Keratitis is corneal infection (viral, bacterial, fungal, & protozoan). Initial symptoms are eye pain, photophobia, tearing, +/- loss of vision. Three important types of keratitis are Herpes simplex, Pseudomonal and gonococcal (cause of virulent keratitis); and Acanthamoeba keratitis.
350,000 (US); 7,950,000 (Global)
Corneal infection (viral, bacterial, fungal, & protozoan);
Estimated: 1 day to many weeks:
Eye pain, photophobia, tearing, +/- loss of vision, and loss of transparency; [ABX Guide]
Keratitis is inflammation of cornea. Slit lamp exam shows +/- hypopyon (WBCs in anterior chamber), hyyphema, synechiae, and glaucoma. The same organisms can cause conjunctivitis and keratitis. May progress to endophthalmitis in advanced cases; [ABX Guide: Ocular Keratitis] The two leading causes of blindness in the world from keratitis are caused by trachoma and vitamin A deficiency. Contact lenses are a major factor in keratitis in the U.S. A dendritic pattern on fluorescein staining of the cornea indicates the presence of herpes simplex keratitis, but it is seen in only a minority of cases. [Harrisons, 18th Ed, p. 344] Incidence rates are 11/100,000 in the US and 799/100,000 in Nepal. Bacteria cause 65-90% of all microbial keratitis with the main agents being S. aureus, S. pneumoniae, Pseudomonas, and Moraxella. Refractive surgery, especially laser assisted in-situ keratomileusis (LASIK) is associated with Nocardia and Mycobacterium species. Acanthamoeba keratitis is associated with contact lens and the use of homemade saline to clean them. Other forms of keratitis are syphilitic, vaccinia, adenoviral, and candida. Keratitis may be associated with Herpes zoster ophthalmicus, onchocerciasis, leishmaniasis, microsporidiosis, and African trypanosomiasis. [PPID, 8th Ed, p. 1539-52] Other fungal causes are Aspergillus and Fusarium spp. [Cohen, p. 983] Vesicles on the eyelid may be seen in herpes simplex keratitis. Interstitial keratitis is associated with uveitis; it is rare in the US and usually caused by infections, most commonly a late complication of congenital syphilis. [Merck Manual, p. 925, 926] Three important types of keratitis are: 1.) Herpes simplex (the most common cause of central corneal ulcer); Pseudomonal and gonococcal (cause of virulent keratitis); and 3.) Acanthamoeba keratitis. [Cecil, p. 2527-8]
Corneal scrapings for culture and stains if infection suspected; [PPID, p.1508] See Amebic meningoencephalitis, Aspergillosis, Fusariosis, Microsporidiosis, Nocardiosis, Nontuberculous mycobacterial infections, Phaeohyphomycosis, and Varicella;
SIGNS & SYMPTOMS
O conjunctivitis, acute
S skin blister or vesicles
Skin or Mucous Membranes (Includes Conjunctiva)
REFERENCES FOR CASES/YEAR
1. (US) "The major risk in the U.S.: contact lens wear." [ABX Guide] "Based on NAMCS and NHAMCS-OPD data, an estimated 700,000 doctor's office and outpatient clinic visits for keratitis occurred in 2010, including 280,000 visits for corneal ulcers." [MMWR "Estimated Burden of Keratitis--United States, 2010" https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6345a3.htm] If one assumes that each patient had 2 office visits, then 700,000/2 = 350,000 cases of keratitis per year in the U.S.
2. (Global) WHO estimated in 2003 7.6 million people visually impaired or blind as a result of trachoma; [Gorbach, p. 226] The two leading causes of blindness from keratitis are trachoma and malnutrition (vitamin A deficiency). In the US, contact lens play a major role. Herpes simplex can cause keratitis, "but is seen in only a minority of cases." [Harrisons, 18th ed., p. 344] Guesstimate: Add 7.6 million for trachoma cases in 2003 to estimate of cases in US every year: 7.6 million + 350,000 = 7,950,000.