Fungal Keratitis


Article Author:
Gabriel Castano


Article Editor:
Pradeep Kumar Mada


Editors In Chief:
Shane Havens
Jim Wang
Koushik Tripathy


Managing Editors:
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Frank Smeeks
Kristina Soman-Faulkner
Benjamin Eovaldi
Radia Jamil
Sobhan Daneshfar
Saad Nazir
William Gossman
Pritesh Sheth
Hassam Zulfiqar
Navid Mahabadi
Steve Bhimji
John Shell
Matthew Varacallo
Ahmad Malik
Mark Pellegrini
James Hughes
Beata Beatty
Hajira Basit
Phillip Hynes


Updated:
6/4/2019 7:11:36 PM

Introduction

Bacteria, viruses, and fungi can cause infectious keratitis. Fungal keratitis (FK) was first documented in 1879 and incidence has been increasing for the past 30 years. It is accountable for 40% to 50% of all isolated keratitis cases. FK develops rapidly and can lead to corneal ulcers and vision loss, so early diagnosis and prompt treatment are essential to prevent long-term complications.[1][2]

Around 70 different fungi have been implicated in the causation of fungal keratitis; yeast and filamentous fungi (septate and non-septate) are the most relevant.

Trauma and immunocompromised state are the most prevalent risk factors associated with fungal keratitis. It is also believed that the fluid transport across the endothelium plays an important role in the spread of the infection.

Etiology

Worldwide, Aspergillus species are the most frequent isolate in FK. An Indian study on FK reports that Aspergillus species is the most common isolate (27% to 64%), followed by Fusarium (6% to 32%) and Penicillium (2% to 29%).[3]

Another common fungal organism causing keratitis is Fusarium. Fusarium species are found in soil, water, and on plants throughout the world, especially in warmer climates. Past studies on FK have found that eye injuries caused by vegetative matter account for most reported cases; for example, being hit in the eye with a palm branch.

In one study, 275 patients were confirmed with FK. Of those, 198 patients were diagnosed by positive fungal cultures. They reported that sensitivity of fungal culture was 72.0%. Among these patients, 210 fungal isolates belonging to 17 genera and 29 species were isolated. The isolates of Fusarium were the most common (49.5 %), followed by Aspergillus (18.6 %), Candida (12.4 %), and other genera (19.5 %) such as Alternaria, Acremonium, Cladosporium, and Beauveria. Among these isolates, the predominant species were with Fusarium solaniAspergillus fumigatus, and Candida glabrata, accounting for 56.6% of the isolated fungi.[4]

Epidemiology

Like most infectious diseases, geographical location and socioeconomic status influence prevalence. In the United States, warm places like Florida have an incidence of 35%, while colder places like New York can be as low as 2%. In the United States, Candida and Aspergillus are most frequently isolated in fungal keratitis. Aspergillus is most common in northwestern states. Fusarium is the most common cause of fungal keratitis in warmer climates. 

An estimated 30 million persons in the United States use soft contact lenses. Contact use can lead to microbial keratitis, which has an incidence approximately of 4 to 21 per 10,000 users. Wearing the lenses overnight is an aggravating factor. A CDC investigation of 130 reported FK cases from 2005 to 2006, reported more than 60% had used a contact lens solution, and 37 of these cases resulted in cornea transplant surgery.

Studies have shown a higher incidence in males, with the majority of the patients between the ages of 16 and 49. It occurs more often in patients with a history of trauma, and those frequently outdoors.[4][5]

Pathophysiology

Usually, FK results from fungi access into the corneal stroma through a defect in the epithelium; this is the reason the disease is associated with trauma. Once in the tissue, the fungi start to replicate in the anterior chamber, a space protected by the cornea, and posteriorly, by the iris diaphragm and pupil. The cornea and conjunctiva create the protective anatomic barrier against pathogens, that is the reason, when penetrated by trauma it is no longer impermeable. [6][7]

The cornea is avascular, and on top of its barrier capacity, has restricted defense mechanism, dendritic cells, and immunoglobulins, making it easy to be colonized by fungi. The fungal organisms can spread from into the sclera and intraocular structures, causing severe infections such as endophthalmitis, panophthalmitis, or scleritis. These have difficult treatments and may lead to vision or eye loss.

Zygomycetes is known to cause the rapid and severe destruction of the extraocular and rhinocerebral soft tissues; however, due to the avascular nature of the corneal tissue, it behaves less aggressively in keratitis.

Histopathology

Coarse granular infiltration of the corneal epithelium and the anterior stroma is the main finding in FK, and having low neutrophils is a positive finding as they are the ones that contribute to the destruction of the cornea with intent to control the causative agent. The union of the fungi and the host antibodies is usually surrounded by a ring (showing infiltration); the fungal hyphae normally are parallel to the corneal surface and lamellae.

History and Physical

Most patients present with pain, redness, blurred vision, sensitivity to light, excessive tearing, or discharge within 24 to 36 hours after the trauma. Elevated edges, branching ulcers, feathery margins, rough texture, and satellite lesions are specific for FK.

Evaluation

Approaches for patient evaluation vary, but the smear must be done as soon as is suspected. Because fungi have the predilection to penetrate deeper layers of the cornea, tissue swabbing is usually inadequate in confirming a fungal agent. Corneal scrapings are recommended. Ideally, every sample should be sent for polymerase chain reaction (PCR) and culture. Cultures usually take 1 to 35 days. Another major disadvantage of the fungal cultures is low sensitivity, especially for cases that have been treated with antifungal agents. PCR testing has been established as a better way to get an FK diagnosis and takes 2 to 3 hours. The obstacle to using PCR is that it requires very specialized equipment that might not be available. Therefore, Kue et al. suggested implementing a dot essay, which is highly sensitive and can detect a wide variety of fungus. Confocal microscopy is a noninvasive technique and another method for FK diagnosis.[8]

Ophthalmologists perform ophthalmic B-scan ultrasound if there is a suspicion of posterior segment involvement or endophthalmitis. Biopsy of the corneal body is a procedure that can be done if previous studies are negative. There has not been an improvement with broad-spectrum antibiotics, but this is not routinely done.

Treatment / Management

Natamycin eye drops are frequently used for FK. They inhibit the growth of fungi by inhibiting transport of amino acids and glucose across the plasma membrane by binding to ergosterol and inhibiting membrane transport proteins. It has negligible absorption when taken orally, so it is not useful for systemic infections. [9][10][11]

Other agents used in FK are amphotericin B, voriconazole. Voriconazole has better penetration into the eye and is purported to be a superior alternative to natamycin. However, recently published clinical trials have reported equal or inferior efficacy of 1% voriconazole (reconstituted from injection vial) compared with 5% natamycin eye drops in FK. These results are contradictory to experimental and in vitro data. Sharma conducted a study of 118 patients where 58 patients were treated with voriconazole and 60 patients with natamycin. Despite the frequency of healed or resolving ulcers being similar on day 7 (natamycin 35/54, 65%; voriconazole 34/50, 68%), at the final visit the percentage of patients who had healed corneal ulcer were significantly higher in the group treated with natamycin (50/56, 89.2% versus 34/51, 66.6%; p=0.005). 

In a 10-year retrospective study, Gina analyzed 73 cases of fungal keratitis and reported a microbiological cure was achieved in 72 corneas (98.6%). Forty-one (56.2%) were cured with medical therapy alone, and 32 (43.8%) required therapeutic keratoplasty (TKP) only once. Among the 32 that were treated with TKP, 17 (53.1%) maintained a clear graft.

Differential Diagnosis

  • Bacterial keratitis: Pseudomonas and Staphylococcus aureus are the most common culprits
  • Herpes simplex keratitis
  • Herpes zoster keratitis 

Prognosis

The prognosis depends on the depth, extension of infection, and timing of treatment initiation. Some patients can be cured microbiologically by topical antifungals alone, and in some patients, keratoplasty is needed. The Descemet membrane, an interior basement membrane near the aqueous humor, is impermeable to bacteria but can be breached by fungal hyphae, leading to endophthalmitis; endophthalmitis is a rare consequence of fungal keratitis that causes a poor prognosis.

Complications

  • Endophthalmitis
  • Permanent blindness

Pearls and Other Issues

  • Aspergillus species are the most common isolate in fungal keratitis worldwide. 
  • Elevated edges, branching ulcers, feathery margins, rough texture, and satellite lesions are specific for fungal keratitis.
  • Diagnosis is by corneal scrapings. Samples should be sent for PCR and cultures.
  • Natamycin eye drops are frequently used.

Enhancing Healthcare Team Outcomes

The majority of patients with fungal keratitis present to the emergency room or to their primary care provider; in order to expedite the referral process to an ophthalmologist, a multidisciplinary approach in diagnosis and care is vital. Any delay can lead to vision loss and permanent blindness. The majority of patients with fungal keratitis are managed as outpatients and treated with antifungal therapy for at least 12-16 weeks. Close follow up is required to ensure that the symptoms are not worsening. The eventual outcome depends on factors like patient overall health, the status of the immune system and other comorbidity. Patients with a mild infection who are promptly treated have a good outcome but in patients with an infection that has spread into the sclera, the prognosis is guarded. Data indicate that at least 30% of patients with fungal keratitis develop corneal perforation or fail to respond to drug therapy.[12][13]


  • Image 6314 Not availableImage 6314 Not available
    Contributed by Gabriel Castano, MD
Attributed To: Contributed by Gabriel Castano, MD

Interested in Participating?

We are looking for contributors to author, edit, and peer review our vast library of review articles and multiple choice questions. In as little as 2-3 hours you can make a significant contribution to your specialty. In return for a small amount of your time, you will receive free access to all content and you will be published as an author or editor in eBooks, apps, online CME/CE activities, and an online Learning Management System for students, teachers, and program directors that allows access to review materials in over 500 specialties.

Improve Content - Become an Author or Editor

This is an academic project designed to provide inexpensive peer-reviewed Apps, eBooks, and very soon an online CME/CE system to help students identify weaknesses and improve knowledge. We would like you to consider being an author or editor. Please click here to learn more. Thank you for you for your interest, the StatPearls Publishing Editorial Team.

Fungal Keratitis - Questions

Take a quiz of the questions on this article.

Take Quiz
A 64-year-old female with a history of hypertension presented with two weeks duration of right eye blurry vision, purulent discharge, and foreign body sensation preceded by eye trauma. One week prior to the presentation, while working on a farm, a tiny invisible dust particle got into her right eye and she developed irritation of the eye. What could be the most likely etiology of the following choices?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Which infection typically does not cause hypopyon?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
What is the most common organism causing fungal keratitis in worldwide?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
What is the best method for early identification of organism in fungal keratitis?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Which is not a specific feature for fungal keratitis?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Which fungal keratitis has a brown macroscopic appearance?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Natamycin eye drops are frequently used for fungal keratitis. What is the mechanism of action for natamycin?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up

Fungal Keratitis - References

References

Tena D,Rodríguez N,Toribio L,González-Praetorius A, Infectious keratitis: microbiological review of 297 cases. Japanese journal of infectious diseases. 2018 Oct 31     [PubMed]
Mittal R,Ahooja H,Sapra N, Corneal     [PubMed]
Sharma N,Sahay P,Maharana PK,Singhal D,Saluja G,Bandivadekar P,Chako J,Agarwal T,Sinha R,Titiyal JS,Satpathy G,Velpandian T, Management Algorithm for Fungal Keratitis: The TST (Topical, Systemic, and Targeted Therapy) Protocol. Cornea. 2018 Oct 16     [PubMed]
Al-Hatmi AMS,Castro MA,de Hoog GS,Badali H,Alvarado VF,Verweij PE,Meis JF,Zago VV, Epidemiology of Aspergillus species causing keratitis in Mexico. Mycoses. 2018 Sep 26     [PubMed]
Cho CH,Lee SB, Comparison of clinical characteristics and antibiotic susceptibility between Pseudomonas aeruginosa and P. putida keratitis at a tertiary referral center: a retrospective study. BMC ophthalmology. 2018 Aug 20     [PubMed]
Zapp D,Loos D,Feucht N,Khoramnia R,Tandogan T,Reznicek L,Mayer C, Microbial keratitis-induced endophthalmitis: incidence, symptoms, therapy, visual prognosis and outcomes. BMC ophthalmology. 2018 May 3     [PubMed]
Shimizu E,Yamaguchi T,Yagi-Yaguchi Y,Dogru M,Satake Y,Tsubota K,Shimazaki J, Corneal Higher-Order Aberrations in Infectious Keratitis. American journal of ophthalmology. 2017 Mar     [PubMed]
Padzik M,Szaflik JP,Baltaza W,Perkowski K,Dybicz M,Chomicz L, In vivo confocal microscopy and in vitro culture techniques as tools for evaluation of severe Acanthamoeba keratitis incidents Annals of parasitology. 2017     [PubMed]
Farrell S,McElnea E,Moran S,Knowles S,Murphy CC, Fungal keratitis in the Republic of Ireland. Eye (London, England). 2017 Oct     [PubMed]
Hodkin MJ,Gustus RC, Fungal Keratitis Associated With Airborne Organic Debris and Soft Contacts Lenses: Case Reports and Review of the Literature. Eye     [PubMed]
Sun CQ,Lalitha P,Prajna NV,Karpagam R,Geetha M,O'Brien KS,Oldenburg CE,Ray KJ,McLeod SD,Acharya NR,Lietman TM, Association between in vitro susceptibility to natamycin and voriconazole and clinical outcomes in fungal keratitis. Ophthalmology. 2014 Aug     [PubMed]
Fontana L,Moramarco A,Mandarà E,Russello G,Iovieno A, Interface infectious keratitis after anterior and posterior lamellar keratoplasty. Clinical features and treatment strategies. A review. The British journal of ophthalmology. 2018 Oct 24     [PubMed]
McElnea E,Power B,Murphy C, Interface Fungal Keratitis After Descemet Stripping Automated Endothelial Keratoplasty: A Review of the Literature With a Focus on Outcomes. Cornea. 2018 Sep     [PubMed]

Disclaimer

The intent of StatPearls is to provide practice questions and explanations to assist you in identifying and resolving knowledge deficits. These questions and explanations are not intended to be a source of the knowledge base of all of medicine, nor is it intended to be a board or certification review of Surgery-Ophthalmology. The authors or editors do not warrant the information is complete or accurate. The reader is encouraged to verify each answer and explanation in several references. All drug indications and dosages should be verified before administration.

StatPearls offers the most comprehensive database of free multiple-choice questions with explanations and short review chapters ever developed. This system helps physicians, medical students, dentists, nurses, pharmacists, and allied health professionals identify education deficits and learn new concepts. StatPearls is not a board or certification review system for Surgery-Ophthalmology, it is a learning system that you can use to help improve your knowledge base of medicine for life-long learning. StatPearls will help you identify your weaknesses so that when you are ready to study for a board or certification exam in Surgery-Ophthalmology, you will already be prepared.

Our content is updated continuously through a multi-step peer review process that will help you be prepared and review for a thorough knowledge of Surgery-Ophthalmology. When it is time for the Surgery-Ophthalmology board and certification exam, you will already be ready. Besides online study quizzes, we also publish our peer-reviewed content in eBooks and mobile Apps. We also offer inexpensive CME/CE, so our content can be used to attain education credits while you study Surgery-Ophthalmology.