Acanthamoeba Keratitis, or AK, is a rare but serious rare disease involving the eye – the cornea, the clear window at the front of the eyes – that can result in partial vision loss or complete blindness.
AK is still considered a rare disease and is included in the Orphanet database (ORPHA67043) and with an estimated prevalence of 1–9/100,000. The numbers of reported cases worldwide is increasing year after year, mostly in contact lens wearers, although cases have also been reported in non-contact lens wearers. Contact lens wearers typically seek medical help late, because they are used to minor irritations in the eye. (1)
The rare disease is caused by microscopic free living amoeba (FLA) called Acanthamoeba that are commonly found in water sources and dust. Most types of Acanthamoeba are harmless to humans but can cause a serious infection if they come in contact with the cornea. If this is infected or damaged, it can extremely painful.
Those who wear contact lenses have a higher risk of exposure to the bacteria. Improper lens hygiene, such as using tap water to wet the lenses or not cleaning or disposing the cases, can increase the probability of infection.
It is both difficult to diagnose and difficult to treat. So, if you wear contact lenses, have been in contact with water and are experiencing itchy, watery eyes, pain, sensitivity to light, redness, and/or blurred vision – PLEASE GO TO YOUR EYE DOCTOR IMMEDIATELY.
Figure: Acanthamoeba can enter the eye by attaching to contact lenses (1), the depleted immune activity allows binding to the epithelial layer (2) and the amoeba can begin to feed on the epithelial cells (3). Micro-abrasions on the epithelial layer provides an opportunity for the amoeba to access the Bowman’s membrane and stroma of the patient (4). Drug pressure can instigate encystation of the parasite (5) which can then begin reinfection upon removal of this pressure (6).
Acanthamoeba has a life cycle of two modes:
The TROPHOZOITE stage is an active or alive & kicking mode
When the parasite feeds, grows and replicates itself, in this stage is when you might experience a lot pain, light sensitivity and/or sometimes decrease in vision.
The CYST stage is when is a dormant or sleeping mode
Does not show much activity, meaning when the parasite protects itself from attack by developing into a cyst or as I referred to it a house – forming a protective wall around itself which helps the amoeba to survive in conditions that are not favourable for survival, in other words they go in to hibernation being able to survive for long periods of time and unfortunately one cannot predict when they will become active.
Acanthamoeba are harmless to humans but can cause a serious infection if they come in contact with the cornea. If this is infected or damaged, it can be very painful...
Acanthamoeba Keratitis early diagnosis is a key factor and how, is for many, a dilemma.
Acanthamoeba Keratitis, a nasty parasitic infection is one of the most dreadful infection followed by Pseudomonas which is bacterial infection. Early diagnosis is the key but the most important and significant problem is its diagnostic dilemma, which sometimes in experienced hand can be missed or may get disregard if not have taken proper history.
After seeing most Acanthamoeba cases in the last 3 years, I consider myself lucky to have picked them at an early stage of infection, therefore all my patients have achieved vision of 6/7.5 or better. I am very happy to share with you few tips / rules, as how to pick or diagnose AK at early stage or have minimum chance of missing… of course, not 100% but at least less chances of misdiagnosing it.
Rule no.1 Is History
One thing which I have come across and convinced about AK related infections is that, these do not occurs in day or two, instead the parasites actually have been cooking for at least more than 2 weeks or so, so it’s very important to ask the history of the last 1 month or even 2 months back of the patient with their contact lenses.
You should pay attention to this type of history or suspect AK if you hear light sensitivity/ blurry vision / foreign body sensation, especially more when using Contact Lenses (here after referred as CLs), and feeling for 1 or 2 months uncomfortable with CLs,
Please ask these questions:
These are some of the most important questions and does not take long for a doctor to ask. Always suspect AK in CLs patients until proven otherwise
Rule no. 2 is Examination
Main thing to look for is Corneal epithelial disruption, you may not necessarily see clear epithelial defect but you can see superficial punctuate Keratitis or some Sub Epithelial lines or Ridges , or if you are lucky enough you will see clear Pseudo dendritic pattern , but remember early pattern of AK, will not stain with Fluorescein so carefully look for any suspicious pattern in Cornea.
Rule no. 3 Do an imaging OCT and Confocal microscopy
OCT (Optical Coherence Tomography), as patients are usually photophobic, examination can sometimes get difficult, please do OCT if you have the possibility or have it down at another location, by doing this, you can see epithelial changes and most importantly Radial keratoneuritis representing white ridges in Stroma or Sub epithelium.
Confocal microscopy, If you doubt and have facility to have Confocal microscopy, or can get it done from somewhere else, please do before corneal scrapes.. Personally I have picked more cases with Confocal then Corneal scrapes, although not 100% but can even some can pick early stages with AK cysts while performing Confocal… Corneal Scrapes and Epithelial PCR Scrape epithelium and send for PCR , Lesion should always be scraped , even if Confocal positive. Results may take up to 10 days but at least if positive, one can act accordingly,
Remember, not always but usually outcome are better if picked within 6 weeks of onset of infection.
Do not start steroid drops on the eye until you have ruled out possibility of AK (wait till AK corneal scrape result with can take 10 days or PCR that can take 3 days). 10 % of cases can be Poly microbial, so keep the patient on Antibiotics even if get positive results of AK with Confocal or Scrapes . Always act promptly with keeping a track of days of infection, CLs related infection are not easy to treat especially now with fungal infections are more and more getting diagnosed.
Always suspect of AK if corneal ulcer is not responding or is responding to conventional antibiotics slow.
In the end, I would say:
Regarding treatments for Acanthamoeba Keratitis, what we have experienced till now – based on a non standard protocol – that each doctor/country does have their own protocol. It is important that the sooner you are diagnosed the better! The first weeks are very intense but vitally important to adhere to. Look for professionals with experience in Acanthamoeba Keratitis.
Usually once AK is confirmed, you will be given drops and/or pills (depends on each doctor) and you will have to take these eye drops every hour for several days 24/7, then moving to every hour (except the night) and depending on how the treatment is working they will adjust accordingly.
Important, do not underestimate the pain and ask for painkillers if needed, each person deals with pain in a different way and it is important you get some rest throughout the first weeks.
Practical online course: Managing Acanthamoeba Keratitis as an Ophthalmology Resident – by Nour Yanna Atassi MS and Alanna Nattis, DO, FAAO – CovalentCareers – (2020)