Small animal ophthalmology Flashcards
Conjunctivitis and keratoconjunctivitis sicca, feline ophthalmology
Describe the anatomy of the conjunctiva
- Thin transparent pink mucous membrane
- Starts at limbus and covers globe (bulbar conjunctiva) and lines inner aspects of upper/lower eyelids (palpebral conjunctiva)
- Space formed called conjunctival sac
- Lines both sides of third eyelid
- Fornix is the “u-turn” of conjunctiva
- Freely mobile apart from attachments at the limbus and eyelid margin
Describe the physiology of the conjunctiva
- Rich vascular supply to allow rapid healing
- Sparse nerve supply
- Provides the only lymphatic drainage of the eye
Describe the appearance of the CALT
- Conjunctival associated lymphoid tissue
- Appears as little follicles, roughened areas of conjunctiva
Describe the nervous supply of the conjunctiva
- Supplied by CNV ophthalmic brnach
- Easy to anaesthetise with topical anaesthetic
- Facilitates minor surgery e.g. conjunctival biopsy
Describe the common clinical signs of acute conjunctivitis
- Uni or bilateral
- Hyperaemia (conjunctival redness)
- Chemosis
- Swelling or thickening
- Mild irritation e.g. mild blepharospasm
- Discharge (lacrimation)
- Pruritus may be seen in allergic conjunctivitis and may lead to self trauma
Describe the potential appearance of discharge in conjunctivitis
- Mucoid
- Purulent
- Mucopurulent
- Haemorrhagic
Describe mucinosis in Shar Pei dogs
- Mimics chemosis but is normal for breed
- Muzzle also looks swollen
Describe medial canthal pocket syndrome
- Normal variation in dolicephalic breeds
- Have naturally deep set eyes
- Mucus accumulates at medial canthus, should be flushed away naturally but does not occur properly in these breeds
- No treatment indicated, can flush with contact lens solution every few days
Describe the clinical signs of chronic conjunctivitis
- Hyperaemia, discharge etc. as for acute
- Thickening (squamous metaplasia of epithelium)
- Hyperpigmentation
- Follicular hyperplasia
Describe what is meant by follicular hyperplasia
- Nodule like structure representing lymphoid tissue
- Most obvious on posterior third eyelid and in conjunctival fornices
- Follicular conjunctivitis common in young dogs, may need treatment but often resolves spontaneously
List the potential aetiological agents of canine conjunctivitis
- Infectious
- Non-infectious
- Extension from local disease
- Secondary to another ocular disease
- Secondary to systemic disease
Describe infectious conjunctivitis in dogs
- Primary infectious uncommon
- Secondary bacterial very common e.g. dry eye, abnormal eyelid conformation, often by commensal G+ve e/g/ Staph, Strep.
- Viral infection v. uncommon e.g. canine herpesvirus-1
- Parasitic uncommon e.g. Thelazia more common in dogs imported from eastern Europe
- Fungal rare in UK
Describe the common sign of bacterial conjunctivitis
Purulent discharge
List the common underlying causes for conjunctivitis in dogs
- Eyelid problem e.g. entropion, ectropion
- Eyelash problem e.g. distichia, ectopic cilia
- Tear film problem e.g. dry eye
- Tear duct infection (dacryocystitis)
- Trauma e.g FB, laceration
- Allergic e.g. atopic dermatitis
- Irritants e.g. smoke sand, neomycin
- Ligneuous conjunctivitis in Doberman
- Radiation induced
What is entropion and how is it treated?
- Inturned eyelid
- Surgical treatment
- Removal of elliptical piece of skin
Describe ectropion as a cause of conjunctivitis
- Everted eyelid margin
- Common in St Bernards, eyelids too big
- “Normal” in many breeds
- If marked, can accumulate debris in sac which predisposes to infection and conjunctivitis
Describe distichiasis as a cause of conjunctivitis
- Extra eyelashes
- Often incidental finding but can cause conjunctivitis
- Unlikely to be causing conjunctivitis if found at 5yo, more likely to be the cause if found at 1yo
Give examples of how conjunctivitis may be an extension from local ocular disease
- Blepharitis eyelid inflammation)
- Lacrimal disease e.g. cherry eye
- Orbital disease e.g. retrobulbar abscess
Give examples of diseases that may have conjunctival involvement
- Anaemia
- Jaundice
- Coagulopathy
- Neoplasia e.g. lymphoma
- Auto-immune disease
- Systemic hypertension
List the breeds that are predisposed to cherry eye
- Bulldog
- Lhasa Apso
- Shih Tzu
- Mastiff breeds
Explain why excision is not recommended as the treatment for cherry eye
- Third eyelid gland produces 1/3rd of tear volume
- Breeds predisposed to cherry eye also predisposed to dry eye
List the potential causes of keratoconjunctivitis sicca
- Most common: immune mediated destruction of lacrimal tissue, stopping fluid production
- Congenital: lacrimal gland aplasia/hypoplasia
- Neurogenic: uniateral, dry eye/dry nose
- Toxic: sulphonamide drugs
- Endocrine disease: diabetes mellitus, hypothyroidism
- Iatrogenic: removal of TEG, some drugs
List the breeds that are predisposed to KCS
- WHWT
- Pug
- Shih Tzu
- Bulldog
Describe the typical presentation of KCS
- Young dog
- Bilateral
- Progressive
- Recurrent conjunctivitis that improves with any topical therapy as anything lubricates eye
- Conjunctivitis
- Sticky discharge
How is KCS diagnosed?
- Shirmer tear test
- Clinical signs
Describe the treatment of KCS
- Lifelong therapy
- Tear substitutes
- Tear stimulations (lacrimogenic) e.g. ciclosporin 0.2% (Optimmune)
- Broad spectrum topical antibiotic to treat secondary Staph infection
What is the main difference between feline and canine conjunctivitis?
Canine usually not infectious, feline usually infectious
List the potential aetiologies of feline conjunctivitis
- Infectious
- Non-infectious
- Extension from local disease
- Secondary to another ocular disease
- Secondary to systemic disease
List the 5 primary agents of feline infectious conjunctivitis
- Chlamydophila felis (bacterium)
- Feline herpesvirus 1
- Feline calicivirus
- Mycoplasma felis
- Bordatella bronchiseptica
Describe the presentation and treatment of feline calicivirus
- TYpically upper respiratory disease, oral ulceration, polyarthritis
- Generally do not test and treat for it as a cause of conjunctivitis
- Anti-viral treatment ineffective
Describe Mycoplasma spp. as a cause of conjunctivitis in cats
- Also found in normal cats
- Diagnosis by PCR
- Topical antibiotic e.g. tetracyclines (Doxycycline)
Describe Bordetella bronchiseptica as a cause of conjunctivitis in cats
- G-ve bacterium
- Affects respiratory tract of cats (and dogs) and rare zoonosis
- Diagnosis: culture and/or PCR
- Treatment: doxycycline
What 3 causes of conjunctivitis are treated by doxycycline in the cat
- Chlamydophila
- Mycoplasma
- Bordetella
Describe the clinical signs of chlamydial conjunctivitis in cats
- Unilateral conjunctivitis, becomes bilateral within a few days
- Chemosis often marked, hyperaemia
- No corneal signs, no corneal ulcer
- Absent or mild upper respiratory disease
Describe the diagnosis of chlamydial conjunctivitis in cats
- Clinical signs
- Conjunctival swab for PCR
- Culture superseded by PCR, lots of false negatives
Describe the treatment of chlamydial conjunctivitis in cats
- Systemic treatment indicated as organism affects resp, GI and repro tract
- Doxycyline antibiotic (5mg/kg BID or 10mg/kg SID for 3 weeks)
- Treat all in contacts with doxy as well
- Amoxyclav good for pregnant queens or kittens
What is the main side effect of doxycycline in cats?
Discolouration of teeth and oesophagitis
Describe the clinical signs of FHV-1 in kittens and youung cats
- Bilateral conjunctivitis in conjunction with upper resp signs (cat flu)
- +/- corneal ulceration
Describe the clinical signs of FHV-1 in adult cats
- Unilateral ocular discharge with mild conjunctivitis
- History of previous upper resp infection
- Wide range of other conditions e.g. sequestrum entropion, eosinophilic keratitis
- Dendritic corneal ulcer (linear ulcer) pathognomic if seen
How can chlamydial and herpes conjunctivitis be distinguished from one another in cats?
Herpes causes coneal diseas, non in chlamydial
Describe the diagnosis of FHV-1
- History and clinical signs most important
- Conjunctival swab for PCR test
- NB PCR will also detect FHV-1 vaccine so less useful in vaccinted cats
Describe the occurrence of FHV-1 conjunctivitis
- FHV is an alphavirus that becomes latent and reactivates under stress
- Hides in trigeminal ganglion on one side, leads to unilateral conjunctivitis
Describe the treatment of herpes conjunctivitis in cats
- Nursing: cleaning eyes, nutrition, rehydration is main treatment
- Antibiotics to prevent/treat secondary bacteria infection (broad spec)
- Topical for eyes e.g. fusidic acid, chloramphenicol
- Systemic for resp involvement e.g. amoxyclav
- Antivirals are ineffective but can use topical ganciclovir or systemic famcyclovir in cases of persistent ulcers, pain and severe ocular signs
Describe the main topical ophthalmic antibiotic treatments used in dogs
- Fusidic acid (Isathal): first choice, treats G+ve common in conjunctivitis i.e. staphs and streps
- Chloramphenicol drops/ointment: broad spec
- Other antibiotics based on culture and sensitivity
Name the layers of the cornea from superficial to deep
- Epithelium
- Basement membrane
- Stroma
- Descemet’s membrane
- Endothelium
Explain why superficial corneal lesions are more painful than deep lesions
Nerve endings present in the epithelium and stroma, not further down
Describe the pathophysiology of corneal oedema
- Collagen fibrils have specific anatomical structure and arrangement which allows light rays to pass through
- Increased water content distorts collagen fibrils which creates opacity
- Occurs when barrier layers (epithelium and/or endothelium) are breached/dysfunctional
Describe the pathophysiology of corneal vascularisation
- Superficial or deep in-growth of blood vessels
- Promotes healing, but can increase scarring
Describe the pathophysiology of corneal pigmentation
- Non-specific response to corneal insult
- Can reduce vision
Describe the process of healing in the corneal epithelium
- Cells slide rapidly across defect within hours to days
- Mitosis increases, reduce size of defect
- Good at healing
- Cells present develop micropodia and walk across cornea
- Rarely requires treatment, antibiotics may be needed only to prevent secondary infeciton
How long does it take for the whole cornea to epithelialise and what is the importance of this?
Takes 7 days - if an ulcer is not improved within a week, then this indicates an underling problem
Describe the process of stromal healing
- Only starts once defect is covered by epithelial layer
- Regeneration from fibroblasts (weeks) and filled in with collagen
- Vascularisation from limbus at a rate of ~1mm/day
- Blood vessels slowly resorbed
Describe the healing of descemet’s membrane
- Elastic, limited ability to repair
- will scar over and bridge the defect, but takes time
Describe the healing of the corneal endothelium
Very poor ability to repair
List the potential causes of corneal ulceration
- Trauma
- Tear film production
- Adnexal conditions
- Primary corneal disease
- Infection
- Neurological disease
Give conditions of tear film production that may lead to corneal ulceration
- Dry eye (quantitative, common in dogs)
- Qualitative tear film problem (uncommon)
Describe the typical appearance of corneal ulcers secondary to dry eye
Circular, punched out appearance, deteriorate rapidly, can be quite deep
List adnexal conditions that may lead to corneal ulcers
- Eylids: entropion, ectropion, eyelid margin mass, trauma
- Eyelashes: distichiasis, ectopic cilia
- Conformation: trichiasis (normal skin hairs contacting eye), lagophthalmos in brachy breeds
Give a primary corneal disease that leads to ulcers
Spontaneous chronic corneal epithelial defect (SCCED)
Give examples of infectious causes of corneal ulcers
- Usually secondary to trauma
- Bacterial keratitis
- Fungal keratitis
Give examples of neurological diseases that may lead to the development of corneal ulcers
- Neuroparalytic keratitis
- Nerotrophic keratitis
Describe neuroparalytic keratitis
- Facial nerve paralysis
- Unable to blink so surface of eye dry and exposed
- May be due to ear disease/surgery e.g. TECA
Describe neurotrophic keratitis
- Reduced or absent corneal sensation
- Trigeminal nerve problem
- Can blink but no sensation of cornea
- Uncommon, may be due to head trauma e.g. RTA
Describe corneal ulcers in brachycephalic breeds
- Very common
- Always potentially serious
- Ability to deteriorate rapidly
- Conformation predisposes to corneal disease: shallow orbit = prominent globe, reduced blinking and poor distributionof tear film as a result of prominent globe, medial lower entropion, nasal fold trichiasis
Give examples of breed typical conditions that predispose for corneal ulcers
- Persian cat medial lower entropion: normal for breed, some cope well, others rub and get corneal ulcers in that area
- Pekingese nasal fold trichiasis: prominent nasal fold rubs on medial corner of eye causing ulcer
Describe the clinical signs of corneal ulcers
- Increased lacrimation
- Blepharospasm
- Photophobia
- Conjunctival hyperaemia
- Ocular discharge
- Corneal oedema
- Reflex uveitis
What is reflex uveitis?
Reflex contraction of the pupil in response to corneal injury, mediated by substance P, requires treatment
List the parts of the routine ophthalmic exam that are relevant to the diagnosis of corneal ulcerations
- Careful examination of both eyes
- Direct observation
- Palpebral and corneal reflex
- ST
- Flourescein dye
- Corneal cytology
- Corneal culture and sensitivity
Name the different types of corneal ulcer
- Superficial
- Stromal
- Desmetocoele
- Indolent
- Corneal facette
Describe the characteristics of superficial ulcers
- Epithelial loss only
- Acute onset
- Painful
- Sharp distinct borders
- Minimal corneal inflammatory response
- +/- reflex uveitis
Describe the treatment of superficial corneal ulcers
- Identify and treat underlying cause
- Prevent secondary infection by using topical antibiotics e.g. fusidic acid q12h, chloramphenicol q8h
- Analgesia e.g. systemic NSAIDs
- Atropine drops (single application)
- Buster collar if rubbing eye
- Recheck in 3-5 days, would expect healing in this time, check 1-2 days in brachy
Describe the characteristics of stromal corneal ulcers
- Loss of epithelium and stroma
- Acute or chronic, superficial or deep
- Fluorescein stains walls and floor of ulcer
- Deep are complex
- Surrounding stroma can be normal or diseased, indicated by Purkinje reflex
- Anterior uveitis common
Describe the characteristics of indolent ulcers
- Specific type of superficial
- Non-healing ulcer
- SCCED/Boxer ulcer
- Can affect any breed but common in boxers
- Typically unilateral, can be bi and recurrent
- Epithelial loss only
- Indistinct, irregular border which becomes under-run with fluorescein dye
- Usually minimal inflamm response but variable
Explain how indolent corneal ulcers develop
Epithelium grows back, but does not adhere to the underlying stroma
Outline the surgical management of indolent corneal ulcers
- Debridement
- Keratotomy or keratectomy
- Either only debride, or debride + keratotomy/tectomy
- All surgical options in conjunction with medical treatment
- 85% heal within 2 weeks with debridement and grid keratotomy
Describe the medical treatment of indolent corneal ulcers
- Similar to that for simple superficial
- Prevent secondary infectionwith fusidic acid, chloramphenicol or topical or systemic tetracycline
- Analgesia e.g. systemic NSAIDs, tramadol
- Atropine drops, 1-2 doses usually enough
- +/- contact lens bandage
- Buster collar
Which types of ulcers are classed as complex?
- Deep stromal
- Melting ulcer
- Desmetocoele
Describe the characteristics of desmetocoeles
- Acute or chronic
- Complete stromal loss down to Descemet’s membrane
- Walls of ulcer usually obvious
- Descemet’s membrane does not stain with fluorescein so walls stained but floor black/clear
- Ophthalmic emergency, high risk of rupture
Describe the treatment of a desmetocoele
- Intensive medical therapy following general principles: antibiotics, analgesia, atropine
- Prompt surgery to provide tectonic support to prevent corneal perforation
What is a melting ulcer?
A deep stromal ulcer, aka keratomalacia
Describe the appearance of a melting ulcer
- Acute, painful
- Copious gelatinous discharge
- Marked corneal oedema
- Marked anterior uveitis (pain, miosis, hypopyon, low IOP)
- Size and position variable
- Edges ill-defined, rounded, soft
- Can progress rapidly and perforate within hours
Explain the pathogenesis of a melting ulcer
- Proteinases and collagenases break down corneal stroma
- These may be of corneal origin: epithelial cells, stromal fibroblasts, WBCs
- Or bacterial infection: Pseudomonas spp, beta-haemolytic Streptococcus spp.
Describe the treatment of deep ulcers
- Similar treatment as simple superficial but more intensive
- Analgesia: NSAIDs, tramadol
- Topical atropine to effect e.g. once daily
- Consider corneal support with contact lens, glue, or graft
- Buster collar
- Monitor closely +/- hospitalise
Outline the diagnostics for complex ulcers
- Corneal cytology: scrape margin of ulcer
- Corneal swab: bacterial culture and sensitivity, fungal culture, swab margin not base
- Care as sampling may cause corneal perforation
Describe the specific topical treatment of melting ulcers
- Assume infected until proven otherwise
- Topical steroids cause local immune suppression and potential collagenase activity, should not be used
- Anticollagenase therapy applied q1-2h for 24h then gradually reduce
- Serum/plasma, serum better
- Na+/L+ EDTA solution
Explain the use of Na+/L+ EDTA solution in the treatment of melting ulcers
Chelates zinc and calcium and therefore inhibits MMPs of bacteria
Discuss the use of N-acetyl-L-cysteine in the treatment of melting ulcers
In vitro good but in vivo can be useful but also can cause necrosis
Explain the use of serum in the treatment of melting ulcers
- Alpha2 macroglobulin and alpha1 antitrypsin
- Most broad spectrum of treatment options
- Does have epitheliotropic properties so can be used for indolent ulcers
- Good at stopping enzyme action and stopping melting
Describe the production and use of serum for the treatment of melting ulcers
- Take blood from animal and put into plain tubes
- Stand and allow to clot, then spin in centrifuge
- Draw off serum
- Can be used directly in eye or stored in syringe or dropper bottle for 3 days
- Can use serum from one species in another, but tend to avoid using cat’s serum for one another due to risk of FeLV
Describe the treatment of indolent ulcers in cats
- Gentle debridement and contact lens
- Do not use keratotomy and phenol
- Keratotomy will lead to formation of sequestrum
Describe the method for debridement of corneal ulcers
- Use sterile swab
- Apply gentle pressure and remove loose epithelium
- May look like too much removed but only abnormal epithelium can be removed
- Ulcer will appear large
Describe the method for keratotomy
- Debride first
- Use 25-27G needle, bevel up
- Hold needle parallel to corneal surface and drag across, do not push
- Create cross-hatch of superficial lines 1mm apart
- Clear cornea to clear cornea i.e. treat entire debrided area +1-2mm into surrounding normal cornea
- Need to expose normal protein in stroma
Briefly outline keratectomy in the treatment of ulcers
- Specialist technique using scalpel, requires microscope
- 100% success rate
In what conditions is
debridement and grid keratotomy indicated?
ONLY in superficial ulcers with non-adherent epithelium, contraindicated in all other types
Outline the surgical treatment of complex ulceers
- Conjunctival grafts from same eye, stitch into position
- Provide immediate tectonic support
- Provide blood supply
- Several types
- Best performed with magnification and microinstrumentation
- Once healed, can trim pedicle so only have circular scar
Describe transposition grafts in the treatment of corneal ulcers
- Sliding advancement of cornea
- Move peripheral cornea to cover the ulcer
- Will come with conjunctiva and see paler opaque region of the conjunctiva over the iris
List the conditions commonly affecting the feline eye
- Trauma
- Conjunctivitis
- Herpes keratitis
- Eosinophilic (proliferative) keratitis
- Corneal sequestrum
- Diffuse iris melanoma
- Uveitis
What are common causes of trauma in the feline eye?
- Cat claw injuries
- RTA
- Blunt trauma to eye
Describe the common appearance of cat claw injuries to the eye
- Laceration of superficial cornea
- Small puncture wounds +/- bleeding in anterior chamber
- historical wounds may have iris adhesions to lens giving unusual shapes
Outline RTAs as a cause of traumatic injury to the feline eye
- Cranial trauma
- Can lead to ocular proctosis (requires a lot of force as globe protected by rim of orbit and ocular ligament, easier in brachy)
- Proctosed globe usually associated with brain or head injury which requires more attention than the eye
- May require enucleation if cannot be replaced
