M6 Eye Infections Flashcards
What are the external components of the eye?
External
* Eyelids
* Conjunctiva
* Sclera
* Cornea
What are the internal components of the eye of concern for eye infections?
Internal
* Anterior consists of
aqueous humor
* Posterior contains
vitreous humor
What defense Mechanisms -Physical & biochemical Barriers does the eye have against infection?
- Eye orbit (bony)
- Eyelids (blinking)/eyelashes (prevent entry of “fomites”)
- Secretions (by lacrimal gland & goblet cells) wash away “outsiders”
- Tough collagenous coat (sclera & cornea) covers intraocular
- Lacrimal secretions such as lysozymes and IgA, secreted locally.
What are the mechanisms that cause infection to the eyes?
Eye infections occur by:
1. Broken barriers (injury-ulceration)
2. Via bloodstream (from other sites)
3. Proximity to sinuses, sinus infections can extend
List the various types of eye infections (6).
- Conjunctivitis (pink eye) (swelling, exudates, burning &
itching) - Blepharitis (inflammation of edges of eyelids)
- Keratitis (cornea- pain & vision issues)
- Endophthalmitis (infection of aqueous or vitreous fluid, pain, vision issues blindness)
- Periocular (canals & ocular cellulitis)
- Uveitis & retinitis (blood-borne)
- Other
Does the eye have normal flora?
The eye is in theory sterile, these organisms might be there in
small amounts and can come from fomites, air, hands, skin close to the eyes, etc. They are transient as they vary with time.
What does the significance of organisms found in eye specimens depend on?
Significance depends upon knowledge of patient’s existing
flora, clinical symptoms/signs and clinical history
See table on slide 5 for some transient flora and their probability.
What is the most common infection of the eyes?
Conjunctivitis
It may be caused by allergies, bacteria or virus (fungi and
parasites less common).
How does age relate to diagnosis for conjunctivitis?
Age is a very important factor for diagnosis:
1. Neonates: N. gonorrhea and Chlamydia trachomatis (trachoma)
2. Children: bacterial like H. inf, S. pneumo and S. aureus
3. Adults: mostly viral, self limited but highly contagious.
Elderly can see bacteria infections again.
What other bacteria’s can cause conjunctivitis with distinct clinical pictures?
- Coryne. diphtheria & C. macginleyi
- Treponema pallidum
- Moraxella lacunata
- Yersinia enterocolitica
- TB
What are the results of the gram stain and other characteristics (tests/results) for Moraxella lacunata?
Moraxella lacunata
* gram negative bacilli end-to-end in pairs
* Proteolytic
* Beta-lactamase neg
What are two types of Chlamydial conjunctivitis?
- Blinding trachoma
* transmission via eye discharges - Inclusion trachoma
* transmission via genital tract
What infection is common after trauma to the eye?
Keratitis (corneal infection)
What makes is Keratitis (corneal infection) very serious?
It is considered critical, loss of eye can occur in 24 hours.
What organisms can cause Keratitis (corneal infection)
- Mostly bacterial (65% to 90%):
S. aureus, S. pneumoniae and P. aeruginosa, also gonococcus and Acinetobacter - HSV, fungus (ambient)
- Acanthamoeba spp.
What is Acanthamoebae?
Acanthamoebae is a free-living amoebae that is found in soil and contaminated water (especially well water that is not chlorinated).
What 3 sites in the body does Acanthamoebae infect?
- Eyes
- Granulomatous Encephalitis (CNS infection)
- Cutaneous
What eye infection due to a parasite is related to poor hygiene of contact lenses?
Causes acanthamoebic keratitis in the eye where the organisms gains access via corneal abrasions and is associated with contact lens use where the user practices poor hygiene. This infection leads to permanent impairment or vision loss.
What two infections can occur due to Acanthamoebae in immunocompromised patients?
- Granulomatous Encephalitis (CNS infection): immunocompromised patients,
infects brain and spinal cord, disseminates to other tissues –> fatal - Cutaneous: Infection occurs via disseminated infection and may occur in immuno-compromised hosts
Who diagnoses Acanthamoebic keratitis?
Ophthalmologist diagnosed
by clinical appearance
What type of specimen is taken to the lab for Acanthamoebic keratitis?
Culture by corneal scraping
What is the basic steps of the process in the lab to access Acanthamoebic keratitis?
- Corneal scrapings or contact
lens or solution planted to
non-nutrient agar with a lawn
of Escherichia coli bacteria. - Inc at 37˚C for 7 days & observe daily, plate under mic @40X, look for trophs or cysts
- Acanthamoebae consume the E. coli and leave trails on the surface
What happens after all the E.coli is consumed by the Acanthamoebic?
When all bacteria consumed;
the organisms encysts
Describe what Endophthalmitis is?
- Infection of the aqueous or vitreous humor (rare)
- Most commonly after surgical trauma (or other trauma)
- Caused by bacteria or virus
How serious is Endophthalmitis?
Sudden and progresses rapidly –> blindness
Pain and decreased vision are symptoms
What organisms can be responsible for Endophthalmitis?
Possible pathogens:
1. S. aureus,
2. S. epidermidis,
3. S. pneumo,
4. other Strep,
5. P. aeruginosa,
6. Klebsiella & other GNB,
7. Candida & others
How is the specimen treated for Endophthalmitis?
In lab treated as any other sterile site, any growth to be
worked up fully and AST done if applicable.
* Critical reporting!
What plates and smear is done for conjunctival swabs?
Processing of conjunctival swabs:
- CA (Choc) CO2, BA O2 or CO2
* swab elution may be used to increased recovery of organisms
Direct gram stain (PMN’s might indicate bacterial cause)
Why is swab elution performed?
Because there are multiple plates.
What plates and smear is done for keratitis?
Processing of invasive eye specimens (ie. keratitis):
* CA (Choc), BA O2 or CO2
, Mac (if required)
* swab elution may be used to increased recovery of organisms
* If fungi and anaerobes are requested specialized media will be
added
* Special requests by Doctor (parasites, TB, etc.)
* Direct gram stain
How are cultures interpreted for conjunctival swabs?
Reading and Recording (conjunctival swabs)
determine significance of growth by:
1. correlation of culture results with direct gram stain
2. organism isolated in culture
3. purity of culture
4. Comparison between eyes if possible
Is an AST performed for organisms found from a conjunctivitis swab?
No AST (interpretation based on blood levels)
How long do you wait before reporting no growth from a conjunctivitis swab?
48 hours incubation before calling “no growth”
How are cultures interpreted for invasive eye specimens?
Reading and Recording (invasive specimens)
1. any growth is considered significant
2. Full ID and AST
How long do you wait before reporting no growth from an invasive eye specimen?
72 hours before calling “no growth”
