Infective keratitis Flashcards
What is keratitis?
Inflammation of the cornea
What is the most common cause of keratitis?
infection (particularly viral and bacterial)
What is the corneal epithelium?
the corneal epithelium forms the primary barrier to microbes and the tear film on the corneal surface
What three groups of bacteria most commonly cause infective keratitis when the corneal epithelium is disrupted?
- Staphylococcus
- Streptococcus
- Pseudomonas
What are 3 bacteria that can penetrate intact corneal epithelium and can therefore cause keratitis without corneal obstruction?
- Neisseria gonorrhoea
- Neisseria meningitides
- Corynebacterium diphtheria
What are 4 risk factors for bacterial keratitis?
- Contact lenses
- Corneal trauma
- eyelid disease
- Immunosuppression
True or false: infective keratitis typically presents unilaterally
True
Give 5 general clinical presentations associated with infective keratitis:
- Ocular pain
- Photophobia
- Reduced visual acuity
- Diffuse conjunctival injection
- Eyelid oedema
Give 3 additional clinical presentations associated with bacterial keratitis?
- Purulent discharge
- area of yellow/white infiltrate with clearly defined margins
- hypopyon in the anterior chamber
What is hypopyon?
Hypopyon is a medical condition involving inflammatory cells in the anterior chamber of the eye
Give 3 important questions to ask when conducting a contact lens history:
- Duration of wear
- Type of contact lens (short/long wear)
- Have they ever slept, showered or swam with their lenses in?
Give 2 examinations used to investigate bacterial keratitis:
1) Snellen chart for visual acuity
2) anterior segment examination using slit lamp or fundoscope
What investigation may be used to gain insight into the causative organism in keratitis?
Corneal scrape/ conjunctival swab
What investigation should be carried out on contact lens wearers if infective keratitis is suspected?
send contact lenses and case off for culture
What guidance should be given to contact lens wearers if infective keratitis is suspected?
contact lens use should be discontinued IMMEDIATLY
What two topical antibiotic therapies are given for bacterial keratitis?
- Fluoroquinolone
- Cefuroxime with gentamicin
What are 5 complications of bacterial keratitis?
- Spread of infection
- Corneal perforation
- Residual dense corneal scarring
- Irregular astigmatism
- Formation of cataracts
What are the two most common viral causes of keratitis?
1) herpes simplex
2) varicella zoster
What type of herpes virus causes viral keratitis?
Herpes simplex virus-2 (HSV-2)
In which structure does HSV establish latency following primary infection?
trigeminal ganglion
Describe the aetiology of herpes simplex epithelial keratitis:
following primary infection, HSV establishes latency in the trigeminal ganglion which can reactivate and move to the corneal epithelium
How can you tell viral and bacterial keratitis apart from examination?
viral keratitis causes epiphora while bacteria keratitis causes purulent discharge
What is epiphora?
Excessive tearing from one or both the eyes without any specific reason.
What is the key diagnostic sign of HSV keratitis?
dendritic ulcers
What are dendritic ulcers?
small green patches seen on fluorescein staining with linear branching morphology associated with HSV keratitis
What is the main treatment for viral keratitis?
topical antivirals (aciclovir ointment) and epithelial debridement
What is the name given to the varicella zoster infection of the ophthalmic branch of the trigeminal nerve?
herpes zoster ophthalmicus
What are 3 clinical presentations specifically associated with herpes zoster opthalmicus?
- Rash in the V1 dermatomal distribution
- Punctate keratitis
- Psuedodendrites
What is punctate keratitis?
small dots caused by cell death when the eye is viewed under high magnification
What are pseudodendrites?
similar to dendritic ulcers but lack the terminal bulb seen in HSV
Name 3 typical symptoms of herpes simplex epithelial keratitis?
- Discomfort, grittiness, red eye, reduced visual acuity and photophobia
- Epiphora
- A previous history of cold sores
Name 4 typical clinical findings on examination for herpes simplex epithelial keratitis?
- Lids and lashes - mild erythema and oedema
- Conjunctiva - diffuse or cicumlimbal injection
- Cornea - dendritic ulcer
- Reduced corneal sensation
What is the most common complication of herpes zoster ophthalmicus?
post-herpetic neuralgia
What is post-herpetic neuralgia?
A complication of shingles, painful, blistering skin rash, which is caused by reactivation of herpes zoster virus.
What are 4 risk factors for fungal keratitis?
- Corneal trauma
- Contact lens wear
- Immunosuppression
- Ocular surface disease
True or false: the visual prognosis of fungal keratitis is generally good
false (it is an aggressive infection)
What would the cornea look like under examination with fugal keratitis?
grey-white stromal infiltrate with fluffy margins. Satellite lesions may be seen. Rapid progression may occur with necrosis and corneal thinning
What treatment is used for fungal keratitis?
topical antifungals (hour installation) and analgesia
What protozoa commonly causes keratitis?
acanthamoeba
Where are acanthamoeba found?
Fresh water and soil
Give 3 clinical presentations specific to acanthamoeba keratitis:
- Ring shaped infiltrate with radial perineural infiltrates
- Epiphora
- Severe pain that is often disproportionate to mild clinical findings
What type of investigation can be used to view acanthamoeba cysts in suspected acanthamoeba keratitis?
confocal microscopy
What antiamoebic agent is commonly used to treat acanthamoeba keratitis?
topical PHMB (polyhexamethylene biguanide)
What surgery can be used to treat very severe cases of infective keratitis?
penetrating keratoplasty (full thickness corneal transplant)
True or false: acanthamoeba keratitis has a poor prognosis relative to other forms of infective keratitis
True
