8 - Pathogenesis of Infectious eye disease Flashcards
the ocular surface is normally well protected from pathgens because it has self defense mechanisms such as
- antimicrobial properties of tears
- sheddng of cells on ocular surface which reduces contact with pathogens
- effective illumnological methods
what are the risk factors that pre dispose eye to infection
- immune status
- ocular morbidity
- CL wear
what are the causes of infection
pathogens such as:
bactera, HSV, CMB, VZV
less common ones:
fungi and protozea e.g. acanthomeaba and toxoplasma
what is normal conjunctival flora
microbiial flora, present on lids and in conjunctival sac from birth + present throughout life (commensal)
what are commensals
inate defence system of eye: compete with pathogens for essential nutrients
what bacteria are normal conjunctival flora
gram positive
- gram +ve cocci
staphylococcus epidermis
staphylococcus aureus
micrococcuus sp - gram +ve baccili
corynebacterium species - anaerobic
-propinibacterium
external hordoleum (stye)
- infection of ciliary sebaceous glands (Zeiss)
- base of eyelashes
- typically steph. aureus
- typical treatment is warm compress
- topical antibiotics needd
blepharitis
- non infective
- chronic or remitting
staph. aureus
staph. epidermis
what are the charecteristics of - staphylococci
- commensals of human skin
- gram positive
- grow on most media
- toxin mediated
can cause ocular surface infection e.g. conjunctivitis. if they penetrate deeper then potentially more severe infections
- common cause of food poisoning + cause damage by production of toxins
difference between orbital cellulitis and pre-septal cellulitis
- orbital cellulitis is rare but life threatening , common in children.
- rises from abcess in sinuses
- proptosis
- lid oedema
- RAPD
- limitation and pain on eye movements
where does the infection lie in preseptal cellulitis
in front of natural barrier
where does the infection lie in orbital cellulitis
in the orbit, behind the septum. it can spread into the cranial cavity
aetiology of pre-septal cellulitis / orbital infection
- sinusitis
- strep. pnemoniae / H influenzae
treatment for pre septal
antibiotics
treatment for pre-septal
antibioticst
treatment for orbital
- antibiotics +/- surgery
characteristics of streptococci
- commensals of mouth +gut
- gram positive cocci - chains
- grow on blood sugar (haemolysis)
- mostly non pathogenic
- can cause conjunctivitis & even deeper orbital infections
streptococci- spectrum of disease
wide (pneumonia, wound and skin infections, sepsis)
- local infection may lead to systemic infection
- toxin mediated
characteristics of haemophillus spp
- commensal of upper respiratory tract
- gram negative rod
- fastidious
spectrum of disease for haemophilus spp.
- local infection / meningitis
- much less since Hib vaccination
conjuncitvitis presentation
- viral
- bacterial
- chlamydial
bacterial conjunctivitis - charcteristics
- rapid onset
- unilateral to bilateral in 1-2 days
- staphylococci/streptococci/ H. influenzae
self limiting
viral conjunctivitis characteristics
- enlargement of pre-auricular nodes
- most common
- unilateral > bilateral in 1 week
viral conjunctivitis - adenovirus
pharyngoconjunctival fever
- most commmon
- associated w respiratory tract infection
- resolves in 2 weeks
epidemic keratoconjunctivitis
- more severe
- lasts 1-3 weeks
- associated w subconjunctival hameorrages
- may get corneal involvement
what is adenovrius
- a DNA virus
- 49 serotypes
spread if contact with secretions e.g coughing/sneezing
- formites (inanimate objects)
what are the 2 forms of chlamydial conjuncitvitis
- trachoma
- acute inclusion conjunctivitis
what is trachoma
- potentially blinding condition due to exposure of ocular tissue
- overcrowding + poor sanitation
- follicular conjunctivitis
what is acute inclusion conjunctivitis
- chronic follicular conjunctivitis
- usually sexually transmitted
- unilateral red eye
- adults
- misdiagnosed
- involves cornea - may be punctate keratitis with sub epithelial infiltrates
charactreristics of chlamydiae
- obligate intracellular parasite
- life cycle resembles viruses
- depend on host cell
- inert infectious particles
- culture not routine
diagnosis of chlamydiae
- serology
- histology (conjunctival scrape)`
- PCR (presence of chlamydial nucleic acid)
conunctival scrape
- using a kamura spatula
- useful for chlamydia
- sample taken from upper and lower sac
how to have an indication of the most effective antibiotic treatment for an infection?
measure the zone of inhibition of bacterial growth
microbial keratitis - bacteria
- bacterial keratitis most common cause of MK
most common bacterial corneal pathogens
- pseudomonas sp (gram -)
- staphylococcous sp ( gram +)
- streptococcus sp (gram +)
where is gram - and gram + most common
-ve in CL associated keratitis
+ve in non CL wearers
risk factors of microbial keratitis: bacteria
- cl wear
- immunosuppression
- ocular surface disease
- trauma
herpetic keratitis
- herpes simplex virus (HSV)
mostly HSV1 as 2 causes genital herpes - varicella zoster virus (VSV)
ophthalmic shingles
mechanisms of bacterial pathogenictiy
- some bacteria produce damage through the colonisation of body surface + release toxins and only invade tissue to limited extent
- some bacteria cause damage by invasion and multiplication in the tissues
non - infectious keratitis
- corneal response to bacterial toxins
- CLARE
- marginal keratitis
- CLPU
marginal keratitis
- inflammatory response to bacerial toxins on lid
- non infective
- managed with combinations of topical steroid and antibiotics + lid hygiene
uveitis
- most cases non infective and idiopathic
infectious analogies of anterior uveitis
- HSV
- VSV
Infectious aetiologies of posterior uveitis
- toxoplasosis
- toxocara
-syphillis
CMV
endophthalmitis characteristics
- usually bacterial and acute
- most cases exogenous e.g surgery trauma
classification of endopthalmitis
- acute post cataract
- chronic pseudophakic
- bleb related
- post traumatic
