30. Microbial Keratitis

Question 1

Every ... causes an ..., but not every ... is infectious.

Answer 1

Every infection causes an infiltrate, but not every infiltrate is infectious.

Question 2

The cornea is an immune ... environment due to being ... and .... ... represent an immune response to a corneal insult. In response to an evading pathogen or insult, the corneal epithelial cells release ... and .... Immune cells are released from .... The ... is an aggregation of ..., ... and ... as part of the inflammatory response.

Answer 2

The cornea is an immune privileged environment due to being avascular and alymphatic. Corneal infiltrates represent an immune response to a corneal insult. In response to an evading pathogen or insult, the corneal epithelial cells release cytokines and chemokines. Immune cells are released from limbal blood vessels. The infiltrate is an aggregation of neutrophils, lymphocytes and macrophages as part of the inflammatory response.

Question 3

Sterile corneal infiltrative events are associated with ... have been previously categorised as ... (CLPU) and ... (CLARE).

Answer 3

Sterile corneal infiltrative events are associated with contact lens wear have been previously categorised as contact lens peripheral ulcer (CLPU) and contact lens acute red eye (CLARE).

Question 4

What should be considered when differentially diagnosing sterile infiltrates and microbial keratitis?

Answer 4

• Consider px history & presentation
• Consider treating all infiltrative events as infectious in nature

Question 5

What are the differences between sterile infiltrate and microbial keratitis in terms of aetiology, prevalence, pain, vision, photophobia, tearing and discharge?

Answer 5

Sterile infiltrate:
* Inflammatory
* More common (22x more common than MK)
* Pain: mild to moderate
* Vision: usually unaffected
* Mild photophobia
* Mild tearing
* Mild discharge (not always)

Microbial Keratitis
* Infective
* Relatively rare
* Increasing & severe pain
* Usually reduced vision
* Moderate/ Severe photophobia
* Intense tearing
* Significant discharge

Question 6

What are the differences between sterile infiltrate and microbial keratitis in terms of numbers, location, shape, size, staining, & staining association?

Answer 6

Sterile infiltrate:
* Sometimes multiple infiltrates
* Peripheral or mid-peripheral
* More likely circular
* < 2.0mm
* Staining possible
* Staining smaller in size than infiltrate

Microbial Keratitis
* Single lesion ulcer, satellite lesions possible
* Anywhere, including central
* More likely irregular shape
* > 1.0mm
* Staining present
* Staining matches ulcer size

Question 7

What are the differences between sterile infiltrate and microbial keratitis in terms of depth,conojunctival response, lid oedema, anterior chamber reaction, and discontinuing CL wear?

Answer 7

Sterile infiltrate:
* Anterior stroma only
* Conjunctival hyperaemia: sectorial, mild to moderate
* No lid oedema
* None or minimal anterior chamber reaction
* Discontinuing CL wear helps resolve infiltrates

Microbial keratitis:
* Anterior to mid stromal, raised edges
* Conjunctival hyperaemia: generalised, moderate to severe (meaty)
* Lid oedema usually present
* Moderate anterior chamber reaction, occasional hypopyon
* Discontinuing CL wear usually worsens microbial keratitis

Question 8

What is the abbreviation for differentiating between sterile infiltrate and microbial keratitis?

Answer 8

PEDALS = Pain, Epithelial defect, Discharge, Anterior chamber, Location & Size

Question 9

What are the differences between sterile infiltrate and microbial keratitis in terms of appearance of fluorescein staining?

Answer 9

Sterile infiltrate
* White/ faint grey colour, distinct margins, circular/ oval
* Stains patchy, incomplete staining pattern

Microbial keratitis
* Grey/green-yellow colour, hazy, ill-defined margins of any shape
* Pools, fills area of tissue excavation

Question 10

What is the name of the grading scale that help differentiate between sterile infiltrate and microbial keratitis? What does it account for and what do the scorings represent?

Answer 10

Modified Aasuri Grading Scale, accounting for multiple infiltrates.
< 8 = non-severe keratitis
> 8 = severe keratitis
> 12 = microbial keratitis

Question 11

Sterile infiltrates can result from the ... response from .... These often present as ... infiltrates, which may have overlying .... There is often a ... of 1-2mm between the infiltrate and the .... There may be confluent ... with delayed ... in to the epithelium and superficial .... Lesions appeaer in areas of direct contact between the ... and ... (... o’clock and ... o’clock)
The risk factors assocaited with this type of sterile infiltrate are: ..., current or recent ... and previous episodes of ...

Answer 11

Sterile infiltrates can result from the toxic or hypersensitivity response from Staphylococcal bacteria exotoxins. These often present as peripheral subepithelial marginal infiltrates, which may have overlying epithelial breakdown. There is often a clear intervening zone of 1-2mm between the infiltrate and the limbus. There may be confluent superficial punctate keratitis with delayed fluorescein staining in to the epithelium and superficial stroma. Lesions appeaer in areas of direct contact between the peripheral cornea and eyelid margin (2-10 o’clock and 4-8 o’clock)
The risk factors assocaited with this type of sterile infiltrate are: anterior blepharitis (staphylococcus), current or recent upper respiratory tract infection and previous episodes of marginal infiltrates

Question 12

What are the two associations with sterile infiltrates?

Answer 12

Blepharitis and contact lens wear (CLPU, CLARE, CLAIK)

Question 13

CLPU stands for .... These have characteristic small, ..., ... ... sterile infiltrates. Other symptoms include ... and ... redness, ... sensation and ... pain. There are up to ...% CLPU px that are asymptomatic.

Answer 13

CLPU stands for contact lens associated peripheral ulcer. These have characteristic small, single, circular focal sterile infiltrates. Other symptoms include limbal and bulbar redness, foreign body sensation and severe to moderate pain. There are up to 50% CLPU px that are asymptomatic.

Question 14

CLARE stands for .... This is characterised by the moderate to severe ... of the conjunctiva. This also associates with small, ..., more ..., focal, sterile infiltrates. Other symptoms include ... pain, ... and ... soon after waking.

Answer 14

CLARE stands for contact lens associated red eye. This is characterised by the moderate to severe circumferential redness of the conjunctiva. This also associates with small, multiple, more diffused, focal, sterile infiltrates. Other symptoms include moderate pain, tearing and photophobia soon after waking.

Question 15

CLAIK stands for .... This is associated with ... infiltration, with or without ... involvment, ... of the cornea. These sterile infiltrates are ... and can present in .... Other symptoms include mild to moderate ..., ... and occasional ....

Answer 15

CLAIK stands for contact lens associated infiltrative keratitis. This is associated with anterior stromal infiltration, with or without epithelial involvment, mid periphery to periphery of the cornea. These sterile infiltrates are small and can present in multiples. Other symptoms include mild to moderate irritation, redness and occasional discharge.

Question 16

Risk factors for sterile infiltrates associated with contact lens wear:
* ... - highest risk between ... yo
* ... > ...
* High ... >...
* Higher ...
* Current or recent ... (Haemophilus influenzae)
* ...
* ... (Staphylococcus)
* Previous episode of ... event (4-6x increased risk)
* Use of ... contact lenses - ...
* ... of contact lens case
* ... purchasing of contact lenses
* ... wear of contact lenses
* ... contact lens material (2x increased risk)
* ... contact lens disinfection system
* ... to contact lenses or lens cases

Answer 16

Risk factors for sterile infiltrates associated with contact lens wear:
* Age - highest risk between 5-29 yo
* Males > Females
* High refractive error >5D
* Higher socio-economic status
* Current or recent upper respiratory tract infection (Haemophilus influenzae)
* Smoking
* Anterior blepharitis (Staphylococcus)
* Previous episode of corneal infiltrative event (4-6x increased risk)
* Use of reusable contact lenses - monthly or fortnightly
* Age of contact lens case
* Online purchasing of contact lenses
* Overnight wear of contact lenses
* Silicon hydrogel contact lens material (2x increased risk)
* Multipurpose contact lens disinfection system
* Water exposure to contact lenses or lens cases

Question 17

What are the 6 differential diagnosis of sterile marginal infiltrates?

Answer 17

• Contact lens associated microbial keratitis
• Rosacea keratitis
• Peripheral keratitis associated with rheumatoid arthritis or another systemic collagen vascular disease
• Mooren’s ulcer
• Phlytenular keratoconjunctivitis
• Terrien’s marginal degeneration

Question 18

What are the treatments for Staphylococcal marginal infiltrates associated with blepharitis? (7)

Answer 18

Lids
* Lid hygiene - warm compresses, lid cleansers, lid debridement
* Antibiotic ointment to reduce bacterial load on lids
* Steroid ointment to reduce lid inflammation
Cornea
* Steroid drops to treat infiltrate -> FML 0.1% loading dose (every 15 mins for first hour, then QID until resolved, slowly taper equivalent to treatment period)
* Antibiotics -> chloromycetin 0.5 drops (chlorsig) QID no taper
* If no improvement -> oral doxycycline
* Emphasise the condition is chronic and requires ongoing compliance to adequately manage symptoms

Question 19

What are the treatments for CL associated marginal infiltrates (CLPU, CLARE, CLAIK)?

Answer 19

”* Cease CL wear -> Signs/ symptoms usually improve rapidly after
* Prescribe antibiotic against staphylococcus and pseudomonas
-> Mild = Tobramycin 0.3% drops (Tobrex)
-> Severe = Fluoroquinolone (ciprofloxacin 0.3% (Ciloxan) or ofloxacin 0.3% (Ofloxacin)
* initially every 15mins then QID, no tapering
* Monitor px closely over first 12-24 hours
* Continue antibiotic for 2 days following epithelium healing, then stop and no taper
* Once epithelium has healed, prescribe steroid -> Fluorometholone acetate 0.01% drops (Flarex) QID until inflammation has resolved
* Slowly taper steroid over equivalent of treatment period

Question 20

What are the long term management for CL associated marginal infiltrates (CLPU, CLARE, CLAIK)?

Answer 20

Long term management - intervene on modifiable risk factors
* Eyelid hygiene maintenance
* Recommend stop smoking
* Avoid or minimise extended CL wear
* Consider hydrogen peroxide cleaning regime
* Consider swapping from SiHy to hydrogel lenses
* Increase frequency of CL and case replacement
* Consider stopping from reusable CLs to daily replacement lenses

Question 21

What is the prognosis of CL associated marginal infiltrates?

(2 points)

Answer 21

• Scarring is rare, but it is does, it will appear as a Bull’s eye scar
• Recurrence is likely

Question 22

There are 4 microbe classes that can cause microbial keratitis: ..., ..., ... and .... All MK infections begin as ... and situates ..... MK may result in corneal .... and possible .... MK keratitis rarely occurs in the absence of ... factors. There severity of MK is based on ..., ..., and .... MK affects both ... and ... quality of life. Even when visual recoery was complete, px demonstrated .... At RVEEH, there are ... cases each year.

Answer 22

There are 4 microbe classes that can cause microbial keratitis: bacteria, virus, fungus and parasites. All MK infections begin as small infiltrates and situates peripherally. MK may result in corneal perforation and possible endophthalmitis. MK keratitis rarely occurs in the absence of predisposing factors. There severity of MK is based on infiltrate sizes, location, and anterior chamber reaction. MK affects both vision related and psychological quality of life. Even when visual recoery was complete, px demonstrated a lower quality of life score following MK. At RVEEH, there are 100 cases each year.

Question 23

What are the 4 risk factors of microbial keratitis?

Answer 23

• Contact lens wear
  *Trauma
• Ocular surface disease
• Post corneal surgery

Question 24

Diagnosis requires careful ... and assessment of ... and .... ... is the gold standard to determine the microbe involved and is recommended in .... Treatment must be initiated ... in suspected MK cases. A delay of even ... can increase the likelihood of ... and ... of the disease.

Answer 24

Diagnosis requires careful history and assessment of signs and symptoms. Corneal culture is the gold standard to determine the microbe involved and is recommended in all cases of MK. Treatment must be initiated urgently in suspected MK cases. A delay of even 12 hours can increase the likelihood of vision loss and duration of the disease.

Question 25

What are the two stages of microbial keratitis treatment?

Answer 25

Sterilisation - intense antibiotic use for a limited period to sterilise the cornea, usually 3-5 days. May take weeks or months against fungi and Acanthamoeba. Healing - treatment aim is to limit further inflammatory damage, prevent superinfection and promote epithelial healing.

Question 26

What are the 6 examination techniques needed for microbial keratitis?

Answer 26

• VA (including pinhole if VA is reduced)
• Corneal sensitivity
• Slit lamp → lids (blepharitis, lid position, trichiasis, lagophthalmos); conjunctiva (injection, discharge); cornea (infiltrate, size, depth, location, epithelial defect - fluorescein or rose bengal staining, stromal thinning, scarring, foreign body); anterior chamber (cells, hypopyon)
• Posterior segment → to rule out endopthalmitis
• Intraocular pressure
• Anterior OCT to determine corneal thickness at infiltrate

Question 27

What are the indications for an laboratory investigation for microbial keratitis? What is the name of the rule?

Answer 27

The 1, 2, 3 rule:
* Anterior chamber reaction of Grade 1+ cells (>10 in a 1mm beam)
* Infiltrate ≥ 2mm
* Location ≤ 3mm from centre of cornea

Question 28

Corneal scraping & culture for microbial keratitis
1. ... the cornea
2. Scrape the ... and ... of the lesion with a ... or ...
3. Transfer to glass slides and apply ...
4. Transfer to ... for most bacteria and fungi If px is a CL wearer, include culture for ...
5. CL & ... should also be cultured
6. ... if indicated if suspect ... or if MK occurs ..., this improves detection rates for ... and ...

Answer 28

Corneal scraping & culture for microbial keratitis
1. Anaesthetise the cornea
2. Scrape the base and leading edge of the lesion with a Kimura spatula or sterile cotton tipped applicator
3. Transfer to glass slides and apply Gram and Giemsa stains
4. Transfer to culture mediums for most bacteria and fungi If px is a CL wearer, include culture for Acanthamoeba
5. CL & CL case should also be cultured
6. PCR if indicated if suspect viral or if MK occurs without a clear underlying cause, this improves detection rates for HSVK and HZK

Question 29

Bacterial keratitis accounts for ...% of all microbial keratitis cases. Approximately ...% of px develop long-term moderate to severe ... (VA <6/18). Bacterial keratitis is the leading cause of ... worldwide. ... or ... MK is of greatest concern as consequent scarring has the potential to cause .... Bacterial keratitis is rare when there is no .... If there is a break, corneal perforation can occur within ... Hours. However, there are bacteria that can invade an intact corneal epithelium, such as .... Other bacteria that is common in bacterial keratitis are ... and ... (G+), ... (G+) and ... (G-). High virulence bacteria gives a higher ..., these include ..., ... and ....

Answer 29

Bacterial keratitis accounts for 90% of all microbial keratitis cases. Approximately 30% of px develop long-term moderate to severe monocular vision loss (VA <6/18). Bacterial keratitis is the leading cause of monocular blindness worldwide. Central or para-central MK is of greatest concern as consequent scarring has the potential to cause substantial vision loss. Bacterial keratitis is rare when there is no break in the corneal epithelium. If there is a break, corneal perforation can occur within 24 Hours. However, there are bacteria that can invade an intact corneal epithelium, such as Neisseria gonorrhoeae. Other bacteria that is common in bacterial keratitis are Staphylococcus aureus and epidermis (G+), Streptococcus pneumoniae (G+) and Pseudomonas aeruginosa (G-). High virulence bacteria gives a higher rate of disease progression, these include Pseudomonas aeruginosa, Streptococcus pneumoniae and Neisseria gonorrhoeae.

Question 30

Name the 7 risk factors of bacterial keratitis

Answer 30

• CL use
• Ocular trauma
• Use of topical steroid medications
• Ocular surgery
• Neurotrophic keratopathy
• Aqueous tear deficiencies
• Immunosuppression

Question 31

Pathophysiology of Bacterial keratitis:
* Altered ocular surface homeostasis creates an ... that permits ...
* Rapid accumulation of ..., ... and ... provokes intense host ... from ..., ..., resident corneal ..., and infiltrating ...
* Inflammaory response releases ..., ... and ... that result in bacterial eradication
* However, these chemicals have a ... on the surrounding stroma that may lead to significant ....

Answer 31

Pathophysiology of Bacterial keratitis:
* Altered ocular surface homeostasis creates an epithelial defect that permits invasion by opportunistic bacteria
* Rapid accumulation of bacterial toxins, exoproducts and cellular debris provokes intense host inflammatory response from corneal epithelium, stroma keratocytes, resident corneal Langerhans cells, and infiltrating leukocytes
* Inflammaory response releases reactive oxygen species, lysosomal enzymes and auteolytic proteins that result in bacterial eradication
* However, these chemicals have a collateral toxicity on the surrounding stroma that may lead to significant scarring.

Question 32

Treatment for Bacterial Keratitis:
* Admission to the hospital should be considered if ... or there is any concern regarding ...
* Significant symptoms (>... on modified ... grading scale) → ... drops e.g. ... ...% (...) or ... ...% (...) - initially ... (every ...mins for 6 hours, then every ... mins until review the ..., then ..., ... until review)
* Topical ... may be needed to ... and also prevent formation of ... → ... ...% ... or ... ...% ...
* Topical ... is ... is elevated
* Cease topical ..., expect in ...
* ... medication as required
* No ... wear in affected eye
* Never ... → instead use ... (without pad) if at risk of ...
* Topical corticosteroids when ... → ... ... after at least ... hours

Answer 32

Treatment for Bacterial Keratitis:
* Admission to the hospital should be considered if there is a large area with significant thinning or there is any concern regarding compliance with the intensive drop regime
* Significant symptoms (>8 on modified Aasuri grading scale) → Fluoroquinolone drops e.g. ciprofloxacin 0.3% (Ciloxan) or ofloxacin 0.3% (Ofloxacin) - initially loading dose (every 15mins for 6 hours, then every 30 mins until review the next day, then hourly, day and night until review)
* Topical cycloplegia may be needed to decrease pain and also prevent formation of synechia → atropine 1% BID or cyclopentolate 1% TID
* Topical ocular hypotension drops is IOP is elevated
* Cease topical corticosteroids, expect in corneal graft px
* Pain medication as required
* No CL wear in affected eye
* Never patch → instead use clear shield (without pad) if at risk of corneal perforation
* Topical corticosteroids when MK is progressively improving with epithelial defect healing → Fluorometholone acetate QID after at least 48 hours

Question 33

When is fortified compounded duotherapy (Aminoglycoside & Cephalosporin) recommended for bacterial keratitis?

Answer 33

• Px at greater risk of perforation
• With deep large ulcers
• In the eldery
• With antimicrobial resistance (cephazolin 5% & gentamicin 1.5%)

Question 34

What is the outcome in the study that compared fluoroquinolone and fortified compounded duotherapy for bacterial keratitis at RVEEH in 2000?

Answer 34

There is no significant difference in visual outcome. Fluoroquinolone had reduced drug toxicity and discomfort, shorter duration of intensive therapy and hospital stay.

Question 35

What is the outcome in the SCUT study that looked at using broad spectrum topica antibiotic treatment of bacterial keratitis + adjunctive therapy of topical prednisolone phosphate 1% (corticosteroid) vs placebo?

Answer 35

At 3 months, there is no benefit of concurrent corticosteroid in conjunction with broad spectrum topical antibiotic when assessed by VA, scar size, time to re-epithelialisation and rate of perforation. But there is also no increase in adverse events, such as risk of perforation, elevated IOP and delay in re-epithelialisation.
At 12 months, the addition of topical corticosteroids within 48-72 hours of initiation of antibiotic therapy resulted in 1 line better VA compared to placebo.

Question 36

There are higher rates of viral keratitis in ...(15-46%) and ...(15-21%) compared to Australia. .... and ... diagnosis is mainly clinically based on ... and ..., and also confirmed by ....

Answer 36

There are higher rates of viral keratitis in China(15-46%) and Egypt(15-21%) compared to Australia. Herpes simplex virus keratitis and Herpes Zoster keratitis diagnosis is mainly clinically based on history and slit lamp examination, and also confirmed by PCR testing.

Question 37

Fungal keratitis is rare, ..., difficult to ... and often result with .... Diagnosis is based on ..., ... and .... Fungal keratitis is most prevalent in ... and ... climates. ...% of all cases of MK at RVEEH were fungal. There are two categories:
* .... → ... spp and ... spp, which are main pathogen in the ... and ...
* ..., ... or ... → ... spp, which is the main pathogen in ... regions

Answer 37

Fungal keratitis is rare, unilateral, difficult to treat and often result with poor visual outcomes. Diagnosis is based on clinical history, signs and corneal scraping. Fungal keratitis is most prevalent in tropics and subtropical climates. 5% of all cases of MK at RVEEH were fungal. There are two categories:
* Filamentous → Fusarium spp and Aspergillus spp, which are main pathogen in the tropics and subtropics
* Non-filamentous, yeast or yeast-like → Candida spp,
which is the main pathogen in temperate regions”

Question 38

What are the 7 risk factors of fungal keratitis?

Answer 38

• Pre-existing ocular surface disease → lid margin disease, lagophthalmos, persistent epithelial defects
• Foreign body + trauma - plant or animal origin
• Previous ocular Sx - penetrating keratoplasty, cataract Sx
• Previous use of corticosteroids
• CL use
• Atopic eye disease
• Immunocompromised px

Question 39

What are the 7 symptoms of fungal keratitis?

Answer 39

• Pain
• Blurry vision
• Photophobia
• Conjunctival hyperaemia
• Tearing
• Discharge
• Foregn body sensation

Question 40

What are the 6 clinical presentations of fungal keratitis from most common to least common?

Answer 40

• Epithelial defect
  *Infiltrate
• Hypopyon
• Corneal thinning
• Satellite lesions
• Ring infiltrates

Question 41

Fungi cannot penetrate ..., therefore it requires a ... or previous ... to enter the cornea. Once the fungi has entered the ..., it can penetrate through an intact ... and into the ... via .... This can therefore cause a ..., neovascularisation and .... Px may be asymptomatic during a ... period where epithelium has ... an .... Px may then experience ..., ... and ... within ... or ....

Answer 41

Fungi cannot penetrate an intact corneal epithelium, therefore it requires a penetrating injury or previous epithelial defect to enter the cornea. Once the fungi has entered the stroma, it can penetrate through an intact Descemet's membrane and into the anterior chamber via proteolytic enzymes. This can therefore cause a Hypopyon, neovascularisation and scarring. Px may be asymptomatic during a latent period where epithelium has healed over an inflammatory and persistent infiltrate. Px may then experience discomfort, photophobia and discharge within days or weeks.

Question 43

What are the 8 signs of Filamentous fungi → Fusarium, Aspergillus?

Answer 43

• Grey-white stromal elevated infiltrate with feathery white borders
• Satellite lesions surround primary infiltrate
• Epitheliual defect or corneal ulcer
• Anterior chamber reaction
• Hypopon
• Inflammatory ring
• Dry-looking surface
• Endothelial plaque formation

Question 44

What are the 4 signs of Non-filamentous fungal keratitis → Candida?

Answer 44

• Yellow white stromal infiltrate
• Epithelial defect or corneal ulcer
• Anterior chamber reaction
• Hypopyon

Question 45

Treatment of Fungal keratitis:
* Majority of anti-fungal medications had very poor ..., especially with .... An ... should not by itself be used as a guide to successful therapy.
* All antifungal agents only ...
* Antifungals can be administered ..., ... and ..., often may require more than one antifungal agent
* Examples of antifungals: Topical ... ...%, Topical ... ...%, Topcial ... ...% “

Answer 45

Treatment of Fungal keratitis:
* Majority of anti-fungal medications had very poor penetration, especially with an intact epithelium. An intact corneal epithelium should not by itself be used as a guide to successful therapy.
* All antifungal agents only inhibit growth of the fungus
* Antifungals can be administered topically, intravenously and orally, often may require more than one antifungal agent
* Examples of antifungals: Topical Natamycin 5%, Topical Voriconazole 1%, Topcial Amphotericin B 0.25%

Question 46

What are the 5 common outcomes of fungal keratitis after receiving intensive medical therapy?

Answer 46

• Corneal perforation
• Evisceration of the contents of the eye
• BCVA <6/60
• Surgerical intervention
• Corneal transplantation

Question 47

Main parasitic pathogens:
Protozoa → ...
* can cause many diseases including ..., amoebic dysentery, ..., and ...
Microsporidia = ... closely related to fungi
Onchocerca = ... (worm) can cause River blindness

Answer 47

Main parasitic pathogens:
Protozoa → Acanthamoeba
* can cause many diseases including African sleeping sickness, amoebic dysentery, malaria, and toxoplasmosis
Microsporidia = unicellular spores closely related to fungi Onchocerca = nematode (worm) can cause River blindness

Question 49

... is the most common protozoan infection. They can survive in ... and exist in two forms, active ... and dormant .... ... are double walled and are ... to disinfection. ... grow and replicate when they are in a .... They often contain bacteria ..., ..., ... and ....

Answer 49

Acanthamoeba keratitis is the most common protozoan infection. They can survive in air, water and soil and exist in two forms, active trophozoite and dormant cysts. Cysts are double walled and are more resistant to disinfection. Trophozoite grow and replicate when they are in a nutrient rich environment. They often contain bacteria legionella, staphylococcus, escherichia and pseudomonas.

Question 50

AK is associated with the use of ... (88-96%), and rarely associated with ... and .... This is commonly transmitted by ... and .... However, with intact epithelium, it can be rapidly removed through ..., ... and the .... AK develops when ... gains access to a ..., allowing ... to invade. They release ... and ... that lead to dissolution of the stroma matrix. This stimulates responses of ..., ... and .... ... may respond to these cells by converting into ... which can prolong infection. This type of infection does not produce ..., therefore re-occurrence is frequent.

Answer 50

AK is associated with the use of soft CL (88-96%), and rarely associated with rigid and OrthoK lenses. This is commonly transmitted by Acanthomoeba contaminating SCLs and adhere to corneal surface. However, with intact epithelium, it can be rapidly removed through tears, blinking and the host immune system. AK develops when Acanthamoeba gains access to a disrupted corneal epithelium, allowing trophozoites to invade. They release cytotoxic proteases and collagenolytic factors that lead to dissolution of the stroma matrix. This stimulates responses of neutrophils, macrophages and Langerhans cells. Trophozoites may respond to these cells by converting into cysts which can prolong infection. This type of infection does not produce immunity, therefore re-occurrence is frequent.

Question 51

What are the 8 symptoms of Acanthamoeba keratitis?

Answer 51

• Severe excruciating ocular pain disproportionate to clinical signs ∵ inflammatory response to corneal nerves (radial neuritis)
• Blepharospasm
• Conjunctiva hyperaemia
• Ptosis
• Odema
• Excessive tearing
• Blurred vision
• Photophobia

Question 52

What are the 6 early signs of Acanthamoeba keratitis?

Answer 52

Early signs are confined to the epithelium:
* Puntate epithelial erosions
* Pseudo-dendrites
* Conjunctiva hyperaemia
* Ptosis
* Excessive tearing
* Decreaes corneal sensitivity

Question 53

What are the 7 stromal signs of Acanthamoeba keratitis?

Answer 53

• Ring infiltrate ∵ immune response to antigen
• Limbitis
• Stromal thinning
• Ulcers with increased diameter and unclear boundaries
• Hypopyon
• Neovascularisation
• Stromal scarring
• Scleritis

Question 54

What are the 6 CL associated risk factors of Acanthamoeba keratitis?

Answer 54

• Poor CL hygiene
• Swimming, showering with CLs
• Extended wear
• Non-compliance with replacement schedules
• Biofilm formation on CLs & case
• Infrequent replacement on cases

Question 55

How is AK assessed?

Answer 55

• Hx - CL wearer, water/ trauma, pain
• VA
• Slit lamp - NaCl staining
• IOP
• Immediate referral

Question 56

How is AK diagnosed in 4 ways?

Answer 56

Corneal scraping, histopathology, PCR & confocal microscopy for Acanthamoeba cysts

Question 57

Treatment for Acanthamoeba keratitis
* P... b... 0.02-0.08% (PHMB) or chlorhexidine 0.02-0.06% (Biguanides)
* Often in combination with p... 0.1% (Diamidine)
* Oral voriconazole (antifungal) → applied every ... for the first ...hours, then ... during waking hours from ...
* Cycloplegic and analgesic may for pain * May take more than ... for initial response to occur
* ... performed early in the disease removes ... and ... limited to the corneal epithelium and facilitates ....
* Use of ... is controversial due to ... in the initial stages of infection. ∴ only used in cases of ... to reduce risk of ... and ....
* May need medication holiday due to ... of treatment
* ... is an additional procedure for progressive disease
* 25% Px will require ...

Answer 57

Treatment for Acanthamoeba keratitis
* Polyhexamethylene biguanide 0.02-0.08% (PHMB) or chlorhexidine 0.02-0.06% (Biguanides)
* Often in combination with propamidine 0.1% (Diamidine)
* Oral voriconazole (antifungal) → applied every hour for the first 48-72hours, then hourly during waking hours from 3 week to several months
* Cycloplegic and analgesic may for pain * May take more than 2 weeks for initial response to occur
* Epithelial debridement performed early in the disease removes trophozoites and cyts limited to the corneal epithelium and facilitates topical drug penetration.
* Use of steroids is controversial due to suppression of immune activity in the initial stages of infection. ∴ only used in cases of intense and persistent stromal inflammation to reduce risk of neovascularisation and corneal scarring.
* May need medication holiday due to epithelial toxicity of treatment
* Amniotic membrane transplantation is an additional procedure for progressive disease
* 25% Px will require corneal transplantation

Question 58

What are the 3 possible outcomes of Acanthamoeba keratitis?

Answer 58

• Early diagnosis VA 6/6
• Late diagnosis VA 6/19
• Extreme cases can cause total blindness and may require enucleation

Question 59

... are a diverse romp of unicellular, spore forming parasites. They are ... pathogen closely related to fungi. ... typically presents as either an acute Keratoconjunctivitis and insidious ... often in ... individuals.
Risk factors include: ..., ..., ... and .... Microsporidia are ..., therefore requires ....

Answer 59

Microsporidia are a diverse romp of unicellular, spore forming parasites. They are waterbourne pathogen closely related to fungi. Ocular microsporidiosis typically presents as either an acute Keratoconjunctivitis and insidious stromal keratitis often in immunocompromised individuals.
Risk factors include: ocular exposure to muddy water, Hx of ocular trauma, CL wear and post ocular sx. Microsporidia are resistant to antimicrobial therapy, therefore requires surgical excision or corneal graft.

Question 60

... is a filarial nematode that causes ... also known as River Blindness. Their larvae are transmitted by bites of infected ... and they can grow in human ... tissues. The microfilariae can migrate into the ... via the ... and can be observed in the ... through slit lamp examination. The death of microfilaiae release ... and ... that can cause an intense ..., resulting gin ... (snowflake opacities). This can develop into a chronic ... with ... and .... This can further cause ..., ..., extensive ..., secondary ... and ....

Answer 60

Onchocerca is a filarial nematode that causes onchocerciasis also known as River Blindness. Their larvae are transmitted by bites of infected blackflies and they can grow in human subcutaneous tissues. The microfilariae can migrate into the cornea via the limbus and can be observed in the anterior chamber or cornea through slit lamp examination. The death of microfilaiae release antigens and bacteria that can cause an intense inflammatory response, resulting gin subepithelial punctate lesions (snowflake opacities). This can develop into a chronic sclerosing keratitis with neovascularisation and scarring. This can further cause iridocyclitis, iris atrophy, extensive synechia, secondary angle closure and open angle glaucoma and peripapillary chorioretinitis.

Question 61

What is the treatment of onchocerca keratitis?

Answer 61

• Oral ivermectin → kills microfilariae; sterilises but does not kill adult worms
• Yearly treatment with ivermectin for 10-15 years may be needed to keep microfilariae densities low