneal pain should be ruled out before the pain is attributed to the conjunctivitis.

Diagnosis

This will depend on the cause of the conjunctivitis, but common tests include:

Fluorescein dye test

Schirmer tear test

Cytology from conjunctival scrapings: examined for cellular alterations, bacteria and inclusion bodies

Culture and sensitivity: from meibomian gland secretions

Conjunctival biopsy: to rule out neoplastic primary causes and goblet cell abnormalities

Specific diagnostic tests for Chlamydophila felis and Feline Herpesvirus such as ELISA and PCR.

Treatment

Routine superficial infections of the eye should be treated with an antibiotic or a combination not routinely used systemically.

Topical therapy is adequate in most cases. Most cases of acute bacterial conjunctivitis will respond within 8-10 days whereas chronic cases may require therapy for a prolonged period of time.

In some cases, cold compresses can be used to decrease conjunctival oedema.

Topical antibiotics available include: chlortetracycline, chloramphenicol and fucidic acid.

Systemic doxycycline may be necessary in cats for C. felis infections.

Corticosteroids can be helpful in non-infectious disorders, but should be avoided in cats where most conjunctivitides are infectious.

Topical cyclosporin is the licensed treatment of Keratoconjunctivitis Sicca.

Topical and systemic antivirals are still being tested and the response to therapy is variable.

In rabbits, treatment involves cleaning the conjunctival fornix followed by topical applications of broad spectrum antibiosis (covering Pasteurella spp or following sensitivity testing) with or without corticosteroids.

Conjunctivitis Learning Resources
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References

Holt, E. (2010) Ophthalmology RVC student notes

Martin, C. (2010) Ophthalmic disease in veterinary medicine Manson Publishing

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