A colour guide to the cornea Flashcards
What can chronic irritation cause?
- vascularisation
- pigment deposits
- scarring
(e. g. d/t dry eye, entropion, LPI (pannus) etc
What might white in a cornea represent?
- scar
- lipid
- calcium
How do you tell if a problem is active, ongoing or an old one that is no longer active?
- look for obvious BVs (in cornea) or eye discharge (tearing or mucus discharge)
- if eye is held open (if it appears to be comfortable)
Another name - corneal pannus
corneal lymphopcytic-plasmacytic infiltrate (LPI)
Are dry eye and LPI usually bilateral or unilateral?
bilateral
Will cytology of the corneal surface be useful if the lesion (corneal ulcer) is inactive?
No
Tx - inactive corneal ulcer
none
Tx - LPI of the cornea (corneal pannus)
- can recur (especially if patient taken off meds - topical ciclosporin and/or topical steroid) too abruptly or early and if there is exposure to sunlight –> maintain low frequency of a drop (once every other day) to keep CS under control
Describe pigment of feline limbus and conjunctiva
cats have little to no pigment in the limbus or conjunctiva and do not normally pigment their cornea the way dogs do.
What is a feline sequestra?
sequestra in cats form in response to chronic irritation, trauma or repeated, subtle microtrauma (small amount of medial canthal entropion, dry eye etc). Sometimes they appear spontaneously without an obvious cause wand we tend to suspect the latter is most likely
Ddx - sequestrum
there is often little room for doubt that the dx in a cat is a sequestrum although a FB and a response around it could also be considered
What might fluorescein reveal around a feline sequestrum plaque?
an ulcer around the sequestrum plaque and other possible ulcerative areas.
What predisposes sequestrum formation?
medial lower eyelid entropion
T/F: STT-1 in cats is rather variable
true - also cats rarely present with dry eye
Tx - feline sequestra
best treated with keratectomy for the removal of the entire sequestrum, this may be followed by corneal grafting (a conjunctival pedicle or a corneo-limbo-conjunctival transposition). REFER for this!
Where does eosinophilic keratitis (EK) usually occur?
normally in dorsolateral cornea
What might a yellowish hue be on an eye?
what is left of fluorescein
What suggests hairs are distichiasis?
their regular and orderly distribution and their position pointing directly at the cornea
When do distichiae cause a lot of irritation or none?
- long/medium soft coats (cocker spaniels) - no obvious irritation
- cats, short coats in dogs - lots of irritation and often keratitis
- many cases sit in between (including some cocker spaniels!)
T/F: some dogs can have distichiae and be asymptomatic but all cats are usually symptomatic
True
Ddx - keratitis in a young cat
- distichiasis (primary)
- other eyelid problems (upper eyelid agenesis and entropion)
- FHV-1
- sequestrum formation
T/F: distichiae are usually bilateral
True
What eyelid problem should you always check for in cats?
- upper eyelid agenesis (this develops dorso-laterally in cats and may be associated with distichiasis). The eyelid and edge and skin may be missing in that region since birth (agenesis) or it might be there but very hypoplastic. In such cases there will be trichiasis too.
Tx - distichiasis
- hair removal (e.g. electrolysis)
- supportive medical tx for the cornea (topical AB such as fucithalmic or chloramphenicol) and preservative free viscous tears such as Celluvisc 1% so cornea can heal naturally in a few days without further trouble).
What can continued irritation (d/t distichiasis) in cats lead to?
- ulcer
- sequestrum
T/F: an active process may be associated with a scar
True - but very rare. This happens when the active process is chronic and there has been time for a scar to develop. In such cases one can also find vascularisation. (e.g. chronic keratitis secondary to a poorly responsive dry eye - KCS)
What does corneal oedema result from?
overhydration of the corneal stroma, which is hydrophilic. The stroma is protected from overhydration by the endothelium anteriorly and the endothelium posteriorly. Overhydration can also happen secondary to vessel ingrowth into the cornea (new vessels are leaky as they frm) but oedema is only localised in such cases.
Ddx - corneal oedema
- ulcerative dz
- intraocular disease (primary/secondary glaucoma, uveitis)
- primary endothelial degeneration
Why do transillumination?
- to look into AC if possible
- see if lens is in the right place or if there are any signs of lens luxation as this can cause secondary glaucoma
Use - ocular US
to examine inside of eye
T/F: primary endothelial degeneration is usually non-symmetrical
True (b/w l and r eyes) but it is a bilateral problem
Tx principles - glaucoma
- primary: careful IOP management
- secondary: deal with the problem that lead to it
What needs to happen in lens luxation?
lens needs to be removed.
What colours do you need to assess the cornea for?
- white
- yellow
- red/pink
- blue
- black
What colour is corneal vascularisation and GT?
red/pink
What colour is a corneal abscess?
white
Describe corneal abscessation
doesn’t really involve the devlopement of a pocket of pus per se but the heavy cellular infiltration of the corneal stroma. This may be infected with bacteria (and rarely depending on location, fungal organisms).
T/F: most corneal ulcers are secondary to something else
True
What might cause decompensation of corneal ulcer healing?
- infection
Ddx - corneal ulcer
- ulcerative dz secondary trauma, possibly d/t FB trapped under TE
Name an AB which has good coverage and corneal penetration
chloramphenicol
What might help avoid corneal melting?
serum eyedrops
How often should you re-examine a corneal ulcer?
- if worried, keep in hospital to observe 2 times a day or once a day, then every 3-4 days. then every 5-7 days.
- the worry is that the cornea may suddenly start melting and perforate
