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Keratitis

Table of contents
Key points ⚡
Succinct notes to superpower your revision
Keratitis\: sight-threatening infection and in
Causes\: bacterial (Staphylococcus, Streptococcus, Pseudomonas), viral (HSV, VZV), fungal (Fusarium, Aspergillus, Candida),
protozoan (Acanthamoeba).
Risk factors\: contact lens wear, corneal trauma, ocular surface disease, immunosuppression.
Bacterial keratitis\: ocular pain, red eye, reduced visual acuity, photophobia, purulent discharge; treat with broad-spectrum
antibiotics, may need surgery in severe cases.
Viral keratitis (HSV)\: discomfort, red eye, dendritic ulcer, reduced corneal sensation; treat with topical antivirals (aciclovir),
avoid steroids.
Herpes zoster ophthalmicus (HZO)\: a
guidelines.
Fungal keratitis\: gradual onset pain, redness, grey-white stromal in
steroids initially.
Acanthamoeba keratitis\: severe pain, ring-shaped in
chlorhexidine, may need corneal transplant.
Complications\: corneal scarring, perforation, endophthalmitis, secondary glaucoma, cataracts.
Article 🔍
A comprehensive topic overview

Introduction

Keratitis or corneal ulcer refers to sight-threatening infection and in
Bacterial and viral keratitis represent the most common forms of microbial keratitis, but rarely the cause may be fungal or
protozoan (acanthamoeba).
The following article aims to provide an overview of microbial keratitis at the level expected of
and foundation doctors.

Bacterial keratitis

Aetiology

The corneal epithelium forms the primary barrier to microbes and the tear
immunoglobulins and other antimicrobial compounds.
Most cases of bacterial keratitis are caused by Staphylococcus, Streptococcus and Pseudomonas species in patients with
a disrupted corneal epithelium.
However, epithelium.
N e i s s e r i a g o n o r r h o e a e , N e i s s e r i a m e n i n g i t i d e s , and C o r y n e b a c t e r i u m d i p h t h e r i a can penetrate an intact
Infections may be polymicrobial (e.g. bacterial and fungal co-infection).
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Risk factors

Risk factors for bacterial keratitis are those which disrupt the healthy corneal epithelium. These include\:
Contact lens wear\: most common risk factor, especially in prolonged use and poor lens hygiene
Corneal trauma\: including previous ocular surgery, foreign body, chemical injury
Ocular surface disease\: dry eye, lid malposition, chronic blepharitis
Immunosuppression\: drugs, immunode

Clinical features

History
Bacterial keratitis commonly causes unilateral symptoms. Typical symptoms may include\:
Ocular pain\: this may be moderate or severe and include symptoms of irritation and foreign body sensation
Red eye
Reduced visual acuity\: this may be near normal to markedly reduced
Photophobia\: intolerance to sunlight or normal room lighting
Purulent discharge
A history of contact lens wear is essential\:
Type of contact lenses used\: daily disposable, monthly or extended-wear
Duration of wear per day
If they have ever slept, showered, or swam with their lenses in
For more information, see the Geeky Medics guide to ophthalmic history taking.
Clinical examination
All patients with keratitis (regardless of underlying aetiology) should undergo visual acuity testing with a Snellen chart and
anterior segment examination (ideally with a slit lamp, but a direct ophthalmoscope with high magniArclight
can be used).
Typical clinical
Lids and lashes\: eyelid oedema in moderate to severe cases
Conjunctiva\: pattern of injection may be circumlimbal (around the cornea) or di
Cornea\: a yellow-white opacity which represents the area of in
overlying epithelial defect will stain green upon application of 2%
Anterior chamber and pupil\: hypopyon (pus-level) and posterior synechiae (adhesion between the pupil margin and
anterior lens surface) in severe cases
Pupil assessment for direct and consensual response to light\: may show a relative a
Figure 1. Bacterial keratitis caused by
Pseudomonas. This external photograph
of the left eye demonstrates di
conjunctival injection, a large area of
white-yellow in
margins in the cornea and hypopyon in
the anterior chamber

Investigations

Bacterial keratitis is a clinical diagnosis.
Relevant investigations may include\:
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Corneal scrapes and conjunctival swabs\: these are performed in severe or treatment-resistant cases to allow
identi
Contact lenses, cases and solutions should also be sent for culture and sensitivity

Management

Contact lens use should be discontinued immediately.
Antibiotic therapy should be commenced\:
Topical antibiotics\: initially with broad spectrum cover (e.g.
duo therapy) until culture results return. Instillation may be up to hourly for the
this can then be tapered o
Oral antibiotics\: may be required in severe cases
Surgery (e.g. corneal transplantation) is rarely required, it is considered only in complicated (e.g. perforation) or medically
refractory cases.

Complications

Complications of bacterial keratitis include\:
Spread of infection\: the infection may spread beyond the cornea into the sclera or within the deeper tissues of the eye,
leading to endophthalmitis.
Corneal perforation in severe cases
Residual dense corneal scarring
Irregular astigmatism
Formation of cataract\: secondary lens opaci
The overall visual outcome is very variable and dependent on a number of factors which include the size and depth of the
infection, time to diagnosis and initiation of treatment, and compliance with therapy.

Viral keratitis

Herpes simplex epithelial keratitis

Aetiology
Herpes simplex virus (HSV) is a dsDNA virus which has two serotypes\: HSV-1 and HSV-2. HSV-1 principally a
lips, and face, while HSV-2 causes genital infection with rare ophthalmic involvement.
Primary infection with HSV is usually acquired in childhood and is commonly subclinical or mild with symptoms of
blepharoconjunctivitis and upper respiratory tract infections.
Following the resolution of the primary infection, HSV travels through the sensory nerve to the trigeminal ganglion,
establishing latency. Subsequent reactivation where the virus replicates and travels back to the periphery, such as the
corneal epithelium, results in epithelial keratitis.
Risk factors
Risk factors for herpes simplex virus infection include\:
Primary infection\: direct contact with infected secretions or lesions
Reactivation/ recurrent disease\: trauma involving the trigeminal nerve, stress, immunosuppression, previous
reactivation
Each attack is associated with a greater risk of recurrence.
Clinical features
Typical symptoms of herpes simplex epithelial keratitis include\:
As with other forms of keratitis\: discomfort, grittiness, red eye, reduced visual acuity and photophobia
Epiphora (watering of the eye) as opposed to purulent discharge seen in bacterial ulcer
A previous history of cold sores
Typical clinical
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Lids and lashes\: mild eyelid erythema and oedema
Conjunctiva\: di
Cornea\: dendritic ulcer (pathognomonic sign) with linear branching morphology and terminal bulbs. The bed of the
ulcer will stain green with
Reduced corneal sensation
Figure 2. HSV keratitis. This external
photograph of the eye demonstrates a
dendritic ulcer following the instillation of

Investigations
HSV keratitis can be diagnosed clinically with the identi
Conjunctival and corneal swabs can be sent for a con
microbial causes of keratitis when the diagnosis is equivocal.
Management
Contact lens use should be discontinued immediately.
Management of HSV keratitis should include\:
Topical antivirals (e.g. aciclovir 3% ointment
Epithelial debridement\: in conjunction with a topical antiviral agent (aims to reduce viral load and promote healing)
Steroids are contraindicated in active epithelial disease\: steroids are only used in close supervision by
ophthalmologists to suppress the immune response in cases with corneal stromal involvement
Patients may need long-term oral antiviral prophylaxis in recurrent disease
Complications
The majority of dendritic ulcers will resolve even without treatment. Prolonged or recurrent disease may result in corneal
scarring, glaucoma, and cataracts.
Other forms of HSV keratitis that involve deeper corneal layers require a longer duration of treatment and their prognosis is
more variable

Herpes zoster ophthalmicus (HZO)

Herpes zoster ophthalmicus refers to the reactivation of the varicella-zoster virus (shingles) a
branch of the trigeminal nerve (V1).
Conjunctivitis and epithelial keratitis occur secondary to direct viral invasion. On examination under
dots (punctate keratitis) or pseudo-dendrites (lacking terminal bulbs, in contrast to HSV keratitis) may be visible on the
cornea.
HZO can a
Geeky Medics guide to herpes zoster ophthalmicus.

Protozoan and fungal keratitis

Fungal keratitis

Aetiology
Fungal keratitis is an uncommon but aggressive corneal infection.
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It is a major cause of visual loss in developing and tropical countries. It is commonly associated with fusarium and
aspergillus species (
immunocompromised.
Risk factors
Risk factors for fungal keratitis include\:
Corneal trauma\: especially with contamination of organic/agricultural matter
Contact lens wear
Immunosuppression\: topical steroids, systemic immunosuppression, diabetes
Ocular surface disease\: dry eyes
Clinical features
Typical symptoms of fungal keratitis are similar to other corneal infections. There is a gradual onset of pain, redness,
reduced visual acuity, photophobia and epiphora.
Typical clinical
Lids and lashes\: redness and periocular oedema
Conjunctiva\: di
Cornea\: grey-white stromal in
necrosis and corneal thinning
Anterior chamber\: in
Figure 3. This external photograph of the
right eye demonstrates di
conjunctival injection, a grey-white
in
and the presence of a small volume of
hypopyon.
Investigations
Relevant investigations may include\:
Corneal scraping, performed early, before commencing treatment\: for Gram and Giemsa staining and for culture, plated
on Sabouraud dextrose agar
PCR analysis
Management
Contact lens use should be discontinued immediately.
Management of fungal keratitis should include\:
Topical antifungals\: hourly installation initially, then tapered according to response
Systemic antifungals\: in severe cases, suspected endophthalmitis and immunocompromised patients
Oral analgesia and topical cycloplegia for pain management
Topical steroids should be avoided in the acute phase, but they may be considered during stages of healing
Penetrating keratoplasty (full-thickness corneal transplant) may be required in progressive disease.
Complications
Visual prognosis is generally poor due to the high rate of complications. Recurrence is common following tapering of
treatment.
Other complications may include\:
Severe in
Corneal perforation
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Acanthamoeba keratitis

Acanthamoeba keratitis is a rare form of microbial keratitis associated with poor visual outcomes.
Aetiology
Acanthamoeba are free-living protozoa commonly isolated from soil, pond, sea, tap water and chlorinated water. In
developed countries, the vast majority of patients with acanthamoeba keratitis are contact lens wearers.
Risk factors
Risk factors for acanthamoeba keratitis include\:
Contact lens wear\: especially associated with swimming with contact lenses and poor hygiene
Corneal trauma
Clinical features
Symptoms are variable but may be severe, including reduced visual acuity, pain, redness, foreign body sensation,
photophobia, epiphora
Characteristically, pain is severe and disproportionate to relatively mild clinical
Typical clinical
Lids and lashes\: mild swelling and erythema
Conjunctiva\: di
Cornea\: classically a ring-shaped in
Pseudodendrites (similar to HZO)
Reduced corneal sensation
Figure 4. Acanthamoeba keratitis. This
external photograph of the left eye
demonstrates severe conjunctival
injection with a corneal ring in
a small volume hypopyon
Investigations
The diagnosis of acanthamoeba keratitis is di
Relevant investigations may include\:
Corneal scrape\: samples for PCR, culture (non-nutrient agar with E. coli overlay) and histology
Contact lenses, cases, and solutions should be sent for culture
Confocal microscopy (if available)\: direct visualisation of acanthamoeba cysts
A corneal biopsy may be considered in culture-negative cases
Management
Contact lens use should be discontinued immediately.
Management of acanthamoeba keratitis should include\:
Topical antiamoebic agents\: topical PHMB (polyhexamethylene biguanide) 0.02% or chlorhexidine 0.02%. Hourly
installation initially, then taper according to the response.
Involved corneal epithelium can be debrided to reduce disease burden and to increase penetration of topical drops
Oral NSAIDs for pain management
Topical steroids
Penetrating keratoplasty (full-thickness corneal transplant)\: considered in cases with severe corneal scarring or extensive
necrosis. Recurrence may occur in grafted tissue.
Complications
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Complications of acanthamoeba keratitis include\:
Extension of disease to involve the sclera
Recurrent infection
Corneal perforation
Overall, the prognosis is poor compared to other forms of microbial keratitis. Prevention is therefore vital. Contact lens
wearers should be educated on avoidable risk factors and be encouraged to seek medical attention early when symptoms
develop.

Summary table

Table 1. Summary of keratitis.
Pathogens Clinical features Management
Bacterial
Viral
Fungal
Protozoan
Pseudomonas
spp.
Staphylococcus
spp.
Streptococcus
spp.
Herpes Simplex
Virus
Varicella Zoster
Virus
Aspergillus spp.
Fusarium spp.
Candida spp.
Acanthamoeba
spp.
Mucopurulent
discharge
Yellow-white
in
clearly de
margins
Hypopyon +
Clear discharge /
epiphora
Epithelial defect
with linear
branching and
terminal bulbs
(dendritic ulcer)
Reduced corneal
sensation
Hypopyon –
Mucopurulent
discharge (less
than bacterial)
Grey-white
in

satellite lesions
Hypopyon +
Clear discharge /
epiphora
Ring-shaped
in
Reduced corneal
sensation
Hypopyon +/-
Topical antibiotics,
and steroids
+/- oral antibiotics
Topical antivirals and
cycloplegics
Topical antifungals
+/ topical antibiotics
+/- systemic
antifungals
Topical PHMB and
chlorhexidine
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References

Kanski JJ, Bowling B. Clinical Ophthalmology\: A Systematic Approach. Edinburgh, Elsevier/Saunders; 2015
Denniston A, Murray P. Oxford Handbook of Ophthalmology. 4th ed. OUP Oxford; 2018.
American Academy of Ophthalmology. 2019-2020 Basic and Clinical Science Course, Section 02\: Fundamentals and
Principles of Ophthalmology. 2019

Image references

Figure 1. Community Eye Health Journal. Bacterial keratitis caused by Pseudomonas. License\: [CC BY-NC 2.0]
Figure 2. Imran Kabir Hossain. HSV Keratitis. License\: [CC BY-SA 4.0]
Figure 3. Community Eye Health Journal. Fungal keratitis. License\: [CC BY-NC 2.0]
Figure 4. Community Eye Health Journal. Acanthamoeba keratitis. License\: [CC BY-NC 2.0]

Reviewer

Dr Vishal Vohra

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Contents

Introduction
Bacterial keratitis
Viral keratitis
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