Keratitis

Keratitis is inflammation of the cornea, a clear and transparent covering over the iris and pupil. Important forms of keratitis include bacterial, herpes zoster, herpes simplex, and Acanthamoeba keratitis. Most corneal injuries and infections are associated with severe pain, although sometimes pain is absent. Other findings include irritation, eye redness, watery or purulent secretion, and impaired vision. Diagnosis is usually based on clinical findings and slit-lamp examination. Keratitis is an emergent disorder that can lead to irreversible vision loss left untreated.

• Epidemiology: most common form of keratitis (∼ 90%) ^[1][2]
• Etiology
  • Mainly: staphylococci; (Staphylococcus aureus), streptococci (Streptococcus pneumoniae), Pseudomonas aeruginosa
  • Syphilis
  • Enterobacteriaceae (including Klebsiella)
  • Risk factors
    • Contact lens use
    • Recent eye surgery or injury
    • Immunodeficiency
    • Lacrimal duct stenosis
• Clinical features
  • Progressive pain
  • Eye redness
  • Foreign body sensation
  • Purulent discharge
  • Photophobia
  • Excessive tearing
  • Blurry vision
  • Conjunctival injection
• Subtypes and variants: Pseudomonas keratitis
  • Caused by Pseudomonas aeruginosa
  • Most common cause of bacterial keratitis in contact lens users ^[3]
  • Fulminant course with severe ulceration
  • Corneal destruction/perforation within 2–5 days ^[4]
• Diagnostics
  • Slit lamp examination
    • Hypopyon: collection of leukocytes at the bottom of the anterior chamber; occurs in severe cases of keratitis
    • Fluorescein staining: round corneal infiltrate or ulcer
      • Creeping ulcer or serpiginous corneal ulcer in pneumococcus infection
      • (Ring‑) ulcer: (ring-shaped) spread of the pathogen in the cornea
      • Thygeson superficial punctate keratitis: point-shaped lesions in the corneal epithelium
  • Cultures are indicated when the corneal infiltrate is large, central, and extends to the deep stroma, for refractory cases, or those with atypical features. ^[2]
• Treatment
  • Topical broad-spectrum antibiotics ^[2]
    • Cefazolin with tobramycin/gentamicin or
    • Ofloxacin or
    • Ciprofloxacin
  • Consider corticosteroids following identification of pathogen and ∼2 days of antibiotic therapy
  • Therapeutic mydriasis may be considered
  • Corneal transplantation in threatened or existing large perforations, small corneal perforations with consistent bacterial growth, or suppuration despite antibiotics ^[4]
• Prevention: Education on contact lens hygiene
• Complications
  • Irreversible vision loss
  • Corneal destruction (potentially leading up to perforation)
  • Leukoma: a dense, white opacity of the cornea caused by scarring
    • Caused by inflammation, injuries, or congenital corneal conditions.
    • Adherent leukoma: part of the iris is attached to the cornea
  • Vascularization into the cornea
  • ↑ Intraocular pressure; if necessary, reduce intraocular pressure during the acute phase
  • Endophthalmitis

Bacterial keratitis should be treated as an ophthalmic emergency because of the risk of irreversible vision loss.

Herpes simplex keratitis

• Etiology: infection due to reactivated herpes simplex virus (HSV) type 1 from the trigeminal ganglion
• Clinical features
  • Similar to viral conjunctivitis, but usually unilateral
  • Eye redness
  • ± Eye pain
  • Foreign body sensation
  • Corneal hypoesthesia
  • Photophobia
  • Blurry vision; can lead to vision loss if untreated
• Diagnostics ^[5]
  • Fluorescein staining: superficial corneal erosions (dendritic ulcers) that resemble the branches of a tree (geographic ulcers may be seen when dendritic ulcers widen in shape)
  • Direct fluorescein antibody test (HSV antigen detection) or polymerase chain reaction (PCR) test
• Treatment for epithelial HSV keratitis ^[6]
  • Topical trifluridine solution or ganciclovir 0.15% gel
  • Oral antiviral (e.g., acyclovir) when topical treatment cannot be administered by the patient, prophylactic treatment after surgery, or refractory cases despite topical treatment
  • Corneal transplantation for patients with severe corneal scarring

Glucocorticoids should not be used in initial treatment of dendritic epithelial keratitis!

Herpes zoster keratitis ^[7][8]

• Etiology: reactivated herpes zoster virus (involvement of the ophthalmic nerve ); see also herpes zoster ophthalmicus.
• Clinical features
  • Prodrome: headache, malaise, fever
  • Impaired vision
  • Eye irritation (foreign body sensation)
  • Photophobia
  • Eye pain
  • In the innervation area of the ophthalmic nerve (forehead, bridge, and tip of the nose):
    • Vesicular eruption
    • Anesthesia dolorosa
• Diagnostics
  • Slit-lamp examination and fluorescein staining
    • 1–2 days: punctate lesions on the corneal surface
    • 4–6 days: pseudodendritic lesions on the corneal surface
• Treatment: oral acyclovir, valacyclovir, or famciclovir

See also “Herpes zoster ophthalmicus.”

Adenovirus

See “Epidemic keratoconjunctivitis.”

• Etiology: Acanthamoeba infection ^[9]
• Characteristics
  • Rare condition
  • Primarily occurs in immunocompetent contact lens wearers
  • Progressive course for several weeks despite an attempt of antibiotic treatment
• Clinical features
  • Severe pain
  • Eye redness
  • Photophobia
  • Epiphora
  • Decrease in vision
  • Corneal ring infiltrate (late-stage) ^[10]
• Diagnostics
  • Slit-lamp examination and/or fluorescein staining: features of epithelitis and stromal disease
  • Culture and microscopy of eye scraping
  • Pathogen detection is often difficult.
• Treatment
  • Topical antiseptic (e.g., chlorhexidine) with propamidine
  • Corneal transplantation for refractory cases

• Etiology
  • Mainly caused by Fusarium (less commonly by Aspergillus and Candida albicans)
  • Ocular injuries caused by plant material contaminated with fungi (e.g., wood, thorn)
  • Use of glucocorticoids and antibiotics increases the risk of fungal infection
• Clinical features
  • Similar to bacterial keratitis: ocular pain, photophobia, decreased vision, eye discharge
  • Often hypopyon
  • Ocular examination: white stromal infiltrate with a feathery border and satellite lesions
• Treatment
  • Antimycotics such as natamycin, nystatin, amphotericin B
  • Ultima ratio: penetrating keratoplasty

References:^[11]

Photokeratitis

• Definition: corneal epithelial damage caused by severe UV light radiation with pronounced pain symptomatology
• Etiology
  • Welding without proper protective eye wear
  • Associated with cosmetic tanning (tanning bed)
  • High levels of UV radiation in high-altitude mountain regions without UV-protective eyewear
• Pathophysiology
  • Necrosis of the corneal epithelial cells → inflammatory reactions, edema, and epithelial cell shedding
  • Symptoms appear after a latent period of approx. 6–8 h
• Clinical features
  • Epithelial damage is initially often asymptomatic
  • Severe pain
  • Photophobia
  • Foreign body sensation
  • Blepharospasm
  • Epiphora
  • Decreased visual acuity
• Diagnostics
  • Bilateral multiple, fine-spotted, superficial, fluorescein-positive corneal epithelial lesions (Thygeson superficial punctate keratopathy)
  • Conjunctival vessel injection
• Treatment
  • Patient briefing
  • Antibiotic eye ointment
  • Immobilization
  • Oral analgesics
• Complications: risk of infection
• Prognosis: usually complete recovery after 24–48 h

Anesthetic eye drops should only be applied for diagnostic purposes Do not initiate pain therapy as improper use can lead to epithelial damage. Elimination of the protective corneal reflex can result in further corneal damage.

Exposure keratopathy

• Definition: keratitis caused by the inability to completely close the eyelids resulting in corneal drying
• Etiology: mainly caused by damage to the facial nerve, e.g., from a stroke

Neurotrophic keratopathy

• Definition: keratitis as a result of corneal sensory loss due to paralysis of the 1^st trigeminal branch
• Etiology
  • Nerve damage
  • Tumor in the nerve path region
  • Chronic herpes infection
• Clinical features
  • Decreased vision; dry eye
  • Early stage: absent corneal reflex; decreased tear break-up time; dry spots on corneal surface
  • Late stage: central circular/oval nonhealing corneal ulcer
  • Complication: corneal perforation
• Treatment
  • Early stage: artificial tears
  • Late stage: prophylactic antibiotic drops; tarsorrhaphy ; amniotic membrane transplantation and conjunctival flap