Module 5 Flashcards
Conjunctiva - anatomy
Bulbar conjunctiva, palpebral conjunctiva and nictitans conjunctiva (palpebral nictitans and bulbar nictitans)
Only fixed at eyelids and limbus
Non keratinised, stratified squamous epithelium.
Goblet cells in outer epithelium; produce mucoid tear film, lymphatics in middle, connective tissue and blood vessels in deepest portion
Bloods vessels - palpebral, malar and anterior ciliary arteries.
Sensory = CN V
Functions: corneal health, eyelid mobility, barrier to micro-organisms and FBs
Commensals: gram +ves staphs, bacilus, corynebacterium. 30-90% normal dogs will have +ve culture so not necessarily significant. Many cultures which are negative due to technique used, does not mean no organisms.
Normal cytology: epithelial cells, occasional bacteria, WBCs rare unless dz.
Immune responses
CALT: conjunctival associated lymphoid tissue.
The only lymphatic drainage system of the entire eye, in substantia propria
CD8+ T cells, plasma cells (secrete IgA)
Inflammation is generated by release of chemical mediators.
Tight junctions between cells together with the rapid renewal and concurrent shedding prevents micro-organisms from penetrating through the conjunctiva
Response to insult
Reactions:
- hyperaemia; distinguish from episcleral or scleral congestion (these would suggest IO dz), location of hyperaemia very important, superficial = conjunctiva, generally more tortuous than deeper vessels, will move as eyeball changes position, and will branch with topical adrenaline. Deeper vessels tend be bigger, rarely branching, and will not blanch.
- Chemosis; acute conjunctivitis, may be so swollen the globe cannot be visualised. Shar pei has this look always due to mucinosis, not a problem unless other ocular problems.
- ocular discharge; serous, mucoid, mucopurulent or purulent. Take samples before examination with topicals or cleaning away.
Congenital conditions of the conjunctiva
Epibulbar dermoid: normal tissue in an abnormal location, lateral limbus and may extend onto cornea or lateral canthus. GSD and St Bernard. Birman cat - genetic. Seen frequently in French Bulldogs!
Conjunctival cysts: rare. Secondary to FHV-1 symblepharon. Parasitic conjunctival and lacrimal cysts.
Conjunctivitis - Infectious
STT and fluorescein! Essential
Infectious:
- Primary infectious is rare in the dog - Canine distemper virus; plus URT and GI signs
- Secondary infection from trauma, FBs, KCS or other ocular disease. Check TEL.
- Cultures not useful always, unless pure growth of single organism. Cytology often more useful.
- fungal/parasitic is rare in the UK
- Primary common in cats. FHV-1, Calici occasionally but more resp signs. Mycoplasma or Chlamydophila.
- Secondary infections in cats following trauma, or viral infection is not uncommon
Conjunctivitis - Infectious. Feline Herpes Virus (FHV-1)
- Primary infection = acute disease, usually young animals
- URT dz, conjunctivitis an corneal ulceration, secondary bacterial infection
- Corneal scarring, symblepharon, epiphora, recurrent conjunctivitis, keratitis, rhinitis
- 80%–>carriers, harbour in CN V, recrudescence = replication in corneal epithelium
- Dx: hx and clinical signs, dendritic ulcers,
- PCR from corneal or conj sample superseded swabs but still results unreliable, routine testing no longer recommended
- Acute: ABs - topical and systemic, anti-virals, not licensed but via cascade. In acute phase anti-virals may reduce sequalae. Ganciclovir - topical. Famiciclovir (penciclovir) - oral for 2-4 weeks, caution renal or hepatic dz. Tear replacements.
Conjunctivitis - Infectious. Chlamydophila felis
Acute, chronic, recurrent
unilateral to bilateral. +/- UTR dz in young cats
No corneal ulceration.
Dx: clinical signs and Hx, definitive dx requires isolation from swabs/PCR
Tx: topical (chlortetracycline) and systemic (doxycycline), all animals in a multi-cat household should be treated 3-6 weeks. Amoxicillin has some benefit. Vaccination for cats entering endemic household.
Conjunctivitis - Infectious. Mycoplasma
Can be isolated from normal eyes too
Self-limiting in a month
Chemosis common
Pseudomembrane - can make conjunctiva pale and friable looking
Dx: symptoms + culture, but responds to tetracyclines so tx as per Chlamydophila
Immune mediate/allergic
Part of atopic dermatitis - examine for skin disease!
type I hypersensitivity reaction in response to allergens
Follicle formation and epiphora
+/- blepharitis
Secondary infection
Cytology/bx = eosinophils
Tx of underlying issue, topical CCS to alleviate ocular signs, topical mast cell stabilisers.
Eosinophilic conjunctivitis
Cats.
Corneal involvement often present.
Traumatic conjunctivitis
Dogs and cats: following fighting or from brambles
Haemorrhage can be significant
Secondary bacterial infection vey common
Check TEL and NL duct
Lacerations usually heal well without intervention
Toxic/chemical conjunctivitis
Hypersensitivity locally to any ophthalmic preparation or home remedy
Sometimes stop topicals for a few days to check these are not causing more problems
More common in cats than dogs
Chemicals - paint splashes, plaster dust. Hx and CS self explanatory
Conjunctival neoplasia
Uncommon
Bx - quick and easy.
Melanoma, SCC, MCT, haemangioma
conjunctivitis secondary to corneal disease
KCS; common cause of secondary bacterial conjunctivitis.
Corneal ulceration; leads to hyperaemia and inflammation of conjunctiva
conjunctivitis secondary to adnexal disease
As a result of irritation or conjunctival exposure, collection of debris from: entropion, ectropion, distichiasis, ectopic cilia, blepharitis, medial canthal pocket syndrome
