Acanthamoeba Keratitis: A Waterborne Parasitic Eye Infection
Acanthamoeba keratitis (AK) is a rare but serious eye infection caused by Acanthamoeba spp., free-living amoebae commonly found in water sources such as tap water, swimming pools, hot tubs, and soil. While relatively uncommon, AK can lead to severe vision loss or even blindness if not promptly diagnosed and treated.
Causes and Transmission
Acanthamoeba spp. are ubiquitous in nature and can be found worldwide in soil, air, and water. The transmission to humans typically occurs through direct contact of the eye with contaminated water sources. This can happen during activities such as swimming, showering, or using contaminated contact lens solutions.
Acanthamoeba keratitis is most common in individuals who wear contact lenses, with an estimated 85% of cases occurring in contact lens wearers in the United States [1]. Practices that can increase the risk of Acanthamoeba keratitis include:
Improper storage and handling of lenses.
Incorrect disinfection methods, like using tap water or reusing cleaning solutions.
Wearing lenses while swimming, using a hot tub, or showering.
Exposure to contaminated water sources.
In 2015, Marie Mason, a British woman, contracted Acanthamoeba keratitis after showering while wearing extended-wear contact lenses. The parasite would have got under the lens then multiplied, leading to persistent symptoms such as eye pain and blurred vision. Despite extensive treatment efforts including medications, eye drops, and multiple cornea transplants over five years, Mason ultimately lost vision in her left eye. As a result, she underwent the removal of her left eye and now uses a prosthetic [2].
In 2007, Advanced Medical Optics recalled its Complete MoisturePlus™ contact lens solutions due to concerns over Acanthamoeba keratitis. The CDC provided data indicating that since January 2005, 46 patients had developed AK infections, with 39 of them being soft contact lens wearers. Out of these, 21 reported using Complete MoisturePlus™ products. The CDC estimates that the risk of developing AK is at least seven times greater for those who used Complete MoisturePlus™ solution compared to those who did not [3].
Symptoms
The symptoms of Acanthamoeba keratitis often mimic those of more common eye infections, which can lead to delays in diagnosis. Symptoms may include:
Severe eye pain
Redness and inflammation of the eye
Sensitivity to light (photophobia)
Blurred or decreased vision
Excessive tearing or discharge from the eye
Feeling of something in the eye (foreign body sensation)
These symptoms can worsen rapidly if not treated promptly [4].
Treatment
Topical Antimicrobial Therapy
The cornerstone of treating Acanthamoeba keratitis involves the use of topical antimicrobial therapy. Ophthalmologists prescribe specific eye drops or ointments containing agents such as polyhexamethylene biguanide (PHMB), propamidine isethionate, or chlorhexidine. These medications are applied to the affected eye to target and eradicate the Acanthamoeba organisms residing on the surface of the eye and within the corneal tissue. The goal of this treatment is to effectively eliminate the infection and prevent further damage to the cornea [4].
Oral Medications
In severe cases of Acanthamoeba keratitis where the infection has penetrated deeper layers of the eye or has proven resistant to topical treatments, oral medications may be necessary. These medications are prescribed to reach amoebae in areas that topical treatments alone may not effectively reach. Oral agents such as systemic antibiotics or antiprotozoal drugs are administered under close medical supervision to enhance the therapeutic outcomes [4].
Corneal Healing Support
Supporting corneal healing is integral in the treatment of Acanthamoeba keratitis, especially to mitigate the damage caused by the infection and promote recovery. Alongside antimicrobial therapy, patients receive corneal healing support through the use of lubricating eye drops and other supportive measures. These measures aim to alleviate symptoms of dryness, discomfort, and inflammation, which are common manifestations of corneal infection. Lubricating eye drops not only provide relief but also aid in maintaining the integrity of the cornea and facilitating its restoration to a healthy state. Additionally, ophthalmologists may recommend protective measures to prevent further irritation or damage to the affected eye during the healing process [4].
Surgical Intervention
In advanced stages of Acanthamoeba keratitis where significant corneal damage has occurred or when medical therapy proves inadequate, surgical intervention may be necessary. Procedures such as corneal transplantation or keratoplasty are performed to replace damaged corneal tissue with healthy donor tissue. Surgical intervention aims to restore visual acuity and alleviate persistent symptoms, particularly in cases where vision-threatening complications have developed. Close post-operative monitoring and ongoing medical care are essential to monitor graft success and ensure optimal visual outcomes [4].
Prevention
Proper contact lens care is fundamental in reducing the risk of infection. This involves adhering strictly to hygiene guidelines, including thorough handwashing with soap and water before handling lenses. Contact lens wearers should use only sterile solutions recommended by their eye care providers for cleaning, disinfecting, and storing lenses. Avoiding shortcuts such as using tap water or saliva for lens cleaning or storing lenses in non-sterile containers is crucial to prevent introducing harmful microorganisms like Acanthamoeba to the eyes [4].
Avoiding contact with contaminated water is equally essential in preventing Acanthamoeba keratitis. Contact lens wearers are advised to use swim goggles while swimming or avoid activities where lenses could come into contact with water from potentially contaminated sources such as pools, hot tubs, and showers. Acanthamoeba thrives in these environments and can easily adhere to contact lenses, increasing the risk of infection. Taking proactive measures to protect the eyes from water exposure helps mitigate this risk significantly [4].
Regular eye exams also play a critical role in early detection and prevention of Acanthamoeba keratitis. Routine visits to an eye care professional enable timely assessment of eye health and detection of any signs of infection or other eye-related issues. Professionals can conduct thorough examinations, including evaluating the condition of the cornea and assessing the overall health of the eyes. Early detection allows for prompt intervention and treatment if infection is suspected, minimizing potential complications and preserving vision [4].
References
https://www.cdc.gov/parasites/acanthamoeba/infection-sources.html
https://www.eyeconx.net/chungandtseeyecare/view/article_208.3conx
https://www.cdc.gov/parasites/acanthamoeba/health_professionals/acanthamoeba_keratitis_hcp.html
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