Keratitis Flashcards
What are the infectious causes of keratitis?
Bacteria
Virus
Protozoa
Fungi
What are the non-infectious causes of keratitis?
Inflammatory Exposure Iatrogenic
When is iatrogenic?
Something resulting from medical treatment
What are the five layers of the cornea?
Epithelium Bowmans membrane Stroma Descemet’s membrane Endothelium
What does keratitis mean?
Keratitis means inflammation of the cornea
What does the term microbial keratits refer to?
Bacterial Keratitis
Fungal keratitis
Keratitis caused by a protozoa
(the term microbial keratitis is reserved for all infectious keratitis but not viral keratitis).
What are the risk factors for microbial keratitis?
Trauma, Contct lens wear , surgery, ocular surface disease, immunosupresion.
Is microbial keratitis a medical emergency?
YES - it is a sight threatening opthalmic emergency.
Is keratitis a sight threatening disease?
Anything that comprimises the itegrit f thecorea isa sight threatening disease.
What is the most common cause of microbial keratitis?
Bacterial Corneal pathogens
Is gram positive or negative bacteria most common in contact lens associated keratitis?
Gram negative
Is gram positive or negative bacteria most common in NON-contact lens associated keratitis?
Gram positive
What are the risk factors for bacterial keratitis?
- contact lenses - increased incidence in contact lens wearers.
- poor contact lens hygiene is a major risk factor!
- in non contact lens wearers risk fators are:
- immunosupression
- ocular surface disease
- trauma
What are the signs of microbial keratitis?
–> Inflitrate (as can be seen in the picture):
- generally central
- large >1mm
- location is anterior to mid-stromal
- full thickness epithelial loss
—> severe hyperamia
—> Anetrior Chamber reaction
- inflammatory cells, flare to form hypopyon (a layer of white blood cells)
—> Lid oedema
What are the symptoms of microbial keratitis?
- Unilateral
- Moderate to severe pain, rapid onset
- Reduced vision (-this depends on where the location of the lesion is i.e. a peripheral lesion is going to affect vision less - look at the picture for reference)
- Photophobia
How do we manage microbial keratitis?
- Immediately discontinuation of lens wear
- Refer to A&E (specialist unit)
–corneal scrape or biopsy to determine specific microbe responsible (gold standard/reference treatment)
–Intensive anti-microbial treatment
Typically used is:
•A group of antibiotics called Fluoroquinolone antibiotics (these have strong gram negative tendencies) - an example of which is levofloxacin.
–close monitoring ( to make sure right drug was used for right microbe and that the sensitivity of the drug was correct )
How does a corneal scrape take place?
A hypodermic needle is used not only to scrape the surface but right at the back of the lesion ( bacteria tend to reside at the back of the lesion). This scraping can be seen in the image.
Once we have a corneal scrapping what do we do?
Place the scrapping in different growth mediums to determine what the microbe is.
e.g. the following growth mediums are used to find the following microbes
- A. Saboraud agar (fungi)
- B. Chocolate agar (fastidious microorganisms, particularly Haemophilus and Neisseria )
- C. Blood agar (Streptococci)
- D. Thioglycolate broth (differentiates between aerobes and anaerobes)
- E. Viral transport media
The letters corrolate with the image.
How can we determine the sensitivity of a bacterium to an antiobiotic?
We place our bacteria in an agar dish. We then add our antibiotic disks.
The zones of inhibition of bacterial growth around the antibiotic disk indicates the sensitivity. Larger disk = more sensitivity of that bacteria to that antibiotic.
Who is microbial keratitis caused by acanthamoeba most common in?
Contact lens wearers- over 90% of cases are contact lens wearers (soft contact lenses)
What are the risk factors for microbial keratitis caused by acanthoeba (2)?
Swimming or showering in contact lenses (use of tap water)
What is acanthamoeba?
A free living protozoa which can be found in domestic water supplies.
What are symptoms of microbial keratitis caused by acanthamoeba?
Intense pain - even early on.
What are signs of Microbial Keratitis caused by acanthamoeba?
Radial perineuritis - this means infiltration around corneal nerves
Anterior stromal infiltrates
Anterior Chamber activity/inflammation
Corneal oedema
Eventually (in progressed/late acanthamoeba keratitis), ring infiltrate forms (as can be seen in the image).
Perforation
How do we manage microbial keratitis that is caused by acanthamoeba?
Immediate referral to ophthalmologist
Biopsy and culture ( to find out microbe responsible)
Treated with biguanides (PHMB or chlorhexadine) and or diamidines (propamidine) - these are basically disinfectants that kill the acanthamoeba in situ.
What is the aetiology of fungal keratitis (4)?
- Rare in Uk: caused by moulds (Aspergillus; Fusarium) or yeasts (Candida)
- Common in patients from warm climate
- Suspect if following trauma whilst gardening
- Recent links with CL care products
What is a difficulty in diagnosing fungal keratitis?
•Signs are similar to bacterial keratitis initially thus it is misdiagnosed.
What is the management for fungal keratitis (2)?
- Antifungals ( only get them from special pharmacies).
- Often requires a corneal graft
What does early acanthamoeba look like?
You see these dendritic (branched) lesions.
What is the most common group of viruses that cause corneal infections?
The Herpes family of Viruses - e.g. the Herpes Simplex Virus (HSV) and the Varicella Zoster Virus (VZV) (chicken pox virus).
What are the two types of Herpes Simplex Virus?
HSV-1 & HSV-2.
(HSV-2 is the one that causes genital herpes)
(HSV-1 causes cold sores)
In children what does Varicella Zoster Virus (VZV) cause?
Chicken Pox
What does the reactivation of Varicella Zoster Virus (VZV) in adults cause?
Shingles
In ophthalmic shingles (caused by Varicella Zoster Virus (VZV)) is the cornea involved?
Most commonly yes - ( in 65% of cases)
What is the aetiology of Herpes simplex keratitis (Herpatic Keratitis)?
(It is thought 90% of the population is seropositive (dormant in cells))
HSV-1 virus
•Primary infection occurs in childhood causing blepharoconjunctivitis (occasionally with corneal involvement).
What is orofacial ulceration?
A fancy name for cold sores
What are signs and symptoms of Herpes Simplex Keratitis?
- Eyelid rash (clear vesicles)
- STARTS as Punctate keratitis leading to dendritic ulcer which can become:
-Geographical ulcer
•Stromal keratitis: oedema, infiltration, vascularisation leading to scarring
–Disciform keratitis (basically having stromal and epithelial keratitis)
What is the treatment for Herpes Simplex Keratitis (2)?
- Anti-viral eye drops - for dendritic ulcer
- May require steroids for stromal disease ( for the late/progressed disease)
Can Herpes Simplex Keratitis be recurrent?
Yes - sadly as it lays dormant it can keep being reactivated even after having previously been treated.
What is adenoviral keratitis caused by?
A complication of adenoviral conjunctivitis.
What is a sign of adenoviral keratitis?
Focal sub-epithelial infiltrates
What is the treatment for adenoviral keratitis?
- usually, resolve themselves, however….
•corticosteroids if severe and a threat to vision
What are the mechanisms of bacterial pathogenicity?
(how are bacteria pathogenic?)
- Bacteria produce damage through the colonisation of the body surface and release of toxins.
- Bacteria can cause damage by invasion and subsequent multiplication in the tissues.
What are common corneal responses to bacterial toxins in contact lens wearers?
- Contact lens associated red eye (CLARE) (hyperaemia)
- Marginal keratitis
- Contact lens peripheral ulcer (CLPU)
If you took a biposy of an ulcer caused by bacterial toxins would you be able to identify the microbe responsible?
No - the ulcer is just a response essentially to a harmful foreign body (a.k.a the bacterial toxin).
Are corneal responses to bacterial toxins deemed as infectious or non-infectious keratitis?
Non-infectious
What’s the treatment for a contact lens peripheral ulcer?
To stop using contacts for a while - the ulcer then usually sorts itself out. (If you got the diagnosis right!).
What is marginal keratitis?
•Inflammatory response to bacterial toxins on lids
In the picture the patient had bacterial blepharitis- the bacteria on the lids released toxins which caused the keratitis you can see as the hyperaemia on the ocular surface.
How is marginal Keratitis managed?
Managed with combinations of topical steroid and antibiotics +/ lid hygiene
Is marginal keratitis deemed infectious?
No its non-infectious.
What is exposure keratitis?
Where exposure of the cornea leads to desiccation and surface damage.
What are some common aetiologies of exposure keratitis (4)?
- Thyroid eye disease
- Facial palsy
- Ectropion
- Lagophthalmos
Why do eye drops need to be preserved with preservatives?
To avoid bacterial contamination
What is potentially dangerous about preservatives in eye drops?
These preservatives are potentially toxic to ocular surfaces (corneal epithelial toxicity) - particularly for patients with chronic conditions that are using these eye drops for long periods of time.
What preservative commonly causes corneal epithelial toxicity and thus what conditions may it be associated with (2)?
Benzalkonium chloride (BAK)
It is commonly associated with the following conditions:
- Punctate keratopathy
- May be associated with conjunctival reaction (hyperaemia, follicles)
What type of a disease is corneal epithelial toxicity caused by preservatives in eye drops prescribed to patients?
An Iatrogenic one - as it is caused by medical professionals/ what they prescribe.
