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Eye disease and therapeutics > Pathogenesis of Infectious Eye Disease > Flashcards

Pathogenesis of Infectious Eye Disease Flashcards

1
Q

What is ocular surface well protected from

A

Pathogens

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2
Q

Examples of risk factors that predispose to ocular infection

A
  • Immune status = px’s who are immunosuppressed naturally or through use of drugs e.g. corticosteroids
  • Ocular morbidity = ocular surface disease
  • Contact lens wear
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3
Q

What does ocular surface have to make sure it remains disease free

A
  • It has natural defence mechanisms
  • E.G. antimicrobial properties of tears
  • E.G. Constant shedding of cells from ocular surface which reduces contact time with pathogen
  • E.G. effective immunological mechanisms
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4
Q

What happens when mechanisms of natural defence mechanisms becomes compromised

A

Predisposes eye to infection

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5
Q

Examples of less common pathogens:

A

Fungi and protozoa e.g. toxoplasma and acanthamoeba

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6
Q

Examples of pathogens in cornea causing infection

A

HSV, VZV, protozoa, fungi

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7
Q

Examples of pathogens in uvea causing infection

A

Bacteria,
CMV, VZV,
Protozoa

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8
Q

Examples of pathogens in endophthalmitis causing infection

A

Bacteria, fungi

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9
Q

Examples of pathogens in lids and conjunctiva causing infection

A

Bacteria, chlamydia, adenovirus, HSV, VZV

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10
Q

What is microbial conjunctival flora

A
  • Non pathogenic bacteria are normally present on the lids and in the conjunctival sac from birth and are present throughout the life (commensal) i.e naturally
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10
Q

What is microbial conjunctival flora

A

Non pathogenic bacteria that is normally present on the lids and in the conjunctival sac from birth and are present throughout the life (commensal) i.e naturally

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11
Q

What does microbial flora i.e non pathogenic bacteria form

A

Form part of the innate defence system of the eye

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12
Q

Role of microbial flora i.e non pathogenic bacteria

A

These bacteria compete with potential pathogens for essential nutrients

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13
Q

Which bacteria doesn’t usually contain commensals

A
  • Gram positive bacteria,
  • Uncommonly environmental fungi
  • Viruses
  • Not normal residents
  • Cornea
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14
Q

What part of eye is sterile environemnt

A

Cornea and anterior chamber so inside of eye

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15
Q

Examples of normal conjunctival flora bacteria commonly present on lids and conjunctiva

A

Gram +ve cocci
- Staphylococcus epidermidis 30-80%
- Staphylococcus aureus 3-25%
- Micrococcus sp. 1-28%
Gram +ve baccilli
- Corynebacterium species . 5-83%
Anaerobic
- Propionibacterium sp. 0-33%

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16
Q

Grame +ve cocci vs Gram +ve baccilli

A
  • Cocci= round shaped bacteria
  • Baccilli = rod shaped
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17
Q

Where are Corynebacterium species found

A

Normal resident on skin and mucosa

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18
Q

Peri-ocular infections location

A
  • Eyelids
  • Conjunctiva
  • Lacrimal system
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19
Q

Orbital infections examples

A

Orbital and pre-septal cellulitis

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20
Q

What is a common eyelid infection

A

Stye

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21
Q

Treatment of stye

A
  • Warm compress
  • Topical antibiotics severe cases
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22
Q

What is external hordoleum

A
  • Stye
  • Infection of ciliary sebaceous gland (Zeis) i.e infection of glands associated with base of eyelashes
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23
Q

What is a common bacteria causing external hordoleum infection

A

Staph. Aureus

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24
Q

What sort of infection is external hordoleum ( stye )

A

Peri-ocular Infections – The Eyelid

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25
Q

Characteristics of external hordoleum

A
  • Lid swelling
  • Redness
  • Tenderness
  • Collection of puss under skin
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26
Q

What happens in an internal hordoleum

A

Meibomian glands can also become infected

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27
Q

Features of blepharitis

A
  • Often non-infective
  • Lid margin disease
  • Infective aetiology
  • May be chronic / remitting = means you have period where signs and symptoms are prominent followed by periods of being free form symptoms
  • Organisms
    - Staph. Aureus,
    - Staph. Epidermidis
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28
Q

What sort of infection is blepharitis

A

Peri-ocular Infections – The Eyelid - non infective lid margin disease

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29
Q

Characteristics of Staphylococci species

A
  • Commensals of human skin
  • Gram positive cocci (clumps)
  • Grow on most media
  • Spherical shapes that aggregate in clusters
  • Result in cell damage and destruction
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30
Q

Spectrum of disease for Staphylococci species

A
  • Local to deep infection
  • Can cause conjunctivitis = ocular surface infections
  • If penetrate deeper into ocular tissues can cause more severe infections
  • Toxin mediated disease
  • Common cause of food poisoning and produce damage through production of toxins
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31
Q

Differentiations between pre sepal cellulitis and orbital cellulitis

A

Pre septal cellulitis:
- No proptosis
- Normal ocular motility
- Normal visual acuity
- Normal RAPD

Orbital cellulitis:
- Proptosis present
- Painful and restricted ocular motility
- Reduced visual acuity
- RAPD present

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32
Q

What age is orbital cellulitis most common in

A

Children

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33
Q

How fatal is orbital cellulitis

A
  • Rare but life threatening
  • It is fatal because the direct communication between orbital cavity and cranial cavity = allows infection to tract into brain = infection spread into cranial cavity
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34
Q

What does orbital cellulitis arise from

A

Abscess in sinuses particularly ethmoid sinus which then spreads into the orbit

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35
Q

What is proptosis

A

Eye pushed forward

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36
Q

Where does infection lie in pre septal cellulitis

A

In front of this barrier

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37
Q

Where does infection lie in orbital cellulitis

A

In the orbit itself so behind the septum

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38
Q

Pre-Septal Cellulitis / Orbital cellulitis - Epidemiology

A
  • Pre-septal (94%) more common : Orbital cellulitis (6%)
  • Both more common in children (75% <5yrs)
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39
Q

Pre-Septal Cellulitis / Orbital Infection - Aetiology

A
  • Sinusitis 80-90%
  • Strep. Pnemoniae / H. influenzae = most common viruses
  • Most common organism of it is streptococcus species
40
Q

What is source of infection for pre septal cellulitis and orbital infection

A

Source of infection is from sinuses = ethmoid sinus, maybe frontal or maxillary sinus

41
Q

Pre-Septal Cellulitis / Orbital Infection - Diagnosis

A

CT scan most helpful

42
Q

Pre-Septal Cellulitis / Orbital Infection - Treatment

A

Pre-septal
- Antibiotics – depend on severity
Orbital cellulitis
- Intravenous antibiotics +/- surgery
- Referred = emergency same day

43
Q

Streptococci characteristics

A
  • Commensals of mouth / gut = normal commensals of skin and mucosal tissue BUT can cause conjunctivitis and deeper orbital infections e.g orbital cellulitis
  • Gram positive spherical bacteria that form cocci (chains)
  • Grow on blood agar (haemolysis) = this bacteria breaks down blood = clear zone around bacterial colonies is evidence of hemolysis
  • Many species of it are non pathogenic
44
Q

Streptococci - spectrum of disease

A
  • Wide (pneumonia, wound and skin infections, sepsis, and endocarditis, meningitis)
  • Local infection may lead to systemic infection
  • Toxin mediated disease
45
Q

Haemophilus spp - characteristics

A
  • Commensal of upper respiratory tract
  • Gram negative rod
  • Fastidious
    -Grows on chocolate agar = variant of blood agar
46
Q

Haemophilus spp - spectrum of disease

A
  • Local infection / Meningitis = can also cause pneumonia and meningitis
  • Much less since Hib vaccination
47
Q

What can Haemophilus spp cause

A

Is common cause of conjunctivitis especially in children in sinusitis

48
Q

What sort of pathogen is Haemophilus influenzas

A
  • Opportunistic pathogens i.e usually live in their host without causing disease
  • But cause problems only when other factors e.g. reduced immune function or chronically inflamed tissues create an opportunity for infections
49
Q

Features of conjunctivitis

A
  • Commonest eye infection
  • All people / All ages / All geographic areas
  • Self limiting infection
  • Most common in children
50
Q

Presentation of pathogens in conjunctivitis

A
  • Viral
  • Bacterial
  • Chlamydial
51
Q

Lab evaluation for conjunctivitis

A
  • Often not done – cause it tends to resolve itself
  • Scrapings / Swabs – for below and those diseases that fail to respond to broad spectrum antibiotics
  • Exception for this is conjunctivitis occurring in first few months of life = ophthalmia neurotaria = reffered intensive treatment
52
Q

Bacterial Conjunctivitis - Characteristics

A
  • Rapid onset
  • Unilateral then bilateral after 1-2 days
  • Staphylococci / Streptococci / H. influenzae
53
Q

Bacterial Conjunctivitis acute vs chronic

A

Acute
- Staphylococcus aureus (children & adults)
- Strep. Pneumo / H. influenzae (children)

Chronic
- Due to exotoxins
- Staphylococci / Moraxella / Enterobacteriacae
- May be difficult to eradicate and treat

54
Q

What sort of infections is bacterial conjunctivitis

A

Self limiting infection caused by variety of bacterial species

55
Q

Visible feature/symptom of bacterail conjunctivitis

A

Present with purulent puss like discharge with eyelids stuck together in morning on waking

56
Q

What can bacterial conjunctivitis become

A

Chronic

57
Q

Viral Conjunctivitis - what is it caused by and associated with

A
  • Most common (probably) cause of Conjunctivitis
  • Caused by adenovirus subtypes
  • Associated with colds and flu
58
Q

Features of bacterial conjunctivitis

A
  • Clinical
  • Acute
  • Unilateral then bilateral in 1/52
  • Often pre-auricular nodes = lymph nodes that sit just in front of ear
  • Self-limiting
    - Few days only to couple weeks in severe cases
    - Resolves itself without complication
    - Usually no sequelae
59
Q

Viral Conjunctivitis - Adenovirus - Pharyngoconjunctival fever

A
  • Commonest
  • Pharyngitis / Conjunctivitis / Fever
  • Associated with upper respiratory tract infection
  • Resolves within 2/52
60
Q

Viral Conjunctivitis - Adenovirus - Epidemic keratoconjunctivitis

A
  • More severe
  • Lasts 1-3/52
    -Associated with subconjunctival haemorrhages 33%
  • May get corneal involvement
  • Sub-epithelial infiltrates 20-30%
61
Q

Features of adenovirus

A
  • Virus
    - DNA virus
    - 49 serotypes
  • Spread
    - Fomites (inanimate objects) and transmitted into eye through hand to eye contact
    - Spread by contact with secretions following coughing and sneezing
62
Q

What are the two forms of Chlamydial Conjunctivitis

A
  1. Trachoma
  2. Inclusion conjunctivitis
63
Q

Features of Chlamydial Conjunctivitis - trachoma

A
  • Poor sanitation and overcrowding
  • In developing countries - Africa and Australia
  • Multiple untreated infection
  • Follicular conjunctivitis
64
Q

Treatment of trachoma

A

Antibiotics e.g. tetracycline and erythromycin

65
Q

What can trachoma cause

A
  • Causes entropion and ectropion = leads to exposure of ocular surface with extensive scarring
  • Potentially blinding condition
66
Q

What is trachoma

A

Palpebral conjunctival scarring

67
Q

Chlamydial Conjunctivitis - acute inclusion conjunctivitis features

A
  • Chronic follicular conjunctivitis
  • Usually sexually transmitted
  • Unilateral red eye
  • Usually mild / diffuse
  • Involves cornea
  • May be some punctate keratitis with epithelial infiltrates
  • Initially diagnosed as bacteria infection – affects both eyes
68
Q

Chlamydial Conjunctivitis - acute inclusion conjunctivitis treatment

A

Topical antibiotics e.g. chloramphenicol but keeps coming back

69
Q

Who does acute inclusion conjunctivitis affect more

A

More commonly affects adults

70
Q

Chlamydiae characteristics

A
  • Obligate intracellular parasite
  • Type of bacteria but life cycle resembles viruses
  • Depend on host cell
  • Inert infectious particles
  • Culture not routine
71
Q

Chlamydiae diagnosis

A
  • Serology
  • Histology (inclusions)
  • PCR
72
Q

Conjunctival scrape

A
  • Using a Kamura spatula
  • Useful for chlamydia
  • Sample taken from upper and lower conjunctival sac
73
Q

Conjunctival/ eyelid margin swabs

A
  • Indicated for severe or persistent infections
  • Topical anaesthesia
  • Sweep conjunctival sac
  • Send to lab urgently in transport medium
74
Q

Culture media

A
  • Chocolate (aerobic and anaerobic) = most common
  • Blood agar
  • Mc Conkey agar (coliforms) = - gram
  • Sabouraud dextrose (fungi)
75
Q

Antibiotic sensitivity

A
  • Uses antibitoics impregnated paper discs which are plated onto the agar plate
  • Then bacteria grows on the plate
  • Measure zone of inhibition of bacterial growth = give indication of most effective antibiotic treatment of infection
76
Q

Cornea susceptible to microbial infection caused by which microbes

A
  • Bacterial e.g. Pseudomonas
  • Viral e.g. Herpes Simplex
  • Fungal e.g. Fusarium
  • Protozoal e.g. Acanthamoeba
77
Q

What is a major risk factor for development of bacterial and Acanthamoeba keratitis

A

Contact lenses

78
Q

Microbial keratitis - bacteria:

A
  • 60-90% of all microbial keratitis = most common cause of microbial keratitis
  • The commonest bacterial corneal pathogens are:
    - Pseudomonas sp. (Gram -ve)
    - Staphylococcus sp. (Gram +ve)
    - Streptococcus sp. (Gram +ve)
  • Gram –ve bacteria most common in contact lens-associated keratitis
  • Gram +ve in non-contact lens wearers
79
Q

Microbial keratitis - bacteria risk factors

A
  • Contact lens wear – risk dependent on modality of wear, more in overnight soft lens wearers i.e EW = poor lens hygiene
  • Immunosupression
  • Ocular surface disease
  • Trauma
80
Q

What is present in early stages of Herpes Simplex Virus (HSV)

A

Dendritic ulcer = early stages of this condition where the infection is localised to the epithelium

81
Q

Viral keratitis caused by herpes viruses - give examples

A

Herpes Simplex Virus (HSV)
- Primary / Recurrent / Congenital
- Most HSV-1 subtype causes HSV (HSV-2 causes genital herpes)
Varicella Zoster Virus (VZV)
- Ophthalmic shingles (corneal involvement in 65% when effects ophthalmic division of trigeminal nerve)
- Causes chicken pox

82
Q

Mechanisms of bacterial pathogenicity

A
  • Some bacteria produce damage through the colonisation of the body surface and release of toxins from bacteria and only invade the tissue to a limited extent
  • Some bacteria cause damage by invasion and subsequent multiplication in the tissues
  • Others have mixture of local invasion and local toxicity
83
Q

Non-infectious Keratitis features

A
  • Corneal response to bacterial toxins
  • Toxin mediated
  • Contact lens associated red eye (CLARE) = response to bacterial toxins, associated with EW
  • Marginal keratitis
  • Contact lens peripheral ulcer (CLPU) = localised disruption
84
Q

Differnces between CLPU and bacterial keratitis

A

Bacterial keratitis is
- More serious sight threatening infection
- Where infiltrate is much smaller
- Often associated with damage to overlying epithelium.
- These areas of infiltration tend to be peripheral just inside limbus small less than 1mm

85
Q

Treatment for non infectious keratitis

A

Discontinuation of lens wear for while

86
Q

Marginal keratitis type of infection

A
  • Inflammatory response to bacterial toxins on lids that bacteria produce
  • Non-infective
87
Q

Marginal keratitiis management

A

Managed with combinations of topical steroid and antibiotics to reduce bacterial load of lid margin +/- lid hygiene

88
Q

What is marginal keratitis associated with

A

Associated with increase bacterial colonization of lid margins

89
Q

What type of disease is microbial keratitis

A

Lid margin disease

90
Q

Uveitis classification and aetiology

A

Classification
- Anterior = iris and ciliary body anterior part e.g. plars of plicata
- Intermediate = pars of planna of ciliary body
- Posterior = choroid
- Panuveitis

Aetiology
- Infectious = small cases
- Non-infectious

91
Q

What are most cases of uveitis

A

Most cases of uveitis are non infective and have inflammatory aetiology or no known cause

92
Q

Definition of uveitis

A

Inflammation extends through uvea

93
Q

Parts of uvea tract

A

Iris, ciliary body, choroid

94
Q

What organisms that gives rise to infectious uveitis

A

Anterior
- Herpes simplex virus (HSV)
- Varicella zoster virus (VZV)

Posterior
- Toxoplasmosis
- Toxocara = worm infection
- Syphilis
- Cytomagalovirus (CMV) = immunosuppressed

95
Q

Endophthalmitis - characteristics and classification

A

Characteristics
- Usually bacterial & acute
Most cases exogenous
-Surgery / Trauma
- Internal ocular structures exposed to exogenous micro-organisms usually bacteria – can occur as result of trauma or surgery e.g cataract or glaucoma surgery = penetrative surgery to eye
- Site threatening infection

Classification
- Acute post-cataract
- Chronic pseudophakic
- Bleb-related
- Post-traumatic

96
Q

Treatment of endopthalmitis

A

Needs to be treated with high doses of antibiotic injected directly into eye

97
Q

Infection Control

A
  • Patients may present to the optometrist in practice with an infectious illness and pose a risk of cross infecting the optometrist or passing on the infection to other patients through use of medical devices
  • Optometrists themselves may also be harbouring infectious disease, which they may be at risk of passing on to their patients
  • The practice environment may pose a microbiological hazard and provide an infection risk to both staff and
    patients

Eye disease and therapeutics (9 decks)

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