Viral The most common causes of viral keratitis include
herpes simplex virus (HSV) and
varicella zoster virus (VZV), which cause
herpes simplex keratitis and herpes zoster keratitis (a subtype of
herpes zoster ophthalmicus) respectively. • In those who wear contact lenses, bacteria are the most common causative agent of keratitis, with 90% of cases being due to a bacterial pathogen. Of those 90% of cases,
Pseudomonas aeruginosa is responsible for 40%.
Staph aureus and
streptococci are other common bacterial pathogens responsible for infectious keratitis in contact lens wearers.)
Amoebic •
Acanthamoebic keratitis :* Amoebic infection of the cornea is a serious corneal infection, most often affecting
contact lens wearers. It is usually caused by
Acanthamoeba. On May 25, 2007, the U.S.
Center for Disease Control issued a health advisory due to increased risk of
Acanthamoeba keratitis associated with use of
Advanced Medical Optics Complete Moisture Plus Multi-Purpose eye solution.
Parasitic •
Onchocercal keratitis, which follows
Onchocerca volvulus infection by infected
blackfly bite. These
blackfly,
Simulium, usually dwell near fast-flowing African streams, so the disease is also called "river blindness". Microbial keratitis (due to bacterial, fungal, or parasitic pathogens), as opposed to viral keratitis, is more commonly associated with the formation of
corneal ulcers. Other risk factors for corneal ulcer formation include contact lens use, keratitis in the setting of eye trauma, underlying corneal disease or ocular surface diseases (such as severe
chronic dry eye). Infectious keratitis sometimes presents as corneal edema, or with a
hypopyon (a collection of inflammatory cells in the
anterior chamber of the eye). ==Classification (by stage of disease)==