Keratitis is caused by
Causes of keratitis
 
Infective keratitis
Bacterial
Viral
Fungal
Chlamydial
Protozoal
Spirochactal
 
Allergic keratitis
Phlyctenular keratitis
Vernal keratitis
Atopic keratitis
 
Trophic keratitis
Exposure keratitis
Neuroparalytic keratitis
Keratomalacia
Atheromatous ulcer
 
Keratitis associated with diseases of skin and mucous membrane.
Keratitis associated with systemic collagen vascular disorders.
Traumatic keratitis, which may be due to mechanical trauma, chemical trauma, thermal burns, radiations.
 
Idiopathic keratitis e.g.,

Mooren's corneal ulcer
Superior limbic keratoconjunctivitis
Superficial punctate keratitis of Thygeson
Bacteria
Atopy
Protozoa
All