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OV3017 Eye Disease > 8 - Pathogenesis of Infectious eye disease > Flashcards

8 - Pathogenesis of Infectious eye disease Flashcards

1
Q

the ocular surface is normally well protected from pathgens because it has self defense mechanisms such as

A
  1. antimicrobial properties of tears
  2. sheddng of cells on ocular surface which reduces contact with pathogens
  3. effective illumnological methods
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2
Q

what are the risk factors that pre dispose eye to infection

A
  1. immune status
  2. ocular morbidity
  3. CL wear
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3
Q

what are the causes of infection

A

pathogens such as:
bactera, HSV, CMB, VZV

less common ones:
fungi and protozea e.g. acanthomeaba and toxoplasma

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4
Q

what is normal conjunctival flora

A

microbiial flora, present on lids and in conjunctival sac from birth + present throughout life (commensal)

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5
Q

what are commensals

A

inate defence system of eye: compete with pathogens for essential nutrients

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6
Q

what bacteria are normal conjunctival flora

A

gram positive

  • gram +ve cocci
    staphylococcus epidermis
    staphylococcus aureus
    micrococcuus sp
  • gram +ve baccili
    corynebacterium species
  • anaerobic
    -propinibacterium
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7
Q

external hordoleum (stye)

A
  • infection of ciliary sebaceous glands (Zeiss)
  • base of eyelashes
  • typically steph. aureus
  • typical treatment is warm compress
  • topical antibiotics needd
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8
Q

blepharitis

A
  • non infective
  • chronic or remitting

staph. aureus
staph. epidermis

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9
Q

what are the charecteristics of - staphylococci

A
  • 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

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10
Q

difference between orbital cellulitis and pre-septal cellulitis

A
  • 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
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11
Q

where does the infection lie in preseptal cellulitis

A

in front of natural barrier

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12
Q

where does the infection lie in orbital cellulitis

A

in the orbit, behind the septum. it can spread into the cranial cavity

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13
Q

aetiology of pre-septal cellulitis / orbital infection

A
  • sinusitis
  • strep. pnemoniae / H influenzae
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14
Q

treatment for pre septal

A

antibiotics

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15
Q

treatment for pre-septal

A

antibioticst

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16
Q

treatment for orbital

A
  • antibiotics +/- surgery
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17
Q

characteristics of streptococci

A
  • commensals of mouth +gut
  • gram positive cocci - chains
  • grow on blood sugar (haemolysis)
  • mostly non pathogenic
  • can cause conjunctivitis & even deeper orbital infections
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18
Q

streptococci- spectrum of disease

A

wide (pneumonia, wound and skin infections, sepsis)

  • local infection may lead to systemic infection
  • toxin mediated
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19
Q

characteristics of haemophillus spp

A
  • commensal of upper respiratory tract
  • gram negative rod
  • fastidious
20
Q

spectrum of disease for haemophilus spp.

A
  • local infection / meningitis
  • much less since Hib vaccination
21
Q

conjuncitvitis presentation

A
  • viral
  • bacterial
  • chlamydial
22
Q

bacterial conjunctivitis - charcteristics

A
  • rapid onset
  • unilateral to bilateral in 1-2 days
  • staphylococci/streptococci/ H. influenzae

self limiting

23
Q

viral conjunctivitis characteristics

A
  • enlargement of pre-auricular nodes
  • most common
  • unilateral > bilateral in 1 week
24
Q

viral conjunctivitis - adenovirus

A

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

25
Q

what is adenovrius

A
  • a DNA virus
  • 49 serotypes

spread if contact with secretions e.g coughing/sneezing
- formites (inanimate objects)

26
Q

what are the 2 forms of chlamydial conjuncitvitis

A
  • trachoma
  • acute inclusion conjunctivitis
27
Q

what is trachoma

A
  • potentially blinding condition due to exposure of ocular tissue
  • overcrowding + poor sanitation
  • follicular conjunctivitis
28
Q

what is acute inclusion conjunctivitis

A
  • chronic follicular conjunctivitis
  • usually sexually transmitted
  • unilateral red eye
  • adults
  • misdiagnosed
  • involves cornea - may be punctate keratitis with sub epithelial infiltrates
29
Q

charactreristics of chlamydiae

A
  • obligate intracellular parasite
  • life cycle resembles viruses
  • depend on host cell
  • inert infectious particles
  • culture not routine
30
Q

diagnosis of chlamydiae

A
  • serology
  • histology (conjunctival scrape)`
  • PCR (presence of chlamydial nucleic acid)
31
Q

conunctival scrape

A
  • using a kamura spatula
  • useful for chlamydia
  • sample taken from upper and lower sac
32
Q

how to have an indication of the most effective antibiotic treatment for an infection?

A

measure the zone of inhibition of bacterial growth

33
Q

microbial keratitis - bacteria

A
  • bacterial keratitis most common cause of MK
34
Q

most common bacterial corneal pathogens

A
  • pseudomonas sp (gram -)
  • staphylococcous sp ( gram +)
  • streptococcus sp (gram +)
35
Q

where is gram - and gram + most common

A

-ve in CL associated keratitis
+ve in non CL wearers

36
Q

risk factors of microbial keratitis: bacteria

A
  • cl wear
  • immunosuppression
  • ocular surface disease
  • trauma
37
Q

herpetic keratitis

A
  • herpes simplex virus (HSV)
    mostly HSV1 as 2 causes genital herpes
  • varicella zoster virus (VSV)
    ophthalmic shingles
38
Q

mechanisms of bacterial pathogenictiy

A
  • 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
39
Q

non - infectious keratitis

A
  • corneal response to bacterial toxins
  1. CLARE
  2. marginal keratitis
  3. CLPU
40
Q

marginal keratitis

A
  • inflammatory response to bacerial toxins on lid
  • non infective
  • managed with combinations of topical steroid and antibiotics + lid hygiene
41
Q

uveitis

A
  • most cases non infective and idiopathic
42
Q

infectious analogies of anterior uveitis

A
  • HSV
  • VSV
43
Q

Infectious aetiologies of posterior uveitis

A
  • toxoplasosis
  • toxocara
    -syphillis
    CMV
44
Q

endophthalmitis characteristics

A
  • usually bacterial and acute
  • most cases exogenous e.g surgery trauma
45
Q

classification of endopthalmitis

A
  • acute post cataract
  • chronic pseudophakic
  • bleb related
  • post traumatic

OV3017 Eye Disease (19 decks)

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