Ophthalmology Conjunctiva and Cornea Flashcards
What type of epithelium is the conjunctiva
Non-keratinised stratified squamous epithelium
Special cells in different locations of conjunctiva
At fornix: mucus producing goblet cells
At limbus: antigen-presenting langhans cells
In what parts of the eye is the conjunctiva closely adhered to the underlying substantia propria
At limbus (where it is continuous with corneal epithelium)
In the eyelid
Normal resident population on the eyelid
Gram +ve cocci
- Staph intermedius
- Diphtheroids
3 layers of the cornea
Corneal epithelium (strat squamous)
Stroma
Endothelium
Characteristics of corneal epithelium repair and fluorescein staining
Stem cell population at the limbus; cells migrate the centre
Ulcer should heal within 5 days due to this
Epithelium = barrier to water-borne molecules; fluorescein only taken up when there is a break in epithelium
Corneal stroma characteristics
Made of collagen fibrils arranged 20nm apart (<wavelength of light) so cornea is transparent
When water gets into the cornea distorts the fibrils and causes opacity
= barrier to non-aqueous things
Corneal endothelium characteristics
Pumps water out to keep cornea transparent (relatively dehydrated)
NB: limited healing capacity except in young animals so any damage from trauma or high pressure is likely perminent
Why can corneal ulcers can miosis
Due to nociceptive trigeminal nerve supply
How must drugs be designed to cross the whole cornea
Must have polar and non-polar moiety
- Because the epithelium is a barrier to polar substances
- Stroma is a barrier to non-polar things (non-aqueous)
e.g chloramphenicol, dexamethasone alcohol, prednisolone acetate
What are dermoids
- Which breed and where are they commonly found
Congenital misplacement of normal skin tissue often with hair
- Seen in brachycephalics at medial canthus
Mechanism behind corneal scarring
Collagen fibrils caused to aggregate e.g alkali burn from lime
what material should be used to close the cornea
8/0 vicryl
What is chronic superficial keratitis; presentation, aetiology, breed
= CD4 T lymphocyte mediated keratitis seen in german shepherds wit UV light as a factor
Presents as a vascular, fibroblastic sheet of pannus
Treatment with lifelong topical steroid or cyclosporine
What breed is predisposed to punctate keratitis and what is it
Daschunds
= a multifocal immune mediated keratitis
What do we see with feline eosinophilis keratitis
White infiltrating cellular mass
Can have vascularisation and cottage cheese deposit
Cytology shows inflammatory infiltrate with lots of eosinophils
What is corneal oedema and general cause
= build up of water in the stroma due to endothelial incompetence
How can corneal odema lead to non-healing ulcers
Generation of epithelial bullae which then rupture
What are lipid keratopathies assoacited with
Prior corneal pathology; new vessels forming to repair the lesion are leaky so lipid escapes
What is lipid arcus associated with
Hyperlidiaemia
e.g in diabetes mellitus, hypothyroidism
What does a thin ring of lipid <few mms in eye mean
Stromal lipid dystrophy = due to stromal metabolic defect NOT systemic abnormality
Difference in effects of acid vs alkali chemical exposure of cornea
For acid, irrigation usually enough
FOr alkali, can lead to melting ulcers and may need to remove affected tissues
What is corneal dystrophy also known as
Boxer ulcer
How does corneal dystrophy work
Problem in relationship between corneal epithelial cells and basement membrane; may relate to fewer hemidesmosomes
-> Get impaired movement of cells across the surface of the eye and cells not well adhered
so ulcers can’t heal
Treating boxer ulcer/corneal dystrophy
Debride off the detached epithelium using a diamond burr
= Grid keratotomy
Infectious causes of corneal ulceration
FHV-1; see classic dendritic ulcers
Pseudomonas; produces MMPs to destroy collagen to allow bacteria in and breaks down cornea (can get melting ulcer if neutrophils also product MMPs)
Endogenous causes of corneal ulceration
Keratoconjunctivitis sicca
Corneal dystrophy (leads to boxer ulcers)
What are dendritic ulcers pathognomic of
FHV-1 infection
What leads to development of a melting ulcer
INvading bacteria (e.g pseudomonas) produce MMPs/collagenases to break down cornea
Neutrophils respond and also produce MMps
–> Get breakdown of tissue and melting ulcer
What alternative (to diamond burr) method can we use to perform grid keratotomy in non healing superficial ulcer
Tetracaine first
Then just use cotton bud
How would we deal with a midstromal depth healing ulcer
Put in a contact lens to protect the eye
What does a clear part in the middle of an ulcer which is non-oedematous suggest
Stroma here has been lost; this is a deep ulcer
Possible treatment option for a deep/non-healing ulcer
Conjunctival pedicle flap; used to cover ulcer
Gives physical support and blood borne factors
What is the appearance of a melting ulcer and what is the risk that might happen
Corne turns white and fluid
_ risk is perforation of the cornea
How to treat a melting ulcer
Vigorous antibiosis e.g fluoroquinolones, gentamycin
Anticollagenase treatment: autologous serum (contains macroglobulins), acetyl cystine (binds zinc), EDTA (binds calcium)
WHat kind of sutures could we use to hold the cornea together in case of large melting ulcer
mattress sutures; until it heals
What is a corneal sequestrum and what species is it seen in
Cats
= black/brown necrotic area of stroma
Symptoms of conjunctivitis
Redness is seen on the lid and the globe mucosa
Oedema
Irritation with some blepharospasm but not severe pain
Ocular discharge
Lymphoid changes
In which breed of dogs do we see immune-mediated conjunctivitis and what is the aetiology
German shepheds
= lymphocytic-plasmocytic conjunctivitis
+ also see depigmentation of 3rd eyelid due to cellular infiltrate
Treatment = lifelong steroid drops or cyclosporine drops
What infectious causes of conjunctivitis in cats
FHV-1 (treat with famciclovir)
CHlamydial ; unilateral then bilateral; treat with tetracyclines
+ bacteria
What virus can cause conjunctivitis in dogs
Canine distemper
Which antibiotic is good for the eye (due to molecular properties)
Chloramphenicol
Which dogs do we see pigmentary keratitis. in
Brachcephalics with prominent globes and nasal fold hair
Dry eye
