Keratitis

Keratitis is inflammation of the cornea. It is an ophthalmic emergency when infectious because rapid stromal melting, perforation, and endophthalmitis can cause permanent blindness within days.

• Infectious causes: bacteria (Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus pneumoniae, Serratia, Moraxella), fungi (Fusarium, Aspergillus, Candida), viruses (herpes simplex, varicella zoster, adenovirus), and parasites (Acanthamoeba, microsporidia).
• Non-infectious causes: contact lens related sterile infiltrates, exposure and neurotrophic keratopathy, dry eye, marginal keratitis (hypersensitivity to staphylococcal antigens), peripheral ulcerative keratitis in rheumatoid arthritis and granulomatosis with polyangiitis, phlyctenular disease, ultraviolet and chemical injury, and toxic reactions to topical drugs.
• Risk factors: contact lens wear (overnight wear, poor hygiene, swimming or showering in lenses), trauma (vegetable matter, soil), ocular surface disease, corneal anaesthesia, previous surgery, immunosuppression, topical steroid use, and lid disease.

• Pain (marked in bacterial, herpetic, and Acanthamoeba disease; reduced in neurotrophic disease), photophobia, redness, tearing, discharge, blurred vision, foreign body sensation.
• Eyelid swelling, ciliary or mixed injection, a corneal epithelial defect with stromal infiltrate (white or grey opacity), stromal oedema, folds, anterior chamber cells and flare, and hypopyon in severe disease.
• Features pointing to a cause: purulent discharge with a sharply demarcated ulcer (bacteria), feathery margins and satellite lesions (fungi), dendritic ulcer (herpes simplex), ring infiltrate with radial perineuritis and severe pain (Acanthamoeba), peripheral ulcer (autoimmune), and absent sensation (neurotrophic).

• History: lens wear, trauma, previous herpes, topical drugs, immune status.
• Slit lamp with fluorescein: size, depth, location of the infiltrate and epithelial defect, anterior chamber reaction, hypopyon, thinning, and perforation (Seidel test); measure lesion size in two dimensions and record photographs.
• Corneal sensation testing before instillation of anaesthetic.
• Corneal scraping for smear and culture is indicated when the infiltrate is central, larger than 1 to 2 mm, deep, has a hypopyon, is unresponsive to initial therapy, or has an unusual appearance: Gram and Giemsa stains, potassium hydroxide or calcofluor white preparations, and culture on blood agar, chocolate agar, Sabouraud agar, and thioglycollate or non-nutrient agar with Escherichia coli overlay. Culture contact lenses, cases, and solutions. PCR for herpes viruses and Acanthamoeba; confocal microscopy for fungal hyphae and Acanthamoeba cysts.
• Systemic workup for peripheral ulcerative keratitis and bilateral non-infectious disease: rheumatoid factor, anti-CCP, ANCA, ANA, ESR, CRP, and urinalysis.

• Discontinue contact lenses; do not patch the eye; do not use topical anaesthetic for pain relief.
• Empirical therapy for presumed bacterial keratitis after scraping:
  • Small peripheral ulcers: moxifloxacin 0.5 percent or levofloxacin 1.5 percent, 1 drop every 1 to 2 hours while awake, tapering as the response occurs.
  • Large, central, or vision threatening ulcers: loading dose every 5 minutes for 5 doses then hourly day and night for 24 to 48 hours; or fortified cefazolin 50 mg/mL with tobramycin 14 mg/mL hourly alternating.
• Cycloplegia: cyclopentolate 1 percent or atropine 1 percent once or twice daily for pain and to prevent synechiae.
• Oral analgesia: paracetamol 1 g every 6 hours and, if necessary, an oral NSAID short course.
• Review within 24 to 48 hours initially, with a shift of therapy by culture and response.
• Topical corticosteroids are used only after the organism is identified and controlled, usually after 24 to 72 hours of effective therapy in bacterial disease, and avoided in fungal, Acanthamoeba, and active epithelial herpetic disease.
• Perforation or imminent perforation: cyanoacrylate glue for perforations up to 2 to 3 mm, bandage lens, patch graft, or therapeutic keratoplasty. Oral doxycycline 100 mg twice daily and topical medroxyprogesterone or ascorbate may help with collagenolysis. Intraocular spread or endophthalmitis requires vitreous tap and intravitreal antibiotics.
• Non-infectious keratitis: lubrication, treat lid disease, topical corticosteroid, and immunosuppression (prednisolone 1 mg/kg daily, methotrexate, cyclophosphamide, or rituximab) for autoimmune peripheral ulcerative keratitis, in consultation with a rheumatologist.
• Prevention: contact lens hygiene (daily disposables, no sleep or swimming in lenses, rubbing and rinsing cases), and prompt care for corneal abrasion.
• Complications: scarring, neovascularisation, perforation, secondary glaucoma, cataract, endophthalmitis, and permanent visual loss.