The Latest Thinking on Infectious Keratitis
Key findings
- Keratitis, mostly due to infection, accounts for approximately 1 million health care visits in the U.S. annually
- Symptoms of infectious keratitis can include decreased vision, photophobia, pain and redness in the affected eye. Patients with sudden onset of eye pain or decreased vision should be promptly (<24 hours) examined by an ophthalmologist
- Infectious keratitis may be either microbial (due to bacteria, fungi, or parasites such as Acanthamoeba) or viral. Microbial keratitis is also called "infectious corneal ulcer"
- Wearing contact lenses is the major risk factor for microbial keratitis in the U.S. and contact lens wearers should be reminded to practice good lens hygiene
- Herpes simplex virus (HSV) and varicella-zoster virus (VZV) are the major etiologies of viral keratitis. HSV keratitis usually results from reactivation of latent HSV type 1, and VZV keratitis usually occurs as a complication of herpes zoster ophthalmicus
Corneal infection can cause vision loss through corneal scarring or perforation. In a recent JAMA paper, infectious disease physicians Marlene L. Durand, MD, and Miriam B. Barshak, MD, and cornea specialist James Chodosh, MD, MPH, from Massachusetts Eye and Ear and Massachusetts General Hospital, reviewed for non-ophthalmologists the latest thinking about the diagnosis, treatment and prevention of infectious keratitis.
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Overview
Infectious keratitis is usually unilateral, and symptoms often include decreased vision, photophobia and eye pain and redness. Patients with new onset eye pain or decreased vision should be promptly seen by an ophthalmologist.
Infectious keratitis is subdivided into two types:
- Microbial keratitis (often called infectious corneal ulcer)—In the U.S. the principal risk factor is contact lens wear; some other risk factors are eye trauma and chronic ocular surface diseases, including severe dry eye
- Viral keratitis—In the U.S., usually caused by herpes simplex virus (HSV) or varicella-zoster virus (VZV)
Microbial Keratitis
Major pathogens are bacteria such as Pseudomonas, Staphylococcus aureus, and streptococci; fungi (yeasts such as Candida or molds such as Fusarium and Aspergillus); and Acanthamoeba, a genus of amoebae that can be present in tap water and contaminate contact lens cases.
In the U.S., approximately 90% of microbial keratitis cases are due to bacteria, while molds cause as many as half of the keratitis cases in tropical regions of the world.
Candida primarily causes keratitis in patients with chronic ocular surface disease, while risk factors for mold keratitis include eye trauma and contact lens wear.
Acanthamoeba keratitis is rare, but approximately 85% of U.S. cases occur in patients who wear contact lenses.
Diagnosis—Flashlight examination may reveal conjunctival injection (redness) and a white opacity in the cornea. A slit lamp examination is required to determine the extent of the keratitis and the presence of intraocular inflammation. Intraocular inflammation is usually sterile but rarely may represent intraocular infection (endophthalmitis), a vision-threatening complication.
Identification of the particular pathogen that is causing a microbial keratitis case requires a culture of the corneal ulcer. Some clinical features, however, may provide clues as to the type of pathogen involved. Corneal ulcers due to molds often have indistinct borders and satellite lesions, for example, while Acanthamoeba keratitis is typically characterized by marked eye pain out of proportion to the extent of corneal inflammation, and perineural corneal infiltrates (early cases) or a ring corneal infiltrate (advanced cases).
Treatment of microbial keratitis involves frequent antibiotic eye drops (e.g., hourly for two days, tapering to every four hours by day 7). Ointments generally provide insufficient antibiotic concentrations. Patients who wear contact lenses should suspend their use.
Initial treatment is usually empirical, typically with a topical fluoroquinolone or with topical broad-spectrum antibiotics compounded by a compounding pharmacy. The antibiotic regimen may be modified based on culture results. The American Academy of Ophthalmology has published pathogen-specific treatment recommendations in Ophthalmology.
Fungal keratitis should be treated with topical antifungal agents such as natamycin; oral antifungal agents, such as voriconazole, are added in some cases. Acanthamoeba keratitis treatment options are limited and include topical chlorhexidine and polyhexamethylene biguanide; corneal transplantation is often necessary.
Treatment failure may occur if the infection is due to an antibiotic-resistant pathogen or the patient is unable to administer eye drops. Repeat cultures and hospital admission for eye drop administration may be necessary.
Prevention—Patients who wear contact lenses should be educated about the hazards of poor lens care, such as sleeping in lenses, reusing the same lens case for prolonged periods, or storing lenses in tap water (or anything other than sterile solutions designed for storing contact lenses).
HSV Keratitis
Herpes simplex virus is estimated to cause 1.5 million keratitis cases worldwide each year. Most cases result from reactivation of latent HSV type 1 from the trigeminal ganglion.
Diagnosis—Under a slit lamp, HSV keratitis appears as a dendritic or geographic pattern of epithelial ulceration or as an infiltrate in the corneal stroma.
Treatment of HSV epithelial keratitis is with a topical antiviral (e.g., ganciclovir gel) or oral antiviral (e.g., acyclovir). The other forms of HSV keratitis are treated with a corticosteroid eye drop plus an oral antiviral agent.
Prevention—Chronic oral acyclovir prophylaxis can reduce the likelihood of HSV keratitis recurrence, which otherwise is very common.
VZV Keratitis
Varicella zoster virus typically causes VZV keratitis in the setting of herpes zoster ophthalmicus, which is herpes zoster in the distribution of the trigeminal nerve's ophthalmic division.
Diagnosis—Acute VZV keratitis typically occurs within one month of the onset of herpes zoster ophthalmicus. Herpes zoster ophthalmicus usually manifests as a unilateral vesicular rash (shingles) on the upper face. Approximately one-fifth of patients develop vesicles on the nasal tip or sides of the nose, which may correlate with eye involvement.
Treatment—Patients with herpes zoster ophthalmicus should be referred to an ophthalmologist, and referral should be urgent if there are ocular symptoms or signs such as pain, redness or blurred vision. Moderate to complete corneal anesthesia complicates herpes zoster ophthalmicus–related keratitis in approximately 60% of cases and can lead to complications such as neurotrophic corneal ulceration, superinfection, scarring or perforation.
Acute herpes zoster ophthalmicus is treated with oral acyclovir, valacyclovir or famciclovir.
Prevention—Vaccination with recombinant zoster vaccine is highly effective in preventing shingles (97% efficacy for ages 50–69 years; 91% for age ≥70).
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