Keratitis

Keratitis is a medical condition defined by inflammation of the cornea. The cornea is the clear, dome-shaped structure located on the front surface of the eye. When this area becomes inflamed, it can lead to significant discomfort and health risks. Common symptoms include moderate to intense pain and a gritty sensation in the eye. Patients may also experience impaired eyesight, redness, and photophobia, which is a sensitivity to light.

To diagnose keratitis, doctors typically rely on clinical signs observed during an eye examination. If a doctor suspects an infectious cause, they may perform corneal scrapings. These samples are then evaluated using a microbiological culture or other specialized testing. This process helps identify the specific pathogen, or germ, causing the infection. Identifying the exact cause is vital because the treatment depends entirely on the type of infection present.

Viral keratitis is one major category of the condition. The most common causes are the herpes simplex virus (HSV) and the varicella zoster virus (VZV). Herpes simplex keratitis occurs when latent HSV reactivates within the ophthalmic nerve. This nerve is the V1 branch of the trigeminal nerve. This infection often presents with a dendritic pattern, which means the inflammation looks like branching tree limbs in the corneal epithelium.

Another viral type involves the varicella zoster virus. Approximately 8% to 20% of shingles cases involve the eyes as herpes zoster ophthalmicus. This also involves the reactivation of the virus in the V1 branch of the trigeminal nerve. VZV keratitis often appears about one month after the onset of shingles symptoms. It can cause clouding of the cornea. In about 50% of cases, inflammatory infiltrates appear in the stromal layer, which is a deeper part of the cornea.

Bacterial keratitis is another significant type, often linked to injury or contact lens use. For people wearing contact lenses, bacteria are responsible for 90% of keratitis cases. Among those cases, a bacterium called Pseudomonas aeruginosa causes 40%. This specific pathogen is dangerous because it produces enzymes that can digest the cornea. Other common bacterial pathogens include Staphylococcus aureus and various streptococci. Poor hygiene, such as using tap water or failing to replace lens cases, can lead to a biofilm. A biofilm is a layer of bacteria that can colonize lenses and cases.

Other infectious agents include fungi and amoebas. Fungal keratitis can be caused by Aspergillus fumigatus or Candida albicans. Amoebic keratitis is a serious infection often caused by Acanthamoeba. This organism is commonly found in tap water, which poses a risk to contact lens wearers. In 2007, the U.S. Center for Disease Control issued a health advisory regarding an increased risk of Acanthamoeba keratitis linked to a specific eye solution.

There are also non-infectious forms of keratitis caused by environmental factors. Exposure keratitis, or exposure keratopathy, happens when the cornea becomes too dry because the eyelids do not close completely. Photokeratitis is caused by intense ultraviolet radiation, such as snow blindness or welder's arc eye. Additionally, contact lens acute red eye (CLARE) is a non-ulcerative, sterile form of keratitis. This is associated with Gram-negative bacteria colonizing the contact lenses.

Treatment for infectious keratitis must be urgent to prevent the condition from progressing. Doctors use antibacterial solutions like levofloxacin or moxifloxacin for bacterial infections. For viral infections like HSV, they may use topical ganciclovir or oral medications like acyclovir. It is important to avoid steroid eye drops for certain viral ulcers. Using steroids on a dendritic ulcer caused by HSV can cause the ulcer to become "amoeboid" or "geographic" in shape. This means it spreads into a large, map-like shape. While many cases are treated successfully, some infections can cause corneal scarring, perforation, or even loss of the eye.