What is it?
It is inflammation of the cornea caused by Acanthamoeba, a protozoan commonly found in the soil, earth and water—in the sea, from the tap and in swimming pools. The Acanthamoeba has two stages: trophozoites and cysts, the latter is resistent to extreme environments to guarantee its survival.
When this bacteria infects the cornea, the patient presents with red eye, poor vision, intolerance to light, watering eyes and above all, eye pain.
In the initial phase, the corneal epithelium, the outermost layer, gets infected and dotted lesions forming lines that represent the epithelial cells invaded by this bacteria. As the disease progresses, the most profound layers, such as the corneal stroma, are invaded by the Acanthamoeba and the inflammatory cells manifesting itself as corneal opacity and a loss of transparency, commonly in the shape of a ring.
One of the typical manifestations of this infection is neuritis (inflammation of the corneal nerves), which is the reason for the intense eye pain. These symptoms and manifestations are very similar to herpes simplex keratitis which must be taken into account as treatment for it is totally different.
Causes and risk factors
Even though the Acanthamoeba is found in practically all places and environments, Acanthamoeba keratitis is not as common as you may think. The main risk factor of cornea infections is wearing contact lenses, especially soft ones.
More than 90% of patients with keratitis caused by this protozoan are contact lens-wearers. The majority do not have a good hygiene routine or have gone swimming while wearing them.
Contact lens-wearers have to take special precaution to prevent Acanthamoeba infections. A good hygiene routine for your contact lenses, their case and your hands when handling them is fundamental.
Leaving your contact lenses in their case for a few days without using them or changing the disinfection solution is also risky as the protozoans can proliferate in these cases.
The most well-know risk factor for contact lens-wearers is wearing them while in the water, whether it be for swimming pool- or sea-based activities. For this reason, wearing contact lenses for water activities is completely forbidden.
The earlier the treatment starts, the better the prognosis for the disease. That said, treatment for topical Acanthamoeba that involves various types of eyedrops and ointments may have adverse effects on the eyes. For this reason, before treating Acanthamoeba keratitis, other causes must be ruled out and as accurate as possible a diagnosis must be reached.
Unfortunately, nowadays, it is not easy to quickly identify the Acanthamoeba in the cornea. Samples are taken from the patient's cornea to identify it using a special culture or a molecular biology technique called polymerase chain reaction, but these tests are available in specialist centres and the cost is high.
Cysts of this protozoan in the cornea can also be identified using a corneal tomography although the absence of cysts does not rule out their presence and the images of cysts can be confused with inflamed cells. In many cases, the diagnosis has to be made clinically as this disease cannot be objectively ruled out or diagnosed.
One of the anti-Acanthamoeba eyedrops is not available in Spain, so it must be requested from overseas with permission from the Spanish Ministry of Health, while the other is not sold and has to be specially prepared in the centres with the means to do so. Other eyedrops with adjuvant effects that alleviate the eye pain must be added as part of the treatment. Due to the high resistance of the cystic state of this protozoan, treatment for Acanthamoeba keratitis must last at least 4-6 months.
Professionals who treat this pathology
Frequently asked questions
If I don't wear contacts, can I still get a Acanthamoeba infection?
It's very unlikely. However, if you do activities in the swimming pool or sea, you're recommended to wear swimming goggles at all times. These goggles, in addition to protecting the eyes from the germs in the water and that cause eye infections like conjunctivitis, also protect the eyes from cholorine and sea salt irritation.
What type of contact lenses have the lowest risk of their user getting Acanthamoeba keratitis?
According to the studies, rigid gas-permeable contact lenses carry the lowest risk of infection by this protozoa. When it comes to soft contact lenses, the disposable dailies, that is to say the ones used every day and thrown away after, have the lowest risk.