Clinical features of conjunctivitis:
Diffuse hyperemia, chemosis, ocular discharge (serous, mucoid or mucopurulent) and blepharospasm.
Hyperemia
diffuse redness of conjunctiva is due to engorged capillaries. There may be injection of the larger conjunctival blood vessels as well. The conjunctival vessels are mobile and tortuous.
episcleral injection
by engorged straight vessels over the sclera that do not move and usually indicate intraocular disease.
Trick to tell apart deep vessels and superficial vessels
Hyperemic vessels can be ‘blanched out’ with a drop of epinephrine. Deep vessels will not ‘blanch out’.
chemosis
edema and appears as a ‘swelling’ or thickening of the conjunctiva.
Exudate
Conjunctival discharge may be mucoid, mucopurulent, purulent, eosinophilic, septic etc. Cytology should be performed on any ocular discharge.
Causes of conjunctivitis in the dog
In the dog, conjunctivitis is most commonly caused by KCS, environmental irritants and allergies. Recently, canine herpes virus 1 has been associated with conjunctivitis in dogs.
Causes of conjunctivitis in the cat
In the cat, conjunctivitis is usually due to an infectious agent: Feline Herpes Virus (FHV1), Chlamydia felis and possibly Bartonella, are the most common causes.
These are important considerations when determining treatment for conjunctivitis.
Using corticosteroids in feline conjunctivitis
Steroids are contraindicated for infectious etiologies, so they are rarely indicated in feline conjunctivitis. Use of steroids (topical or systemic) may cause recrudescence of FHV1 ocular disease. Feline conjunctivitis will be covered in a separate chapter with feline ocular diseases.
Causes of conjunctivitis in the horse
In the horse, ulcers and intraocular disorders are common causes of conjunctivitis and must be ruled out prior to initiating treatment. Conjunctivitis is associated with many systemic diseases (see equine chapter).
Differentials for conjunctivitis in the dog
KCS, irritants, allergies, follicular conjunctivitis, lymphoid hyperplasia
Corticosteroids to use after you’ve ruled out corneal ulcers
Use the least potent drug that is effective for problem:
Hydrocortisone- mild allergies and irritants – does not penetrate cornea
Dexamethasone – follicular conjunctivitis, strong steroid, penetrates cornea
Prednisolone acetate penetrates cornea (prednisolone phosphate does not). It is not usually indicated for treatment of conjunctivitis but is used for anterior uveitis.
allergies as a cause of conjunctivitis
They may be due to atopy, food, contact, medications etc. It
treatment of allergies
These patients may respond to topical antibiotics +/- steroids, and topical mast cell blockers (ketotifen).
Presentation of dogs who present for follicular conjunctivitis
This diagnosis is specific for a clinical presentation seen in young dogs. Conjunctival hyperemia with variable degrees of discomfort and ocular discharge are present bilaterally. The only abnormality found is lymphoid hyperplasia on the bulbar aspect of the third eyelid.
Treatment of follicular conjunctivitis
The clinical signs resolve with use of topical dexamethasone (NPDex) every 8 hours then tapered to the lowest dosing frequency that controls the clinical signs. The dogs generally ‘outgrow’ this condition at 18-24months of age.
Corneal Ulcers:
(loss of corneal epithelium exposing corneal stroma)
Nasal-lacrimal obstruction/dacryocystitis - clinical signs
These patients have copious tearing and purulent discharge. They are not usually painful until flushing or manipulation of the duct is attempted. Fluorescein does not exit the nares but may have purulent discharge from the puncta when flushed.
Cause of N-S obstruction and dacrocystitis
Causes of nasal-lacrimal obstruction are foreign body, dental abscess, neoplasia of sinus or trauma.
oral/otic disease affecting the eye is common in what species
This is a common problem in rabbits.
KCS in dogs should be ruled out with what other disease and why?
KCS should be ruled out in dogs with chronic otitis due to inflammation associated with the parasympathetic nerve as it runs with the facial nerve through the petrous temporal bone.
Retrobulbar disease
Infection, inflammation or tumor in the tissue surrounding the eye will cause varying degrees of conjunctival hyperemia, injection and discharge.
Equine dfdx for conjunctivitis
Parasites, SCC, solar (actinic), blunt or sharp trauma, eyelid abnormalities need to be ruled out as causes of conjunctivitis. Topical BNP is a good first choice when no underlying cause is seen. Any case that does not resolve in a day or two should be reassessed.