Bact /fungal Microbial keratitis (bacterial, fungal)

• What is microbial keratitis?

  It is a sight-threatening infection of the cornea.
• What are the commonest bacterial corneal pathogens?

  commonest bacterial corneal pathogens are:

  • Pseudomonas sp. (Gram -ve)
  • Staphylococcus sp. (Gram +ve)
  • Streptococcus sp. (Gram +ve)
  • other Gram -ve organisms sp., Staphylococcus sp., and Streptococcus sp.
• Why are severe contact lens-related infections often Gram-negative?

  Because they are particularly associated with Pseudomonas species.
• What proportion of infectious keratitis cases in temperate regions is caused by fungal infection?

  A small proportion.
• How does the prevalence of fungal keratitis differ between temperate and tropical climates?

  In tropical climates, it can cause up to 50% of cases.

  Fungal infection causes a small proportion of infectious keratitis cases in temperate regions;
• What are the most common fungal corneal pathogens?

  The The most common fungal corneal pathogens are:

  • Candida sp. (yeast-like)
  • Fusarium sp. (filamentous)
  • Aspergillus sp (filamentous)
• What are the predisposing factors for bacterial keratitis?

  • Contact lens wear (4–5 times higher incidence)
  • Ocular surface disease (e.g., corneal exposure, chronic epithelial defect)
  • Ocular trauma or surgery
  • Immune compromise
  • Topical steroid use
  • Lid margin infection
• What is the risk of microbial keratitis associated with overnight corneal reshaping contact lenses?

  It is similar to rates associated with daily wear soft contact lenses.
• What are the main risk factors for contact lens-related microbial keratitis?

  Increased days of wear,

  poor hygiene,

  youth,

  male gender,

  smoking,

  and internet purchase of lenses.
• What symptoms are associated with microbial keratitis?

  Pain, redness, photophobia, discharge, blurred vision, and awareness of a spot on the cornea.
• What is a common sign of microbial keratitis?

  Lid oedema.
• How does fungal keratitis differ in signs from bacterial keratitis?

  Fungal keratitis may have deep lesions, feathery edges, and satellite lesions.
• What are the differential diagnoses for microbial keratitis?

  • Corneal infiltrative lesions (contact lens related or marginal keratitis)
  • Acanthamoeba keratitis (suspect if multiple infiltrates or dendritiform lesions)
• What should practitioners do if they recognize their limitations in managing microbial keratitis?


  They should seek further advice or refer the patient elsewhere.
• What are the non-pharmacological management steps for microbial keratitis?

  • Cease contact lens wear
  • Retain lenses and cases for culture if needed
• When is emergency referral indicated for microbial keratitis?

  If there is an infiltrate >1mm, multiple lesions, or signs suggestive of fungal or acanthamoeba keratitis.
• What is the empirical treatment for lesions less than 1mm in the absence of sight-threatening characteristics?

  Fluoroquinolone monotherapy, such as levofloxacin or moxifloxacin.
• What is the recommended dosing schedule for fluoroquinolone treatment?

  Hourly for 48 hours, then every 2 hours for 72 hours, then every 4 hours for 7 days.
• What should be done if a patient with microbial keratitis does not show improvement?

  Refer the patient the same day if not healing or if symptoms worsen.
• What is the management protocol for suspected fungal keratitis?

  • Emergency referral to ophthalmologist
  • Advise patient on urgency
  • Retain lenses and lens case for culture
• What is the role of corneal scraping in the management of microbial keratitis?

  It is used for culture and determination of antibiotic sensitivities.
• What is the drug of choice for fungal keratitis caused by yeasts?

  Amphotericin B (as 0.15% eye drops).
• What are the treatment strategies for fungal infections?

  • Topical antifungal eye drops (e.g., natamycin, voriconazole)
  • Possible oral antifungal therapy
• What is the significance of the GRADE system mentioned in the guidelines?

  It assesses the level of evidence and strength of recommendations.
• What is the plain language summary of microbial keratitis?

  • Serious infection of the cornea
  • Usually caused by contact lens wear
  • Symptoms include redness, pain, and blurred vision
  • Requires urgent treatment
• What is the usual cause of microbial keratitis?

  The usual cause is bacterial infection, but some cases are due to fungal infection.
• What happens to the cornea during microbial keratitis?

  The clear tissue becomes cloudy due to infection.
• What is the typical treatment approach for serious cases of microbial keratitis?


  Referral to an ophthalmologist for specimen collection and intensive antibiotic treatment.
• What may be added to treatment once the infection is controlled?

  Steroid eye drops may be added.
• What advice is given to patients regarding contact lenses after a keratitis infection?

  Patients will be advised on whether it is safe to wear lenses again.
• What are the main risk factors for CL-related MK?


  CL-related MK are:

  • increased days of wear
  • poor hand, lens and storage case hygiene
  • youth
  • male gender
  • smoking
  • internet purchase of lenses, particularly cosmetic lenses
• What do ocular surface disease predisposing factors include?

  Ocular surface disease, including:

  • corneal exposure
  • corneal decompensation
  • chronic epithelial defect
  • neurotrophic keratopathy, e.g. secondary to HSK or diabetes
• Where is Fungal Keratitis (filamentous) usually from?


  Fungal keratitis (filamentous) is usually secondary to trauma involving organic material; it can also be contact lens or solution related
• How is Fungal Keratitis (yeast like) a predisposing factor?


  Fungal keratitis (yeast-like) most usually complicates ocular surface disease or in immunocompromised patients
• What are Signs of microbial keratitis (bacterial, fungal)?


  Lid oedema

  Epiphora

  Discharge (mucopurulent or purulent)

  Conjunctival hyperaemia and infiltration

  Corneal lesion usually single (central or mid-peripheral)

  Anterior chamber activity (flare, cells, hypopyon or coagulum if severe)
• What are the corneal signs of MK (bacterial, fungal)?

  Corneal lesion usually single (central or mid-peripheral)

  • excavation of epithelium, Bowman’s layer, stroma (tissue necrosis)
  • stromal infiltration beneath lesion
  • stromal oedema with folds in Descemet’s membrane
  • endothelial fibrin plaque beneath lesion
  • optical coherence tomography (OCT) may be helpful in determining depth of involvement
• How does Fungal Keratitis differ to Bacterial Keratitis?


  Fungal keratitis produces similar signs to bacterial keratitis; 

  however, it has been claimed that deep lesions, 

  those having a feathery edge, 

  raised profile, 

  presence of satellite lesions 

  and the presence of endothelial plaque are all features suggestive of a fungal as opposed to a bacterial infection. 

   

  Fungal keratitis may develop more slowly

   (however, Fusarium infection can progress rapidly and invasively)
• What are the Differential Diagnosis?


  Corneal infiltrative lesions (contact lens related or marginal keratitis)

  • peripheral, small (0.5-1.5 mm) with less anterior chamber response
  • not a marker for increased risk of bacterial infection

  Acanthamoeba keratitis .  

  Suspect AK if 

  multiple epithelial or subepithelial infiltrates, 

  perineural infiltrates 

  or dendritiform epithelial lesions

   

   
• What is the optoemtric non pharmacological management?


  Cease contact lens wear. Warn contact lens wearers not to discard their lenses or lens cases, but to retain them if needed for culture
• What are the optometric pharmacological management? 


  Emergency (same day) referral is indicted if any of the following signs are present:

  • infiltrate >1mm
  • 2 or more adjacent lesions
  • location 3mm or less from corneal centre
  • AC reaction (≥10 cells in a 1mm beam (≥ 1+ on the SUN scale)
  • signs suggestive or fungal or acanthamoeba keratitis
  • high likelihood of poor patient compliance to treatment