Ocular Microbiology

Question 0

What two complications can infective keratitis progress to?

Answer 0

1. Perforation

2. Endophthalmitis (intraocular infection)

Question 1

What are two serious complications of orbital cellulitis?

Answer 1

1. Meningitis

2. Intracranial sinus thrombosis.

Question 2

Name four constituents of tear film which have direct antimicrobial function?

Answer 2

1. Lysozyme
2. Lactoferrin
3. IgA
4. Lymphocytes and cells of the monocyte-macrophage system (MALT in the conjunctiva).

Question 4

Name three commensal microorganisms found on periocular skin.

Answer 4

1. Staphylococcus epidermidis (most common)
2. Staphylococcus aureus (less common)
3. Propionibacterium acne (common, as are a variety of fungi).

Question 5

Name five bacteria which are found on the conjunctiva of normal subjects.

Answer 5

1. Corynebacterium
2. Neisseriae
3. Moraxella
4. Staphylococci
5. Streptococci

Question 6

Name five techniques for obtaining specimens from the eye for microscopy and culture (can be either external or intraocular techniques).

Answer 6

1. Conjunctival swab (avoid lid margin and lashes)
2. Conjunctival scrape (usually everted upper lid)
3. Corneal scrape (eg. from base of corneal ulcer)
4. Anterior chamber tap (eg. infective endophthalmitis) - but low yield
5. Vitreous biopsy (definitive for infective endophthalmitis)

Question 7

What does the escherischia coli-seeded agar culture medium grow? (eg. following corneal scrape of ulcer)

Answer 7

Acanthamoeba

Question 8

True or false: Serology is a useful investigation in suspected toxoplasma retinochoroiditis.

Answer 8

False in most cases.

Question 9

True or false: blood cultures are sometimes indicated if an endogenous aetiology is suspected.

Answer 9

True.

eg. Orbital cellulitis; endophalmitis.

Question 10

How can ocular antimicrobial therapy be administered? 5 ways.

Answer 10

1. Topically (drops or ointment)
2. Subconjunctival injection
3. Periocular/orbital injection
4. Injection directly into the vitreous cavity
5. Systemically

Many preparations penetrate the cornea well and adequate drug levels in the aqueous can be achieved, however most ABx fail to reach the vitreous and so direct intravitreal injection is necessary.

Question 11

Name 5 non-specific barriers to infection.

Answer 11

1. Lids
2. Lashes
3. Blinking
4. Tear flow
5. Epithelium

Question 12

True or false: bacterial commensals are not likely to become pathogenic when mechanical barriers are disrupted.

Answer 12

False.

Eg. Corneal abrasion, intraocular surgery.