Pathogenesis of Infectious Eye Disease Flashcards
What is ocular surface well protected from
Pathogens
Examples of risk factors that predispose to ocular infection
- Immune status = px’s who are immunosuppressed naturally or through use of drugs e.g. corticosteroids
- Ocular morbidity = ocular surface disease
- Contact lens wear
What does ocular surface have to make sure it remains disease free
- 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
What happens when mechanisms of natural defence mechanisms becomes compromised
Predisposes eye to infection
Examples of less common pathogens:
Fungi and protozoa e.g. toxoplasma and acanthamoeba
Examples of pathogens in cornea causing infection
HSV, VZV, protozoa, fungi
Examples of pathogens in uvea causing infection
Bacteria,
CMV, VZV,
Protozoa
Examples of pathogens in endophthalmitis causing infection
Bacteria, fungi
Examples of pathogens in lids and conjunctiva causing infection
Bacteria, chlamydia, adenovirus, HSV, VZV
What is microbial conjunctival flora
- 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
What is microbial conjunctival flora
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
What does microbial flora i.e non pathogenic bacteria form
Form part of the innate defence system of the eye
Role of microbial flora i.e non pathogenic bacteria
These bacteria compete with potential pathogens for essential nutrients
Which bacteria doesn’t usually contain commensals
- Gram positive bacteria,
- Uncommonly environmental fungi
- Viruses
- Not normal residents
- Cornea
What part of eye is sterile environemnt
Cornea and anterior chamber so inside of eye
Examples of normal conjunctival flora bacteria commonly present on lids and conjunctiva
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%
Grame +ve cocci vs Gram +ve baccilli
- Cocci= round shaped bacteria
- Baccilli = rod shaped
Where are Corynebacterium species found
Normal resident on skin and mucosa
Peri-ocular infections location
- Eyelids
- Conjunctiva
- Lacrimal system
Orbital infections examples
Orbital and pre-septal cellulitis
What is a common eyelid infection
Stye
Treatment of stye
- Warm compress
- Topical antibiotics severe cases
What is external hordoleum
- Stye
- Infection of ciliary sebaceous gland (Zeis) i.e infection of glands associated with base of eyelashes
What is a common bacteria causing external hordoleum infection
Staph. Aureus
What sort of infection is external hordoleum ( stye )
Peri-ocular Infections – The Eyelid
Characteristics of external hordoleum
- Lid swelling
- Redness
- Tenderness
- Collection of puss under skin
What happens in an internal hordoleum
Meibomian glands can also become infected
Features of blepharitis
- 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
What sort of infection is blepharitis
Peri-ocular Infections – The Eyelid - non infective lid margin disease
Characteristics of Staphylococci species
- Commensals of human skin
- Gram positive cocci (clumps)
- Grow on most media
- Spherical shapes that aggregate in clusters
- Result in cell damage and destruction
Spectrum of disease for Staphylococci species
- 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
Differentiations between pre sepal cellulitis and orbital cellulitis
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
What age is orbital cellulitis most common in
Children
How fatal is orbital cellulitis
- 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
What does orbital cellulitis arise from
Abscess in sinuses particularly ethmoid sinus which then spreads into the orbit
What is proptosis
Eye pushed forward
Where does infection lie in pre septal cellulitis
In front of this barrier
Where does infection lie in orbital cellulitis
In the orbit itself so behind the septum
Pre-Septal Cellulitis / Orbital cellulitis - Epidemiology
- Pre-septal (94%) more common : Orbital cellulitis (6%)
- Both more common in children (75% <5yrs)
Pre-Septal Cellulitis / Orbital Infection - Aetiology
- Sinusitis 80-90%
- Strep. Pnemoniae / H. influenzae = most common viruses
- Most common organism of it is streptococcus species
What is source of infection for pre septal cellulitis and orbital infection
Source of infection is from sinuses = ethmoid sinus, maybe frontal or maxillary sinus
Pre-Septal Cellulitis / Orbital Infection - Diagnosis
CT scan most helpful
Pre-Septal Cellulitis / Orbital Infection - Treatment
Pre-septal
- Antibiotics – depend on severity
Orbital cellulitis
- Intravenous antibiotics +/- surgery
- Referred = emergency same day
Streptococci characteristics
- 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
Streptococci - spectrum of disease
- Wide (pneumonia, wound and skin infections, sepsis, and endocarditis, meningitis)
- Local infection may lead to systemic infection
- Toxin mediated disease
Haemophilus spp - characteristics
- Commensal of upper respiratory tract
- Gram negative rod
- Fastidious
-Grows on chocolate agar = variant of blood agar
Haemophilus spp - spectrum of disease
- Local infection / Meningitis = can also cause pneumonia and meningitis
- Much less since Hib vaccination
What can Haemophilus spp cause
Is common cause of conjunctivitis especially in children in sinusitis
What sort of pathogen is Haemophilus influenzas
- 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
Features of conjunctivitis
- Commonest eye infection
- All people / All ages / All geographic areas
- Self limiting infection
- Most common in children
Presentation of pathogens in conjunctivitis
- Viral
- Bacterial
- Chlamydial
Lab evaluation for conjunctivitis
- 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
Bacterial Conjunctivitis - Characteristics
- Rapid onset
- Unilateral then bilateral after 1-2 days
- Staphylococci / Streptococci / H. influenzae
Bacterial Conjunctivitis acute vs chronic
Acute
- Staphylococcus aureus (children & adults)
- Strep. Pneumo / H. influenzae (children)
Chronic
- Due to exotoxins
- Staphylococci / Moraxella / Enterobacteriacae
- May be difficult to eradicate and treat
What sort of infections is bacterial conjunctivitis
Self limiting infection caused by variety of bacterial species
Visible feature/symptom of bacterail conjunctivitis
Present with purulent puss like discharge with eyelids stuck together in morning on waking
What can bacterial conjunctivitis become
Chronic
Viral Conjunctivitis - what is it caused by and associated with
- Most common (probably) cause of Conjunctivitis
- Caused by adenovirus subtypes
- Associated with colds and flu
Features of bacterial conjunctivitis
- 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
Viral Conjunctivitis - Adenovirus - Pharyngoconjunctival fever
- Commonest
- Pharyngitis / Conjunctivitis / Fever
- Associated with upper respiratory tract infection
- Resolves within 2/52
Viral Conjunctivitis - Adenovirus - Epidemic keratoconjunctivitis
- More severe
- Lasts 1-3/52
-Associated with subconjunctival haemorrhages 33% - May get corneal involvement
- Sub-epithelial infiltrates 20-30%
Features of adenovirus
- 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
What are the two forms of Chlamydial Conjunctivitis
- Trachoma
- Inclusion conjunctivitis
Features of Chlamydial Conjunctivitis - trachoma
- Poor sanitation and overcrowding
- In developing countries - Africa and Australia
- Multiple untreated infection
- Follicular conjunctivitis
Treatment of trachoma
Antibiotics e.g. tetracycline and erythromycin
What can trachoma cause
- Causes entropion and ectropion = leads to exposure of ocular surface with extensive scarring
- Potentially blinding condition
What is trachoma
Palpebral conjunctival scarring
Chlamydial Conjunctivitis - acute inclusion conjunctivitis features
- 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
Chlamydial Conjunctivitis - acute inclusion conjunctivitis treatment
Topical antibiotics e.g. chloramphenicol but keeps coming back
Who does acute inclusion conjunctivitis affect more
More commonly affects adults
Chlamydiae characteristics
- Obligate intracellular parasite
- Type of bacteria but life cycle resembles viruses
- Depend on host cell
- Inert infectious particles
- Culture not routine
Chlamydiae diagnosis
- Serology
- Histology (inclusions)
- PCR
Conjunctival scrape
- Using a Kamura spatula
- Useful for chlamydia
- Sample taken from upper and lower conjunctival sac
Conjunctival/ eyelid margin swabs
- Indicated for severe or persistent infections
- Topical anaesthesia
- Sweep conjunctival sac
- Send to lab urgently in transport medium
Culture media
- Chocolate (aerobic and anaerobic) = most common
- Blood agar
- Mc Conkey agar (coliforms) = - gram
- Sabouraud dextrose (fungi)
Antibiotic sensitivity
- 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
Cornea susceptible to microbial infection caused by which microbes
- Bacterial e.g. Pseudomonas
- Viral e.g. Herpes Simplex
- Fungal e.g. Fusarium
- Protozoal e.g. Acanthamoeba
What is a major risk factor for development of bacterial and Acanthamoeba keratitis
Contact lenses
Microbial keratitis - bacteria:
- 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
Microbial keratitis - bacteria risk factors
- 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
What is present in early stages of Herpes Simplex Virus (HSV)
Dendritic ulcer = early stages of this condition where the infection is localised to the epithelium
Viral keratitis caused by herpes viruses - give examples
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
Mechanisms of bacterial pathogenicity
- 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
Non-infectious Keratitis features
- 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
Differnces between CLPU and bacterial keratitis
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
Treatment for non infectious keratitis
Discontinuation of lens wear for while
Marginal keratitis type of infection
- Inflammatory response to bacterial toxins on lids that bacteria produce
- Non-infective
Marginal keratitiis management
Managed with combinations of topical steroid and antibiotics to reduce bacterial load of lid margin +/- lid hygiene
What is marginal keratitis associated with
Associated with increase bacterial colonization of lid margins
What type of disease is microbial keratitis
Lid margin disease
Uveitis classification and aetiology
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
What are most cases of uveitis
Most cases of uveitis are non infective and have inflammatory aetiology or no known cause
Definition of uveitis
Inflammation extends through uvea
Parts of uvea tract
Iris, ciliary body, choroid
What organisms that gives rise to infectious uveitis
Anterior
- Herpes simplex virus (HSV)
- Varicella zoster virus (VZV)
Posterior
- Toxoplasmosis
- Toxocara = worm infection
- Syphilis
- Cytomagalovirus (CMV) = immunosuppressed
Endophthalmitis - characteristics and classification
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
Treatment of endopthalmitis
Needs to be treated with high doses of antibiotic injected directly into eye
Infection Control
- 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
