What is Keratitis (Infectious)?
Keratitis is inflammation of the cornea, the clear front surface of the eye that helps focus light. When the inflammation is caused by bacteria, viruses, fungi, parasites, or other microorganisms, the condition is referred to as **infectious keratitis**. It is an eye‑emergency because the cornea is essential for vision; untreated infection can lead to scarring, permanent vision loss, or even loss of the eye.
Infectious keratitis most often follows a disruption of the corneal surface—such as a scratch, contact‑lens wear, or exposure to contaminated water—and allows pathogens to invade the corneal tissue. Prompt recognition and treatment are critical for preserving visual function.
Common Causes
The majority of infectious keratitis cases are linked to one of the following organisms or risk‑factors. The list below includes the most frequently encountered causes:
- Bacterial infection – Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pneumoniae, and Moraxella species are the usual culprits, especially in contact‑lens wearers.
- Viral infection – Herpes simplex virus (HSV) is the leading viral cause; varicella‑zoster virus (VZV) can also affect the cornea.
- Fungal infection – Common after eye trauma with vegetative material; Fusarium, Aspergillus, and Candida species are typical.
- Parasitic infection – Acanthamoeba spp. are especially associated with poor contact‑lens hygiene and exposure to freshwater.
- Contact‑lens related factors – Overnight wear, poor cleaning solutions, or reusable lenses increase bacterial colonisation.
- Ocular trauma – Small scratches, foreign bodies, or chemical burns breach the corneal epithelium, providing entry points for microbes.
- Dry eye or ocular surface disease – Chronic irritation weakens the protective tear film, making infection more likely.
- Immune compromise – Diabetes, HIV/AIDS, or systemic immunosuppressive therapy lower the eye’s ability to fight infection.
- Environmental exposure – Swimming in lakes, hot tubs, or using contaminated eye cosmetics can introduce pathogens.
- Previous eye surgery – Procedures such as LASIK, cataract extraction, or corneal grafts can disturb corneal integrity.
Associated Symptoms
The clinical picture varies with the organism, but patients with infectious keratitis typically notice one or more of the following:
- Redness of the eye (particularly around the cornea)
- Severe, gritty or burning eye pain
- Blurred or decreased vision
- Photophobia (sensitivity to light)
- Watery or purulent discharge
- Feeling of a foreign body in the eye
- Swelling of the eyelids (eyelid edema)
- White or yellowish infiltrates/ulcers visible on the cornea under slit‑lamp examination
When to See a Doctor
Because infectious keratitis can progress rapidly, you should seek ophthalmic care **immediately** if you experience any of the following:
- Eye pain that is worsening rather than improving
- Rapid decline in visual acuity (e.g., difficulty reading signs, recognizing faces)
- Heavy discharge (especially thick, yellow‑green, or pus‑like)
- Visible white spot or ulcer on the cornea
- History of recent eye trauma, surgery, or contact‑lens wear combined with any symptoms above
- Persistent redness that does not improve after 24‑48 hours of over‑the‑counter artificial tears
Delaying evaluation can increase the risk of corneal scarring and permanent vision loss.
Diagnosis
Ophthalmologists use a combination of history taking, visual‑acuity testing, and specialised eye examinations to confirm infectious keratitis:
- Detailed history – Recent contact‑lens use, trauma, swimming, systemic illnesses, and medication use.
- Visual acuity test – To quantify any loss of vision.
- Slit‑lamp biomicroscopy – A magnified view of the cornea that reveals ulcers, infiltrates, and the pattern of inflammation.
- Fluorescein staining – A yellow dye that highlights epithelial defects; a “black‑spot” on a blue light indicates ulceration.
- Microbiological sampling – Scraping of the corneal ulcer for Gram stain, culture, PCR, or confocal microscopy, especially when bacterial or fungal infection is suspected.
- Other tests – In cases of suspected viral keratitis, a viral PCR or corneal impression may be performed. For Acanthamoeba, confocal microscopy or a non‑nutrient agar culture is used.
Prompt sampling before starting topical antibiotics improves the chance of identifying the organism and tailoring therapy.
Treatment Options
Treatment is dictated by the underlying pathogen, severity of ulceration, and patient risk factors. The primary goals are to eradicate infection, reduce inflammation, prevent corneal scarring, and restore vision.
Medical Management
- Topical antibiotics – Broad‑spectrum agents (e.g., fluoroquinolones such as moxifloxacin) are initiated empirically. If a specific bacterium is identified, therapy may be narrowed.
- Topical antivirals – For HSV keratitis, oral acyclovir (400 mg 5×/day) or topical trifluridine ointment is used.
- Topical antifungals – Natamycin 5% drops are first‑line for filamentous fungi; amphotericin B 0.15% may be used for yeast.
- Anti‑Acanthamoeba agents – Chlorhexidine 0.02% combined with polyhexamethylene biguanide (PHMB) 0.02%; treatment often lasts weeks.
- Corticosteroid drops – May be added once the infection is under control (usually 48‑72 h after antibiotics) to limit scarring, but never in active fungal or Acanthamoeba infection.
- Pain control – Oral analgesics (e.g., ibuprofen) or cycloplegic drops (e.g., cyclopentolate) to reduce ciliary spasm.
- Adjunctive dry‑eye therapy – Preservative‑free artificial tears to maintain ocular surface moisture.
Procedural / Surgical Interventions
- Corneal debridement – Mechanical removal of necrotic tissue to improve drug penetration.
- Therapeutic penetrating keratoplasty – Full‑thickness corneal transplant for severe, non‑responsive ulcers or perforation.
- Lamellar keratoplasty – Partial‑thickness graft for localized lesions.
- Amniotic membrane transplantation – Promotes healing and reduces inflammation in refractory cases.
Home Care & Supportive Measures
- Strict adherence to drop schedule; use a pill‑box or alarm to avoid missed doses.
- Do not wear contact lenses until cleared by the ophthalmologist.
- Use protective eyewear (e.g., goggles) when swimming or working with chemicals.
- Maintain good hand hygiene before handling eye drops.
- Follow up as directed—often daily in the first week.
Prevention Tips
Many cases of infectious keratitis are avoidable with simple protective habits:
- Proper contact‑lens hygiene – Wash hands, use fresh solution nightly, avoid rinsing lenses with tap water, and replace lenses and cases as recommended.
- Limit overnight wear – If your lenses are not approved for continuous use, remove them before sleeping.
- Eye protection – Wear goggles during sports, gardening, or any activity that could cause a corneal scratch.
- Prompt treatment of eye injuries – Rinse the eye with sterile saline and seek care if pain or redness develops.
- Manage dry eye – Use preservative‑free lubricating drops and treat underlying conditions (e.g., meibomian gland dysfunction).
- Avoid contaminated water – Do not swim in freshwater lakes or hot tubs with contact lenses in place.
- Regular eye exams – Especially for contact‑lens users, diabetics, or those with a history of ocular surgery.
Emergency Warning Signs
If any of the following occur, seek emergency ophthalmic care immediately (e.g., go to an eye‑emergency department or call 911 if vision loss is rapid):
- Sudden, severe loss of vision or “blank” spot in the visual field.
- Rapid increase in eye pain despite treatment.
- Marked swelling of the eyelid or surrounding face.
- Purulent (yellow/green) discharge that worsens.
- Signs of corneal perforation – sudden deep pain, watery discharge, or a noticeable “hole” in the cornea.
- Fever > 38 °C (100.4 °F) accompanying eye symptoms, suggesting systemic infection.
Key Take‑aways
Infectious keratitis is a potentially sight‑threatening condition that demands prompt recognition and treatment. Understanding the common causes—especially contact‑lens misuse, trauma, and exposure to contaminated water—helps patients take preventive steps. If you notice redness, pain, discharge, or visual changes, do not delay seeking professional care. Early, targeted antimicrobial therapy combined with diligent follow‑up offers the best chance for full recovery and preservation of vision.
References:
- Mayo Clinic. “Keratitis.” May 2024. https://www.mayoclinic.org/diseases-conditions/keratitis/symptoms-causes/syc-20352527
- American Academy of Ophthalmology. “Infectious Keratitis.” 2023 Clinical Practice Guidelines.
- Cleveland Clinic. “Keratitis (Corneal Inflammation).” https://my.clevelandclinic.org/health/diseases/17057-keratitis
- CDC. “Acanthamoeba Keratitis.” https://www.cdc.gov/parasites/acanthamoeba/keratitis.html
- National Eye Institute (NEI). “Herpes Simplex Keratitis.” https://nei.nih.gov/health/herpes-simplex-keratitis
- World Health Organization. “Prevention of Eye Infections.” 2022.