Epidemiology

The annual incidence of infectious keratitis has been increasing due to higher rates of contact lens use, and is now 2.5 to 800 per 100,000 per year.​​[3]​ Patients affected by contact lens-related infectious keratitis are usually between 25 and 40 years old, reflecting the age distribution of contact lens users,​​​ although contact lens-related infections are also encountered in younger and older patients. No clear sex differences are borne out in epidemiological studies.​​[3]​​​ 

The most common causes of bacterial keratitis include Pseudomonas aeruginosa, Staphylococcus aureus, coagulase negative staphylococci, and Streptococcus pneumoniae.[3][4]​​​​[5][6]

Herpes simplex keratitis is an important cause of corneal blindness in the developed world.​​​​[5][7]​​

The annual incidence of fungal keratitis has been estimated to be 1 to 1.4 million cases; it is most prevalent in tropical and subtropical regions. In temperate regions, fungal keratitis is uncommon and mostly occurs in people with a history of corneal transplantation or ocular surface disease (e.g., blepharitis).[3][8]

Acanthamoeba keratitis accounts for up to 5% of all cases with contact lens use a major risk factor.[3][9][10]

Non-infectious keratitides

Heterogeneous, and their incidence depends on the underlying aetiology. Peripheral ulcerative keratitis (a type of autoimmune keratitis) associated with systemic autoimmune diseases is of special concern to primary care physicians. Peripheral ulcerative keratitis has an incidence of 3 cases per million per year according to one study from England.[11]​​

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