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
- Herpesvirus: Feline Calicivirus, Herpesvirus in the dog, horse and cow
Mycoplasma
Bacterial conjunctivitis: acute or chronic
Mycotic conjunctivitis
Parasitic conjunctivitis: [Thelazia lacrymalis|Thelazia]]
Sicca-related conjunctivitis: KCS
Allergic/immune-mediated conjunctivitis
Eosinophilic conjunctivitis of cats
Miscellaneous: actinic-related conjunctivitis, lipogranuloma, ligneous conjunctivitis
Physical irritation
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 licenced treatment of Keratoconjunctivitis Sicca.
Topical and systemic antivirals are still being tested and the response to therapy is variable.
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References
Holt, E. (2010) Ophthalmology RVC student notes
Martin, C. (2010) Ophthalmic disease in veterinary medicine Manson Publishing