conjunctivitis and dry eye

• You are presented with a dog with recurrent conjunctivitis in both eyes. The right eye is shown on the RHS, Schirmer tear test readings are 13mm/min in the right eye and 9mm/min in the left eye. What is the most likely diagnosis?


  KCS in both eyes
• The conjunctival surfaces are thin transparent/pink mucous membranes. This starts at the limbus, forms continuous sheet over eyelids, third eyelid and globe.

  The conjunctiva is freely mobile apart from attachments at limbus and eyelid margin, this allows free movement of ocular structures.

  • Conjunctival oedema (chemosis) or subconjunctival haemorrhage can be marked

  This structure contributes to tear film (goblet cells produce mucin), and is lubricated by tear film
• The conjunctiva provides the only lymphatic drainage of the eye (C.A.L.T - conjunctival-associated lymphoid tissue).

  • Chronic antigenic stimulation causes lymphocytes to form active follicles (follicular hypertrophy)
• label the image

  A) palpebral conjunctiva

  B) bulbar conjunctiva

  
• label the image

  A) palpebral

  B) bulbar

  
• The conjunctiva has sparse sensory innervation (ophthalmic branch of trigeminal), this means that it is easy to anaesthetise with topical anaesthetic, and it has a rich vascular supply so can undergo rapid healing. Bulbar conjunctiva overlies the sclera so there are two layers of blood vessels.
• Differential diagnoses for a discharging eye varies between the type of discharge….

  • Purulent discharge
  • Bacterial conjunctivitis
  • Foreign bodies
  • KCS (dry eye) with a secondary bacterial infection
  • Thick/tenacious discharge
  • KCS (dry eye) - thick discharge stuck to the eye is characteristic for this disease
  • Serous (watery) discharge
  • Ocular pain e.g., Corneal ulcers causing increased lacrimation
  • Tear overflow (epiphora) due to reduced nasolacrimal drainage
  • Haemorrhagic discharge
  • Coagulopathies
  • Ocular trauma
• acute conjunctivitis can be unilateral or bilateral. signs include...

  • Hyperaemia (redness)
  • Chemosis (oedema)
  • Swelling/thickening
  • Discharge
  • Lacrimation vs mucoid, purulent, mucopurulent or haemorrhagic
  • Mild irritation/blepharospasm
  • Occasionally pruritic (e.g. allergic conjunctivitis)
• chronic conjunctivitis involves thickening of the squamous metaplasia of the epithelium. signs include...

  • Hyperpigmentation
  • Follicular hyperplasia (especially posterior third eyelid and in conjunctival fornixes)
• Mucinosis is common in Shar Pei dogs and this mimics chemosis (conjunctival oedema) but is normal for Shar Peis.

  
• ‘Medial canthal pocket syndrome’ is where mucus accumulates at the medial canthus. This occurs in Dolichocephalic breeds with naturally deep-set eyes (enophthalmos) e.g. Dobermann, Standard Poodle. No treatment is necessary but the owner may need to clean the dogs eyes more often.

  
• secondary bacterial infection is a common cause for conjunctivitis. involves commensal Gram positive organisms, e.g. Staphylococcus spp and Streptococcus spp
• Adnexal = supporting structures around the eye
• conjunctivitis can be secondary to adnexal diseases such as...

  • entropion (inversion of the eyelid margin)
  • ectropion (which can get so severe that the eye has both ectropion and entropion)
  • eyelid masses
  • ectopic cilia (arise from a follicle inside/near the meibomian gland and emerge through conjunctiva at right angles to the cornea.)
  • distichiasis (extra eyelashes emerge from meibomian gland orifices - can be an incidental finding)
  • dry eye
  • tear duct infections (dacryocystitis)
• Epiphora is tear overflow due to poor tear drainage this can be due to…

  • Congenital atresia/agenesis of part of nasolacrimal system or malposition tear punctum. This is common and usually non-painful
  • Obstruction by foreign or inflammatory material. This may cause dacryocystitis
• • Dacryocystitis is the cause of most conjunctivitis in rabbits. This is often due to an underlying cause, e.g., overlong molar roots pressing on the nasolacrimal duct causing a blockage. This is often recurrent, so treatment is aiming to manage the condition rather than cure, this involves nasolacrimal duct flushing
  • NB single lower nasolacrimal puncta which is larger than in cats and dogs
• immune-mediated is the most common cause of dry eye but others include…

  • Congenital
  • Lacrimal gland aplasia/hypoplasia
  • Neurogenic
  • Unilateral, dry eye/dry nose
  • Toxic
  • Sulphonamide drugs can cause this and be identified on history
  • Endocrine disease e.g., diabetes mellitus, hypothyroidism
  • Iatrogenic e.g., removal of the third eyelid gland in a case of cherry eye
• Keratoconjunctivitis sicca (KCS) is local immune-mediated destruction of lacrimal tissue (lacrimal gland and third eyelid (nictitans) gland). This is a common cause of canine conjunctivitis, especially in the WHWT, Pug, Shih Tzu, Bull dog, CKCS, English cocker spaniel etc. This usually affects young–middle aged dogs and is often bilateral.
• Clinical signs of KCS are…

  • Recurrent conjunctivitis that improves with any topical therapy as anything lubricates the eye!
  • Tacky mucoid-mucopurulent discharge stuck to ocular surface (overcompensation of mucin due to the lack of the aqueous component of the tear film)
  • Blepharospasm
  • +/- Corneal ulceration
  • Corneal changes with chronic KCS such as corneal vascularisation (to heal itself and also increase nutrition - the tear film provides nutrition), fibrosis and pigmentation which can lead to reduced vision.
  • Distorted Purkinje image (due to a lack of shine from the tear film)
• Diagnosis of dry eye involves a Schirmer tear test and early treatment (for the immune-mediated form) is best (before lacrimal tissue is destroyed). This requires lifelong therapy to control the progressive disease involving…

  • Tear substitutes - there are various false tear preparations in eye drop, gel or ointment formulation
  • Tear stimulants (lacrimogenic) e.g., Cyclosporine 0.2% (Optimmune - licensed first line treatment)
  • Broad spectrum topical antibiotic to treat secondary infection (this often isn't used as if the animal has its own tears they are then able to clear the infection)
• Treatment of canine conjunctivitis involves…

  • Treatment/removal of the underlying cause
  • Topical antibiotic therapy such as
  • Fusidicacid (Isathal®) this is a licensed product in the UK. This is the first choice as it treats Gram positive organisms most commonly found in canine conjunctivitis (Staph spp, Strep spp)
  • Chloramphenicol drops/ointment
  • Other antibiotics based on culture & sensitivity