You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Fungal keratitis and explain in detail?
Fungal keratitis is a fungal infection of the cornea, which can lead to blindness. It generally presents with a red, painful eye and blurred vision. There is also increased sensitivity to light, and excessive tears or discharge.It is caused by fungal organisms such as Fusarium, Aspergillus or Candida.Fungal keratitis has a worldwide distribution, but is more common in the tropics. Around 1 million people become blind every year due to fungal keratitis. Theodor Leber first described a case of fungal keratitis caused by Aspergillus in 1879.

Signs and symptoms
The symptoms of fungal keratitis typically emerge over 5-10 days and present with a painful eye, blurred vision, and redness of eye. There is increased sensitivity to light, and excessive tears or discharge. The symptoms are markedly less as compared to a similar bacterial ulcer. Symptoms may be noted to persist after contact lenses are removed, or following antibiotic treatment.Signs: The eyelids and adnexa involved shows edema and redness, conjunctiva is chemosed. Ulcer may be present. It is a dry looking corneal ulcer with satellite lesions in the surrounding cornea. Usually associated with fungal ulcer is hypopyon, which is mostly white fluffy in appearance. Rarely, it may extend to the posterior segment to cause endophthalmitis in later stages, leading to the destruction of the eye. (Note: Fungal endophthalmitis is extremely rare)

Causes
Fungal keratitis has been reported to be caused by more than 70 different fungi, of which Fusarium, Aspergillus and Candida are responsible for 95% of cases.A. flavus and A. fumigatus are the most common types of Aspergillus to cause fungal keratitis. F. Solani is the most common type of Fusarium and others include Curvularia and Acremonium. C. albicans, C. guilliermondii and C. parapsilosis are the main types of Candida to cause fungal keratitis.

Pathophysiology
The precipitating event for fungal keratitis is trauma with a vegetable / organic matter. A thorn injury, or in agriculture workers, trauma with a wheat plant while cutting the harvest is typical. This implants the fungus directly in the cornea. The fungus grows slowly in the cornea and proliferates to involve the anterior and posterior stromal layers. The fungus can break through the descemets membrane and pass into the anterior chamber. The patient presents a few days or weeks later with fungal keratitis.

Diagnosis
The diagnosis is made by an ophthalmologist/optometrist correlating typical history, symptoms and signs. Many times it may be missed and misdiagnosed as bacterial ulcer. A definitive diagnosis is established only after a positive culture report (lactophenol cotton blue, calcoflour medium), typically taking a week, from the corneal scraping. Recent advances have been made in PCR ref 3./immunologic tests which can give a much quicker result.

Classification
Infectious keratitis can be bacterial, fungal, viral, or protozoal. Remarkable differences in presentation of the patient allows presumptive diagnosis by the eye care professional, helping in institution of appropriate anti-infective therapy.

Prevention
Prevention of trauma with vegetable / organic matter, particularly in agricultural workers while harvesting can reduce the incidence of fungal keratitis. Wearing of broad protective glasses with side shields is recommended for people at risk for such injuries.

Treatment
A presumptive diagnosis of fungal keratitis requires immediate empirical therapy. Natamycin ophthalmic suspension is the drug of choice for filamentous fungal infection. Fluconazole ophthalmic solution is recommended for Candida infection of the cornea. Amphotericin B eye drops may be required for non-responding cases, but can be quite toxic and requires expert pharmacist for preparation