Due to the relative rarity of<unk>  <unk>  compared to other causes of keratitis (bacterial, viral, etc.), it is often misdiagnosed, especially in the early stages of the disease.<unk>  should be considered in all patients who use contact lenses, and following corneal abrasions or trauma. A thorough history should be obtained, especially relating to contact lens use and any recent changes contact in lens solution, exposure of the eyes to water or foreign objects, and symptoms that the patient is experiencing. The symptoms classically attributed to<unk>  include decreased or blurred vision, sensitivity to light (photophobia), redness of the eye (conjunctival hyperemia), and pain out of proportion to physical exam findings. Another clinical feature that can distinguish<unk>  from bacterial causes of keratitis is a lack of discharge from the eye. On physical exam, findings will depend on the stage of the disease. Early manifestations in the cornea can be seen as punctate keratopathy, pseudodendrites, and epithelial or subepithelial corneal deposits. These features can lead an examiner to confuse<unk>  with a viral keratitis, such as that caused by varicella zoster virus or herpes simplex virus. As the disease progresses and infiltrates the corneal stroma, a classic "ring infiltrate" may be present on examination (although this is only seen in about 50% of cases). Corneal ulceration, or in severe cases, perforation, can also occur and may be accompanied by hypopyon. In cases of keratitis, diagnosis is typically achieved through evaluation of corneal scrapings. Scrapings are taking from the cornea, and plated on agar for culture, and also can be stained using Gram stain and Giemsa stain to differentiate between bacterial keratitis and<unk> . To culture<unk> , scrapings are placed on a non-nutrient agar saline plate seeded with a gram-negative bacteria such as E. coli. If<unk>  are present, they will reproduce readily and become visible on the plate under 10–20 times objective on an inverted microscope. Polymerase chain reaction (PCR) can be used to confirm a diagnosis of<unk> , especially when contact lenses are not involved. Confocal microscopy is a non-invasive technique that allows visualization of<unk>  in vivo in cases in which corneal scraping, culture, and cytology do not yield a diagnosis.
Acanthamoeba keratitis
Herpes simplex keratitis
Fungal keratitis
Nummular keratitis
Neurotrophic keratitis
Diffuse lamellar keratitis
Peripheral ulcerative keratitis
Interstitial keratitis