Herpes Simplex Keratitis: This is a common cause of keratitis, especially in individuals with a history of herpes simplex virus infection. It can lead to corneal scarring and vision loss if not treated promptly.

Bacterial Keratitis: This condition is often associated with contact lens use or trauma to the cornea. Symptoms include severe pain, redness, and discharge.
Fungal Keratitis: Typically seen in individuals who have suffered an injury to the cornea, especially from vegetable matter. It can also occur in contact lens users.
Acanthamoeba Keratitis: This is a rare but serious infection of the cornea caused by a parasite. It is often associated with contact lens use, especially if lenses are not properly cleaned and maintained.
Dry Eye Syndrome: While not an infection, dry eye syndrome can cause significant discomfort and can increase the risk of developing keratitis.

Syphilis: Ocular syphilis can cause a range of symptoms including keratitis. Given the potential for severe and irreversible damage, syphilis must be considered, especially in patients with risk factors.
Lyme Disease: Neuro-ophthalmic manifestations of Lyme disease can include keratitis, among other symptoms. Early diagnosis is crucial to prevent long-term complications.
Sarcoidosis: This autoimmune disease can affect the eyes in various ways, including causing keratitis. It's essential to consider sarcoidosis due to its potential for multi-organ involvement.

Cytomegalovirus (CMV) Retinitis: Although more commonly associated with retinal disease, CMV can cause keratitis, particularly in immunocompromised patients.
Mycobacterial Infections: Such as tuberculosis, can rarely cause keratitis, especially in endemic areas or in immunocompromised individuals.
Leishmaniasis: A parasitic infection that can cause ocular manifestations, including keratitis, in rare cases, particularly in travelers to or residents of endemic areas.